US3358046A - Selective chlorination - Google Patents

Description

United States Patent 3,358,046 SELECTIVE CHLORINATION Robert D. Oifenhauer, Hopewell Township, Mercer County, and Paul G. Rodewald, Jr., Rocky Hill, N.J., assigngrs to Mobil Oil Corporation, a corporation of New ork No Drawing. Filed Aug. 2, 1965, Ser. No. 476,720 16 Claims. (Cl. 260650) The present invention relates to an improved process for producing certain dichlorinated aromatic hydrocarbons. More particularly, it involves the selective or directed dichlorination of certain alkylaromatic hydrocarbons followed by at least partial dealkylation of the chlorinated intermediate.

There is a substantial need for improved chlorination techniques possessing such advantages as selectivity in regard to the orientation of chlorine substituents in the product, easy control of the degree of chlorination, simplicity, the use of inexpensive and readily available reactants, the capability of chlorinating substances which are difficult to chlorinate, or avoiding or minimizing side reactions. For example, the commercial grade of para-dichlorobenzene contains substantial percentages of isomeric impurities. Further meta-dichlorobenzene is commonly prepared from meta-dinitrobenzene or meta-chloronitrobenzene, rather than the much less expensive benzene, by a complex process involving the reduction of nitro groups to amino groups followed by diazotization and treatment of the diazonium salt with cuprous chloride; hence a cheaper and more convenient method of preparation is desirable.

It has now been found that one or more of the aforesaid advantages can be obtained in the treatment of certain cyclic hydrocarbons, especially certain alkylated benzenes, by a simple direct chlorination technique in combination with partial or full dealkylation of the chlorinated material, as described in detail hereinafter.

Broadly, the process of the present invention comprises reacting elemental or gaseous chlorine with an alkylaromatic hydrocarbon of the group consisting of monoalkyl, paradialkyl and symmetrical trialkyl aromatic hydrocarbons containing at least 2 carbon atoms in each alkyl group and a total of at least 4 alkyl carbon atoms to form a predetermined nuclearly dichlorinated alkylaromatic hydrocarbon and dealkylating said dichlorinated alkylaromatic hydrocarbon to remove at least one alkyl group therefrom.

Other aspects of the invention relate to the use of acatalyst in the chlorination reaction, preferably a mild chlorination catalyst, as exemplified by iodine; the pre- 3,358,046 Patented Dec. 12, 1967 and an isopropyl (or sec-pentyl) group, it is possible to control the dealkylation so that the latter radical is split off after chlorination while the more strongly bonded ethyl group is retained on the aromatic ring. This enhances the versatility of the process of this invention in providing for the formation of a wide variety of dichlorinated alkylaromatic compounds as final products.

The present process has a powerful directive effect on chlorination that extends beyond the action of the alkyl radicals in blocking chlorine atoms from substitution on aromatic ring carbon atoms already bearing alkyl substituents, as is apparent from the tendency disclosed hereinafter towards selective dichlorination in forming a compound of predetermined chlorine orientation even when 4 or 5 of the ring carbon atoms of an alkylated benzene reactant are unsubstituted.

For the chlorination and dealkylation steps of the new process, the type and orientation of the alkyl substituents on the aromatic ring compound are important. Various alkyl radicals differ greatly in their directive influence in determining the number of chlorine atoms accepted and their location on the ring carbon atoms. In addition, the degree of the severity of the dealkylation reaction required to split off an alkyl substituent differs for different alkyl radicals.

For the present purposes, each alkyl substituent should contain at least two carbon atoms, and the total number of alkyl carbon atoms per molecule of the compound to be chlorinated should amount to at least four in order to provide sufficient directive force to orient the addition of the two chlorine atoms in the desired manner. The less hydrogen there is on the alkyl carbon atom connected directly to the aromatic ring, the more powerful is the orienting influence of that alkyl substituent on the subsequent dichlorination reaction. Also, the directing infiuence of an alkyl substituent increases with the number of carbon atoms in the alkyl group. Thus, a tertiary-butyl group has a greater directive influence on dichlorinating than a sec-butyl substituent, and the latter exerts a more powerful orienting effect than a primary butyl group. Similarly, but to a considerably lesser degree, a normal octadecyl radical has a more powerfuldirecting influence than the smaller number of carbon atoms in an ndecyl group which in turn effects orientation more than an n-hexyl radical. A rather severe dealkylation is needed to split off an ethyl radical, whereas a tbutyl or seepentyl group can be removed in a milder reaction. A

ferred dealkylation agent, namely substantially anhydrous aluminum chloride and the chlor nation of certain specific alkylated benzenes. This invention also encompasses combinations of an initial step of alkylating an aromatic hydrocarbon followed by the aforesaid chlorination and dealkylation reactions.

The novel process is not only simple and inexpensive but also highly selective, so that it is possible in many instances to obtain dichlorinated compounds of high purity without employing special and involved purification techniques. By suitable selection of alkyl substituents on the aromatic ring of the material to be chlorinated, a powerful directive influence may be exercised with the result that it is possible to not only orient the two chlorine atoms as desired but also to minimize the formation of monochlorinated, trichlorinated, etc. by-product, as well as unwanted dichloro isomers in many cases. Moreover, by employing an alkylaromatic hydrocarbon having two or three types of alkyl substituents of different bonding characteristics with an aromatic nucleus, such as an ethyl plurality of alkyl substituents (either identical or dilferent alkyl radicalsl-has a stronger orienting'effect than a single alkyl group of the same type attached to benzene, for example; and this is thought to be due only in part to the blocking eifect' of the plurality of alkyl radicals.

In view of these effects, in selectively dichlorinating a monoalkylbenzene to form ortho-dichlorobenzene, the single alkyl substituent should contain at least four carbon atoms and a tertiary alkyl radical is distinctly preferable to either a secondary or primary radical group here. On the other hand, any or all of the alkyl radicals may be ethyl groups in cases where a para-dialkyl or symmetrical trialkylaromatic hydrocarbon is being selectively dichlorinated.

The orientation of the two chlorine substituents is different for the aforementioned monoalkyl, para-dialkyl, and symmetrical trialkyl aromatic hydrocarbon classes of reactants. For example, a monoalkylbenzenejis chlorinated in the 3 and 4 positions so the chlorine atoms have ortho orientation relative to one another. In the case of a para-dialkylbenzene, the chlorine atoms are'in para orientation relative to one another, and for a symmetrical trialkyl compound, as exemplified by 3,5-di-(secpentyD-l-ethylbenzene, meta orientation ofthe chlorine 1 atoms occurs.

Various known techniques for alkylating or selectively alkylating aromatic hydrocarbons may be utilized in certain embodiments of the present invention wherein an initial alkylation step provides alkylaromatic hydrocarbons of the aforesaid general types suitable for the selective dichlorination reaction. Such alkylations may be carried out in several stages where two or three different alkyl radicals are being attached to the aromatic nucleus. It is not always necessary to start the process with an unsubstituted hydrocarbon, such as benzene, for at least some benzene derivatives which are either fully or partially alkylated for the present purposes are now commercially available, as exemplified by t-butylbenzene and 'ethylbenzene.

Direct chlorination is employed in the instant process, that is, uncombined, free or elemental chlorine gas rather than a compound thereof is reacted with the alkylaromatic hydrocarbon. This reaction may desirably be carried out in a closed vessel by introducing gaseous chlorine below the surface of the hydrocarbon liquid in the vessel. The hydrocarbon may be heated if necessary to maintain it in the liquid state in order to provide intimate contact with the chlorine, and a chlorination catalyst is desirably added to the liquid to obtain commercially feasible reaction rates. Substitution of chlorine atoms for hydrogen atoms occurs only on the nuclear or ring carbon atoms of the aromatic compound according to all present indications.

The temperature of the chlorination reaction does not appear to be critical. For illustration, the temperature of this reaction may be maintained in the range of about to 100 C., and it is usually held between about 20 and 40 C. for most purposes. In any event, the temperature should not be allowed to rise to the point where there is any tendency to split off alkyl substituents from the alkylaromatic compound or to produce uncontrolled chlorination. The reaction pressure likewise does not appear to be critical, and it is customarily maintained at or near atmospheric pressure for convenience. The quantity of chlorine used is typically the stoichiometric amount required for dichlorination (i.e., a 2:1 chlorinezhydrocarbon molar ratio) or a slight excess. Nothing appears to be gained by introducing a large excess of the chlorine gas, and, in some instances, it may effect further chlorination.

A catalyst may be present in the usual catalytic amounts of about 0.5 to percent by weight of the hydrocarbon, for example. Chlorination catalysts in general are suitable for the instant process including iodine, ferric chloride, cupric chloride, ferric bromide, 0r antimony pentachloride. These are well known nuclear substitution chlorination catalysts. Mild chlorination catalysts are recommended to avoid any possible cleavage of alkyl radicals, and present indications favor the use of iodine as the preferred catalyst.

During this chlorine substitution, hydrogen chloride is released as a reaction product. All of the hydrogen chloride is desirably removed from the reaction zone, and the amount evolved may be measured by conventional techniques to determine the degree of chlorination of the hydrocarbon at any particular stage of the reaction. The addition of a hydrogen chloride acceptor, such as calcium oxide, is desirable in some instances to eliminate or minimize acid-catalyzed cleavage of an alkyl group, as occurs to some extent in the dichlorination of t-butylbenzene.

The dichlorinated alkylaromatic compound may be readily dealkylated in whole or in part by several techniques. For example, the material may be dealkylated by flowing it through a dealkylation catalyst bed heated to 450 C. of silica-alumina gel beads of the type disclosed in Schwartz Patent No. 2,900,349, which catalyst is commonly employed for cracking petroleum fractions. A preferred dealkylation technique involves dissolving the compound in 2.5 times its weight of benzene, heating the mixture to reflux temperature (usually 85 C.)

and adding.

a small amount of substantially anhydrous aluminum chloride (Al Cl catalyst. The reaction occurs under substantially but not absolutely anhydrous conditions, as it is believed that the presence of at least a trace of water is necessary for the reaction to proceed. The dealkylation conditions should, of course, not be so severe as to simultaneously produce dechlorination. The reaction severity may be readily regulated to achieve either complete or partial dealkylation, according to desire, by increasing one or more of such factors as the dealkylation temperature, the time of dealkylation or the quantity of the aluminum chloride present to increase dealkylation severity and decreasing them to reduce the severity.

The products of this invention are mainly known compounds having varying known uses. For example, paradichlorobenzene is a moth repellent, orthoand metadichlorobenzenes are valuable solvents and dichlorinated alkylbenzene products of the type disclosed in the examples, which follow may be used as intermediates in the production of insecticides of the carbamate type.

For a better understanding of the nature and objects of this invention, reference should be had to the following illustrative examples of a few of the many specific embodiments of the invention. All proportions are expressed in terms of weight and all temperatures as degrees centigrade unless otherwise stated.

Example I.-Alkylati0n of benzene.

A flask containing 19.5 grams (0.25 mol) benzene and 5.0 g. (0.019 mol) of anhydrous aluminum chloride is equipped with a stirrer, condenser, and a dropping funnel. Isopropyl chloride in the amount of 58.9 g. (0.75 mol) is added dropwise to the flask while the mixture is constantly stirred and maintained at a temperature of 50-60 C. during the addition and for 15 minutes there after. The reaction takes places under substantially anhydrous conditions with a trace of moisture present. Next. the contents of the flask are cooled and poured out onto a mixture of ice and hydrochloric acid. The resulting mixture is allowed to separate into two layers. The aqueous layer is withdrawn and extracted twice with ethyl ether and the ether extracts are added to the organic product layer. The liquid organic mixture is dried over anhydrous sodium carbonate, filtered, and the solvent is distilled off at a temperature of 35 C. Vapor phase chromatograms and infrared spectra indicate that the product remaining in the distillation apparatus consists of 97.2% 1,3,S-triisopropylbenzene, 2.1% unidentified higher products, and 0.7% diisopropylbenzene and the yield amounts to 88%.

Chlorination 0f triisopropylbenzene Gaseous chlorine in the amount of 15.0 g. (0.21 mol) is slowly passed through a fritted glass gas delivery tube into a flask containing a hot (100 C.) solution of 0.25 g. (0.001 mol) of iodine as a chlorination catalyst in 20.0 g. (about 0.1 mol) of 1,3,5-triisopropylbenzene. The product is 2,6-dichloro-1,3,5-triisopropylbenzene and this material is isolated in 95% yield by dissolving in ether, extracting with aqueous sodium thiosulfate sodium carbonate, drying over anhydrous sodium carbonate, filtering, and distilling off, the solvents. This dichlorination proceeds smoothly without the formation of by-products. Further experimentation indicates that adding a few grams of excess chlorine does not result in the formation of trichlorotriisopropylbenzene, and also that chlorination is very slow in the absence of a catalyst.

Dealkylatian of chlorinated intermediates A quantity of 2,6-dichloro-1,3,5-triisopropylbenzene amounting to 1.00 g. (0.0037 mol) is added to 10.0 g. (0.128 mol) of benzene in a glass flask and heated to reflux at C.; then 0.25 g. (about 0.001 mol) of Al Cl is also introduced. The mixture is refluxed for 15 minutes under substantially anhydrous conditions with only a trace of water present, and then it is poured onto a mixture of ice and hydrochloric acid and allowed to separate into aqueous and organic layers. The aqueous layer is then removed and extracted twice with ethyl ether, and the ether extracts are combined with the organic layer of the reaction products. The resulting liquid is dried over anhydrous sodium carbonate and filtered; then the filtrate is distilled at a temperature of 80 to driveoff the ether and benzeneThe residue from the distillation is found to be substantially pure rn-dichlorobenzene in a yield of 87% which is not believed to be the optimum yield. No isomeric dichlorobenzene impurities are detectable by analytical procedures sensitive to 0.5% of the ortho and para isomers.

Example lI.Chlrination of T erfiary-butylbenzene- In similar chlorination apparatus, a mixture of 6.7 g. (0.05 mol) of t-butylbenzene and 3.0 g. of calcium oxide is heated to 100 C. and 0.25 g. (about 0.001 mol) of iodine is added before 12.0 g. (0.169 mol) of chlorine gas is passed into the solution through a delivery tube. The calcium compound is a hydrochloric acid acceptor which minimizes the formation of p-dichlorobenzene by acid catalyzed cleavage in this reaction mixture. Conversion amounts to 93% and the product mixture is composed of about 80% of 3,4-dichloro-1-t-butylbenzene and the 2,5-i-somer in about a 50:1 ratio along with trichloro-tbutylbenzene and a considerably smaller amount of pdichlorobenzene. The latter two by-products are removed by distilling ofl the dichloro-t-butylbenzenes at a temperature of 67 C. at 4 millimeters.

Dealkylation A glass flask containing 1.03 g. (0.0051 mol) of the distilled dichloro-t-butylbenzenes and 2.5 g. (0.032 mol) of benzene is heated to reflux the contents at 85 C., and then 0.25 g. (about 0.001 mol) of aluminum chloride is added. After refluxing for 5 minutes, the reaction products are poured onto a mixture of ice and hydrochloric acid and allowed to settle into two layers. The aqueous layer is then drawn oh and extracted twice with ethyl ether. The ether extracts and the organic product layer are combined, dried over anhydrous sodium carbonate, filtered and the solvents are distilled off at temperatures ranging up to about 170 C. The yield of dichlorobenzenes amounts to 75% of theory and the isomer distribution is determined by vapor phase chromatography and the infrared spectrum to be 98% orthoand 2% parawith no detectable meta-dichlorobenzene.

Example lII.,t-B utylation of ethylbenzene Chlorination Upon chlorinating the 4-t-butyl-l-ethylbenzene in the manner of the preceding examples, a 72% yield of 2,5- dichloro-4-t-butyl-l-ethylbenzene is obtained.

Dealkylation Upon dealkylating the dichlorinated butylethylbenzene in a mixture of benzene and aluminum chloride at 85 C. as described hereinbefore, the butyl group is split off and 2,S-dichloro-1-ethylbenzene is obtained in high yield. The identity of this material is established by comparing its infrared spectrum with that of samples of 2,5 and 2,6- dichloro ethylbenzene prepared by other methods. The product here may be used as an intermediate in the preparation of insecticides of the carbamate class or type.

Upon extending the time of the dealkylation reaction considerably, the ethyl group is also split otf .of the benzene ring and the product is p-dichlorobenzene with 1% of the meta isomer as an impurity. This is a considerably higher degree of purity than that of the available commercial grade of this compound; hence the present product is a better intermediate for organic syntheses. p-Dichlorobenzene' is also a well known moth proofing agent.

Example I V.A lkylation Aluminum chloride is employed as a catalyst in reacting 1 mol of ethylbenzene with 2 mols of 2-bromopentane at a temperature of about 0 C. in preparing 3,5-di-(secpentyl -1-ethylbenzene in 65 yield.

Chlorination Dealkylatiort This dichlorination product is partially dealkylated using benzene as a solvent and aluminum chloride as a catalyst by refluxing over a period of 10 minutes at 85 C. The yield amounts to approximately of mixed dichloroethylbenzenes. Analysis by vapor phase chromatography and the infrared technique indicates the isomeric mixture to be 86%, 2,6-dichloro-l-ethylbenzene and 14% of the 2,4-isomer. This mixture is useful as a precursor in the production of insecticides of the carbamate type. In addition, the mixture may be converted into essentially pure m-dichlorobenzene by subjecting the material to more severe dealkylation conditions.

While the instant process has been described in considerable detail in the examples and other disclosure herein; nevertheless, it will be apparent to those skilled in the art that many variations or modifications in the process may be made within the purview of this invention, especially inrespect to reactants, catalysts and reaction conditions. Accordingly, the invention should not be construed as restricted in any particulars except as may be recited in the appended claims or required by theprior art.

We claim:

1. A process which comprises reacting gaseous chlorine, in the presence of a nuclear substitution chlorination catalyst with an alkylaromatic hydrocarbon of the group 'consisting of monoalkyl, para-dialkyl and symmetrical trialkyl benzenes containing at least 2 carbon atoms in each alkyl group and a total of at least 4 alkyl carbon atoms to form a nuclearly dichlorinated alkylaromatic hydrocarbon and dealkylating said dichlorinated alkylaromatic hydrocarbon to remove at least one alkyl group therefrom.

2. A process according to claim 1 in which said chlorination is catalyzed with iodine.

3. A process according to claim 1 in which said dihalogenated alkylaromatic hydrocarbon is dealkylated with a mixture of benzene and substantially anhydrous aluminum chloride.

4. A selective chlorination process which comprises reacting a sufficient quantity of chlorine gas with 1,3,5-triisopropylbenzene in the presence of a nuclear substitution chlorination catalyst to form 2,6-dichloro-1,3,5-triisopropylbenzene and thereafter dealkylating said chloroalkylbenzene to produce metadichlorobenzene.

5. A selective chlorination process which comprises reacting a suflicient quantity of gaseous chlorine with tertiary-butylbenzene in the presence of a nuclear substitution chlorination catalyst to form 3,4-dichloro-1-t-butylbenzene and thereafter dealkylating said chloroalkylbenzene to produce ortho-dichlorobenzene.

6. A selective chlorination process which comprises reacting a sufi'icient quantity of gaseous chlorine with 4-tbutyl-l-ethylbenzene in the presence of a nuclear substitution chlorination catalyst to form 2,5-dichloro-4-tbutyl-l-ethylbenzene and thereafter dealkylating said chloroalkylbenzene to produce 'paradichlorobenzene.

7. A selective chlorination process which comprises reacting a sufiicient quantity of gaseous chlorine with 4-tbutyl-l-ethylbenzene in the presence of a nuclear substitution chlorinationcatalyst to form 2,5-dichloro-4-t-butyll-ethylbenzene and thereafter partially dealkylating said chloroalkylbenzene to produce 2,5-dichloro-1-ethy1benzene.

8. A selective chlorination process which comprises reacting a sufficient quantity of gaseous chlorine with 3,5- di-(sec-pentyl)l-ethylbenzene in the presence of a nuclear substitution chlorination catalyst to form dichloro- 3,5-(sec-pentyl)-l-ethylbenzene and thereafter dealkylating said chloroalkylbenzene to produce meta-dichlorobenzene.

9. A selective chlorination process which comprises reacting a sufficient quantity of gaseous chlorine with 3,5-di-(sec-pentyl)-l-ethylbenzene in the presence of a nuclear substitution chlorination catalyst to form dichloro-3,5-di-(sec-pentyl)-l-ethylbenzene and thereafter partially dealkylating said dichloro-3,S-di-(sec-pentyl)-1- ethylbenzene to produce dichloro-l-ethylbenzene.

10. A process of selectively dichlorinating an aromatic hydrocarbon which comprises alkylating an aromatic hydrocarbon to produce an alkylaromatic hydrocarbon of the group consisting of monoalkyl, para-dialkyl and sy-rnmetrical trialkyl benzenes containing at least 2 carbon atoms in each alkyl group and a total of at least 4 alkyl carbon atoms, reacting gaseous chlorine with said alkylaromatic hydrocarbon in the presence of a nuclear substitution chlorination catalyst to form'a nuclearly dichlorinated alkylaromatic hydrocarbon and dealkylating said dichlorinated alkylarornatic hydrocarbon to remove at least one alkyl group therefrom.

11. A process according to claim in which benzene is alkylated by reaction with an alkyl halide.

12. A selective chlorination process which comprises reacting benzene with a sufficient quantity of isopropyl chloride to form triisop-ropylbenzene, reacting a sufficient quantity of gaseous chlorine with said triisopropylbenzene in the presence of a mild nuclear substitution chlorination catalyst to form 2,6-dichloro-1,3,5-triisopropylbenzene and thereafter dealkylating said chloroalkylbenzene in the presence of benzene and substantially anhydrous aluminum chloride to produce meta-dichlorobenzene.

13. A selective chlorination process which comprises reacting ethylbenzene with tertiary-butyl chloride-to form 4-t-butyl-1-ethylbenzene, reacting a sufficient quantity of gaseous chlorine with said 4-t-butyl-1-ethylbenzene in the presence of a mild nuclear substitution chlorination catalyst to form 2,5-dichloro-4-t-butyl-1-ethylbenzene and thereafter dealkylating said chloroalkylbenzene in the presence of benzene and substantially anhydrous aluminum chloride to produce par-a-dichlorobenzene.

14. A selective chlorination process which comprises reacting ethylbenzene with tertiary-butyl chloride to form 4-t-butyl-l-ethylbenzene, reacting a sufficient quantity of gaseous chlorine with said 4-t-butyl-l-ethylbenzene in the presence of a mild nuclear substitution chlorination catalyst to form 2,5-dichloro-4-t-butyl-l-ethylbenzene and thereafter partially dealkylating said chloroalkylbenzene in the presence of benzene and substantially anhydrous aluminum chloride to produce 2,5-dichloro-l-ethylbenzene.

15. A selective chlorination process which comprises reacting ethylbenzene with 2-bromopentane to form 3,5- di-(sec-pentyl)-l-ethylbenzene, reacting a sufiicient quantity of chlorine gas with said 3,5-di-(sec-pentyl)-1-ethylbenzene in the presence of a mild nuclear substitution chlorination catalyst to form dichloro-3,5-di-(sec-pentyl)- l-ethylbenzene and thereafter dealkylating said dichloroalkylbenzene in the presence of benzene and substantially anhydrous aluminum chloride to preduce meta-dichlorobenzene.

16. A selective chlorination process which comprises reacting ethylbenzene with 2-bromopentane to form 3,5- di-(sec-pentyl)l-ethylbenzene, reacting a sufficient quantity of gaseous chlorine with said 3,5-di-(sec-pentyl)-lethylbenzene in the presence of a mild nuclear substitution chlorination catalyst to form dichloro-3,5-di-(sec-pentyl)- l-ethylbenzene and thereafter partially dealkylating said dichloro-3,5-(sec-pentyl)-l-ethylbenzene in the presence of benzene and substantially anhydrous aluminum chloride to produce dichloro-l-ethylbenzene.

References Cited UNITED STATES PATENTS 1,334,033 3/1920 Houlehan 260- 672 2,327,938 8/1943. Stevens et a1 260-672 X 2,707,197 4/ 1955 Souillard. 2,744,150 5/1956 Enos 260-672 X 2,790,819 4/1957 Godfrey 260650 X LEON ZITVER, Primary Examiner. N. I KING, 111., H. MARS, Assistant Examiners.

Claims (1)

1. A PROCESS WHICH COMPRISES REACTING GASEOUS CHLORINE, IN THE PRESENCE OF A NUCLEAR SUBSTITUTION CHLORINATION CATALYST WITH AN ALKYLAROMATIC HYDROCARBON OF THE GROUP CONSISTING OF MONOALKYL, PARA-DIALKYL AND SYMMETRICAL TRIALKYL BENZENES CONTAINING AT LEAST 2 CARBON ATOMS IN EACH ALKYL GROUP AND A TOTAL OF AT LEAST 4 ALKYL CARBON ATOMS TO FORM A NUCLEARLY DICHLORINATED ALKYLAROMATIC HYDROCARBON AND DEALKYLATING SAID DICHLORINATED ALKYLAROMATIC HYDROCARBON TO REMOVE AT LEAST ONE ALKYL GROUP THEREFROM.