CA2026506C - Process for the reductive dehalogenation of polyhaloaromatics using calcium and methanol - Google Patents

Abstract

A process for the reductive dehalogenation of halogenated aromatics. The process comprises reacting halogenated aromatics with sodium or calcium in the presence of a lower alcohol selected from the group comprising methanol, ethanol or isopropanol and mixtures thereof in order to convert the halogenated aromatics to hydrogenated aromatics. The halogenated aromatics are preferably reacted with sodium in the presence of methanol under reaction conditions whereby said sodium is in molten form. The preferred starting sodium/methanol/halogen molar ratio ranges from 30-40/15-20/1. The process is particularly useful for dechlorinating polychlorinated biphenyls found in electrical transformer oil.

Description

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TITLE OF THE INVENTION
Process for the reductlve dehalogenatlon of polyhaloaromatlcs.
FIELD OF THE INVENTION
The present invention relates to a process for the dehalogenatlon of halogenated aromatlcs. Thls process lnvolves reactlng halogenated aromatlcs wlth sodlum or calclum ln the presence of a low molecular welght alcohol, preferably methanol.
lo BACKGROUND OF THE INVENTION
The dlsposal of halogenated aromatlc compounds such as polychlorinated biphe~yls ~PCBs) has, ln recent years, become a problem of growlng concern, especially because of the potentlal envlronmental hazard resultlng from the accumulatlon of large amounts of such types of compounds .
The use of sodlum as a dechlorinatlng agent for varlous types of allphatlc and aromatic chlorlde~ 1B well establlshed and sodlum stlll appears to be the metal of cholce ln current and future research in the area of PCB
treatment. The ultlmate purpose of the research done ln PCB treatment 18 obvlously to provlde effectlve dechlorination processes that can be carrled out ~afely and efficiently at costs that are as minlmal as posslble.
At the pre~ent time, one of the most reliable processes used to dechlorinate PCBs 1B a process by whlch the -2- 2Q~5~
~, compounds are heated until decomposltion occurs. The process lnvolves the use of extremely hlgh temperatures.
Among the ma~or drawback~ of this type of proce~s, one may mention the formatlon of highly toxic benzofuran compounds which appear to be even more hazardous than the PCBs them6elves.
The usefulness of the proces6 uslng llthlum or 60dium in the presence of alcohol3 and THF to dechlorlnate non-aromatic organic compounds ha6 been recognlzed in the prior art for many year~. Hence, aliphatlc halide~, which are normally qulte reactlve compounds, especlally when nucleophilic substitution or elimination of the hallde lon is de~lred, have been dehalogenated using sodium or llthium in the presence of an alcohol and thls type of reaction is well documented ln text books as well as ln other types of prlor art publications.
Flrstly, a number of ba61c organlc chemistry textbooks describe dechlorination reactlons lnvolving lithium or 60dlum in the presence of alcohol and THF. Tn the third edition of "Advanced Organic Chemlstry", Harch, at page 390, mentions that a good reduclng agent for the removal of halogen atom~ ln a non-aromatlc polyhalo compound ~including vinyl, allyllc, geminal, and even bridgehead haloqens) is llthlum or sodiu~ and t-BuOH in tetrahydrofuran. Solomons, ln the third edltion of ~Organic Chemi~try~, teaches the dehydrohalogenatlon of

-3- 2~J~'3 jjl~

alkyl halides using a variety of strong bases such a~ the sodium salts o~ various alcohols.
In a slmilar fashlon, Horrison and Boyd, in the fifth edltion of "Organic Chemlstry", descrlbe a reactlon for the dehalogenation of al~yl halides using potassium hydroxide and ethanol (pp. 265-266), as well as reactions for the dehydrohalogenation of vicinal dlhalldes also uslng potassium hydroxide wlth an alcohol (pp. ~20-421).
Horrlson and Boyd also mention that typically, aryl halides undergo nucleophilic substitution only with extreme difficulty. The authors state that lt 18 not posslble to use aryl halides as alkyl halldes are used, for example, in the Friedel-Craft~ reaction Ipage 1034-1035).
It therefore appears from the textbooks referred to above that nucleophlllc substitutlon of halide~ ha~
been mainly performed on allphatic halides, the same reactlon being difflcult to operate on aromatlc halides.
This findlng is also exemplified in the following publications referring to dechlorination of varlous type~
of non-aromatic compounds.
Xornel et al., ln ~PCB destruction. a novel dehalogenation reagent", Journal of Hazardous Materlal~, 12 ~1985), 161-176, descrlbe the use of polyethylene glycol and sodium hydroxlde in the dechlorlnatlon of PCBs at a temperature ranglng from 60 to 100~C. According to _4_ 2~2~ o~

the author3, alkali polyethylene glycolate complexes are malnly used because of thelr relatlve stablllty wlth regard to water and atmospherlc oxygen. The proce~s described by Kornel et al. lnvolves the prevlous S preparatlon of a dehalogenating agent which consists ln mlxlng polyethylene glycol wlth pota~slum hydroxlde and heatlng the solutlon untll potasslum hydroxlde has fully dl~olved. The reagent 18 then reacted wlth the PCB
contalning solution. Hence, the wor~ of Kornel et al.
mainly lnvolves the u~e of alcohollc sodlum hydroxlde or polyethylene ~lycol/metal hydroxide ln the dechlorinatlon of PCBs.
In U.S.P. 4,377,471, Brown et al. dlsclose a process for dechlorlnatlng PC~s that requires the use of sodlum metal and an aprotlc ion-complexlng solvent amongst whlch a certaln number of ethers such a~ ethylene glycol dimethyl ether may be selected. This process, whlch appears to be carrled out at room temperature, does not appear to refer to or suggest the use of any alcohol solvent to perform the dechlorinatlon of the PCB
contamlnated solutlon.
In U.S.P. 2,717,851 lssued to Lldov and in U.S.P. 2,676,132 to Bluestone, the authors descrlbe a proce~s through which a chlorlnated compound, such as heptachloroblcycloheptene, is treated wlth an ethanollc potasslum hydroxlde so~ution with the vlew to partlally -5- 2~2~ Os ;. ,_ dechlorinate the given compound. Thu~, the proces~
de~crlbed by Lldov leads to the removal of one chlorlne atom on the heptachloroblcycloheptene molecule.
Grlffin et al., ln "Perchloro cage compounds. I.
Structural Studles", Journal of Organlc Chemlstry, Vol.
29, 196q, pages 3192-3196, teach a proce~s for dechlorlnatlng chlorinated organlcs. The proce~ lnvolves reactlng small piece~ of metallic sodlum wlth a ~olution comprlslng the compound to be dechlorinated along wlth t-butyl alcohol in tetrahydrofuran. The reactlon appears to be performed at relatlvely low temperatures. The process de~cribed by Grlffln is aimed at removing chlorlne atoms from non-aromatic organic compounds.
Wllcox et al., in ~The Synthesis of 1,4-dlchloroblcyclo[2.2.1]heptanen, Journal of Organlc Chemlstry, Augu~t 1964, pages 2209-2211, descrlbe a proces~ by whlch a chlorinated compound 1- partly dechlorinated using lithlum and t-butyl alcohol in tetrahydrofuran.
Soloway et al., in "Reactions of Isodrln and Endrln", Journal of American Chemical Soclety 82, ~1960), pages 5377-5385, de~crlbe a method for dechlorinatlng non-aromatlc compounds ln n-amyl alcohol and xylene using ~odlum. Slmllarly, Stedman et al., ln ~The blrd-cage ketone, hexacyclo[5.4.1Ø0Ø0]dodecan-~-one, and some of its derlvatives", Journal of Canadlan Chemlstry 32, 2J2~0~

~1967), pages 35-38, teach the dechlorlnatlon of non-aro~atic chlorinated compounds using t-butyl alcohol and llthlum wlre cut lnto small piece~.
Von Doering et al., in "The addltlon of dlchlorocarbene to olefins", Journal of American Chemlcal Soclety, (1954), pages 6162-6165, descrlbe a dehalogenation process ln which metallic sodlum is used along with methanol. Methanol is added dropwise wlth rapld stlrring after sodium has been added to the solution contalning the halogenated compound to be reduced, the coDpound to be dechlorinated being a non-aromatlc compound. The methanol u~ed in this proco~s 18 wet methanol.
In the Gassman et al. reference entltled "The chemistry of 7-substltuted norborneses. The reaction of blcyclo[2.2.1]hept-2-en-7-one wlth peracid~, Journal of Canadian Chemistry, ~1964), Vol. 29, pages 160-163, the authors describe a dehalogenatlon process uslng t-butyl ln tetrahydrofurane wlth flnely chopped lithlum wlre. The process 1~ applled to non-aroDatic compounds.
Hence, the prior art processes descrlbed above mostly refer to the use of sodlum or lithlum along with various alcohols to partially dehalogenate certain types of mainly halogenated compounds. In fact, most of the reactions carried out ln these references are directed at selectlvely removlng chlorlne from certain posltlons ln _7_ ~a~
"~

cycllc and acyclic aliphatlc chlorides for the preparation of certaln novel chemlcals or for baslc research. One obvlous common factor among the~e references i8 that all the chlorinated compounds that have 80 far been treated are allphatic, cyclic or acyclic. Aliphatlc halides, as mentioned earller in the Horrlson and Boyd reference, are normally much more reactlve than aromatlc halldes, partlcularly when nucleophillc substitutlon or ellmlnatlon of the hallde lon 1~ concerned. In fact, ~ome basic organlc chemlstry textbooks seem to suggest that reactlons lnvolvlng nucleophillc substltutlon of aryl halldes are not deslrable slnce they have to be conducted under harsh experlmental condltions and since they are overall lnefficient.
Therefore, the development of sultable alternatlves to presently exlstlng processes for dehalogenatlng haloaromatics, partlcularly for decontamlnatlng methanollc extracts of PCB contamlnated 8011, methanol washlngs of PCB and Askarel containers, hlgh concentratlon levels of PCB and Askarel ln transformer 0118 and for treatlng neat PCBs and Askarel, would be hlghly de~lrable.
SUHHARY OF THE INVENTION
In accordance with the present lnvention, there 18 provided a process for the reductlve dehalogenation of halogenated aromatics. The process compri~es reactlng -8- ~ Q ~

halogenated aromatics wlth sodlum or calclum in the presence of a lower alcohol such as methanol, ethanol or isopropanol, preferably methanol, to convert the halogenated aromatlcs to hydroqenated aromatlcs.
Preferably, the process of the present lnvention 18 performed under condltions whereby sodlum 18 ln melted form. The use of a lower alcohol such as methanol ln the dehalogenation process avoids extenslve polymerlzatlon from PCBs and polyhalogenated aromatlcs and also helps to prevent decomposltlon of the oil ln whlch the substance~
to be dehalogenated may be found.
Thus, when lt 18 deslred to prevent oll decomposltlon, the use of methanol ln quantltles not exceedlng half the molar amount of sodlum was found to be deslrable. By doing 80, the oil 18 kept lntact and even lts color, a faint yellow, 1B not altered by the reactlon.
Furthermore, the ma~or products formed under these condltlons are those resultlng from the dechlorlnatlon of PCPs such as blphenyl. On the other hand, the absence of methanol ln a reactlon mlxture contalnlng oll affords a vlscous dark black gum resultlng from the extenslve decomposltlon of the oll and polymerlzatlon of the aromatlc halides. In these lnstances, ldentlflcatlon of the dechlorlnated products 18 difflcult.
When calclum 1B used as the dechlorlnatlng agent, lt 18 used ln a commerclally avallable form, that CA 02026~06 1998-12-24 is in granular form or as turnings, in a lower alcohol, preferably methanol, at room temperature. However, there are, in this case, no specific molar ratio limitations between the metal and methanol. Hence, the reaction using calcium and methanol is suitable to dechlorinate PCBs or Askarel in methanol. It may be a one step process if it is desired to reduce the PCB concentration in a given PCB solution or as a repetitive two step process if it is desired to eliminate PCBs.
Ethanol and isopropanol can be used as suitable alcohols but for economical and performance considerations, methanol is the preferred alcohol. Also preferred is the use of a nitrogen atmosphere when performing the reaction with sodium.
The process of the present invention can therefore be employed to dehalogenate various types of PCBs or other polyhalogenated aromatics at various concentrations such as those found in transformer oils.
Some prior art literature refers to the use of alcoholic metal hydroxides such as MaOH/ROH in dehalogenation reactions. The present invention refers to the use of alkali or alkaline earth metal in alcohols (e.g. Na-ROH). Hence, the process of the present invention is to be distinguished from other processes that require the use of alcoholic sodium hydroxi~e or polyethylene glycol/metal hydroxide. Basically, each ~3~ 0~

reactlon proceeds with different chemlstry ln terms of mechanlsms and products.
The pre~ent invention will be more readily lllustrated by referring to the following de~crlption.
DETAILED DESCRIPTION OF THB INVENTION
The present lnventlon relates to a process useful to dehalogenate polyhaloaromatic compounds and partlcularly to dechlorlnate polychlorlnated blphenyls present ln transformer oll. It lnvolves reacting halogenated aromatlcs in a lower alcohol such as methanol, ethanol or isopropanol with elther sodlum or calclum, preferably but not necessarlly under a nitrogen atmosphere.
COHPOUNDS TO BE DEHALOGENATED
The process of the present lnventlon may be used to dehalogenate a wide variety of halogenated aromatlcs at various concentratlons. The proce~s is to be employed mainly ln the dechlorlnatlon of polychlorinated blphenyls IPC~s) although lt 18 to be understood that lt could be used ln the reductlve dehalogenatlon of other types of aromatlc compounds.
HETALS
Two types of metal are malnly contemplated for use ln the proces~ of the present invention. One metal, sodlum, i~ an alkall metal and one metal, calclum, is an o ~
alkaline earth metal. The form in which the metals are used may vary dependlng on the nature of the metal ltself.
In the case of sodlum, if dehalogenatlon 18 conducted above the melting polnt of this metal, that 18 above 97~C, the form of the metal is not crltlcal since sodlum will be ln a llquid, active form. At room temperature however, sodlum must first be brought to lts reactlve sand form. It is to be noted that dehalogenatlon at room temperature normally requlres longer reactlon tlmes and is lesg efflclent than dehalogenatlon performed at temperatures above the melting point of sodlum.
Tn the case of calcium, the temperature at which the reaction 18 performed and the form of the metal are not crucial factors ln the reaction. In fact, calclum may be used ln granular form o~ as turnings wlth methanol as the solvent.
ALCOHOLS
The alcohols that may be used ln the context of the present invention are malnly lower alcohols such as methanol, ethanol and lsopropanol. Hethanol has been found to be the most suitable alcohol which could be used both ln terms of cost and efficiency. However, ethanol and isopropanol are to be vlewed as possible alternatives.
It i8 mostly preferred to use sodlum and methanol as reactants in the dehalogenatlon process of the present lnventlon. The starting sodlum/methanol~halogen .,.,,_ ~ ~ 2 ~ ~ 0 ~
molar ratio may be in the following range- 30-40-15-20-1.
Further development has shown that a 2~ ratlo is the most practical ratlo slnce lt requires less sodlum and affords evenly effectlve reaction condltlons.
PROCESS
Reactlon mechanl~m It i8 belleved that the dehalogenatlon of the present lnventlon can proceed through two posslble mechanlsms. Thu~, the reactlon could pos~lbly proceed through elther an electron transfer/hydrogen abstractlon mechanlsm that invoIves the formatlon of radical anlons and radical~ or through an abstractlon/ellmlnation mechanlsm that lnvolves the formatlon of benzynes as reactlve lntermediates.
In the process of the present inventlon, slmllarly to other proces~es that require the use of metals such as ~odlum to dehalogenate polyhalogenated aromatlcs such as PC~s, the prlnclpal PCB dechlorlnatlon step involves an electron transfer process. As shown in Scheme 1 below, the metal tran~fers an electron to the aromatic halide, ArCl, to form a radlcal anlon (I) whlch then loo~es a chloride lon to yield radical (II).
Subsequently, radical (IIJ abstracts hydrogen to yield the de~lred dechlorlnated product.

~ ~ a V S

~ M e ~ A~ _ a Ar ~ Ar a~ (2) A~ ~ MdOH ~ A~ - H

Sch~me 1 In addition to the general mechanism shown above that describe~ the involvement of radicals and radical anions in the dehalogenation process, it appears that other lntermediates, such as benzyne, may also be involved.
As shown in Scheme II below, the strongly basic methoxlde anion, MeO , generated ln BitU from the reactlon of methanol with the metal, may abstract hydrogen from one of the biphenyl rings in a PCB molecule (III) to produce anion (IV). Dechlorlnatlon of ~IV) would then proceed by e11minatlng the chloride anion resulting ln the formatlon of benzyne lntermedlate ~V). The formation of such lntermedlate 1B made po~slble by the pre~ence of several ~_ 2 Q 2 ~
negative chlorine atom~ on the aromatlc rlngs of PCB8.
These atoms, through their negative lnductlve effects, render the aromatic hydrogens ~llghtly acldlc thus favorlng reaction wlth the strongly baslc methoxlde lon.
gubsequent ellmination of the chlorlde lon from (IV) glves the benzyne lntermedlate (V). Repetltlon of thls abstraction/elimlnatlon process would thus lead to another effectlve route for PC~ dechlorlnation.

2 MdDH ~ 2 M ~ 2MbO M + H2 a a .
abso~cd~n a~) ~ + McOH

III IV

Cl - a , Cl~Cl ~ ~ dechlorinated din~ination products Scheme 2: i -..
It ls to be noted that thls second mechanlsm 18 not fully understood and that lts validity wlth regard to the present system iB uncertain. A ve~y strong base 8uch -15- ~ ~ 2 ~ ~ O ~

as an amlde anion (NH2) 18 normally requlred to generate benzyne from aromatlc halldes. However, the presence of several chlorine atoms ~as election wlth drawing groups) or PCBs may render some hydrogens on the ring acldic enough to react wlth the weaker base methoxlde anlon to glve (IV).
a) When uslnq sodium If sodium ls to be employed as the prlnclpal actlve component in the process, a sultable vehicle ~uch as transformer oll is first used to melt the sodlum at a temperature of about 100~C ln order to transfer it into one of lts most reactlve forms; As mentioned earlier, the sodium particle size is not crltical.
Once sodium has been brought to its melted form ln the transformer oil, the dechlorlnatlon process 18 carried out at approxlmately the same temperature as the melting polnt of ~odium, thus allowlng sodium to stay in lts reactive form. One of the alcohols referred to above 18 used to stop polymerization from taking place and to stop the decompositlon of the oll whlch can be recycled and used again. The alcohol that is preferred 18 methanol. The use of an lnert gas is lmportant, for safety consideratlons. However, the reactlon proceeds ln the absence of lnert atmosphere.
In the absence of alcohol, particularly methanol, but under otherwise identlcal conditions, ~ ~ ~ 2 ~

dehalogenatlon takes place wlth a smaller amount of sodlum, that ls approximately half the amount requlred when an alcohol is present. However, under these condltion~, dehalogenatlon i8 often accompanled wlth oll destructlon and exten~lve polymerlzatlon, partlcularly from the blphenyls present ln the solutlon.
It 1~ lmportant to note that sodlum 18 the preferred metal to be used. When slmllar dehalogenatlon 18 attempted wlth llthlum metal in~tead of sodlum under otherwlse identlcal condltlons, the halogenated aromatlcs remaln almost lntact wlth very llttle dehalogenatlon taklng place. If THF ls added to a PCB mlxture contalned in oll and sub~tantial heat 18 applled to the proces~, that 1~ a temperature over 170~C for a perlod exceedlng 17 hours, more than 25% of the original concentratlon of the halogenated aromatlcs remaln lntact.
In fact, lt ls the presence of oll that apparently reduces the reactlvlty of llthlum. If no oll 18 present ln the PCB mlxture, Ll can be used to dechlorlnate PCBs ln a sultable organlc solvent such as THF. However, the use of THF ls not recoDmended for commercial use because of the followlng factorsl it iB
corroslve, hazardous, expenslve and unde~lrable because of ..
the ~lgnificant side reactlon that takes place between lithium and THF. In fact, ln some lnstances, lithlum -17- 2Q2~

placed ln contact with a solutlon containing PCBs, THF and oll will react wlth THF but not with the PCBs.
Thus, numerous advantages result from the use of a lower alcohol ~uch as methanol in a dehalogenation process. Hence, methanol apparently particlpates in the reduction process. It also appears to prevent oil decomposition and leads to a clean formation of blphenyl products while reducing the possibility of polymer formatlon. Also, the low cost of methanol renders the process readlly feaslble commercially.
The reaction descrlbed above can proceed uslng various conditions. Firstly, different temperatures may be used. The reaction has been found to proceed at room temperature but the speed of the reaction is increased lf the temperature is above the meltlng polnt of sodium.
Also, the reaction time may range between 1 and 24 hours.
Furthermore, different concentrations of halogenated aromatics can be treated under the conditions set forth above. For example, concentrations of over 100,000 ppm of PC~s can be easily treated using the method of the present invention. It is to be understood, however, that concentratlons below the 100,000 ppm mark can also be treated.
The process is partlcularly useful to treat methanollc extracts of PCB contamlnated soil, methanol _ 2~26~
wa~hings of PCB and A~karel containers, PCB and As~arel in transformer oll a~ well as neat Askarel.
b) When u~lnq calclum When it i~ desired to use calcium in the dehalogenation proce~ of the pre~ent inventlon, calcium is to be added to a mixture containlng the halogenated aromatics in a lower alcohol ~uch as methanol at a temperature close to room temperature. Other types of alcohols such as ethanol and lsopropanol could also be used to perform the dehalogenatlon uslng calclum, provlded that methanol i~ present.
The following examples are provided to illu~trate rather than llmlt the scope of the present invention.
Rxaaple 1 Reductlve dechlorlnatlon of Askarel uslng sodium ln methanol.
2.01 g of sodium were heated in 50 ml of transformer mineral oil at a temperature of 105~C. After having melted sodium, the mixture wa~ rapldly stlrred to transfer sodium into a very reactlve ~and form. The oil was then carefully cooled down 80 that sodlum could stay in lts reactlve sand form. 1.040 g of Askarel lArochlor 1260 (40%) in trlchlorobenzenes~ ln 1.410 g of methanol was added to the above mlxture under nltrogen and the -19- 2~2~06 reactlon mixture was heated ~ust above the meltlng polnt of sodlum for 30 minutes. Under these conditlons, sodlum stayed as a flne powder ln a very reactlve for~. The mlxture was then cooled down to room temperature 80 that the reactlon vessel could be agltated to get the chlorinated aromatlcs from the wall of the flask into the reacting area. The mlxture, plnk ln color, was heated for another 30 minutes and a yellow color was obtalned. At thls stage, a sample was withdrawn from the reactlon mlxture and analyzed by GC/ECD. After quenchlng wlth water, clean up wlth acld and extraction with hexane, the GC/ECD showed complete dlsappearance of the 20,800 ppm Askarel that was originally present in the oil. An external standard of 1 ppm Arochlor 1260 was used to monitor the dechlorination proce~s. GC/ECD analysis showed no pre~ence of Askarel after treatment.
Furthermore, chloride analysis by HPLC ion chromatography showed complete recovery of the organo-chlorine ln Askarel as sodium chlorlde.
Example 2 When sodlum was replaced by llthlum, under condltions otherwise simllar to those of Example 1, no reactlon was observed. It 18 only when the reaction mlxture was heated above 150~C that only about 70~ of the PCBs ln Askarel were degraded. The presence of the -20- 2 ~ 2 ~ 6 ,.~

transformer oll seems to deactlvate lithium whlch otherwlse 18 known to dehalogenate aromatlc halldes ln polar solvent~.
Thus, when mlxing llthium (1.128 g, 0.16 mole) and A~karel 11.6718 g) in tran~former mineral oll (50 ml) contalnlng methanol (2.58 g~ at room temperature, no reaction was observed. When the mixture was heated for 2 hours at 105~C, no reactlon was observed. The mlxture was then heated between 150 and 17S~C for 2 hours. It is after this drastlc heatlng that only about 70S of the Arochlor 1260 in Askarel dlsappeared. Thls example demonstrate~ the necesslty to use sodlum as an alkall metal in the process of the pre8ent lnventlon.

ExaDple 3 Dechlorlnatlon of Arochlor 1248 uslng calcium in methanol.
To 0.23 g of Arochlor 1248 in 100 ml of methanol, 2.0 g of calcium were added under a nltrogen atmosphere at room temperature. The mixture was then stirred and an immedlate reactlon took place. After the disappearance of calcium, that is approxlmately 40 mlnutes, a 200 ul sample was taken out, neutralized with 0.5 ml of water and then extracted with 1 ml of hexane.
GC analysis indicated dlsappearance of about 50% of the PCBs. The reaction mlxture was then sub~ected to a second treatment outllned as follows.

-21- 2 ~ ~ ~ S db Unreacted PCBs and thelr organic produats were extracted into 2 X 100 ml of hexane and hexane was subsequently evaporated on a water pump at room temperature to avoid 108~ of PCBs. The re~idual untreated PCBs were dis~olved in 100 ml of methanol and treated wlth 2.01 g of calcium for 1 hour at room temperature. The reaction mixture wa~ worked up as described above. GC and GC/MS analysls showed dl~appearance of more than 95% of the PCBs wherea~ blphenyl ~m/e 154), mono-chlorobiphenyl 10(m/e 188) and dl-chlorobiphenyl (m~e 122) formed in almost equal amounts.

Exa-ple 4 Dechlorination of Askarel.
15The condltlons clted ln ~xample 3 for the dechlorlnation of Arochlor 1248 were repeated for the dechlorinatlon of Askarel. To a mlxture of Askarel (1.5990 gl in methanol (100 ml), 2.04 g of calcium were added and the mixture was stirred at room temperature untll calcium metal disappeared. Hexane extractlon was then performed to prepare unreacted Askarel for the second treatment. The second treatment also lnvolved the use of 2.04 g of calcium and 100 ml of methanol. After the disappearance of calclum GC/Mass analysis lndlcated that close to 99% of Askarel had dlsappeared. The products formed were mainly blphenyl and partially hydrogenated CA 02026~06 1998-12-24 Mono- and di-chlorobiphenyls, traces of cyclohexylbenzene and cyclohexenylbenzene are also formed.

Example 5 When the experimental conditions of Examples 3 and 4 were used replacing methanol with iso-propanol and terbutanol or THF, no appreciable dechlorination was observed.

Claims (26)

1. A process for the reductive dehalogenation of halogenated aromatics with sodium or calcium and a lower alcohol selected from the group consisting of methanol, ethanol, isopropanol and mixtures thereof, said process comprising:
a) when calcium is used:
- preparing a mixture comprising halogenated aromatics and calcium in said lower alcohol as a solvent;;
- allowing calcium to react with said halogenated aromatics; and - recovering products resulting from the reductive dehalogenation of said halogenated aromatics;
b) when sodium is used:
- preparing a mixture comprising halogenated aromatics in mineral oil, sodium in reactive form and said lower alcohol, said lower alcohol being present in an amount sufficient to prevent oil decomposition and polymerization of said halogenated aromatics when the reductive dehalogenation takes place;
- heating said mixture to a temperature above the melting point of sodium to cause said sodium to react with said halogenated aromatics; and - recovering products resulting from the reductive dehalogenation of said halogenated aromatics.

2. A process according to claim 1, wherein said lower alcohol is methanol.

3. A process according to claim 1, wherein said calcium is used in granular form or as turnings.

4. A process according to claim 1, wherein said dehalogenation reaction is carried out at room temperature when calcium is used.

5. A process according to claim 1, wherein said lower alcohol acts as a solvent when calcium is used.

6. A process according to claim 1, wherein said halogenated aromatics are polychlorinated biphenyls.

7. A process according to claim 2, wherein the starting sodium/methanol/halogen molar ratio ranges from 2-40/1-20/1.

8. A process according to claim 7, wherein the starting sodium/methanol/halogen molar ratio is 2/1/1.

9. A process according to claim 1, wherein the dehalogenation reaction is carried out under nitrogen atmosphere when sodium is used.

10. A process according to claim 1, wherein said halogenated aromatics are contained in a mineral oil or in soil.

11. A process for the reductive dehalogenation of halogenated aromatics in mineral oil, said process comprising:
- preparing a mixture comprising halogenated aromatics, sodium in reactive form and a lower alcohol selected from the group consisting of methanol, ethanol and isopropanol and mixtures thereof, said lower alcohol being present in an amount sufficient to prevent oil decomposition and polymerization of halogenated aromatics when the reductive dehalogenation takes place;
- heating said mixture to a temperature above the melting point of sodium to cause said sodium to dehalogenate said halogenated aromatics; and - recovering said products resulting from the reductive dehalogenation of said halogenated aromatics.

12. A process according to claim 11, wherein said halogenated aromatics are contained in transformer oil.

13. A process according to claim 11, wherein said lower alcohol is methanol.

14. A process according to claim 11, wherein said halogenated aromatics are polychlorinated biphenyls.

15. A process according to claim 11, wherein the starting sodium/methanol/halogen molar ratios ranges from 2-40/1-20/1.

16. A process according to claim 15, wherein the starting sodium/methanol/halogen molar ratio is 2/1/1.

17. A process for the reductive dehalogenation of halogenated aromatics, said process comprising reacting halogenated aromatics with calcium in a solvent selected from the group consisting of methanol, ethanol and isopropanol and mixtures thereof and recovering the products resulting from the reduction of said halogenated aromatics.

18. A process according to claim 17, wherein said solvent is methanol.

19. A process according to claim 17, wherein said calcium is used in granular form or as turnings.

20. A process according to claim 17, wherein said dehalogenation reaction is carried out at room temperature.

21. A process according to claim 17, wherein said halogenated aromatics are polychlorinated biphenyls.

22. A process according to claim 17, wherein said halogenated aromatics are contained in soil.

23. A process for the treatment of soil contaminated with halogenated aromatics to dehalogenate said halogenated aromatics, said process comprising:
- preparing a methanolic extract of said soil;
- reacting said extract with calcium; and - recovering the products resulting from the dehalogenation of said halogenated aromatics.

24. A process according to claim 23, wherein said calcium in in granula form or as turnings.

25. A process according to claim 23, wherein said reaction is carried out at room temperature.

26. A process according to claim 23, wherein said halogenated aromatics are polychlorinated biphenyls.