CA1273924A - Thermal imaging method - Google Patents

Abstract

THERMAL IMAGING METHOD
6810 Abstract of the Disclosure A thermal imaging method for forming color images is provided which relies upon the irreversible unimolecular fragmentation of one or more thermally unstable carbamate moieties of an organic compound to effect a visually discernible color shift from colorless to colored, from colored to colorless or from one color to another.

Description

~Lf~¢~2~

THERMAL IMAGING METHOD
Background of the Invention 1. Field of the Invention This invention relates to heat sensitive recording eLements particularly useful for making color hard copy, to 5 a method of imaging using said elements and to novel organic compounds useful as the image-forming materials in said heat-sensitive recording elements.

2. Description of the Prior Art -A variety o~ thermal imaging systems for producing 10 color images have been proposed, and several have been mentioned in Kosar, J., Light-Sensitive Systems: Chemistry and Application of Nonsilver Halide Photographic Processes, New York, John Wiley and Sons, Inc., 1965, pp. 402-19. In one type of heat sensitive recording system, a first sheet 15 containing a first reagent is superposed with a second sheet containing a second reagent and one of the reagents is meLted or vaporized by the itnagewise application of heat and trans~erred for reaction with the other reagent to form a color image. In another type of "transferring system", 20 images are formed by sequentially transferring two or more dyes carried on separate donor sheets to a common receptor ~heet by melting or volatilization. In thermal imaging systems of the "self-containing" type, a single sheet is used and the imagewise heating of the heat-sensitive sheet 25 produces a coLor image, for example, by rendering a coating layer transparent to reveal the color of a background layer, by initiating the chemical reaction of two or more reagents to form a colored product or by bleaching, coloring or changing the color of a single reagent. In most o~ the ,~?~
_ I _ ~73~

non-silver thermal imaging ~ystems in commercial u~et color imageS are formed using two or more reagents that usually are encapsulated or otherwise isolated from each other until melted and mixed upon imagewise heating.
A number o~ compounds which undergo a color change from a colorless to a colored form, from one color to another color or from a colored to a colGrless form upon application of heat have been disclosed. For example, U.S.
Patent No. 3,723,121 discloses several thermochromic 10 materials for laser beam recording including inorganic compounds, such as, black copper (II) oxide which decomposes to red copper (I) oxide upon hea~ing and organic compounds, such a~, polyacetylene compounds which subsequent to treatment with ultraviolet light undergo two changes in 15 color, first to red then to yellow, as the temperature is increased. U.S. Patent No. 4,242,440 discloses another class of heat-sensitive polyacetylene compounds which exhibit color changes, for example, gold to red, brown to orange and gold to orange, which color changes are 20 reversible. U.S. Patent No. 3,488,705 discloses thermally unstable organic acid salts of triarylmethane dye~ useful in electrophotographic elements as sensitizing dyes that are decomposed and bleached upon heating. U.S. Patent No.

3,745,009 reissued as Re. 29,168 and U.S. Patent ~o.
25 3,832,212 disclose heat-sensitive compounds for thermography containing a heterocyclic nitrogen atom substituted with an -OR group, for example, a carbonate group that decolorize by undergoing homolytic or heterolytic cleavage of the nitrogen-oxygen bond upon heating to produce an RO+ ion or 30 RO' radical and a dye base or dye radical which may in part fragment urther. U.S. Patent 4,380,629 discloses styryl-like compounds which undergo coloration or bleaching, reversibly or irreversibly via ring-opening and ring-closing in response to acti~ating energies such as light, heat, 35 electric potential and so on.

~2~73~-~2~

Summa~y of the Invention -The present invention is concerned with a new class of heat-sensitive organic compounds and with their use in thermal imaging systems for optical recording and S particularly for color hard copy for forming color images.
In particular, the formation of col~r images in accordance with the present invention relies upon the irreversible unimolecular fragmentation of one or more thermally unstable carbamate moieties of an organic compound to effect a lO visually discernible color shift from colorless to colored, from colored to colorless or from one color to another.
Unlike many of the thermal imaging materials employed previously, the heat-sensitive compounds of the present invention may be used to produce color images of 15 pictorial quality for color hard copy. Because the subject compounds undergo a unimolecular fragmentation, the change in spectral absorption characteristics, e.g., from the visible to the non-visible region of the spectrum or from the non-visible to the visible region of the spectrum can be 20 achieved rapidly and efficiently and without the problems associated with isolating and then bringing two reagents together to effect image formation. Because the framentation is irreversible, changes in image density, e.g., in the highlight areas due to a reversal in bleaching 25 or in the saturated areas due to a reversal in coloration are obviated. Also, the framentation can be achieved at moderately elevated temperatures above ambient temperatures so that the heat required for effecting the fragmentation can be kept below levels that would cause deformation or 30 distortion of the imaging layer or other layers of the heat-sensitive element. Moreover, the subject heat-sensitive compounds may comprise various classes of dyes thereby permitting the selec~ion of a wide range of colors as may be desired not only for monochromes but for 35 full color images, and since image formation does not involve transfer and registration of separate colors, multicolor images of excellent sharpness and resolution can be readily obtained.
It is, therefore, the primary object of the 5 present invention to provide a method of thermal imaging and heat-sensitive recording elements uSéful therein for producing a color image which employ a new class of heat-sensitive organic compounds.
It is another object of the present invention to 10 provide novel compounds useful as heat-ssnsitive color image-forming materials.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the methods 15 involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the products and compositions possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the 20 scope of the application of which will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.
De~cription of the Preferred Embodiments In accordance with the present invention, a method of thermal imaging is provided which comprises heating imagewise a heat-sensitive element comprising a support carrying at least one layer of an organic compound capable 30 of undergoing an irreversible unimolecular fragmentation of at least one thermally unstable carbamate, moiety, said organic compound initially absorbing radiatiol- in the visible or the non-visible region of the electromagnetic spectrum and ~aid imagewise heating effecting said 3S irreversible unimolecular ragmentation of said carbamate moiety whereby the ab~orption of said organic compound is visibly changed in said layer in an imagewise pattern corresponding to said imagewi~e heating. By "visua11y changed" is meant a change in color from colorless to 5 colored, from colored to colorless or from one coLor to another color that is visually disce~nible to the eye.
Typical of the compounds that may be employed in the subiect method are those represented by the formula (I) ~M (X-~q ~p D
10 wherein M is a carbamate moiety; X is -N=, -S02-, or -CH2-;
D taken with X and M represents the residue of an organic dye; q is 0 or 1; and p is a whole number of at least 1 and usually is a whole number of 1 to 3. Preferably, M has the formula (II) Z-~-wherein R is alkyl usually having 1 to 4 carbon atoms;
-S02Rl wherein Rl is alkyl usually having 1 to 6 carbon atoms; phenyl; naphthyl; or phenyl substituted with alkyl usually having 1 to 6 carbon atoms, alkoxy usually having 1 20 to 6 carbon atoms, halo, such as chloro or bromo, trihalomethyl, such as, trichloromethyl or trifluoromethyl, cyano, nitro, carboxy, -CO~R2R3 wherein R2 and R3 each are hydrogen or alkyl usually having 1 to 6 carbon atoms, -C02R4 wherein R4 is alkyl usually having 1 to 6 carbon atoms or 25 phenyl, -CORs wherein R5 is amino, alXyl usuaily having 1 to 6 carbon atoms or phenyl, -NR6R7 wherein R6 and R7 each are hydrogen or alkyl usually having 1 to 6 carbon atoms, -SO2-NR8Rg wherein R8 and Rg each are hydrogen, alkyl usually having 1 to 6 carbon atoms or benzyl and Z is an 30 acyloxy group, -~-ORlo wherein Rlo i5 tert-alkyl or -~CH2)2Y
wherein Y is an electron-withdrawing group.
The novel compounas of the pre~ent invention may be represented by the formula ~273~

(III) ~M'--~X)q }p D
wherein p, q, X and D have the ~ame meaning given above and wherein M' has the formula Z'-N-R
5 wherein R has the ~ame rneaning given above and Z' is -C-O ~-R' wherein ~' is halomethyl, for example, methyl substitùted with one, two or three halo groups, such as, chloro or bromo; or alkyl containing 1 to 20 carbon atoms.
Preferably, said R' is alkyl, e.g., methyl, ethyl, propyl, 10 butyl, octyl, decyl, dodecyl, octadecyl or eicosanyl.
As noted above, the heat-sensitive compounds of the present invention may comprise various classes of dyes, and D as defined in the foregoing formulae may comprise the residue of a triarylmethane dye, a xanthene dye, a rhodamine 15 dye, a fluoran dye, an azocarbocyanine dye, a benzylidine dye, a thiazine dye, an acridine dye, an aminoanthraquinone dye or other dye containing a nitrogen atom possessing a lone pair of electrons, which when substituted with said acyloxy group to form said carbamate moiety, will be 20 color-shifted. Preferably a tert-alkoxy carbonyl group, such a~, tert-butoxycarbonyl is used as the acyloxy group to i~olate the lone pair of electrons on the nitrogen atom of the organic dye to effect said color shifting. The fragmentation of the resuIting carbamate moiety upon 25 application of heat releases said lone pair of electrons to effect a visually discernible change in the spectral absorption characteristics of the dye, preferably, from colored to colorless or colorless to colored.
The use of tert-butoxycarbonyl as a protecting 30 group for nitrogen functionalities is well known, and the thermal lability, i.e., instability of this protecting group at 150C-170C is mentioned in Greene, Theodora W., .f.'~

Protective Groups in Organic Synthesis, New York, John WiLey and Sons, Inc., 1981, page 326. The thermal lability of O-t-alkyl sulfonyl carbamateg is discussed by Roach, Louise C. and Daly W.H., Olefin Synthesis via Pyrolysis of 5 O-t-Alkyl N-To1uene-p-Sulfonylcarbamates, Chemical Communications, p. 606-607 (1970). ,' Illustrative of the classes of compo~nds that may be empl~yed in the present method are those represented in the following formulae;
A~ B

( 1 ) \C~
~ -E

wherein A is phenyl moiety or a naphthyl moiety; B is a

4'-oxo-1'-phenylidene moiety or a 4'-oxo-l'-naphthylidene moiety, said A and B moieties being substituted or l o lo unsubstituted, and E is -SO2-N- C-O(CH2)2Y wherein Ro is, 15 for example, alkyl having l to 4 carbon atom~ and Y is an electron-withdrawing group, preferably an electron-withdrawing group having a po~iti~e sigma value greater than 0.6 as defined by Hammett's Equation.
Preferred electron-withdrawing groups include.nitro, cyano, 20 -SO2CH3, -S2 ~ , -SO2 ~ H3, -COC~3~ -SO2~(cH2ph)2 -SO2N(CH3)2 -CHO, -COOH, -COOCC2H5 and CONH2.

N ~ ~ ~ ~ R12 A~

~ E
(2) ~

wherein each Rll, the same or different, is alkyl; each R12, the same or different~ is an electron-withdrawing group; A~
is an anion and E has the same meaning given in formula (1) above.

jJ~

(3) E A~3 wherein A~ is an anion and E has the same meaninq given in formula (1) above.

A~ B
--C~
~ SO-- I --Z ' (4) wherein A is a phenyl moiety or a naph~hyl moiety; B is a 10 4'-oxo-phenylidene moiety or a 4'-oxo-naphthylidene ~oiety;
R" is alkyl usually having 1 to 4 carbon atoms and Z' has the same meaning given in formula (III) above.
Preferred compounds of this type are those having the formula ~73~

R ~ R

(4a) ~ SO2- N - Z ' wherein ~1 is hydrogen, alkyl usually containing 1 to 6 carbon a~oms, alkoxy usually containing 1 to 6 carbon atoms or hydroxy; R2 and R4 each are hydrogen, alkyl usually

5 containing 1 to 6 carbon atoms, alkoxy usually containing 1 to 6 carbon atoms or halo, such as, chloro or bromo; Rl and R2 taken together represent the carbon atoms necessary to complete a fused benzene ring; R3 is hydrogen, alkyl usually containing 1 to 6 carbon atoms, alkoxy usually containing 1 10 to 6 carbon atoms, hydroxy, -~,N-(dialkyl)amino wherein said alXyl usually contains 1 to 6 carbon atoms, piperidino, pyrrolidino, N-methylpiperizino, morpholino, or thiomorpholino R5 and R6 each are hydrogen, alkyl usually containing 1 to 6 carbon atoms, alkoxy usually containing 1 15 to 6 carbon atoms or halo, such as, chloro or bromo R7 is hydrogen, alkyl usually containing 1 to 6 carbon atoms, alkoxy usually containing 1 to 6 carbon atoms or hydroxy; R6 and R7 taken together represent the carbon atoms necessary to complete a fused benzene ring; R" is alkyl usually 20 containing 1 to 4 carbon atoms and Z' has the same meaning given in formula (III) above.

~ 7~

, ~/ C ~1~ A~

(5) S02- N -z' wherein m and n each are whole numbers from 2 to 6; R" is alkyl usually having 1 to 4 carbon atoms; A~ is an anion and Z' has the sar.le meaning given in formula (III) above.
In preferred compounds of this type, m and n are the same and m and n each are 2.

R10 ~ ~ ~ R

(6) ~2 wherein each R8, the same or different, is alkyl usuall.y containing 1 to 20 carbon atoms; each R9, the same or 10 dif~erent, and each R10, the same or different, are hydrogen, alkyl usually having 1 to 6 carbon atoms; alkoxy usually having 1 to 6 carbon atoms; halo, such as, chloro or bromo, -SO2Rll is alkyl usually having 1 to 6 carbon atoms, phenyl or phenyl substituted with alkyl usually having 1 to 15 4 carbon atoms; carboxy; -CoNRl2Rl3 wherein Rl~ and R13 each are hydrogen or alkyl usually having 1 to 6 carbon atoms;
-Co2R14 is alkyl usually having 1 to 6 carbon atoms or phenyl; cyano; nitro; trihalomethyl, such as trichloromethyl 3~

or trifluoromethyl; -CoRl5 wherein Rl5 is amino, alkyl usually having 1 to 6 carbon atoms or phenyl; -NR16R17 wherein Rl6 and R17 each are hydrogen or alkyl usually having l to 6 carbon atoms or -so2-NRl8Rl9 wherein Rl8 and 5 Rl9 each are hydrogen, alkyl usually having 1 to 6 carbon atoms or benzyl; R" is alkyl usually having l to 4 carbon atoms; ~ is an anion and Z' has the same ~eaning given in formula (III) above. It will be understood that said R9 and R10 may be ortho, meta or para to said N atom.
In preferred compounds of this type, said R9 groups are the same and are ha~o, -SO2Rll or -SO2-NR18Rl9 and said RlO groups are the same.

R 2 Q~,)~ R 2 2 (7~ ~ CH2--N--Z ' 52Rl wherein R20 is piperidino, pyrrolidino, morpholino, 15 methylpiperidino, N-cyclohexylamino, N-alkyl-N-cyclohexylamino wherein said alkyl usually has l to 6 carbon atoms, N-benzyl-N-cyclohexylamino; R21 is hydrogen, alkyl ~sually having l to 6 carbon atoms, halo, such as, chloro or bromo, amino including mono- or di-aLkyl amino R22 iS
20 hydrogen, alkyl usually having l to 6 carbon atoms, alkoxy usually having l to 6 carbon atoms or halo, such as, cloro or bromo; R23 is hydrogen, alkyl usually containing 1 to 6 carbon atoms, phenyl, ~-piperidino, ~-methylpiperidino, N-pyrrolidino, N-morpholino or -NR25R26 wherein R25 is 25 hydrogen, benzyl, alkyl containing l to 6 carbon atoms, acyl, such as, acetyl or cycloalkyl, such as, cyclohexyl and R26 is hydrogen, alkyl usually having l to 6 carbon atoms, ~273~

alkoxy usually having 1 to 6 carbon atoms, benzyl or halo, such as, chloro or bromo R24 is hydrogen, alkyl usualLy having 1 to 6 carbon atoms or alkoxy usua~ly having 1 to 6 carbon atoms; Rl is alkyl usually having l to 4 carbon 5 atoms; A~ is an anion; and Z' has the same meaning given in formula (III) above.

~ ~ r ~ ~ ~2 (8) ~ SO2- N - Z

wherein each R27, the same or different, are hydrogen, alkyl usually having 1 to 6 carbon atoms, alkoxy usually having 1 10 to 6 carbon atoms or N,N-(dialkyl)amino wherein said alkyl usually contains 1 to 6 carbon atoms; R" is alkyl usually having 1 to 4 carbon atoms; Aa is an anion; and Z' has the same meaning given in formula (III) above, said R27 groups being ortho, meta or para to said 0 atom.

29 ~28 ~ ~ R

l~=o (9) ~

wherein R28 is alkyl usually having 1 to 20 carbon atoms or the same as Z'; each R29, the same or different and each R30, the same or different, ar~ hydrogen, alkyl usually having 1 to 6 carbon atoms alkoxy usually having 1 to 6 ~;~7~

carbon atoms, halo, such as, chloro or bromo; -So2R3l wherein R3l is alkyl usually having l to 6 carbon atoms, phenyl or phenyl substitute~ with alkyl usually having 1 to 4 carbon atoms; carboxy; -Co~R32R33 wherin R32 and R33 each 5 are hydrogen or aLkyl usually ha~ing 1 to 6 carbon atoms.
-CoR34 wherein R34 is alkyl usually having l to 6 carbon atoms or phenyl; cyano; nitro; trihalomethyl, such as, trichloromethyl or trifluoromethyl; -coR35 wherein R35 is amino, alkyl usually having l to 6 carbon atoms or phenyl;
lO -NR36R37 wherein R36 and R37 each are hydrogen or alkyl usually having 1 to 6 carbon atoms or -So2-NR38R39 wherein R38 and R39 each are hydrogen, alkyl usually having 1 to 6 carbon atoms or benzyl and æ ~ has the same meaning given in formula (III) above. It will be understood that said R29 15 and R30 groups may be ortho, meta or para to said N atom.
In preferred compounds of this type, said R29 and said R30 groups are the same. Preferably, said R29 groups are halo, alkyl, alkoxy, -So2R3l or -So2-NR38R39, said R30 groups are hydrogen or the same as said R29 groups, and R28 20 is the same as Z'.

~;~ CU=N--N

( 10) wherein R40, R41 and R42, the same or different, are hydrogen, alkyl usually having 1 to 6 carbon atoms; R43 is hydrogen, carboxy, -CoNR44R45 wherein R44 and R45 each are 25 hydrogen or alkyl usually having 1 to 6 carbon atoms, -Co2R46 wherein R46 is alkyl usually having 1 to 6 carbon ~2~3~

atoms, alkoxy usually having 1 to 6 carbon atoms, nitro, cyano or halo, such as, chLoro or bromo; U is a nucleophilic group, such as, nitro or cya~o; and Z' has the same meaning given in formula (III) above. It will be understood that Z' S said R43 may be ortho, meta or para .to said -N-.
In preferred compounds of this type, U is cyano and R43 is -Co2R46.

R40 R ~, ~ ~ CH- N- N ~

(11) R42 A~ R

wherein R40, R41, R42, R43 and Z' have the same meaning 10 given above and A~ is an anion /' ~ \R 5 2 (12) Z R49 wherein R47 is alkyl usually having 1. to 6 carbon atoms, phenyl, phenyl substituted with alkyl usually having 1 to 4 carbon atoms or halo, such as, chloro or bromo, R48 and R49 15 each are hydrogen or alkyl usually having 1 to 6 carbon atoms, R50 is hydrogen, alkyl usually having 1 to 6 carbon atoms, alXoxy usually having 1 to 6 carbon atoms or an 3~

electron-withdrawing group; R51 and R52, the same or different, each are electron-withdrawing groups; R47 and R48 taken together represent the carbon atoms to form a 5- or 6-membered N-heterocyclic ring, such as, an indolino ring;
5 R51 and R52 taken together represent a 5- or 6-membered heterocyclic ring, such as, a rhoda~ine ring; and Z' has the same meaning given in formula (III) above. By electron-withdrawing group is meant a group having a positive sigma value according to Hammett's Equation. Examples of lO preferred electron-withdrawing groups include nitro, cyano, carboxy, -CoNR53R54 wherein RS3 and R54 each are hydrogen or alkyl usually containing 1 to 6 carbon atoms, -CoR55 wherein R5$ is alkyl usually having 1 to 6 carbon atoms, phenyl or phenyl substituted with alkyl usually having 1 to 4 carbon 15 atoms; and -So2NR56Rs7 wherein R56 and R57 each are hydrogen, alkyl usually having 1 to 6 carbon atoms or benzyl.

R58 N ~ ~ ~' R58 wherein each R5~, the same or different, is alXyl usually 20 containing 1 to 20 carbon atoms or ~ wherein each R59, the same or different, and each R60, ~he same or different, are hydrogen, alkyl usually having 1 to 6 carbon atoms;
alkoxy usually having 1 to 6 carbon atoms, halo, such as, chloro or bromo; -SO2R61 is alkyl usually having 1 to 6 25 carbon atoms, phenyl or phenyl substituted with alkyl usually having 1 to 4 carbon atoms; carboxy; -CoNR62R63 wherein R62 and R63 each are hydrogen or alkyl usually ~2~3~2~

having 1 to 6 carbon atom~; Co2R64 wherein R64 is alkyl usually having l to 6 carbon atoms or phenyl; cyano; nitro;
trihalomethyl, such as trichloromethyl or trifluoromethyl;
-CoR65 wherein R65 is amino, alkyl usually naving 1 to 6 5 carbon atoms or phenyl; -NR66R67 wherein R66 and R67 each are hydrogen or alkyl usually havin~ 1 to 6 carbon atoms or -S02-NR68R69wherein R68 and R69 each are hydrogen, alkyl usually having l to 6 carbon atoms or benzyl: and Z' has the same meaning given in formula (III) above.

71 R70 R70 ~71 R72 ~ ~ ~ R72A~

(14) ~ CH ~ N ~ Z' S2 Rl wherein each R70 the same or different, is alkyl usually containing 1 to 20 carbon atoms; each R71 the sama or different, and each R72, the same or different, are hydrogen, alkyl usually having 1 to 6 carbon atoms; alkoxy 15 usually having 1 to 6 carbon atoms; halo, such as, chloro or bromo; -So2R73 wherein R73 is alkyl usually having 1 to 6 carbon atoms, phenyl or phenyl substituted with alkyl usually having 1 to 4 carbon atoms; carboxy; -CoNR74R75 wherein R74 and R75 each are hydrogen or alkyl usually 20 having 1 to 6 carbon atoms; -Co2R76 wherein R76 is alkyl usually having 1. to 6 carbon atoms or phenyl; cyano; nitro;
trihalomethyl, such as trichloromethyl or trifluoromethyl;
-CoR77 wherein R77 is amino, alkyl usually having 1 to 6 carbon atoms or phenyl, -NR78R79 wherein R78 and R79 each 25 are hydrogen or alkyl usually having 1 to 6 carbon atoms or -SO2-NR80R81 wherein R80 and R81 each are hydrogen, alkyl usually having 1 to 6 carbon atoms or benzyl; Rl is alkyl ~2`~

u~ually having 1 to 4 carbon atoms; A~ is an anion; and Z' has the same meaning given in formula (III) above. It will be understood that said 71 and R72 may be ortho, meta or para to ~aid ~ atom.
The compoun~s set out in ~ormulae (1) to (3) above are known and their use in photogra~hic products and processes as aLkali-bleachable light-screening dyes, for example, antihalation and color correction filter dyes forms the subject matter of U.S. Patents Nos. 4,304,833, 4,304,834 10 and 4,258,118, respectfully. It will be appreciated that the 2-sulfo and the 2,7-di-sulfo-substituted xanthenes of formula (2) that are disclosed in U.S. Patent No. 4,304,834 also may be employed in the present invention and that the 2-sulfo and 2,7-di-sulfo-substituted indolinyl xanthenes 15 disclosed and claimed as photographic light-screening dyes in U.S. Patent No. 4,258,119 also are useful.
The co~pounds of formulae (4) to (14) represent novel compounds of the present invention and may be synthesized in a conventional manner. For example, the 20 compounds of formulae (4) and (4a) may be synthesized by treating a 3,3-disubstituted-2,3-dihydrobenz[d]isothiazole-l,l-dioxide with potassium or sodium hydride to generate the sulfonamide anion for reaction with a t-alkyl chloroformate to yield the corresponding N-t-alkoxycarbonyl-substituted 2S compound. The N atom of said N-t-alkoxycarbonyl is then alkylated using an alkyl iodide or other suitable alXylation agent to yield the final product. The 3,3-disubstituted-2,3-dihydrobenz[d]isothiazole-1,1-dioxides employed as the 3tarting materials are known compounds and form the subject 30 matter of U.S. Patent No. 4,191,689 (where the 3,3-substituent~ ultimately comprising the A and B moieties are the same) and of U.S. Patent No. 4,311,839 where the 3,3-substituent~ ultimately comprising the A and B moietie~
are different).

~Z~3~2~

The compounds of formulae (S), (6) and (8) ~ay be synthesized by t~eating leuco intermediates of the general structure ~/` )~
~502NHR "

5 with potassium or sodium hydrides and then reacting with, for example, a di-tert-alkyl dicarbonate, an N-(t-alkoxycarbonyloxy) phthalimide or a halo-substituted-t~
alkoxycarbonyl chloride to form the corresponding N-t-alkoxycarbonyl intermediate followed by oxidation using, 10 for example, p-chloranil to give the final product. The oxidation step also may be carried out electrochemically.
Leuco intermediates useful as the starting materials for the compounds of formulae (5) and (6) and the synthesis thereof are disclosed in U.S. Patents Nos. 4,258,118 and 4,304,834, 15 respectively, and also in U.S. Patent No. 4,416,971. Dyes useful in forming the leuco intermediates for the compounds of formula (5) form the subject mat~er of U.S. Patent No.
4,405,788.
The compounds of formula (7) al~o may be 20 synthesized from an alkylsulfonamide leuco intermediate in the same manner as described for the compounds of formulae (5), (6) and (8). The leuco intermediate may be prepared by reducing a fluoran starting material to the alcohol, converting the alcohol to the bromo-methyl substituted 25 compound with hydrogen bromide and then reacting with ammonia and a sulfonyl chloride to give the leuco intermediate. Alternatively, the bromo-methyl compound may be reacted with the salt of a substituted sulfonylcarbamate. Fluoran dyes are well known in the art ~0 and typical dyes useful as ~tarting materials for the 2~

compounds of formula (7) are disclosed in U.S. Patent No.
~,959,571.
The compounds of formula (9) may be synthesized by treating the starting rhodamine with sodium or potassium 5 hydride and then reacting with, for example, a di-tert-alkyl dicarbonate to form the final product. Where R28 is alkyl rather than Z', the rhodamine starting material, after treating with the hydride is reacte~ with an alkyl halide and then with the di-tert-alkyl dicarbonate. Various 10 9-phenylxanthenes including rhodamines useful as the ~tarting materials have been disclosed in the art, ~or example, in Venkataraman, K., ~he Chemistry of Synthetic , Academic Press, Inc., New York, 1952, pp. 746-754.
The compounds of formulae (10) and (11) may be 15 synthesized, for example, by coupling the diazonium salt of an appropriately substituted aniline with a l,3,3-trialky-2-methyleneindoline to give the corresponding 2-formyl-1,3,3-trialkyl-(3H)-indolinium chloride phenyl hydrazone intermediate which is then used for subse~uent reaction.
20 For the compounds of formula (10), the hydrazone intermediate is reacted with potassium cyanide to give the corresponding 2-cyano hydrazone followed by reaction with a di-tert-alkyl dicarbonate to give the final product. To prepare compounds with different nucleophilic groups, U, the 25 cyano group may be replaced by reacting the ~
2-cyano-hydrazone product in the dark with a silver salt providing the desired U substituent, for example, silver nitrite. For the compounds of formula (11), the 2-cyano-hydrazone products of formula (10) are reacted with 30 the appropriate silver salt to provide the desired anion, A~. The synthesis of the above-denoted intermediates and of the diazocarbocyanines produced therefrom is well known and described in Gordon, P.F. and Gregory, P., Organic Chemistry in Colour, Berlin-Heidelberg-New York, Springer-Verlag, ~Z~3~2~

1983, page 87 and in Japanese Application, Laid-open ~o.
34719/72, Laid-open date November 22, 1972.
The compounds of formulae (12) and (13) may be synthesized by treating a benzylidene dye or a thiazine dye, 5 respectively, with potassium or sodium hydride to generate the nitrogen anion followed by reaction with, for example, a di-tert-alkyl dicarbonate to give the final products.
Benzylidene and thiazine dyes are well Xnown classes of dyes and various dyes of these types have been disclosed. For 10 example, various benzylidene dyes and their synthesis is disclosed in U. S. Patent No. 3,728,374, and various thiazine dyes and their synthesis is described in Venkataraman, K., The Chemistry of Synthetic ~yes, Academic Press, Inc., New York, 1952, pp. 791-795.
The compounds of formula (14) may be prepar~d in the same manner as the compounds of formula (7) using the desired rhodamine as the starting material.
The anion A~3 associated with the compounds of formulae (2), (3), (5), (6), t7), (8), (11~ and (14) may be 20 any single atomic ion or ionic group composed of a plurality of atom~ having a negative charge, for example, halide, such aq chloride, bromide or iodide, nitrate, tetrafluoroborate, perchlorate, periodate, acetate, oxalate, tosylate, sulfate, methane sulfonate, methane hydrogen disulfonate, m-benzene 25 hydrogen disulfonate, trifluoroacetate, hexafluoroace~ate, hexafluorophosphorate, azide or trifluoromethanesulfonate.
The following examples are given to further illustrate the present invention and are not intended to limit the scope thereof.

"Q ~t~fl E:xam~le 1 Prepar~tion of the compound having the ~ormula !3 ~3 Cl S02N- C - OC(CB3i~

Compound A having the following Eormula (A) H~¦
~ 52~l3 .
wa3 used as the starting material in step (a) below.
(a) Compound A ~7.5g, 0.013 mole~ was dissolved in 100 ml of dry tetra~hydrofuran. The solution was cooled to 5- - 10C and ~odium hydride (0.54g, 0.014 mole, 60% oil 10 dispersion) wa~ added portionwise. After the addition was complete, the ~ixture was gtirred for 1.5 hours warming to 20-C. The pale green solution was cooled to lO-C and di-tert-bu~yl dicarbonate (3~35g, OoO15 mole) in 30 ml o~
tetrahydrofuran wa~ added dropwise over one-half hour. The 15 reaction mixture wa~ then 3tirred at room temperature for one-half hour. TLC showed no more ~tarting compound A and one new spot. The reaction mixture was filtered through Celite*and evaporated to dryness to give 8.23g (92~ yield) of the t-butyoxycarbonyl-substituted leuco dye haviny the 20 formula ~B) 2 N C OC~CH3)3 *Trade Mark -21-~ ..

~2~3 g!2~

(b) The leuco dye prepared above (70 mg., 0.102mmole) was dissolved in dry methylene chloride (3 ml) and p-chloranil (2 equivalents, 50 mg) was added. A few drops of methanol were added to aid solu~ility and the mixture was 5 allowed to stir at room temperature until TLC (methylene chloride/hexane 2:1) showed that consumption of starting material was complete (2 hours). The solvents were evaporated and the residue triturated well with ethyl acetate and to~uene to remove excess p-chloranil. The crude 10 x~nthene was then redissolved in methylene chloride, and one equivalent of distilled trimethylchlorosilane (13 ~1) was added all at once. TLC (3% methanol in methylene chloride) showed a quantitative change in Rf of the cyan spot in 3-5 minutes, and the reaction mixture was evaporated and 15 subjected to high vacuum.
The crude dye product was applied to a flash silica gel column with methylene chloride to remove non-dye impurities. Further elution with 5% methanol in methylene chloride and collection of appropriate fractions gave 35 mg 20 (48%) of the title compound. NMR was consistent with the prOposed ~trUcture- ~max 665 nm/Epsilon 68,000 as meagured in methanol.
Compound A was synthesi~ed accordin~ to the procedure set forth in Example 1 of U.S. Patent No.
25 4,258,118.
As a further proof of structure, the ring-closed form of the title compound having the formula ~ ~2 was prepared as follows:

~7~

The cyan dye synthesized in Example 1 (70 mg, 0.097 mmole) was di~solved in 2 ml ~-methylpyrroLidinone and immersed with stirring into a pre-heated 180~C oil bath.
Stirring was continued, and over the next several minutes, 5 gas evolution was noted and the mixture lessened in color noticeably. After 5 minutes the miXture was allowed to cool and then poured into ice water. The precipi~a~e was centrifuged, w~shed with water, centrifuged again, dissolved in methylene chloride, dried over sodium sulfate and 10 evaporated. No cyan color was noted in solution, although some discoloration was noted. The residue from high vacuum pumping weighed 60 mg (105% of theory) and showed a small dark spot at the origin with only one mobile UV active spot (Rf 0.8, methylene chloride, silica gel). A short column of 15 silica gel eluted with methylene chloride gave a clear solution from which 46 mg (81% of theory) of a pale cyan film was obtained upon evaporation. NMR was consistent with the proposed ring-closed structure.
Example 2 Preparation of the compound having the formula 2--N--C--~(CH3) 3 3~3t24 Compound C having the following formula CH~ N ~) (C) ~ ~ ~ 3 was used as the starting material in step (a) below.
(a) Potassium hydride (83 mg, 2.07 mmole, 1.3 5 equivalents, washed with hexane, dried under nitrogen) was stirred as a slurry in dry tetrahydrofuran under nitrogen, and a dry tetrahydrofuran solution of Compound C (1.00 g, 1.59 mmole) in 5 ml tetrahydrofuran was added dropwise via syringe at room temperature. The mixture was allowed to sit 10 until effervescence ceased (about 10 minutes~ and then a dry tetrahydrofuran solution of N-(t-butoxycarbonyloxy) phthalimide (417 mg, 1.0 equivalent) was added dropwise.
Though the reaction mixture turned dark red shortly, TLC
(hexane/m~thylene chloride 1:2) indicated a clean reaction.
15 After 2 hours at room temperature, small additional portions of potassium hydride and the phthalimide reagent were introduced as ~olid~, and after 4 hours, the mixture was filtered through Celite and evaporated to give 1.28 g of foam. Chromatography (flash, silica gel, methylene 20 chloride/hexane 2:1) gave a one spot product, 804 mg (69%
yield) of the t-butoxycarbonyl-substituted leuco dye having the formula ~ ~ Cl (D) ~ SO~N - ~--CC(CH3 3 ~21~7~

(b) The leuco dye prepared above (800 mg, 1.09 mmole) was di~solved in 15 ml of methylene chloride/methanol (approximately 10:1), and p-chloranil (2.0 equivalents, 2.19 m le, 538 mg) was added all at once. The mixture was 5 allowed to stir at room temperature until no leuco dye was seen on TLC (about 2 hours~. Following evaporation and high vacuum pumping, the residue was triturated with ethanol (3 times) and filtered to remove most of the excess chloranil.
The residue was again evaporated under high 10 vacuum, re-dissolved in dry methylene chloride and allowed to stir at room temperature as one equivalent of freshly distilled trimethylchlorosilane (118mg, 140 ~1) was introduced all at once. ~fter 10 minutes at room temperature, this mixture was evaporated and the residue 15 subjected to flash chromatography on a short silica gel column. Impurities were removed by successive elutions with methylene chloride.
The desired dye product was eluted with 10%
methanol in methylene chloride to give 630 mg of the title~
20 compound. TLC showed one major spot with a slight contaminant. NMR showed the t-butoxycarbonyl group intact.
AmaX 552 nm/Epsilon 86,500 as measured in methanol.
Compound C was synthesized according to the procedures set forth in U.S. Patent No. 4,304,834 and 5 Example 6 of U.S. Patent No. 4,416,971.
Example 3 Preparation of the compound having the formula ~ ~Xo~
C}~3 O
S02N--C----cc(c~3)3 ~273~4 Compound E having the following formula ~0 -~~

(E~ ~ So2NHcH3 was used as the starting material in step (a) below.
(a) Compound E (176 mg, 0.33 mmole) aissolved in 4 S ml of dry tetrahydrofuran was treated with sodium hydride (1.2 equivalents of 50~ oil dispersion, 21 mg) until effervescence ceased (about 0.5 hour). A tetrahydrofuran solution of N-(t~butoxycarbonyloxy)phthalimide (1.2 equivalents, 112 mg) was added dropwise with stirring at 10 room temperature under nitrogen and the mix~ure was allowed to stir overnight. The tetrahydrofuran was evaporated and the residue partitioned with methylene chloride/aqueous bicarbonate. After mutual back extractions, the organic layer was dried and evaporated to give a foam which showed 15 essentially one spot on TLC at higher Rf than the s~arting material. A short flash column chromatography gave 200 mg (96% yield~ of the desired t butoxycarbonyl-substituted leuco dye of the following formula as a white foam.

. ~ .
0~
~,~

(F) ~ 52 ( 3 3 ~L~73~

(b) The oxidation of the leuco dye material obtained in step (a) was efficiently and quantitatively realized by electrochemical oxidation in acetonitrile solvent in the presence of tetrafluoroborate. After S evaporation of the solvent and removal of excess salts by partitioning between methylene chlorlde and water, the methylene chloride layer was dried and evaporated to give the title compound as very pure dye by NMR. ~ max 451 nm/Epsilon 43,300 as measured in acetonitrile.
A sample of the title compound dissolved in N,N-dimethylformamide and heated at 175~C for several minutes darkened considerably but the water precipitated solids showed loss of the t-butoxycarbonyl group by nmr and resonances expected for the ring-closed material.
Compound E used as the starting material in step (a) above was prepared as follo~s:
(i) 3,6-Dichlorosulfofluorescein (3.0g, 7.40 m le) and 4 equivalents of sodium phenolate (3.44 g, 29.6 mmole) were combined in approximately 6 ml of dry 20 N-methylpyrrolidinone and stirred under nitrogen at 110C
for 2 hours~ The mixture was heated to 160C briefly, allowed to cool and poured slowly into a mixture of ice and lN hydrochloric acid with good stirring. The precipitate was filtered off, washed well with water, taken up in 25 methylene chloride, dried over sodium sulfate, filtered and evaporated.
The material was subjected to flash chromatography on silica gel using successive elutions of methylene chloride with 2% methanol, 5% methanol and 10% methanol.
30 The 5% methanol in methylene chloride elution gave the purest band of the compound of the formula -~7-~0 ~--o~3 (i) ~ sO3~

having a bright yellow spot at Rf 0.35 (3~ methanol in methylelle chloride) 1.28g (33~ yield), ~ max 440 nm as measured in methanol.
(ii) Compound (i) (1.28g, 2.46 mmole) was di~solved in phosphorus oxychloride (20 ml) and treated with stirring at 60C for 4 hours (drying tube). Most of the phosphorus oxychloride was evaporated in vacuo and the residue ~as evaporated from toluene one time. Following a brief high 10 vacuum pumping, the residue was dissolved in methylene chloride and allowed to stir vigorously with an equal amount of conc. ammonium hydroxide for several hours (approximately 50 ml each). The organic layer was separated, the aqueous phase extracted again with methylene chloride and the 15 combined organic phases washed with brine and dried over sodium ~ulfate.
Following evaporation, the residue was subjected to flash chromatography on silica gel using methylene chloride as eluent. 700 mg (55% yield) of pure compound o 20 the formula ~~~
1'~ ,.

was collected, only slightly contaminated with a higher running spot, yellow in color, which gives solutions of the ~7~

product a mildly fluorescent appearance. NMR for compound (ii) was consistent with the proposed structure.
(iii) Compound (ii) (300 mg, 0.58 m~ole) was dissolved in methylene chloride (3 ml), and 3 ml of lN
5 sodium hydroxide was added. A five fold excess of iodomethane (0.2 ml) was then added ~nd the mixture stirred vigorously. A few crystals of tetrabutyl ammonium chloride catalyst were added and vigorous stirring continued. After 20 minutes, TLC showed complete conversion to the 10 N-methylated compound of the formula ~0~0~

~ N - CH3 tiii) ~ S2 The methylene chloride layer was separated, washed with water, brine, dried over sodium sulfate and evaporated. NMR
of the re~idue showed contamination only by a small amount 15 of catalyst which could be removed by filtration through a silica gel plug.
(iv) Compound (iii) (170 mg, 0.32 mmole) was dis~olved in 6 ml of ethylacetate and approximately 100 mg methanesulfonic acid and 1 ml water were added. The mixture 20 was brought to gentle reflux under nitrogen and approximately 300 mg of powdered zinc were added in portions over the next hour. After further reflux for an additional hour (solution goes yellow >pale red >yellow), Tl.C
showed that reduction was complete. Af~er cooling, the 25 mixture wa~ filtered and evaporated. The residue was di~solved in methylene chloride and carefully extracted with aqueou~ bicarbonate. The methylene chloride layer was dried and evaporated to give Compound E virtually pure by NMR.

~ 73~2~L

Example 4 Preparation of the compound having the formula o OCH3 3 ~ CH3 CH3 ~ _ CH3 ~ I fH3 11 -S2- N-~C OC(CH3)3 Compound G having the formula (CH3)3C- Si (CH3)2 OCH3 3 ~ ~ - CH3 (G) ~ S02 was employed as the starting material in step (a) below.
(a) Compound G (950 mg, 1.76 mmole),was allowea to stir in dry tetrahydrofuran at room temperature for 2 hours with 30% exce~s of potassium hydride (100 mg) to generate 10 the sulfonamide anion. A pale pink solution resulted.
Meanwhile an excess (approximately 20 fold) of t~butyl chloroformate for reacting with the sulfonamide anion wa~ prepared as follow3:
t-Butanol (1.31g, 17.6 mmole) was dissolved in dry 15 tetrahydrofuran (10 m) and cooled to 0C with stirring under nitrogen. Two equivalents of phosgene (3.5g, 35 mmole, 28 ml of 12.5% solution in benzene) were then added dropwise

7~2~

over a period of 10 minutes. Pyridine (1 equivalent, 1.4 ml) was then added dropwise and the mixture allowed to stir at 0C for 2.5 hours. The precipitate was filtered and the filtrate evaporated in vacuo below room temperature.
5 The residue was dissolved in tetrahydrofuran and added dropwise to the room temperature sol~tion of the sulfonamide anion. This mixture was allowed ~o stir at room temperature for 2 hours to give a pale yellow solution. The solvent was evaporated and the residue chromatographed (flash, sio2, 10 methylene chloride) to give partial ~esol~tion of 2 spots of close Rf. The upper spot proved to be the desired N-t-butoxycarbonyl-substituted compound, 388 mg (35%
yield).
(b) Tetraethylammonium fluoride was dried by 15 azeotroping in benzene for 2 hours (Dean Stark trap) followed by evaporation and high vacuum pumping.
The compound prepared in step a (385 mg, 0.6 mmole) was dissolved in dry tetrahydrofuran (15 ml) and 2 equivalents of methyl iodide (172 mg, 75 ml~ was added with 20 stirring under nitrogen at room temperature. The previously dried tetraethylammonium fluoride ~30 mg, 2.5 equivalents) was then introduced and the mixture allowed to stir vigorously at room temperature. A yellow color was noted immediately and after atirring overnight, TLC (methylene 25 chloride/acetone 9:1) showed no starting material; the product was a pale yellow spot at slightly lower R~. The mixture was filtered, evaporated and placed under high vacuum for 10 minutes. The crude material was filtered through a 3ilica gel pad with methylene chloride/acetone to 30 remove quaternary salts and evaporated to give 336 mg of yellow foam, one ~pot on TLC in three different solvent sy~tems. NMR and IR were consistent with the proposed structure ~max 380 nm/Epsilon 19,700 as measured in N,N-dimethylformamide.

~273~

Compound G used as the starting material in step (a) above was ~ynthe~i~ed in a known manner as disclo~ed, for example, in aforementioned U.S. Patents Nos. 4,191,689 and 4,311,839.
S Example 5 Preparation of the compound having the formula Cl~

CH2 1 ( 3~3 Compound H having the formula (H) ~ CH2 NH502CH3 10 was used as the starting material in step (a) below.
(a) Compound H (1.65g, 2,83 mmole) was dissolved in dry tetrahydrofuran t25 ml) under nitrogen and sodium hydride (163 mg of 50% oil dispersion, 1.2 equivalents) was added all at once at room ~emperature with stirring.
15 Evolution of hydrogen proceeded at a rather slow rate and stirring was continued until judged nearly complete ~1.5 hours).

3L2~7;3~

A dry tetrahydrofuran solution of N-(t-butoxycarbonyloxy)phthalimide (1.1 equivalents, 3.11 mmole, 819 mg) was then added dropwise and the darkening solution was allowed to stir overnight at room temperature.
5 TLC (methylene chloride) showed good product formation; the mixture was evaporated in vacuo using a large flask and the residue partitioned well with methyiene chloride and aqueous bicarbonate.
Combined organic layers were washed with brine, 10 dried over sodium ~ulfate and evaporated to a foam, 2.17g.
After high vacuum pumping, the material was dissolved in the minimum amount of methylene chloride and a rapid precipitation of a grey solid resulted, 670 mg. This solid proved to be sub~tantially pure t bu~oxycarbonyl-substituted 15 leuco dye having the following formula as determined by TLC
and NMR.
H ~ C~3 ~ CH2- ~ - C - oc(cH3)3 (J) ~ gO3CH3 (b~ The leuco dye prepared above (670 mg, 0.98 mmole) was stirred in methylene chloride/methanol (15 ml of 20 about 10:1) and chloranil (2 equivalents, 1.96 mmole 483 mg~ was added at room temprature. Stirring was continued until TLC (methylene chloride) showed no leuco dye remaining (2.5 hours). The mixture was evaporated and the residue triturated well with toluene to remove excess chloranil.
25 ~he residue wa~ subjected to high vacuum for one-half hour and ~hen disso~ved in dry methylene chloride. Trimethyl silyl chloride (1.2 equivalents, 150 ~1) was added and the mixture allowed to stir at room temperature for one-half hour before being evaporated again.
The residue was chromotographed on a flash silica gel column using, in sequence, methylene chloride, 3%
5 methanol in methylene chloride and 6% methanol in methylene chloride. The 3% methanol wash eluted some colorless, ring-closed material. The 6% methanol elution gave fractions containing the desired product as dark green-black solutions. Evaporation and pumping gave the title compound 10 as a black solid, 400 mg. (57% yield). NMR was consistent with the proposed structure. ~max 455nm/Epsilon 15,400 --AmaX 605nm/Epsilon 15,700 as measured in methanol.
Compound H used as the starting material in step (a) above was synthesized as follow~.
(v) 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran (8.0g, 15.5 mmole) was dissolved in 200 ml dry ~etrahydrofuran and stirred at room temperature while boron trifluoride etherate (8.8g, 6.6 ml, 61 mmole) was added. The intitially clear solution became greenish-black 20 due to the open carboxylate form of the dye. Sodium borohydride (1.82g, 48 mmole) was ~hen added and the mixture allowed to stir at room temperature under nitrogen (initial ice ba~h cooling). The mixture slowly evolved ga~ and began to lighten in color after about 15 minutes. After stirring 25 at room temperature for 3 hour~, TLC showed complete reaction (aliquo~ ~uenched wi~h dilute hydrochloric acid and extracted into methylene chloride).
The reaction mixture was quenched by pouring into 600 ml of water containing 25 ml of conc. hydrochloric 30 acid. After thorough shaking, the product precipitated as a greenish oil. The supernatant was decanted and extracted with methylene chloride in a ~eparatory funnel and these extracts combined with a methylene chloride solution of the oily precipitate. The methylene chloride solutio~ was 35 wa~hed with brine, dried over ~odium sulfate and ~il2~

evaporated. The concentrated solut;on was filtered through a small ~ilica pad with methylene chloride and tetrahydrofuran to remove an origin impurity and the filtrate evaporated to 5.8g (74% yield) of crude product 5 comprising the compound of the following formula as a pale green-grey foam.

<~} N ~a ( 3 (v) CH20H

(vi) The crude product obtained in step (v) above (5.8 g, 11.5 mmole) was dissolved in methylene chloride (100 10 ml) and the mixture purged with nitrogen with ice bath cooling. HBr gas was then introduced and the mixture allowed to stir in the cold. The course of the reaction was followed by TLC on silica using methylene chloride as eluent. After 0.8 hour, all of compound (v) had been 15 consumed. After a further 10 minutes of stirring, the mixture was carefully added with shaXing to approximately 300 ml of saturated sodium bicarbonate solution in a large Erlenmeyer. The pale orange solution reverted to greenish grey and the phases were separated in a separatory funnel.
20 The aqueous phase was washed with methylene chloride, the combined organic phases washed with bicarbonate, brine, dried over sodium sulfate and evaporated. After high vacuum, the crude product comprising the compound of the following formula waq obtained as a paLe greenish-grey 25 solid, 5.8g ~90% yield).

~2'7.31~2~

13 ~1 U 13 C~2Br (vi) ~

(vii ) The crude material obtained in step (vi) above (3.8g, 6.7 mmole) was added in one portion to 250 ml of methanol previously saturated with arnmonia gas and the 5 mixture left to stir at room temperature overnight. After this time, some solids were still not dissolved and TLC
(methylene chloride/hexane/l:l) confirmed the presence of the starting material. The temperature of the mixture was raised to 50C with an oil bath as fresh ammonia was 10 admitted with constant stirring. ~fter about 4 hours, all solids had dissolved and again the solution was allowed to stir at room temperature overnight.
TLC sh~wed no starting material, 50 the mixture was purged with nitrogen and evaporated to dryness. High 15 vacuum pumping left 3.6g of crude residue which was dissolved in dry pyridine (25 ml), and 1.8 equivalents of methanesulfonyl chLoride was added (12 mmole, 0.9 ml). This mixture was allowed to stir at room temperature overnight and then most of the pyridine was removed in vacuo. The 20 residual oil was triturated well with cold 1~ hydrochloric acid, the crude solid filtered, washed well with water, taken up in methylene chloride, washed with cold lN
hydrochloric acid, water, brine, dried over sodium ~ulfate and evaporated to give a foam. Chromatography on silica 25 with methylene chloride followed by 10% ether in rnethylene chloride ~ave material which by NM~ was of sufficient purity to be used as the starting r~terial in Example 5 above.

~z~

The compound of Example 5 also was synthesi~ed as follows:
Methanesulfonamide (4.0g, 42 mmole), 6.96g potassium carbonate and ll.Og di-tert-butyl dicarbonate were 5 refluxed in acetone for 8 hours, and the reaction mixture allowed to cool and then filtered. The crude product was triturated well with warm methanol to remove insoluble potassium carbonate and the methanol evaporated and subjected to high vacuum to give as pure product, the 10 potassium salt of N-t-butoxycarbonyl-methanesulfonamide.
The leuco benzyl bromide compound of formula (vi) (10.2 g, 18 mmole) was dissolved in dry N-methylpyrrolidinone with the potassium salt of the sulfonamide prepared above (1.5 equivalents, 27 mmole, 15 6.29g) and the mixture allowed to stir at room temperature overnight under a nitrogen atmosphere. An aliquot was withdrawn and injected into water to give a crude solid which showed nearly quantitative reaction by TLC (methylene chloride). The reaction mixture Wa5 poured into ice/water 20 and the crude product filtered off and washed well with water. The material was taken up in methylene chloride, dried, concentrated and filtered through a short Florisil pad to give ll.Og of grey solid upon evaporation. TLC
showed only 8mall impurities. Recrystallization from 25 toluene/hexane gave compound J as off-white granular crystals, melting point 140C (dec.), 9.3g (76% yield).
The leuco dye (Compound J) was converted to the dye product using the same procedure described in step b of Example 5 above.

r ~
3~3~4 Example 6 Preparation of the com~ound having the formula CE ~ Cl~

~ S2N - C oC(CH3)2CC13 The starting material used in step (a) below was 5 Compound C as used in Example 2 above.
(a) Compound C (2g, 0.00317 mole) was dissolved in 25ml of tetrahydrofuran under nitrogen. Sodium hydride (0.13g, 0.00349 mole) was added and the mixture stirred for one hour at room temperature. To this solution 10 2,2,2-trichloro-tert-butoxycarbonyl chloride (1.14g, O.00475 mole) in 5 ml of tetrahydrofuran was added dropwise over 30 minutes. The reaction mixture was stirred at room temperature for 3 hours. TLC (ethyl acetate/n-hexane--25:75) showed only a small amount of starting Compound C.
lS The reaction mixture was poured into water and extracted with methylene chloride. The methylene chlorlde was dried over sodium sulfate and evaporated to give a pink solid which was washed with hexane to yield 2.2g of the corre~ponding trichloro-tert-butoxycarbonyl leuco dye.
(b) The leuco dye prepared above (lg, 0.0011~
mole) was dissolved in 10~ methanol/methylene chloride and chloranil (0.5g, 0.00203 mole) was added. The reaction mi~ture wa~ ~tirred at room temperature for 3 hour~. TLC
(ethyl acetate/n-hexane--25:75) showed that no more of the 25 leuco dye was present. The reaction mixture was ~'73~

precipitated into ether. The precipitate was collected, dissolved in methylene chloride and 0.5 ml of chlorotrimethylsilane was added and stirred for 30 minutes.
The methylene chloride solution was stirred with 20g of 5 acidic alumina for 15 minutes. The alumina was filtered off and washed with 2~5% methanol/methylene chloride. The title compound was recovered in a yield of 0.80g from the 2.5 methanol/methylene chloride wash.
The title compound (0.25g) was dissolved in a 10 minimum amount of N-methylpyrrolidinone and heated to 195C. Samples were taXen at 5, 10, 15, 20 and 30 minutes for thin layer analysis. TLC ~silica gel using ethyl acetate/n-hexane--25:75) indicated that only a smaLl amount of title compound was present after 15 minutes and that the 15 product after heating was the ring-closed compound of the following formula, which structure was consistent with ~MR.

~CU~Icuu~l The above-denoted ring~closed compound and the corresponding N-methyl ring-closed compound were heated in 20 N-methylpyrrolidinone and observed to remain colorle~s even at 200C. The methyl compound after heating at 185U-195C
for 50 minutes was found to be stable, that i8, the N-methyl group remained in tact.

~73~

Example 7 Preparation of the compound having the formula IH3 ~ / I N ~ Cl~
Cl ~ 5o7- N - C - oC(CH3)2C2Hs Compound C as set out in Example 2 was used as the 5 starting material in step (a) below.
(a~ Sodium hydride (50 mg of 50% dispersion in oil, 1.25 equivalents) was allowed to stir in dry tetrahydrofuran (5 ml) under nitrogen at room temperature as a dry tetrahydrofuran solution of Compound C (530 mg, 0.84 10 mmole) was added dropwise. Following the addition, the mixture was allowed to stir at room temperature for one-half hour to give a homogeneous pale yellow solution. To this ~olution was added dropwise, an excess of textiary-amylchloroformate. The pink mixture was stirred at room 15 temperature for 2 hours and TLC (methylene chloride/n-hexane 2:1) showed good product formation. The mixture was evaporated and the residue chromatographed (flash, silica gel, methylene chloride/n-hexane 2:1) to afford 600 mg (96%
yield) of the leuco dye of the following formula as a white 20 foam.

~ ~73~

~ H~l (K)Cl ~ S0 - l~ 3 ~ oC(CH )2C2Hs (b) The purified leuco dye (600 mg, 0.8 mmole) and p-chloranil (396 my, 2 equivalents) were allowed to stir at room temperature in methylene chloride with a little 5 methanol to aid solution. After 2 hours, TLC indicated that no starting material re~ained. The mixture was evaporated and the residue triturated well with toluene and ethyl acetate and the re~idue subjected to high vacuum pumping.
The residue was dissolved in methylene chloride and 10 trimethylsilyl chloride (0.15 ml) was added. After room temperature stirring for 20 minutes, the mixture was evaporated. Chromatography on silica gel (flash) with methylene chloride followed by 2% me~hanol in methylene chloride and 5% methanol in methylene chloride gave 4S0 mg 15 of title compound as purified dye. ~max 551nm/Epsilon 87,500 a~ measured in methanol.
Example 8 Preparation of the compound having the formula ~r~J~--r ~3 o - N - C OC(CH3)3 A ~ample of the leuco dye D prepared in Example 2 above was oxidized elec~rochemacally in acetonitrile and (CH3)4 ~ ~4~ as working e~ectrolyte. The oxidation resultPd in the formation of a ~ignificant amount of a purple 5 impurity. Chromatography (fla~h, silica gel, 6%
methanol/methylene chloride) gave ~ubstantially pure material. A sample of purified mat~erial was coated in polyvinyl-N-pyrrolidinone on a glass plate and one-half of the coated sample was heated on a heating platen. After one 10 minute at 170C some density remained in the heated portion.
Example 9 Preparation of the compound having the formula 3 ~ ~4 52- N - C - OC(CH3)3 A sample of the leuco dye B prep æ ed in Example 1 above was oxidized electrochemically in ~,~-dimethyl-formamide using (Bu)4~3kF4~ as working electrolyte. The oxidation was not totally clean as a second cyan material was evident. Chromatography (flash, silica gel, 6%
20 methanol/methylene chloride) gave a sample of good purity.
As in Example 9, a sample of the compound was coated in polyvinyl-N-pyrrolidinone on a glass plate and one-half of the coated sample was heated on a heating platen. Again, some difficulty was encountered in obtaining an excellent 25 Dmin when the coating was kept at 170C. for 1-2 minute~.

3l273~

Example 10 Preparation of the compound having the formula Cl ~ Cl 3 CH
~ 0 1 3 l~ - OC(CH ) Th~ leuco dye D as prepared in Example 2 (1.18g, 5 1.61 mmole) was dissolved in methylene chloride with 2 equivalents of p-chloranil (795 mg, some methanol added to aid solubility) and allowed to stir at room temperature for 3 hours (no starting material remaining). The mixture was evaporated and the residue triturated well with ethyl 10 acetate to remove the chloranil.
250 mg of this mixture was then taken up in methylene chloride and a 25% molar excess of trimethylsilyL
azide (0.32 mmole, 40 ~1) was added. After stirring at room temperature for 15 minutes, TLC showed little change in Rf 15 for the dye, but a new orange-brown lead spot (trimethylsilyl chloranil). After evaporation, a short flash silica gel chromatography using methylene chloride, th~n 3% methanol in methylene chloride and 6% methanol in methylene chloride gave a one spot product, 190 mg of 20 magenta qolid. NMR indicated high purity. ~max 55 nm/Epsilon 105,000 as measured in methanol.

~73~

Example 11 Prepara~ion of the compound having the formula O O
C - OC(CH3)3 I C( 3)3 Cl ~ N ~ o ~ ~1 3',6'-Bis(p-chloroanilino3fluoran (3.73g, 000068 5 mole) was stirred in 50 ml dimethyl sulfoxide; sodium hydride (0.98g of a 50% oil dispersion, 0.0204 mole) was added portion-wise over 20 minutes. A dark green mixture formed which was heated to 40C over 30 minutes. After cooling to room temperature, di-tert-butyl dicarbonate 10 (4.45g, 0.0204 mole) in 10 ml of dimethyl sulfoxide was added dropwise over 5 minutes; the mixture changing from dark green to red-orange. After heating a~ 40C for 3 hours, a second chæ ge of 50% sodium hydride ~0.49g~ was added, heating at 40~C was extended for 3 more hours, 15 followed by addition of a second charge of di-~ert-butyl dicarbonate (8.90g) and subsequent heating for 1 hour at The mixture was cooled to room temperature and cautiously poured into 250 ml of water with stirring; this 20 mixture was ex~racted twice with 250 ml portions of ether.
The ether extracts were combined and washed with five 200 ml portions of water, then set over sodium sulfate to dry.
Filtration and evaporation of solvent left 6.8g of a viscous red-orange syrup. This was subjected to high pressure 25 column chromatography (~ilica gel, methylene chloride eluant). There was obtained 2.18g pale pink, amorphous :~27;3 ~

solid. Thig wag recrystallized from 12:1-hexane:methylene chloride ~o provide 1.42g jagged rleedles, which were crushed to a pale cream powder, m.p. 214-215C (dec.), m/e 751, nmr ~CDC13) ~upports th~ title structure.
Example 12 Preparation of the compound having the formula O O
Il 11 CH3 1 0c(CH3)3 1 OC(CH3)3 ¢~N~N ~)3 CH3(~
~ ~=0 3',6'-Bis(2,5-dimethylanilino)fluoran (20~, 0.037 mole) in 175 ml dry dimethyl sulfoxide was treated portion-wise with 10 sodillm hydride (5.34g 50% oil dispersion, 0.111 mole) over l.S hours. The mixture was heated to 45C for 2 hours, it became blue-green. Di-tert-butyl dicarbonate (24.23g, 0.111 mole) in 25 ml dimethyl sulfoxide was added over 5 minutes producing a red-orange mixture. This was heated to 65C for 15 2.S hours (caution: foaming may be encountered during early heating). After cooling to room temperature, the mixture wa~ poured into 2 liters of ice-water, followed by filtration. The pasty ~olid, so obtained, was dissolved in methylene chloride and washed several times with water 20 (sodium chloride added to break emulsions). After drying (Na2S04), the methylene chloride extract was concentrated to a small volume and subjected to high pressure column clu~omatography (SiO2; 90:1~)-cyclohexane/ethyl acetate eluant). There was obtained 5.4g purified product as a 25 faint orange amorphous solid.
The 3',6'~Bis~2,5-disr~ethylanilino~fluoran used above wa~ synthesizea as follow~:

~Z~3~

2,5-Dime~hylaniline (78.5g, 0.648 mole) wa~ mixed with 3',6'-dichlorofluoran ~59.$3g, 0.162 mole) in 300 ml of sulfolane. Anhydrous aluminum chLori~e (43.2g, 0.324 mole) was addad portion-wise ov~r 45 mi~utes. The resulting S mixture was heated to 150C for 2.5 hours, the~ pou~ed into 2 liters of cold 10% hydrochloric acidO The pasty solid collected by filtration, was dissolved in ethyL acetate, the ~esidual water removed and then the solvent ev~porated. The residue was triturated repeatedly with ether to provide lO 45g. of crude product, which was used in the above preparation without further purification.
Example 13 Preparation of the compound having the formula O O
C-oc(cH3)3 c-OC(C~3)3 CH3 ~ ~ ~ ~ ~ 3 ~C=O

lS The title compound was prepared according to the procedure described in Example ll above using 0.1g of 3',6'-bis(p-methylanilino)fluoran, 3.5 equivalent~ of sodium hydride and 10 equivalents of di-tert-butyl dicarbonate and was obtained as a white solid (yield lg, melting range 20 196-197C).

-4~-~73~4 Example 14 Prep~ration of the compound having the formula O
I -OC(CH3)3 C - OC(CH3)3 3 ~ ~ ~ OCH3 C=O

The title compound was prepared according to the S procedure described in Example 11 above using 3g of 3',6'-bis(p-methoxyanilino~fluoran, 3.~ equivalents of sodium hydride and 3 equivalents of di-tert-butyl dicarbonate and was obtained a~; a tan solid (yield 19, melting range 196-200C. Decomp~) Example 15 Preparation of the compound ha~ing the formula -n ~;~OC (CH3~ 3 N ~ol~ N~L

~C_O

3',6'-Bis(4-methylanilino)fluoran (l.Og) and 0.35g of sodium hydride were stirred at room temperature for 2 15 hours and then stirred at 45C for another 30 minutes.

~z~z~

n-Bromooctane (0.34 cc., 1 equivalent) was added by syringe and after stirring briefly at 45C, the reaction mixture was placed on an oil bath warmed to 65C. Stirring was continued and the reaction brought to completion by very small additions of n-bromooctane. Monitoring by TLC showed a very clean conversion to the mono-N-octyl fluoran.
The oil bath temperature was reduced to 45C and di-tert-butyl dicarbonate ~0.4g, 1 equivalent3 was added. TLC showed about 50% conversion within 30 minutes. The oil bath temperature was increased to 50C and small quan-tities of sodium hydride and di-tert-butyl dicarbonate were added. Heating was continued for 2 hours and then -the reaction mixture was allowed to cool over-night.
The reaction mixture was poured in-to 300 cc water con-taining 100 cc ethyl aceta-te with vigorous stirring and the organic layer separated, washed with water and brine, dried over sodium sulEate and concentrated to dryness. The residue was triturated with methylene chloride twice and then applied to a medium length medium pressure silica geL column in a minimum amount of methylene chloride. After eluting with methylene chloride and 1% to 8% methanol/methylene chloride, the silica gel containing the desired band of material was removed from the column. Extraction of this ma-terial with acetone gave 483 mg of the title compound as an off-white solid, mel-ting range 196-197C.

~ 739!2~

Example 16 Prepara-tion of the compound having the formula C - oC(CH3)3 ~H3 C=O

The -title compound was prepared according to the pro-cedure given in Example 15 above using 0.5g of 3',6'-bis (p-methy-lanilino)fluoran, about 3.5 equivalents of sodium hydride, 1 equivalent of methyl iodide and 2-3 equivalents of di-tert-butyl dicarbonate (yield 35 mg, melting range 138-142~C).
Example 17 Prepara-tion of the compound having the formula 1l f~l7-n C OC(CH3)3 CH30 ~ ~ ~ OCH3 ~C=O

The title compound was prepared according to the proce-dure given in Example 15 above using 1.77g of 3',6'-bis(p-meth-oxyanilino)fluoran,3.5 equivalents of ~.~3~

sodium hydride, l equivalent of n-bromooctane and 1.1 equivalent~ of di-tert-butyl-dicarbonate and was obtained as a tan solid (yield O.9g, melting range 200-215C).
Example 18 Preparation of the compound having the formula C ~ CH3 ~- 0 - c(CH3)3 - CH - N- N ~

(a) In a S00 ml threeneck roundbottom flask equipped with a mechanical stirrer, a thermometer, an addition funnel and a vent to an exhaust bubbler, ethyl 10 m-aminobenzoate (ll.Sg, 0.07 mole) was dissolved in a solution of 140 ml of water containing 22 ml of conc.
hydrochloric acid. The almost colorless solution was cooled in a ice-salt bath to -l~C and a solution of sodium nitrite ~5.07g, 0.0735 mole) in 25 ml of water was added beneath the 15 surface of the aniline-HCl solution over a period of 30 minutes while ~tirring. After stirring for another 20 minutes in the cold, the reaction mixture gave a positive test for HNO2 with s~arch iodide paper. Sulfamic acid was added until no HN02 could be detected by the starch iodid~
20 test. While the reaction mixture was stirred at -2C.
1,3,3-trimethyl-2-methyleneindoline (12.139, 0.07 mole) was addsd dropwise over a period of 1.5 hours while stirring.
The reaction temperature was kept below 0C. The reaction mixture was diluted with about 500 ml of brine solution and ¢~

the orange solids collected on a filter. The solids were recry-stallized from 300 ml of boiling water to yield 13.5g. of 2-formyl-1,3,3-trimethyl-(3H)-indolium chloride m-carbethoxyphenyl hydrazone of formula L below after drying over P20s in vacuum.
~max 445nm/Epsilon 42,000 as measuxed in methanol.

CH`_ N - ~H ~

CH3 jlOC2H5 ~ (b) Compound L (8.5g, 0.022 mole), 150 ml of methylene-chloride and 50 ml of water were charged in-to a 500 ml threeneck roundbottom flask equipped with a mechanical stirrer, thermometer and nitrogen inlet and outlets. The mixture was rapidly stirred at 21C under a nitrogen atmosphere while KCN (5.54g, 0.085 mole) was added portionwise during about 5 minutes. After rapid stir-ring at room temperature for 48 hours, -the orange organic phase was separated and dried over sodium sulfate. (The excess cyanide in the water layer was destroyed by the addition of cold NaOCl).
The organic phase was evaporated under reduced pressure to yield

8.71g of orange solids. The solids were triturated with 200 ml of ether and filtered to give 5.88g of a yellow solid. The solid sample (5.88g) was rich in the new compound, ~-cyano-2-formyl-1, 3,3-trimethylindoline m-carbethoxyphenyl hydrazone of formula M
below.

3~

CH~ CH3 ~ ~ CN ~

(M) CH3 ICl OC2H5 (c) A 500 ml threeneck roundbottom flask equipped with a thermometer, nitrogen in~et and outlet, a condenser, and a magnetic stirrer was charged with 150 ml methylene 5 chloride, di-tert-butyl-dicæ bonate (5.24g, 0.024 mole) 4-dimethylaminopyridine (1.32g, 0.019 mole) and Compound M
~7.33g, 0.019 mole) as a solid~ mixture which contained about 30-40% of the ionic cyanide species. The orange solution was stirred under a nitroqen atmosphere at room 10 temperature overnight. After washing the reaction solution with water (3 X 75 ml), it was dried over sodium sulfate and evaporated under reduced pressure to yield 14.6g of an orange syrup. Thin layer analy~is (silica gel elut~d with a mixture ethyl aceta~e/n-hexane-3:7) revealed a new colorle~s lS compound and a yellow compound that corresponded to the unreacted ionic ~tarting compound component. The new compound was isolated by preparative column chromato~raphy (silica gel colu~n elu~ed with 3:7 ethyl acetate/n-hexane) to yield 9.2g of the title compound as an almost colorle~s 20 solid. The as~igned structure was supported by ma~s spectroscopy and NMR.

?11, 27 31 b~ 4 Example 19 Preparation of the compound having the formula CH3 CH3 ~ - - c~CH3)3 CH _ N - ~ ~
CH3 1lOC2 5 Silver nitrite (0.353g, 0.0023 mole) was added to 5 a coLd (about 5C) solution of the compound of Example 18 (0.51g, 0.0011 mole~ in 40 ml of tetrahydrofuran while stirring. Stirring at room temperature and in the dark continued for 4~ hours. The reaction mixture was filtered to remove ~gCN and exce~s AgN02. Evaporation of the 10 filtrate gave approximately 0.5g of an orange viscous syrup from which the title coi~pound (260 mg) was isolated by chromatography (silica gel eluted with 7:3 n-hexanelethylacetate). The structural assignment wa~
aupported by mass spectroscopy and NMR.

~ 2~3~

Example ~0 Preparation of the compound ~ving the formula C 3 3 1l - CH N-1 ~ 3)3 CH3 1lOC2H5 . _. .

In a small round bottom flask fitted wnth magnetic S stirring bar, the compound of Example 18 (O.lOg, 0.0002 mole) and silver tetrafluoroborate (0.039g, 0.0002 mole) were dissolved in 5 ml acetone. The mixture was stirrea about 45 minutes and allowed to stand overnight. Thin layer analysis (silica gel eluted with a mixture of lO ethylacetate/n-hexane~-30:70) showed only a trace of starting hydrazone compound. ~he reaction mixture wa~
filtered to remove AgCN and the yellow filtrate diluted with about 2-3 volumes of n-hexane. The precipitate that formed was filtered and pre~sed to give llO mg of the title l5 compound as a yellow solid. ~he assigned structure was ~upported by NMR.

Example 21 Preparation of the compound having the formula C--OC(CH3)3 CH = N--N

~H

N03~) 0 In a 50 ml threeneck roundbottom flask equipped 5 with nitrogen inLet, magnetic stirrer and condenser, the compound of Example 18 (0.64 g, 0.0013 mole) was dissolved in 35 ml of acetone to give a clear yellow solution. Silver nitrate (0.22g, 0.0013 mole) was added and the reaction mixture stirred for about one hour. Stirring was continued 10 overnight and thin layer analysis (silica gel eluted with a mixture of ethyl acetate/n-hexane--30:70) indicated that the reaction was substan~ially complete. The reaction mixture was filtered to remove AgCN and the yellow filtrate evaporated to yield 960 mg of yellow syrup. The syrup was 15 dissolved in 15 ml of acetone, charcoal treatëd and filtered through Celite. The light yellow filtrate was diluted with about 5 ml of acetone rinse and then abou~ 40 ml of n-hexane was added to the cloud point. The precipitate of tiny crystalline spheres that formed were filtered and pressed to 20 yield 450 mg of the title compound as a light yellow powder. The assigned struture was supported by NMR.

7~

Example 22 Preparation of the compound having the formula CH ~ CH3 ' ~- -C(CH3)3 CH = N- N ~

~OC2H5 O

(a) In a 500 ml threeneck roundbottom flask 5 equipped with a mechanical stirrer, a thermometer, an addition funnel and a vent to an exhaust bubbler, ethyl m-aminobenzoate (5.75g, 0.035 mo~e) was dissolved in a solution of 70 ml of water containing 11 ml of conc.
hydrochloric acid. The almost colorless solution was cooled 10 in an ice-salt bath to -1C and a solution of sodium nitrite (2.54g, 0.0368 mole) in 15 ml of water was added beneath the surface of an aniline HCl solution over a period of 30 minutes while stirring. After stirring for another 20 minutes in the cold, the reaction mi~ture gave a positive 15 test for HNO2 with starch iodide paper. Sulfamic acid was added until no HNO2 could be detected by the ~tarch iodide test. While the reaction mixture was stirred at -2C
3,3,2-trimethylindoline (5.6g, 0.035 mole) wàs added dropwise over a period of 1.5 hours while stirring. The 20 reaction temperature ws kept below 0C. The product as set out in formula (N~ below was collected on a filter and purified by column chromatography (silica gel, 5% methanol in methylene chloride). Characterized by M/e~ 336, ~max 443nm.

~3,~

(b) Compound (N) (744mg, 2 mmole) was dissolved in methylenechloride 925ml) containing 4-dimethylaminopyridine (488mg, 4 mmole) and di-tert-butyl dicarbonate (872mg, 4 S mmole) added at room temperature with stirring. The reaction mixture was refluxed for 4 hours and the title compound was isolated by column chromatography (silica gel, 4% n-hexane) and crystalization from n-hexane.
Characterized by M/e- 435 and NMR.
Example 23 Preparation of the compound having the formula c\3 ,,, CN
N-- ~ CH- C \
C - O 1l 2 1C(CH3)3 Compound O having the following formula was used as the starting material below.

~73~2~

CH - N ~ CH - C

(o) b The nitrogen anion of Compound N was generated by adding 1.5 equivalents of sodium hydride to 300 mg of Compound N in dimethyl sulfoxide and then 2 equivalents of 5 di-tert-butyl-dicarbonate was added. The reaction mixture was warmed at about 30C and allowed to stir overni~ht.
Thin layer chromatography using 5~ ethyl acetate/n-hexane showed a colorless compound which turned yellow upon heating. Water work up followed by preparative silica gel 10 chromatography gave 370 mg of pure title compound as a faint yellow oil. The assigned structure was supported by mass spectroscopy. ~ max 338 nm/Epsilon 19,200 as measured in methanol.
Example 24 Preparation of the compound having the formula f C -OC(CH3)3 ~ - oC(CH3)3 ¦ ~

1=0 OC(CH3)3 ~ 73~ 6335~-1576 (a~ the intermediate having the formula ( P ) ~ ~

was prepared by treating 2,7-dianilinophenothiazonium chloride t3.24g, 0.00774 mole) with sodium hydride (3 5 equivalent3) in 150 ml of dry dime~hyl sulfoxide over 1.5 hour~ at ambient temperature. The mixture was heated to 45C over 40 minute~ and di-tert-butyl dicarbonate (3 equivalentq) was subsequently added over 10 minute~. The reaction mixture was poured into 750 ml of water and 10 iltered to provide a pa~ty precipitate which was dissolved in 300 ml of methylene chloride and dried over sodium s~lfate. After filtration the ~iltrate's volume wa~ reduced to 50 ml, and it was applied to a Waters* High Pre3~ure ~hromatography 3ys~em (~ilica gel ~ubstrate). The mixture 15 was eluted with 80:20-hexane:ethyl acetate to provide 900 mg. purified intermediate (Compound P~ tructure conirmed by NMR and ma88 ~pectroqcopy).
(b) The title compound was prepared by redction of the above intermediate tComPound P) followëd by in- itu 20 treatment with excess di-tert-butyl dicarbonate. Thu3, the intermedia~e (0.99, 0.00174 mole) was ~tirred under nitrogen in a mixture of methylene chloride (65ml) and water (20ml) containing ~odi~m dithionite (0.9lg, 0.00522 mole), a couple of cry~tal~ of tetrabutyl ammonium chloride, and ~odium 25 bicarbonate (2 19g, O.Q261 mo1e). The blood-red mixture became ~traw-yellow when reduction wa~ complete. The ; methylene chloride layer wa~ transferred to a concent~ation fla~k (containing ~ome solid Na2S204 and NaHCO3) under *Trade Mark _59_ ",,~

~ 63356-1576 nitrogen. The methylene chloride was removed under reduced pre3sure. The residue was diasol~ed in 65 ml of tetrahydrofuran and transEerred under nitroge~ ~o a reac~ion flaqk containing a little Na2S2o4 and NaHCO3 plus one ml 5 water. Di-tert-butyl dicarbonate (19.62g, 0.09 mole) was added portion-wiqe in 60 ml of tetrah~drofuran over 4.5 hours to the refluxing solution of the reduced intermediate. The reaction was Eollowed by thin layer chromatography (80:20 n-hexane:ethyl acetate eluant) and 10 isolated by column chromatography. M/e~ calculated: 682, found 682.
The thermal "bleaching" of the compounds of Ex~mple3 1 to 6 and 10 were evaluated by heating a qample of each compound in polyvinyl pyrrolidone coated on a gla~
15 pla~e. The coatings were prepared by combining approxirnately equal weights of compound and polyvinyl pyrrolidone in a suitable solvent, for example, methanol or 2 methoxyethanol, appplyiny a layer of the coating ~olution on a glaqs plate using a $12 Miro~, and allowing the coating 20 to air ~ry. The testiny of the sample3 and the result~ a~
determined by vi3ual obqervation were as follow~.
Example l--A sample placed on a hot plate was gradually heated to 175-C. Fading began at about lS0C and bleaching wa~ complete by 175-C. Another ~ample placed on a 25 hot plate preheated to 175~C bleached in approxLmately 90 ~econds.
Example 2--A sample placed on a hot plate wa~
gradually heated and began to bleach at about lSO~C. The sample was ~lowly heated to about 180-1857C over a period of 30 several mlnu~e~ to co~plete bleaching. Another 3ample placed on a hot plate preheated at lB0-185C bleached completely in about 40 3econds.
Additlonal ~ample~ were prepared as describea above except that a 3econd gla~ plate wa~ placed on top of 35 the coating ~o that the layer o~ compound was ~andwiched *Trade Mark -60-~7~

between the two glass plates. A pair of heating platens designed ~or a laboratory hydraulic press ~ere mounted in a movable arrangement to provide a convenient bench-top method of cont~olling temp~rature, and the "sandwich" was S positioned firmly between the pair of heating platens which had been p~eviously heated to and equilibrated at a preselected temperature. In this way, the sample coatings were heated from both directions.
Testing of the compounds of Examples l, 2, 4 and 10 lO in this manner showed substantially quantitative bleaching in 60 seconds at 180C. The compound of Example 3 bleached when heated for 45 to 60 seconds at 180C, and the compound of Example 5 bleached well in 30 seconds at 180C
but had a green tint. The compound of Example 6 showed 15 partial bleaching after 5 minutes at 165C and complete bleaching after l to 2 minutes at 210C.
In carrying out the present invention, the way in which the heat in applied or induced imagewise may be realized in a variety of ways, for example, by direct 20 application of heat using a thermal printing head or thermal recording pen or by conduction from heated image-markings of an original using conventional thermographic copying techniques. Preferably, selective heating is produced in the heat-sensitive element itself by the conversion of 25 electromagnetic radiation into heat and preferably, the light source is a laser beam emitting source such as a gas laser or semiconductor laser diode. The use of a laser beam is not only well suited for recording in a scanning mode but by utilizing a highly concentrated beam, radiant energy can 30 be concentrated in a small area so that it is possible to record at high speed and high density. Also, it is a convenient way to record data as a heat pattern in response to tran~mitted signal~ ~uch a5 digitized information and a convenient way of preparing multicolor images by employing a ~3~

plurality of laser beam sources that emit laser beams of different wavelengths.
For example, using heat-sensitive compounds that absorb radiation at different predetermined wavelengths in 5 the visible wavelength range, such as, yellow, magenta and cyan colored compounds, laser sources are selected that will emit at the wavelengths strongly absorbed by the respective compounds, and multicolor images can be prepared by addressing each color in a separate scan or preferably by 10 addressing all of the colors in a single scan. Either way, the light asorbed by the respective heat-sensitive compounds is converted into heat and the heat initiates the irreversible, unimolecular fragmentation reaction to effect bleaching of the compounds.
In a preferred embodiment, the heat-sensitive element contains an infra-red absorbing substance for converting infra-red radiation into heat which is transferred to the heat-sensitive compound to initiate said fragmentation reaction and effect the change in the 20 absorption characteristics o~ the heat-sensitive compound from colored to colorless, from colorless to colored or from one color to another. Obviously, the infra-red absorber should be in heat-conductive relationship with the heat-sensitive compound, for example, in the same layer as 25 the heat-sensitive compound or in an adjacent layer. Though an inorganic compound may be employed, the infra-red absorber pre~erably is an organic compound, such as, a cyanine, merocyanine, squarylium or thiopyrylium dye and ~ preferably, is substantially non-absorbing in the visible 30 region of the electromagnetic spectrum so that it will not contribute any substantial amount of color to the Dmin areas, i.e., the highlight areas of the image.
In the production of multicolor images via infra-red absorbers, they may be selected such that they 35 absorb radiation at different predetermined wavelengths above 700nm sufficiently separated so that each imaging layer may be exposed separately and independently of the others by using infra-red radiation at the particuLar wavelengths selectively absorbed by the respective infra-red 5 absorbers. As an illustration, the layers of heat-sensitive compound for forming or bleaching yellow, magenta and cyan may have infra-red absorbers associated therewith that absorb radiation at 760nm, 820nm and 880nm, respecti~ely, and may be addressed by laser beam sources, for example, 10 infra-red laser diodes emitting laser beams at these respective wavelengths so that the ye~low imaging layer can be exposed independently of the magenta and cyan imaging layers, the magenta imaging layer can be exposed independently of the yellow and cyan imaging layers, and the 15 cyan imaging layer can be exposed independently of the yellow and magenta imaging layers. While each layer may be exposed in a separate scan, it is usually preferred to expose all of the imaging layers simultaneously in a single scan using multiple laser beam sources of the appropriate 20 wavelengths. Rather than using superimposed imaging layers, the heat-sensitive compounds and associated infra-red ab~orbers may be arranged in an array of side-by-side dots or stripes in a single recording layer.
I~ a further embodiment, multicolor images may be 25 produced using the same infra-red absorbing compound in association with each of two or more superposëd imaging layers and exposing each imaging layer by controlling the depth of focussing of the laser beam. In this embodiment, the concentration of infra-red absorber is adjusted so that 30 each of the infra-red absorbing layers absorb approximately the same amount of laser beam energy. For example, where there are three infra-red absorbing layers, each layer would absorb about one-third of the laser beam energy. It will be appreciated that controlling the focussing depth to address 35 each layer separately may be carried out in combination with ~3~

the previous embodiment of using infra-red absorbers that selectively absorb at different wavelengths in which instance the concentration of infra-red absorber would not have to be adjusted ~or the laser beam energy since the 5 first infra-red dye would not absorb any subtantial amount of radiation at the absorption peaks of the second and third dyes and so forth.
Where imagewise heating is induced by converting light to heat as in the embodiments described above, the 10 heat-sensitive element may be heated prior to or during imagewise heating. This may be achieved using a heating platen or heated drum or by employing an additional laser beam source or other appropriate means for heating the element ~hile it is being exposed imagewise.
The heat-sensitive elements of the present invention comprise a support carrying at least one layer of the above-denoted heat-sensitive compounds and may contain additional layers, for example, a subbing layer to improve adhesion to the support, interlayers for thermally 20 insulating the imaging layers from each other, infra-red absorbing layers as discusse~ above, an anti-abrasive topcoat layer which also may function as a UV protecting layer by including an ultraviolet absorber therein or other auxiliary layers. The heat-sensitive compounds are selected 25 to give the desired color or combination of colors, and for multicolor images, the compounds selected may comprise the additive primary colors red, green and blue, the subtractive primaries yellow, magenta and cyan or other combinations of colors, which combinations may additionally include black.
30 As noted previously, the compounds generally are selected to give the subtractive colors cyan, magenta and yellow as commonly employed in photographic processes to provide full natural color.
The support employed may be transparent or opaque 35 and may be any material that retains its dimensional ~27~

stability at the ~emperature used for image formation.
Suitable supports include paper, paper coated with a resin or pigment, such as, calcium carbonate or calcined clay, synthetic papers or plastic films, such as polyethylene, 5 polypropylene, polycarbonate, cellulose acetate, polyethylene terephthalate and polys.~yrene.
Usually the layer of heat-sensitive compound contains a binder and is formed by combining the heat-sensitive compound and a binder in a common solvent, lO applying a layer of the coating composition to the support and then drying. Rather than a solution coating, the layer may be applied as a dispersion or an emulsion. The coating composition also may contain dispersing agents, plasticizers, defoaming agents, coating aids and materials 15 such as waxes to prevent sticking where thermal recording heads or thermal pens are used to apply the imagewise pattern of heat. In forming the layer(s) containing the heat-sensitive compounds and the interlayers or other layers, temperatures should be maintained below levels that 20 will initiate the fragmentation reaction so that the heat-sensitive compounds will not be prematurely colored or bleached.
Examples of binders that may be used include polyvinyl alcohol, polyvinyl pyrrolidone, methyl cellulose, 25 cellulose acetate but~rate, copolymers of styrene and butadiene, polyrnethyl methacrylate, copolymers of methyl and ethyl acrylate, polyvinyl acetate, polyvinyl butyral, polycarbonate and polyvinyl chloride. It will be appreciated that the binder selected should not have any 30 adverse effect on the heat-sensitive compound incorporated therein and may be selected to have a beneficial effect.
Also, it should be heat-stable at the temperatures encountered during image formation and it should be transparent so that it doe~ not interfere with viewing of 35 the color image. ~here electromagnetic radiation is ~7~

employed to induce imagewise heating, the binder also should transmit the light intended to initiate image formation.
In addition to the above-mentioned reagents, it is desirable to include an acidic substance, for example, a 5 phenol, such as, bis-phenoL A or dodecylresorcinol in the layer of heat-sensitive compound when using the compounds of formula (9) above. Though not essential, the incorporation o~ such a material enhances color formation. Also, an oxidizing agent may be included for the compounds of formula 10 (13).
As a further illustration of the present invention, heat-sensitive compounds of the foregoing Examples and of formulae (a) to (c) below were coated on a polyethylene terephthalate support by combining the compound 15 and a binder and optionally, an infra-red absorber in a common solvent, applying a layer of the coating composition to the support and then drying the coating. In addition to the above, further samples were prepared in the same manner except that the layer of heat-sensitive compound was 20 overcoated with a layer of infra-red absorber. The formulations used for the various coatings are set forth in Table I below wherein cellulose acetate butyrate, polyvinyl pyrrolidone and ethylene/maleic anhydride copolymer used as the binder in the sample coatings are abbreviated as "CAB", 25 "PVP" and "EMA", respectively.

H3 ~ Cl~
¦ 1 3 ~
(a) ~ S02N COC 2 2 2 3 ~3~

(b) ~ ~ ~ ~ Cl ¦ ~ 3 ~

Br~
CH
(c) ~ S02N COCH2CH2 2 3 The coated samples were irradiated using an argon laser (Ar) or a krypton laser (Kr), and the laser beam was 5 focussed to approximately 25 microns in diameter in the imaging layer. The wavelength of the laser bëam emitted in terms of nanometrs (nm), the output in terms of milliwatts (mW) and the scanning speed in terms of inches per second (in./sec.) also are set forth in ~able I.
The infra-red absorber used in the samples and designated "IR Dye" in Table I was the compound having the formula C02C2"s ~12 ~ 2 H2~J 2 Cl ~,~ CH= CH ~ ~CH. CH-< ~ Cl (CH2)3 tC~2~3 S03 ~ so3-HN(Et)3 The compounds of Examples 1 to 10 represent initially colored compounds with Examples 1 and 9 being cyan, Examples 2, 6 to 8 and 10 being magenta, Examples 3 5 and 4 being yellow and Example 5 being black. Compounds (a), (b) and (c) also are initially colored with (a) and (b) being magenta and (c) being cyan.
The compounds of Examples 11 to 24 represent initially colorles~ compounds which upon heating to effect 10 said fragmentation reaction form color with Examples 11 to 17 forming magenta, Examples 18 to 23 forming yellow and Example 24 forming cyan.

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The maximum and minimum transmis~ion densities were measured for the exposed sample coatings 1 to 3 and 5 to 17 using a Macbeth transmission densitometer Model TD504 equipped with an S4 photomultiplier and color Filter Nos.
5 29, 93 and 94 for red (R), green (G), and blue (B), respectively. The results are repo~ted in Table II below.
TABLE II
Sample Dmax/Dmin 1 0.90/0.2~
2 1.31/0.49(Gl 3 1.oo/o.2l(B) 0.49/O.ll(R) 0.30/O.lO(G) 0.53/0.14(B) 6 0.94/0.24tG) 7 0.41/0.24(G) 8 1.25/0.18(G)

9 1.66/0.90(G) 0.58/0.08(R) 0.66/O.ll(G) 0.59/o.ll(B) 11 0.96/0.22(G) 12 0.94/0.24(G) 13 0.59/0O16(R) 14 0.45/0.12(G) 0.45/0/08(R) o.seilo.l2(G) 0.42/O.ll(B) 16 0.95/O.lO(G) 17 0.50/O.O9(R) 0.51/0.13(G) 0.44/0.16(B) Vi~ual observation of exposed samples 18 to 22 indicated that the extent of color formation induced by 35 laser exposure was ~ubstantially equal to the color formation observed by heating the respective samples on a hot plate.

'' ~

~;27~29L

Further sample coatings 23 to 30 were prepared in the same manner described above. Samples 23 to 27 were identical to samples 18 to 22, respectively, as set out in Table I above except that the solvent used for sampLe 27 was 5 1 ml acetone/ethyl acetate (3/1) instead of 2 ml methanol.
Sample 28 was prepared using 0.02g of the compound of Example 12, 0.02g of citric acid and 2 ml of 2~ Butvar in THF and overcoated with IR formulation (2). Sample 29 was prepared using 0.02g of the compound of Example 17, 0.02g of

10 citric acid and 1 ml of 2~ Butvar in THF and overcoated with IR formulation (2). Sample 30 was prepared using 0.02g of the compound of Example 29 and 1 ml of 2% Butvar in THF and wa~ overcoated with IR formulation (2). These coating~ were exposed to a Xrypton laser in the same manner described 15 above. The particular exposure conditions and the maximum and minimum transmissions densities measured for the exposed samples are given in Table III.
TABLE III
Sample Laser ~ OutputScan Dmax/Dmin 20-~-~ (mW)(in/sec) 23 752nm 1201.0 0.64/O.ll(B) 24 752nm 1201.0 1.19/0.20(G) 752nm 1201.0 0.97/0.18(G) 26 752nm 1201.0 1.06/0.20(G) 2527 752nm 12016.0 0.86/0.22(B) 28 752nm 1201.0 0.52/0.24(G) 29 752nm 1201.0 0.88/0.24(G) 752nm 1208.0 0.48/0.24(B) As mentioned previously, the formation or 30 bleaching of color or a change in color is achieved according to the present in~ention by the irreversible unimolecular fragmentation of one or more thermally unstable carbomate moietie~. A~ can be seen from the results presented above, color is formed in the heated areas of the 35 sample coatings compri~ing the initially colorle~s ~2~3~

compounds, such as, sample coatings 1~ to 30. In the sample coatings 1 to 17 comprising the initially colored compounds, color is bleached in the heated areas.
As discussed previously, the heat-sensitive 5 elements of the present invention may be used in various thermal recording systems including thermal printing, thermographic copying and, particular7y, high-speed laser recording to provide high-contrast, high resolution images suitable for viewable color prints and transparencies, color 10 images requiring magnification such as microfilm, color filters for color displays and color sensors, optical disks and so forth. Depending upon the particular application, the heat-sensitive elements may contain insulating layers, reflective, topcoat or other layers and the various layers lS including the imaging layer(s) together with any infra-red absorbing layer(s) may be arranged in the configuration as desired and appropriate.
Since certain changes may be made in the herein described subject matter without departing from the scope of 20 the invention herein involved, it is intended that all matter contained in the above description and examples be interpreted as illustrative and not in a limiting sense.

Claims (35)

1. 6810 What is claimed is:
   l. A method of thermal imaging which comprises heating imagewise a heat-sensitive element comprising a support carrying at least one layer of an organic compound capable of undergoing an irreversible unimolecular fragmentation of at least one thermally unstable carbamate moiety, said organic compound initially absorbing radiation in the visible or the non-visible region of the electromagnetic spectrum and said imagewise heating effecting said irreversible unimolecular fragmentation of said carbamate moiety whereby the absorption of said organic compound is visibly changed in said layer in an imagewise pattern corresponding to said imagewise heating.
2. 2. A method as defined in claim 1 wherein said organic compound initially absorbs radiation in the visible region of the electromagnetic spectrum and said layer or organic compound is heated imagewise by imagewise exposure to a laser beam source emitting radiation at a wavelength strongly absorbed by said organic compound.
3. 3. A method as defined in claim 2 wherein said element comprises at least two layers each containing an organic compound capable of undergoing an irreversible unimolecular fragmentation of at least one thermally unstable carbamate moiety and said organic compounds absorb radiation as predetermined wavelengths in the visible region of the electromagnetic spectrum, said layers of organic compound being heated imagewise by imagewise exposure to a plurality of laser beam sources emitting radiation at the respective wavelengths strongly absorbed by said organic compounds.
4. 4. A method as defined in claim 1 wherein an infra-red absorber is associated with said layer of organic compound for absorbing radiation at wavelengths and above 700nm and transferring said absorbed radiation as heat to said organic compound, said layer being heated imagewise by imagewise exposure to infra-red radiation at a wavelength strongly absorbed by said infra-red absorber.
5. 5. A method as defined in claim 4 wherein said layer of organic compound is heated imagewise by imagewise exposure to a laser source emitting infra-red radiation at a wavelength strongly absorbed by said infra-red absorber.
6. 6. A method as defined in claim 5 wherein said element comprises at least two layers each containing an organic compound capable of undergoing an irreversible unimolecular fragmentation of at least one thermally unstable carbamate moiety and said infra-red absorbers associated with each said layer selectively absorbing infra-red radiation at different predetermined wavelengths above 700nm, said layers being heated by imagewise exposure to a plurality of laser beam sources emitting infra-red radiation at the respective wavelengths selectively absorbed by said infra-red absorbers.
7. 7. A method as defined in claim 5 wherein said element comprises at least two layers each containing an organic compound capable of undergoing an irreversible unimolecular fragmentation of at least one thermally unstable carbamate moiety and said infra-red absorbers associated with said layers absorbing infra-red radiation at the same wavelength or at different predetermined wavelengths above 700nm, said layers of organic compound being heated imagewise by adjusting the depth of focus of said laser beam source to effect imagewise exposure of each said layer with its associated infra-red absorber.
8. 8. A method as defined in claim 1 wherein said organic compound has the formula wherein M is a carbamate moity; X is -N=, -SO2, or -CH2-; D
   taken with X and M represents the residue of an organic dye;
   q is 0 or 1; and p is a whole number of at least 1.
9. 9. A method as defined in claim 8 wherein M has the formula wherein R is alkyl: -SO2R1 wherein R1 is alkyl; phenyl; naphthyl;
   or phenyl substituted with alkyl, alkoxy, halo, trifluoromethyl, cyano, nitro, carboxy, -CONR2R3 wherein R2 and R3 each are hydrogen or alkyl, -CO2R4 wherein R4 is alkyl or phenyl, -COR5 wherein R5 is amino, alkyl or phenyl, -NR6R7 wherein R6 and R7 each are hydrogen or alkyl, -SO2NR8R9 wherein R8 and R9 each are hydrogen, alkyl or benzyl and Z has the formula wherein R10 is tert-alkyl or -(CH2)2Y wherein Y is an electron-withdrawing group having a positive sigma value as defined by Hammett's Equation.
10. 10. A heat-sensitive element which comprises a support carrying at least one layer of an organic compound capable of undergoing an irreversible unimolecular fragmentation of at least one thermally unstable carbamate moiety, said organic compound initially absorbing radiation in the visible or the non-visible region of the electromagnetic spectrum and undergoing a visible change in absorption upon heating to effect said fragmentation of said carbamate moiety.
11. 11. A heat-sensitive element as defined in claim 10 wherein said element comprises at least two layers each containing an organic compound capable of undergoing an irreversible unimole-cular fragmentation of at least one thermally unstable carbamate moiety, said organic compounds absorbing radiation at different predetermined wavelengths in the visible region of the electro-magnetic spectrum.
12. 12. A heat-sensitive element as defined in claim 10 which additionally includes a thermal insulating layer between adjacent layers of said organic compound.
    
    - 76a -
13. 13. A heat-sensitive element as defined in claim 10 wherein an infra-red absorber is associated with said layer of organic compound for absorbing radiation at wavelengths above 700nm and transferring said absorbed radiation as heat to said organic compound.
14. 14. A heat-sensitive element as defined in claim 13 which comprises at least two layers each containing an organic compound capable of undergoing an irreversible unimolecular fragmentation of at least one thermally unstable carbamate moiety and each said layer of organic compound having an infra-red absorber associated therewith.
15. 15. A heat-sensitive element as defined in claim 14 wherein said infra-red absorbers associated with said layers of organic compound selectively absorb radiation at different predetermined wavelengths above 700nm.
16. 16. A heat-sensitive element as defined in claim 14 wherein said infra-red absorbers associated with said layers of organic compound absorb radiation at the same wavelength above 700nm.
17. 17. A heat-sensitive element as defined in claim 14 which additionally includes a thermal insulating layer between adjacent layers of organic compound.
18. 18. A heat-sensitive element as defined in claim 17 wherein said support carries a layer of said organic compound for forming a cyan image, a layer of organic compound for forming a magenta image and a layer of organic compound for forming a yellow image.
19. 19. A heat-sensitive element as defined in claim 18 wherein said infra-red absorbers associated with said layers of organic compound selectively absorb radiation at different predetermined wavelengths above 700nm.
20. 20. A heat-sensitive element as defined in claim 10 wherein said organic compound has the formula wherein M is a carbamate moiety, X is -N=, -S02-, or -CH2-, D taken with X and M represents the residue of an organic dye; q is 0 or 1; and p is a whole number of a least 1.
21. 21. A heat-sensitive element as defined in claim 20 wherein M has the formula wherein R is alkyl; -SO2R` wherein R1 is alkyl; phenyl; naphthyl;
    or phenyl substituted with alkyl, alkoxy, halo, trifluoromethyl, cyano, nitro, carboxy, -CONR2R3 wherein R2 and R3 each are hydrogen or alkyl, -CO2R4 whèrein R4 is alkyl or phenyl, -CORs wherein Rs is amino, alkyl or phenyl, -NR6R7 wherein R6 and R7 each are hydrogen or alkyl, SO2NR8Rg wherein R8 and R9 each are hydrogen, alkyl or benzyl and Z has the formula wherein R10 is tert-alkyl or -(CH2)2Y wherein Y is an electron-withdrawing group having a positive sigma value as defined by Hammett,s Equation.
22. 22. A compound of the formula wherein M' has the formula wherein R is alkyl; -SO2R1 wherein R1 is alkyl; phenyl; naphthyl;
    
    or phenyl substituted with alkyl, alkoxy, halo, trifluoromethyl, cyano, nitro, carboxy, -CONR2R3 wherein R2 and R3 each are hydrogen or alkyl, -CO2R4 wherein R4 is alkyl or phenyl, -COR5 wherein R5 is amino, alkyl or phenyl, -NR6R7 wherein R6 and R7 each are hydrogen or alkyl, -S02NR8R9 wherein R8 and R9 each are hydrogen, alkyl or benzyl, Z' has the formula wherein R' is halomethyl or alkyl; X is -N= , -SO2- or -CH2-, - 78a -D taken with X and M' represents the radical of a color-shifted organic dye; q is 0 or 1; and p is a whole number of at leat 1;
    said Z' being removed from said M' upon the application of heat to effect a visually discernible change in spectral absorption characteristics of said dye.
23. 23. A compound as defined in claim 22 wherein said organic dye is a thiazine dye.
24. 24. A compound as defined in claim 22 wherein p is 1 and q is 1.
25. 25. A compound as defined in claim 24 wherein X is -N=
    and said organic dye is an azocarbocyanine dye.
26. 26. A compound as defined in claim 24 wherein X is -SO2-and said organic dye is a rhodamine dye.
27. 27. A compound as defined in claim 24 wherein X is -SO2-and said organic dye is a triarylmethane dye.
28. 28. A compound as defined in claim 24 wherein X is -CH2-and said organic dye is a rhodamine dye.
29. 29. A compound as defined in claim 24 wherein X is -CH2-and said organic dye is a fluoran dye.
30. 30. A compound as defined in claim 22 wherein p is 1 and q is 0.
31. 31. A compound as defined in claim 30 wherein said organic dye is a rhodamine dye.
32. 32. A compound as defined in claim 30 wherein said organic dye is a benzylidene dye.
33. 33. A compound as defined in claim 22 wherein said R' is methyl.
34. 34. A compound as defined in claim 22 wherein said compound is initially colorless.
35. 35. A compound as defined in claim 22 wherein said compound is initially colored.