United States Patent (19) 11) 4,046,656 Davis et al. 45) Sept. 6, 1977

(54) PHOTOCHLORINATION PROCESS FOR 56) References Cited METHYL AROMATIC COMPOUNDS U.S. PATENT DOCUMENTS

(75) Inventors: Ralph A. Davis; R. Garth Pews, both 2,607,802 8/1952 Britton et al...... 204/158 HA of Midland, Mich. 3,816,287 6/1974 Bockman et al...... , 204/163 R (73) Assignee: The Dow Chemical Company, Primary Examiner-Howard S. Williams Midland, Mich. Attorney, Agent, or Firm-James B. Guffey (57) ABSTRACT (21) Appl. No.: 747,859 The rate of photochlorination of methyl aromatic con pounds, such as toluene, cresol, xylene, toluenesulfonyl 22 Filed: Dec. 6, 1976 chloride, methylnaphthalene, diphenylmethane, etc., is (51) Int. Cl...... B01 1/10 increased when carried out in the presence of bromine. (52) U.S. C...... 204/158 HA; 204/163 R (58) Field of Search ...... 204/158 HA, 163 R 15 Claims, No Drawings 4,046,656 1. 2 zylic hydrogen of the aromatic reactant is replaced by a PHOTOCHLORNATION PROCESS FOR chlorine atom. METHYL AROMATIC COMPOUNDS Methyl aromatic reactants for the photochlorination of which the improved process of the invention is useful BACKGROUND OF THE INVENTION 5 include those of the formula I or II (preferably I). This invention relates to photochlorination of methyl aromatic compounds. H H H Photochlorination of methyl aromatic compounds such as toluene, o- or p-toluenesulfonyl chloride, 3 Arel-R). (R-FA-so-Are-R). chloro-4-methylbenzenesulfonyl chloride, and o-, m- or 10 p-xylenesulfonyl chlorides, is known. See for example (I) (II) British Pat. No. 956,857; British Pat. No. 1,401,038; U.S. Pat. No. 3,230,268; Miller et al., "The Displacement of In the methylated aromatic reactant () or (II) each Aromatic Substituents by Halogen Atoms', Journal of Aris individually an aromatic radical; each R is individ the American Chemical Society, Vol. 79, pp. 4187-4191 15 ually a Y substituent or an aromatic radical, preferably (1957); and Miller, "A Regiospecific Synthesis of 4 a Y substituent; each Y substituent is individually hy Chloroalkylbenzenes", Journal of Organic Chemistry, drogen, chlorine or bromine, preferably hydrogen or Vol. 38, No. 6, pp. 1243-1245 (1973). Although good chlorine, most preferably hydrogen; and each n is indi yields of certain chlorinated products have been re vidually a positive integer, suitably from 1 to 5, prefer ported, the time required to produce chlorinated prod 20 ably from 1 to 3, more preferably 1 or 2, most preferably ucts, in which the benzylic hydrogens have each been 1. replaced by chlorine, are unduly long. As used herein "aromatic radical' includes radicals It would therefore be highly desirable to provide a such as phenyl, biphenyl, naphthyl, phenoxyphenyl, photochlorination process wherein reasonable yields of naphthoxyphenyl, phenylthiophenyl, phenylthionapht methyl aromatic products exhibiting total benzylic hy 25 hyl, aa-dichlorobenzylphenyl, a,a-difluorobenzylphe drogen displacement by chlorine is achieved in reduced nyl and the like, preferably phenyl, biphenyl or naph reaction times, thyl, most preferably phenyl. SUMMARY OF THE INVENTION In the aforementioned aromatic reactants the integer, This invention is an improved process for the photo 30 n, cannot exceed the number of ring positions on the chlorination of methyl aromatic compounds. Such pro aromatic radical, Ar. Further, it is understood that cess comprises contacting the methyl aromatic con when the integer n is less than the number of available pound (hereinafter also referred to as the aromatic reac ring positions on the aromatic radical Ar with which tant) with chlorine in the presence of ultraviolet radia such integer is associated, each of the remaining ring tion and an accelerating amount of bromine. 35 positions is individually occupied by an inert substituent As used herein an "accelerating amount" means an or by a chlorine displaceable (i.e., photodisplaceable) amount of bromine sufficient to measurably increase substituent. (preferably by at least about 25 percent, more prefer Similarly in reactants of the formula I or II wherein ably by at least about 50 percent) the rate of formation the radical R is an aromatic radical, each available ring of a-chloro-substituted methyl aromatic product. position of such radical is individually occupied by an In such process each benzylic hydrogen of the aro inert substituent or by a chlorine displaceable substitu matic reactant is replaced by a chlorine atom, thereby ent. forming the aforementioned a-chloro-substituted aro As used herein the term "inert substituent' means a rnatic product. radical which is not readily displaced from an aromatic Certain of the products thereby produced are valu 45 nucleus by chlorine under photochlorination condi able intermediates for the preparation of selective herbi tions. Suitable inert substituents include, for example, cides, such as N,N-dimethyl-N'-(m-trifluoromethyl hydrogen, fluorine, chlorine, -CF, -OH, -OCF, phenyl)urea; N-ethyl-N-(2-methyl-2-propenyl)-2,6-dini -OCCl3, -SCF, -SCCl3, -SOCF, -SOCCl3 tro-4-(trifluoromethyl)-benzenamine; N-(cyclopropyl -COCF, -COCC -NO, -CN, -NF, and the methyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)-ben like. Preferred inert substituents includehydrogen, fluo zenamine; N',N'-diethyl-2,6-dinitro-4-(trifluoromethyl)- rine, chlorine, -CF, -OH, -OCF, -OCCl3, - 1,3-benzenediamine; N-(2-chloroethyl)2,6-dinitro-N- NO, and -CN. The most preferred inert substituents propyl-4-(trifluoromethyl)-benzenamine; N-butyl-N- are hydrogen, fluorine and chlorine, especially hydro ethyl-2,6-dinitro-4-(trifluoromethyl)-benzenamine; 2,6- gen and chlorine. dinitro-N,N-dipropyl-4-(trifluoromethyl)-benzenamine; 55 As used herein a "chlorine displaceable substituent” is and the like. a radical which is displaced from an aromatic ring by The presence of bromine in the aforementioned pro chlorine under photochlorination conditions. Examples cess substantially reduces the reaction time required to of such chlorine displaceable substituents include bro obtain the aforementioned a-chloro-substituted methy mine, -SOCl, -SOBr, -SOCH, and -COCH. lated aromatic product in reasonable yields (e.g., at least Preferred chlorine displaceable substituents are bro about 40 percent, more commonly at least about 90 mine, -SOCL and -SOBr, especially -SOCl. percent) based upon the methylated aromatic reactant. In the aforementioned reactants the relative ring posi tions of the -CHRY groups and any inert or photodis DETAILED DESCRIPTION OF THE placeable substituents among themselves (e.g., INVENTION 65 -CHRY relative to -CHRY) and between each other This invention is an improved process for the photo (e.g., -CHRY group relative to an inert or photodis chlorination of methyl aromatic reactants to form a placeable substituent) are not critical. Thus, for exam chloro-substituted aromatic products wherein each ben ple, a -CHRY radical can be ortho, meta or para to 4,046,656 3 4. another such radical or to another ring substituent and rine under photochlorination conditions thereby form other ring substituents can be ortho, meta or para to ing two ring chlorinated aromatic moieties. Thus, such each other. reactants are not generally desirable for the preparation Examples of methyl aromatic reactants of the formula of chloro-substituted aromatic products wherein ring I include methyl benzenes such as toluenes (e.g., tolu 5 chlorination is not desired. ene, a-chlorotoluene, p-chloro-a,c-dibromotoluene, m-bromotoluene, methyl p-tolyl sulfone, methyl m-tolyl Further, since each mole of reactant of the formula II ketone, p-toluenesulfonyl chloride, p-cresol, 3,5-dini or IV provides two moles of chloro-substituted aro trotoluene, 3-cyano-5-(trifluoromethoxy)toluene, di matic product and since a single product is generally phenylmethane, etc.), xylenes (e.g., o-xylene, aa'- desired rather than a product mixture, the two reactant dichloro-m-xylene, a,a-dibromo-p-xylene, 1,3-dimeth 10 moieties (i.e., (CHRYAr- or (CHYid-) are prefer yl-5-nitro-benzene, etc.), trimethylbenzenes (e.g., 1,3,5- ably selected such that the photochlorinated product of trimethylbenzene, 5-bromomethyl-1,3-dimethylben the two moieties will be the same. Most preferably both zene, 1,3,5-tris(chloromethyl)benzene, etc.); methyl reactant moieties in such methyl aromatic reactants are naphthalenes such as 2-methylnaphthalene, 1 themselves the same (i.e., the identity and ring positions (bromomethyl)-3-cyano-naphthalene, 4-bromo-2- 15 of the CHRY- or CHY, groups and the remaining methylnaphthalene, 4-methyl-1-naphthalenesulfonyl substituents on both such moieties are identical). bromide, etc.; methyl biphenyls such as p-phenyltol Bromine is employed as an accelerator in the practice uene, m-(4-bromophenyl)toluene, etc.; methyl di of the invention. The source of bromine can be elemen phenyloxides such as p-(phenoxy)toluene, a-bromo tal bromine or a brominated organic or inorganic com meta-(phenoxy)toluene, etc.; methyl diphenyl sulfides pound which releases bromine under photochlorination such as p-(phenylthio)toluene, 1,3-dimethyl-5-(phenyl conditions. Suitable brominated organic compounds thio)benzene, etc.; and the similar methyl aromatic reac include, for example, carbon tetrabromide, bromoform, tants. dibromodichloromethane, bromobenzene, etc. Suitable The methyl aromatic reactants of the formula II in inorganic bromine compounds include for example, clude methylaryl methylaryl sulfones such as bis(p- 25 hydrogen bromide; alkali metal bromides (e.g., lithium tolyl)sulfone, bis(4-methyl-2-naphthyl)sulfone, bis(4- bromide, sodium bromide, potassium bromide, etc.); methyl-3,5-dinitro-phenyl)sulfone and the like. alkaline earth metal bromides (e.g., magnesium bro Especially preferred methyl aromatic reactants are mide, calcium bromide, etc.); and the like. those wherein each Ar is phenyl or substituted phenyl 30 When solvent (discussed hereinafter) is employed and each R is a Y substituent. Such reactants thus have which contains bromine substituents (e.g., bromoben the formula III or IV (preferably III) zene) or when the aromatic reactant (e.g., p-bromotol uene) contains bromine substituents, which bromine (CHY.) substituents are displaced by chlorine under photo 35 chlorination conditions, it is generally unnecessary to charge additional bromine (elemental or in the form of a brominated organic or inorganic compound) to the photochlorination process. (R)s- Elemental bromine is the preferred bromine source. (III) When the bromine source is added separately (i.e., as elemental bromine or as a brominated compound which SO is different from the solvent or the aromatic reactant), it can enter the process in a variety of ways and at various (CHY.) (CHY), times, so long as a sufficient amount is present for a (RT - (RT 45 sufficient time to satisfy the hereinafter presented defini (IV) tion of an "accelerating amount”. wherein Y and n are as hereinbefore defined and R' is an For example, the bromine source can be charged inert or chlorine displaceable substituent as hereinbe initially in conjunction with (e.g., premixed with) sol fore defined. vent, the methyl aromatic reactant or the chlorine feed. Examples of the methyl aromatic reactants of the SO It can also be charged individually at the start of the formula III include toluene, cresol, xylene, ot-bromotol reaction, either as a separate and distinct one shot addi uene, 4-nitrotoluene, 4-bromotoluene, 3,5-dinitrotol tion to the reaction vessel or as a separate and distinct uene, a-chloro-3-cyanotoluene, a,a-dichlorotoluene, continuous feed stream. In addition, it can be added at p-toluenesulfonyl bromide, 2-chloro-p-toluenesulfonyl an appropriate time (or at appropriate times in the case chloride, p-((trichloromethyl)thio)toluene, m-(tri 55 of multiple additions) during the course of the photo chloromethoxy)toluene, p-(trifluoromethoxy)toluene, chlorination after the reaction has been initiated and o-((trifluoromethyl)thio)toluene, p-tolyl trifluoro carried forward for a time in the absence of bromine. methyl sulfone, m-tolyl trifluoromethyl ketone, m-tolyl One preferred embodiment of the invention com trichloromethyl sulfone, p-tolyl trichloromethyl ke prises a staged batch process, wherein photochlorina tone, methyl p-tolyl sulfone, methyl p-tolyl ketone, and tion of the methyl aromatic reactant is conducted in the the like. initial stage in the absence of bromine until the rate of The methyl aromatic reactants of the formula IV reaction measurably decreases. Then bromine is added include tolyl tolyl sulfones such as bis(p-tolyl) sulfone, to the reaction mixture and photochlorination is contin m-tolyl p-tolyl sulfone, bis(3-bromo-4-tolyl) sulfone, ued. In such embodiment, one or more subsequent addi bis(2,6-dinitro-4-tolyl) sulfone, bis(3,5-dimethylphenyl) tional photochlorination stages which are carried out in sulfone, and the like. the presence of bromine can optionally be employed. The sulfone linkage (i.e., the radical -SO-) of the The amount of bromine employed is not particularly reactants of the formulas II and IV is displaced by chlo critical to the practice of the invention so long as at least

4,046,656 7 Similarly when the radical R is an aromatic radical, The condenser outlet is connected to a water scrubber each available ring position of such radical is individu via an ice cooled trap, ally occupied by an inert substituent. A 275 wattsunlamp is used as the source of ultraviolet Representative chloro-substituted aromatic products radiation (i.e., the U.V. source). It is mounted about 6 of the formula W include or,a,a-trichlorotoluenes such inches from the one-liter flask. as (trichloromethyl)benzene, 5-cyano-1,3-bis(tri One mole (191 g) of p-toluenesulfonyl chloride, 300 g chloromethyl)benzene, 4-fluoro-1-(trichloromethyl)- of carbon tetrachloride and 10g of bromine are charged benzene, 4-(trichloromethyl)phenol, 1-(trichlorome to the flask. The sunlamp is turned on and the chlorine thyl)-4-(trifluoromethoxy)benzene, 2,4-dichloro-1-(tri flow is started. Chlorine addition is slow until the reac chloromethyl)benzene, 1,3,5-tris(trichloromethyl)ben O zene, 3,5-dinitro-1-(trichloromethyl)benzene, etc.; chlo tion is initiated (evidenced by HCl evolution). Then the rinated diaryl methanes, such as dichlorodiphenylmeth chlorine is fed, with rapid stirring, as fast as it can be ane, difluoro-bis(p-(trichloromethyl)phenyl)methane, used (about 60 g/hr). The temperature is controlled dichloro-bis(3,5-dinitrophenyl)methane, dichloro between about 75 and about 80' C by CC reflux. naphthyl-phenylmethane, etc.; (trichloromethyl)naph 5 As bromine is passed from the reaction vessel (the thalenes such as 2-(trichloromethyl)naphthalene, 2,4- flask) into the cold trap, it is replaced by adding a 5g bis(trichloromethyl)naphthalene, 4,5-dinitro-2,7-bis(tri portion of bromine after 1 hours and another 5g por chloromethyl)naphthalene, etc.; diaryloxides, such as tion 5 hours after initiation of the reaction. m-phenoxy-(trichloromethyl)benzene, p-(2,4,6-tri The reaction proceeds rapidly and is complete at the chlorophenoxy) (trichloromethyl)benzene, etc.; (tri end of 5 hours. chloromethyl)diarylsulfides, such as 6-phenylthio-3- Analyses of the reaction products in the reaction (trichloromethyl)naphthalene, 4-(p-fluorophenylthio)- mixture taken at various reaction time intervals via (trichloromethyl)benzene, etc.; and similar a-chloro gas-liquid chromatography (GLC) are summarized be substituted methyl aromatic compounds. low. Examples of a-chloro-substituted methyl aromatic 25 products of the formula VI include (trichloromethyl)- benzene, 4-chloro-1-(trichloromethyl)benzene, 4-(tri Chlorinated Reaction Time chloromethyl)phenol, 2,4-dichloro-(trichloromethyl)- . Product 1hrs 3 hrs 4 hrs 5hrs p-CH.ClbCl 2.3% .9% 0.7% .7% benzene, 4-chloro-2,5-difluoro-Otrichloromethyl)ben p-CHClbCl SO.8% 39,69. 16.2% 0.7% zene, 1-(trichloromethyl)-3-(trifluoromethoxy)benzene, 30 p-CCsbC. 45.0% 57.6% 81.6% 97.0% 2-chloro-1-(trichloromethyl)-4-(trichloromethyl)thio)- Unknown 1.7% 0.9% 1.5% .6% benzene, 4-(trichloromethyl)phenyl trifluoromethyl sulfone, 2-cyano-4-(trichloromethyl)phenyl trifluoro methyl ketone, 1,4-bis(trichloromethyl)benzene, 1-(tri After the CC1 is stripped off, 222 g (96 percent) of chloromethyl)-4-(trifluoromethyl)benzene, 4-chloro crude product remains which is analyzed to be 97 per 1,2-bis(trichloromethyl)benzene, 5-cyano-1,3-bis(tri 35 cent p-CldbCCls by GLC. Infra-red (IR) analysis con chloromethyl)benzene, 1,2,3-tris(trichloromethyl)ben firms the identity of the product. zene, 5-chloro-1,2,4-tris(trichloromethyl)benzene, 4 Comparative Photochlorination of p-Toluenesulfonyl nitro-1,3,5-tris(trichloromethyl)benzene, 3,5-dinitro-1- chloride in the Absence of Bromine (trichloromethyl)benzene, 3,5-bis(trichloromethyl)-1- (trifluoromethyl)benzene, and the like. To the reactor of Example I, one mole (191 g) of More preferred chloro-substituted methyl aromatic p-toluenesulfonyl chloride and 300 g of CC are products of the formula VI include for example (tri charged. The mixture is chlorinated with Cl2 at the chloromethyl)benzene, 4-fluoro-1-(trichloromethyl)- maximum chlorine utilization rate under U.V. light at a benzene, 4-chloro-1-(trichloromethyl)benzene, 3-nitro temperature between about 60' and about 70 C for a 1-(trichloromethyl)benzene, 3,5-dinitro-1-(trichlorome 45 total of 6 hours. thyl)benzene, 2,4-dichloro-1-(trichloromethyl)benzene, Chlorination, after initiation, is rapid at first. At the 3-cyano-4-fluoro-1-(trichloromethyl)benzene, 2,4,5-tri end of 2 hours, most of the p-toluenesulfonyl chloride chloro-1-(trichloromethyl)benzene, 4-trichlorome has been reacted, but the major product at this point thyl)phenol, 2-chloro-4-(trichloromethyl)phenol, (p- appears to be 4-chloro-a-chlorotoluene. (trichloromethyl)phenyl) (trifluoromethyl) ketone, tri Continued chlorination for an additional 4 hours (6 chloromethyl m-(trichloromethyl)phenyl ketone and hours total) results in the following product mixture as the like; especially (trichloromethyl)benzene, 4-chloro determined by GLC analysis: 1-(trichloromethyl)benzene, 2,4-dichloro-1-(tri p-CH.CldbCl - 6 mole percent chloromethyl)benzene, 3-nitro-1-(trichloromethyl)ben p-CHCldbCl - 66 mole percent zene and 3,5-dinitro-1-(trichloromethyl)benzene. 55 p-CClsbCl - 28 mole percent At this point the reac Most preferred chloro-substituted methyl aromatic tion has become so slow that an estimated 30 to 35 products of the formula VI include (trichloromethyl)- hours of additional reaction time is necessary to benzene, 4-chloro-1-(trichloromethyl)benzene, and 2,4- convert the balance of the product to p-chloro dichloro-1-(trichloromethyl)benzene. coat-trichlorotoluene. The process of the invention is further illustrated, Comparison of the product distribution after only 1 though not limited by, the following examples. hours in Example I with the product distribution after 6 EXAMPLE hours in the comparative experiment reveals that forma tion of p-CClsbCl in the presence of bromine occurs Photochlorination of p-Toluenesulfonyl chloride in 55 substantially faster than in the absence of bromine. In Presence of Br. addition, the lower reaction temperature generated by A one-liter 3-neck flask is equipped with a sparge the reaction in the absence of bromine further evidences tube, a stirrer and a 16 inch Vigreaux reflux condenser. the slower reaction rate. 4,046,656 9 10 to the reaction mixture. The flask is again irradiated and EXAMPLE II Cl is fed as rapidly as it will react. Chlorination is con Photochlorination of p-Bromotoluene tinued for another hour and 15 minutes. To the reactor of Example I are added 95 g (0.55 The temperature rises rapidly in the initial stage of the mole) of p-bromotoluene and 300 g of CCI. reaction and remains in the 75-80' C range with a Chlorine is fed to match the reaction rate. The solu heavy CC reflux. In the latter stage of the reaction, tion becomes red with bromine almost immediately and temperatures as high as 95-100' are reached. the reaction is controlled at a temperature between 70' A 454g portion, (yield 98.5 percent) of product (98-- and 80' C. The reaction is very rapid for about the first percent p-CldbCCl3) is recovered by stripping off the hour then it proceeds more slowly. After about 1 hour O carbon tetrachloride. the majority of the bromine is distilled off with some Comparative Photochlorination of p-Chlorotoluene in CC. The reaction is continued for another 1 hours at Absence of Bromine a reduced Cl feed and lower temperature (60-70' C). GLC analysis and IR analysis indicates the following To the apparatus of Example IV is added 253 g (2 product composition: 15 moles) of p-chlorotoluene and 300 g of CC. Chlorine is p-chloro-a,a,a-trichlorotoluene - 95 percent fed to the reaction as rapidly as possible. The tempera p-chloro-a,c-dichlorotoluene - 2 percent ture rises to between 90 and 95' C in about 30 minutes Unknown (perhaps ring dichlorinated) - 3 percent and remains there for the duration of the reaction. The product is sampled at various time intervals during the EXAMPLE III course of the reaction. The product distribution at the Photochlorination of 2-Chloro-p-Toluenesulfonyl various times is as follows: chloride in the Presence of Bromine A four-liter chlorination reactor equipped with an 2 hrs Shrs 8 hrs Time 15 mins 15 mins 30 mins internal light well is fitted with a gas sparge tube and a 25 para-C-b-CH 6.9% 0% 0% ten bulb reflux condenser venting to a scrubber. para-Cl-)-CHC 58.8% 14.4% 1.3% The reactor is charged with 2238 g (9.95 moles) 2 para-Cl-)-CHC 33.1% 39.9% 2.0% chloro-p-toluenesulfonyl chloride and 300 ml of CC. para-Cl-d-CCl3 1.2% 45.7% 96.7% A General Electric lamp (H100A4) is used as the light SOC2. 30 A total of 457 grams (99 percent yield) of product mix With the light turned on, Clis fed at about 300 grams ture is recovered after the CC1 is stripped off. per hour after the reaction initiated. The temperatures As is apparent from comparing the data for the com are maintained between 100 and 140 C. parative reaction at 2 hours and 15 minutes with the At the end of 5 hours the reaction rate has slowed data from Example IV, formation of the desired prod and 10 ml of bromine in 50 ml of CCI are added. The 35 uct (i.e., p-chloro-a,a,a-trichlorotoluene) is substan chlorination is continued for an additional 5 hours at tially accelerated in the presence of bromine. between 120' and 150' Cat a somewhat slower chlorine Alternatively, comparison of the product distribution feed rate (70 to 100 g/hr). An analysis of the product at at 8 hours for the comparative experiment with the the end of the additional 5 hour period indicates that it product distribution at 2 hours (i.e., at the completion is 63 percent 2,4-dichloro-a,a,a-trichlorotoluene and 37 of the reaction) in Example IV reveals that the reaction percent 2,4-dichloro-a,c-dichlorotoluene. time required to obtain approximately equivalent prod An additional 5 ml of Brain 50 ml of CC is added and uct distribution is reduced by 6 hours (i.e., by about 75 the chlorination is continued at about 60 g/hr of chlo percent or about a 3-fold decrease) by the addition of rine feed at between 120' and 154' C for an additional 7 bromine to the photochlorination process. hours. 45 A total of 2521 g, 35.5 moles of Clhas thus been fed EXAMPLE W in the 17.5 hour period. This gives a Clefficiency of 84 percent. After stripping under vacuum to remove CC Photo-Chlorination of p-Toluenesulfonyl chloride in a 2556 g portion of product, representing a 98 percent the Presence of Bromine and Using recovery, is isolated. The product is analyzed by GLC, p-Chloro-a,a,a-trichlorotoluene as the Solvent NMR and IR and found to be about 97 percent 2,4- A one-liter chlorination reactor is fitted with a water dichloro-a,a,a-trichlorotoluene. cooled light well, a gas sparge tube, thermometer and a condenser which is vented to a sodium bisulfite scrub EXAMPLE IV ber. A 100 watt UV (8A3611900) bulb is used as the Photochlorination of p-Chlorotoluene in the Presence 55 source of ultraviolet radiation. of Bromine A 381.0 g (2 moles) portion of p-chloro-toluenesulfo To a 1-liter, 3-neck flask, equipped with an 18 inch nyl chloride and 300 ml (447 g) of p-chloro-a,a,a-tri Vigreaux condenser, a stirrer and a gas sparge tube and chlorotoluene are charged to the reactor. The UV light connected via a dry ice trap to a scrubber, is charged is turned on and chlorine is fed to the process as rapidly 253 g (2 moles) of p-chlorotoluene and 300 g of CCI. as the reaction rate and equipment permits. The initial The mixture is partially saturated with Cl and then temperature is 25 C. The theoretical amount of chlo irradiated with a sunlamp. When the reaction is initiated rine (426 g) is fed in 3 hours and 8 minutes. GLC analy (HCl evolution), Cl, is fed as rapidly as possible (with sis at that time indicates that the reaction is about 65 continued irradiation) to maintain a slight excess of Cl percent complete. in the solution. The reaction slows after about 1 hour. 65 Ten ml of Br is then added and the chlorine flow (an Irradiation is stopped and the CC1-Cl-chlorotoluene additional 260 g) is continued for an additional hour and solution which has collected in the dry ice trap is re 32 minutes. The final temperature is 85 C. GLC analy charged to the flask. A 5 ml portion of Bris also added sis indicates that the chlorination is now essentially 4,046,656 11 12 complete (i.e., the reaction mixture is 98+ percent p gen of the reactant is replaced by a chlorine atom, com chloro-a,a,a-trichlorotoluene). A total of 453 g (900 g prising contacting said reactant with chlorine in the recovered minus 447 g solvent) of product is produced, presence of ultraviolet radiation and an accelerating representing a combined product yield of about 98 per amount of bromine. cent. 2. A process of claim 1 wherein the bromine is pro vided by elemental bromine or by a brominated organic EXAMPLE WI or inorganic compound which releases bromine under Photochlorination of p-Cresol in the Presence of photochlorination conditions. Bromine 3. A process of claim 1 wherein the bromine is pro To the apparatus of Example V is charged 200 ml of O vided by the methyl aromatic reactant. CC1 and 325 g (3 moles) of p-cresol. Then 0.5 ml of Br; 4. A process of claim 1 wherein the bromine is pro is added. The 100 watt UV light is turned on and chlo vided by elemental bromine. rine is fed to the process at maximum possible rate. The 5. A process of claim 1 wherein the bromine concen initial temperature is 23' C. Air cooling is used on the tration is between about 0.03 and about 3.0 equivalents light well and the reaction temperature rises to a final 15 of bromine atoms per mole of methyl aromatic reactant. temperature of 85 C. 6. A process of claim 1 conducted at a temperature An additional 5 ml portion of Br is added after the between about 0' and about 200 C. first two hours of operation and the reaction is contin 7. A process of claim 1 conducted in a solvent. ued for 3 hours 52 minutes (5 hours 52 minutes total 8. A process of claim 7 wherein the bromine is pro reaction time). GLC and NMR analyses indicate that 20 vided by the solvent. the final product is 96+ percent a,a,a-trichloro-p- 9. A process of claim 7 wherein the solvent is a al cresol. chloro-substituted methyl aromatic product. After removing the CCI on a roto vacuum, 630 g of 10. A process of claim 1 wherein the methyl aromatic product (97.5 percent yield) is recovered. reactant has the formula 25 EXAMPLE VII (CHY.) Photochlorination of p-Toluenesulfonyl chloride in the Presence of Bromoform O To the reaction vessel of Example V is charged:

p-CHSOCl 191 g (1 M) (R)s. CC 300 g CHBr, 10 g 35 (CHY.) The sunlamp is turned on the vessel and chlorine is fed to the reaction vessel slowly until the reaction is initi (CHY), ated. Then the chlorine is fed, with stirring, as rapidly as (R)s. (R)- it can be used. The chlorine feed rate is thus about 120 wherein each n is individually a positive integer; each Y g/hr for the first 2 hours and about 30 g/hr for the last 40 is individually hydrogen, chlorine or bromine; and each 3 hours, representing a chlorine charge of about 330 g. R" is individually an inert substituent or a chlorine dis The temperature is controlled between 75" and 85' C placeable substituent. by CC1, reflux. Bromine is released slowly and continu 11. A process of claim 10 wherein each n is individu ally throughout the run. No further additions of CHBr, ally a positive integer of from 1 to 3. are necessary. The reaction proceeds rapidly and is 12. A process of claim 10 wherein each n is 1. complete at the end of 5 hours. 13. A process of claim 10 wherein each Y is individu The product distribution obtained (as determined by ally hydrogen or chlorine. GLC analysis) as a function of reaction time is summa 14. A process of claim 10 conducted in a solvent rized below. under reflux conditions. 50 15. A process of claim 10 wherein Chloro-Substituted Reaction Time a. the methyl aromatic reactant is p-toluenesulfonyl Product 1 hrs 3 hrs 5 hrs chloride; (CHCI 10% b. the bromine is provided by elemental bromine, HCl, 57% 27% initially present in an amount of about 6.25 mole p-CldCCls 33% 73% 97-98% 55 percent based upon the moles of p-toluenesulfonyl chloride initially charged and supplemented by 2 After stripping off the CC under vacuum, a 227 g additions of about 3.12 mole percent each during portion (yield) of crude product is recovered. This the course of the photochlorination, based upon the material is 97+ percent p-CldbCC1, (GLC). p-toluenesulfonyl chloride initially charged; and While the invention has been described with refer 60 c. the photochlorination is conducted ence to particular embodiments, it should be understood 1. in carbon tetrachloride as a solvent comprising that such embodiments are not intended to limit the about 60 percent by weight of the reaction mix scope of the instantly claimed invention. ture, What is claimed is: 2. under reflux conditions, and 1. A process for the photochlorination of a methyl 65 3. at a temperature of between about 75" and about aromatic reactant to form an a-chloro-substituted aro 80' C. matic product, in which process each benzylic hydro