US2500388A - Fluorocarbon ethers - Google Patents

Description

Patented Mar. 14, 1950 UNITED STATES PATENT'OFFICE FLUOROCARBON ETHERS Joseph H. Simons, State College, Pa., assignor to Minnesota Mining & Manufacturing Company, St. Paul, Minn., a corporation of Delaware N Drawing. Application July 21, 1948, Serial No. 39,999

where R and R represent saturated aliphatic fluorocarbon radicals which may be the same or different. Saturated aliphatic fluorocarbon radicals are non-cyclic radicals consisting solely of carbon and fluorine atoms wherein the atoms are linked together by single interatomic valence bonds. These compounds correspond to the dialkyl ethers, the hydrogen atoms thereof being entirely replaced by fluorine atoms.

The simplest example, corresponding to dimethyl ether, is di trifluoromethyl ether, CF3O-CF3. This compound is a gas and has a boiling point of about minus 59 C. The compound corresponding to diethyl ether is dipentafluoroethyl ether, C2F5--OC2F5, a gas having a boiling point of about 1 C.

Compounds containing five or more carbon atoms in the molecule have boiling points above room temperature and hence are normally nongaseous, as illustrated by di-n-heptafluoropropyl ether, normal C3F7OC3F7, a liquid having a boiling point of about 56 C. Compounds containing eight or more carbon atoms in the molecule have boiling points near to or above that of Water and may be referred to as high-boiling com ounds. Exampes are normal C4Fg-'-O-C4F9 (di-n-nonafluorobutyl ether), a liquid having a boiling point of about 101 0.; normal C5F11O-C5F11 (di-n-undecafluoroamyl ether), a liquid havin a boiling point of about 138 C.; and normal C6F13O-C6F13 (di-n-tridecafluorohexvl ether), a liquid having a boiling poi t of about 179 C.

Unsymmetrical as well as symmetrical com- ;pounds are included. The lack of symmetry may arise from difierent numbers" of carbon atoms in the side radicals, as in the case of CF3OC2F'5 Itrifluoromethyl-pentafluoroethyl ether). Another type of non-symmetry exists where the radicals differ as to branching, as where one radical is branched and the other is a normal straight chain, illustrated by C2F5-O-CF(CF3) 2, pentafluoroethyl-iso-heptafiuoropropyl ether.

This invention includes not only the monoethers but also the saturated aliphatic fluorocarbon polyethers, which compounds contain twr or more oxygen atoms. Examples are (decafluoro-LZ-dimethoxy ethane), a normall; gaseous compound having a boiling point of abou 13 C.; and

(octadecafluoro diethylene glycol diethyl ether) a high-boiling liquid compound having a boilin; point of about 97 C.

The saturated aliphatic fluorocarbon ether have physical and chemical properties which an in general quite different from those of the cor responding hydrocarbon ethers. They have high degree of chemical inertness; they do no burn or react with oxygen; and they can b heated to high temperatures in Pyrex typ laboratory glassware without reacting or de composing. They do not react with metalli sodium or potassium except at elevated tempera tures. .They are colorless and are apparentl; substantially odorless when in pure form. The; are water-insoluble. They separate out whe1 mixed with liquid hydrogen fluoride, althougl the corresponding hydrocarbon ethers are quit soluble in the latter.

The boiling points are in all cases substantial 1y lower than those of the corresponding hydro carbon ethers, although the molecular weight are much higher, which may be illustrated b1 comparing the above figures with the boilin; points of dimethyl ether (minus 25 C.) anl normal dibutyl ether (141 0.).

These compounds have physical propertie closely similar, in general, to those of the cor responding fluorocarbons havin the same num ber of carbon atoms. The boiling points are 0 the same order, although the values are highe for the lowest members of the series and ar lower for the higher members. Thus the boil ing point of CF3-O--CF3 is about minus 59 C and that of C2F6 is about minus 78 C.; whil that of normal C4F9-O-C4F9 is about 101 C and that of normal CsFm is about 104 C. Thi last point is surprising as it would presumably b expected that the boiling points would always b higher in view of the presence of the additions oxygen atom (or atoms) in the molecule.

These saturated aliphatic fluorocarbon ether: in common with the fluorocarbons, have ex ceptionally low boilin points, low refractive in dices, low dielectric constants, low viscosities an low surface tensions, relative to non-fliiorin :rganic compounds of similar molecular weights.

These compounds have properties which perrnit of use for many of the purposes for which saturated fluorocarbons can be used. They may oe employed as refrigerants, inert diluents for chemical reactions, solvents, fire extinguisher fluids, hydraulic mechanism fluids, heat transfer media, turbine impellants, transformer liquids, dielectrics, and lubricants; and as intermediates in the manufacture of other compounds.

The electrochemical process broadly described and claimed in my copending application, Ser. No. 677,407, filed June 17, 1946, (since abandoned infavor of Ser. No. 62,496, filed November 29, [948) may be employed in preparing compounds of this invention. Briefly, this process involves electrolyzing an ether starting compound in liquid hydrogen fluoride, resulting in the formation of the corresponding saturated fluorocarbon ether, which can be readily separated and purified. Thus, for example, C2F5-O-C2F5 can be made by electrolyzing diethyl ether,

in liquid hydrogen fluoride.

It is not essential to use a hydrocarbon ether as the starting compound, as the latter can contain one or more carbon-bonded side or terminal atoms or radicals other than hydrogen which are replaceable by fluoride in the operation of the process.

An important sub-class of the compounds of the present invention, the members of which are particularly suited to eflicient production by the Lforesaid electrochemical process, consists of those :ompounds wherein each oxygen-bonded carbon atom is a constituent of a .CF2 group, each of which is also bonded to a carbon atom of a sat urated fluorocarbon group. Thus each oxygen- Jonded carbon atom is necessarily a "primary carbon atom (one and only one other carbon atom being directly bonded to it). In the case of :he monoethers this subclass may conveniently be represented by the generic formula:

where R and R, represent saturated aliphatic fluorocarbon radicals and may be the same or different.

The electrochemical process also produces as ay-products various fragmentation products containing fewer carbon atoms than the parent compound, including fluorocarbon ethers of reduced carbon number, and also fluorocarbons resulting from breaking of the oxygen-carbon bonds in the :ase of some molecules.

A simple type of electrolytic cell can be used, employing a nickel anode and an iron or steel 3athode, for example. An iron or steel container :an be used, which may be employed as a cath- Jde, with a cover of iron or steel which is bolted in place. Anode and cathode plates, in alternating array, can be suspended from the cover. A suitable gasket material, and insulating material for electrode mountings and leads, is Teflon (polytetrafluoroethylene). An upper outlet for gaseous products, an upper inlet for charging maierials, and a bottom outlet for liquid products, may be provided. The cell may be provided with a. cooling jacket for maintaining a desired operating temperature.

Commercial anhydrous liquid hydrogen fluoride :an be used. This normally contains a trace of water, but water need not be present and highly anhydrous hydrogen fluoride can be used. Addi- ;ional water can be present, but more than a few The process does not depend upon the generation of free fluorine and the latter, if produced, would result in explosions, electrode corrosion, and undesirable reactions.

A preferred operating pressure is atmospheric pressure and a preferred operating temperature is about 0 0.; but higher and lower operating pressures and temperatures can be employed.

When a gaseous fluorocarbon ether product is being made, it can be withdrawn with and separated from the other gaseous products of the cell. Liquid fluorocarbon ether products separate as a constituent of a liquid which is immiscible with the electrolyte and settles to the bottom of the cell from which it can be withdrawn. The fluorocarbon ether compound can be separated by fractional distillation. Higher product compounds which are in the solid range, likewise will separate from the electrolyte and can be removed.

Example 1 This example illustrates the production of the gaseous fluorocarbon ethers, CF30CF3 and C2F5OC2F5, using dimethyl ether and diethyl ether, respectively, as the starting compounds in the previously mentioned type of electrochemical process.

Use was made of an iron laboratory cell containing a set of nickel anodes and iron cathodes, operating at atmospheric pressure and a temperature of 0. About 200 grams of the ether starting compound was dissolved in about 1800 grams of anhydrous liquid hydrogen fluoride. The solutions were electrolytically conductive and at the operating cell voltage, in the range of 4 to 6 volts D. C., a current density of about 20 amperes per square foot of anode surface was obtained. Additions of the starting compound were made to replenish that consumed.

The mixture of gaseous products of the cell was led through a low-temperature condenser (40 C.) to condense out most of the HF present in the mixture, then through an aqueous calcium chloride bubbler to remove remaining traces of HF, then through an aqueous potassium-sulfiteiodide bubbler to remove traces of OFz, then through an aqueous potassium hydroxide bubbler to remove traces of CO2, then through a dry potassium hydroxide tower to remove traces of water, and then through a liquid air trap to separate the hydrogen from the therein condensed compounds.

The product collected in the liquid air trap was subjected to low-temperature fractional distillation and the fluorocarbon ether fraction was thus isolated and was identified. The molecular weights were determined by the vapor density method. The measured bOiliIlg point and molecular weight values for the respective fluorocarbon ether products are:

The identification of these compounds has also been confirmed by mass spectrograph analyses which-admit of no doubt, since the mass numbers of the ionic fragments can be measured with high precision.

Example 2 400 grams of di-n-butyl ether was dissolved in '1800 grams of anhydrous liquid hydrogen fluoride and electrolyzed in the same manner as in the preceding example, with additional ether being added to replenish that consumed. At the end of 60. hours, 1355 grams of immiscible liquid was removed from the bottom of the cell, and this was washed with potassium hydroxide solution to remove traces of HF, and then fractionally distilled to yield a liquid fraction which was identifled as relatively pure normal C4F9-OC4F9. This fraction had the followingmeasured properties:

Boiling point (at 741 mm.) C 100.7 Refractive index (at 25C.) 1.261 Density (grams/c. c. at 34 C.) 1.689 Dielectric constant (at 20 C.) 1.82 Molecular weight 459 The molecular weight for the pure compound, calculated from the formula, is 454.

This compound has boiling point, refractive index, and density values which are slightly but appreciably lower than those of the normal CaFrs fluorocarbon compound which have been found to be 104 C., 1.267, and 1.765, respectively, and may be compared with the values given above. The formula weight of CsFis is 438.

Ezcample 3 Di-n-amyl ether was electrolyzed in anhydrous liquid hydrogen fluoride in the same manner and fractional distillation of the cell deposit resulted in a main liquid fraction identified as relatively pure normal C5F11OC5F'n, having the following measured properties:

Boiling point (at 755.6 mm.) C 138.4 Refractive index (at 25 C.) 1.268 Density (at 35 C.) 1.758 Dielectric constant (at 20 C.) 1.86 Molecular weight 553 The calculated molecular weight of the pure compound is 554.

Example 4 Di-n-hexyl ether was electrolyzed in anhydrous liquid hydrogen fluoride in the same manner and fractional distillation of the cell deposit resulted in a main liquid fraction identified as relatively pure normal CeF13-OCsF13, having the following measured properties:

Boiling point Ci 179 Refractive index (at 25 C.) 1.278 Density (at 28.5 C.) 1.803 Molecular weight 657 The calculated molecular weight of the pure compound is 654.

Example 5 185 grams of ethylene glycol monobutyl ether, C4H9OCH2CH2OH, was dissolved in 2000 grams of anhydrous liquid hydrogen fluoride and electrolyzed in the same manner as in the preceding examples. An additional 210 grams of the starting compound was added during the run to maintain conductivity. After 62 hours, 396

grams of material had collected in the liquid air trap (see the description of the gaseous products train in Example 1), and this was fractionally distilled to yield a liquid fraction which was identified as relatively pure nonafluorobutyl-trifluoromethyl ether, C4F9O-CF3, having the following measured properties:

Boiling point (at 742.8 mm.) C 35.4 Refractive index (at 27 C.) 1.240 Density (at 27 C.) 1.581 Molecular weight 303 The calculated molecular weight of the pure compound is 304.

Example 6 83 grams of 1,4-dioxane (diethylene dioxide):

H20 CH2 (IJ Hz CH:

was dissolved in 2000 grams of anhydrous liquid hydrogen fluoride and electrolyzed in the same manner, an additional 238 grams of the dioxane being added during the 44 run period to maintain conductivity. The run produced 392 grams of material collected in the liquid air trap, which was fractionally distilled to yield a normally gaseous 40 gram fraction having a boiling point of 13 C. and a molecular weight of 269, which was identified as relatively pure The latter has a formula weight of 270, in close agreement with the measured molecular weight determined from the vapor density. This example illustrates the production of an aliphatic polyether by a process which involves the breaking of a cyclic starting compound.

Example 7 grams of diethylene glycol diethyl ether (diethyl carbitol) was dissolved in 2000 grams of anhydrous liquid hydrogen fluoride and electrolyzed in the same manner, an additional 300 grams of the ethei starting compound being added during the 42 hour run to maintain conductivity. The run produced 307 grams of condensate in the liquid air trap, and 171 grams of immiscible liquid collected in the bottom of the cell. The latter was fractionally distilled to yield a 45 gram liquid fraction which was identified as relatively pure corresponding to the starting compound bui having all hydrogen atoms replaced by fluorine atoms. This fraction had the following measured properties Boiling point (at 737 mm.) C 961 Refractive index (at 30 C.) 1.25l

7 Density (at 285 C.) 1.617 Freezing point (crystals) C 45 Molecular weight 488 The calculated molecular weight of the pure compound is 486.

It was found that the infra-red absorption spectra of the foregoing products in each case revealed strong carbon-fluorine bands and indicated that the material was fully saturated and contained no hydrogen, thus further substantiating the identifications.

The following experiments demonstrate that the fluorocarbon ethers are quite stable in aqueous solutions of bases and mineral acids:

(1) 20 cc. of a 10% aqueous sodium hydroxide solution was placed in a 200 cc. glass ampoule. The solution was degassed and the ampoule evacuated, and then 3.3 grams of CF3OCF3 (di-trifluoromethyl ether) was introduced and the ampoule was sealed and then allowed to stand at room temperature for several days. The ampoule was opened and the solution was titrated for hydrolyzed fluoride. There was no detectable fluoride ion (F-) in the solution, showing that the fluorocarbon ether had not become hydrolyzed to any detectable degree.

(2) The experiment was repeated except that a 10% hydrochloric acid (HCl) solution was used, and 3.4 grams of the fluorocarbon ether was introduced. The solution was found to contain approximately 0.13 milligram of fluoride ion per gram of the fluorocarbon ether, corresponding to less than 0.02% of the total fluorine.

(3) The experiment was again repeated except that a 10% hydriodic acid (HI) solution was used, and 3.0 grams of the fluorocarbon ether was introduced. The solution was found to contain approximately 0.14 mg. of fluoride ion per gram of the fluorocarbon ether, corresponding to less than 0.02% of the total fluorine.

As a measure of the reactivity of the fluorocarbon ethers, a determination was made of the solubility of the gas boron trifluoride (BFs) in C4F9OC4F9 (di-n-nonafluorobutyl ether). Hydrocarbon ethers form stable compounds with this gas, dissolving much more than 1 mol of BF: per mol of other at room temperature. It was found that the solubility in the fluorocarbon ether at room temperature is about 0.01 mol per mol Of C4F9-O--C4F9.

Having described various embodiments of the invention, for purposes of illustration rather than limitation, What I claim is as follows:

1. As new and useful compositions of matter, saturated aliphatic fluorocarbon ethers.

2. Saturated aliphatic fluorocarbon ethers having at least five carbon atoms in the molecule.

3. High-boiling saturated aliphatic fluorocarbon ethers having at least eight carbon atoms in the molecule.

4. The new and useful fluorocarbon ether compounds having the formula:

where R and R represent saturated aliphatic fluorocarbon radicals.

5. As new and useful compositions of matter, saturated aliphatic fluorocarbon polyethers.

6. As new and useful compositions of matter, saturated aliphatic fluorocarbon ethers having from one to three oxygen atoms and from five to twelve carbon atoms in the molecule, each oxygen-bonded carbon atom being directly bonded to one and only one other carbon atom.

JOSEPH H. SIMONS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,066,905 Booth Jan. 5, 1937 2,336,921 Benning et a1 Dec. 14, 1943 2,433,844 Hanford Jan. 6, 1948 2,452,944 McBee et all Nov. 2, 1948 FOREIGN PATENTS Number Country Date 523,449 Great Britain July 15, 1940

Claims (1)

1. AS NEW AND USEFUL COMPOSITIONS OF MATTER, SATURATED ALIPHATIC FLUOROCARBON OTHERS.