Patented Oct. 2, 1951 2,569,441 UNITED STATES PATENT OFFICE 2,569,441 CATALYTC CONVERSEON OF POLY CELOROCYCLOHEXANES TO POLY ... COROBENZENE Francis N. Alquist, Joseph L. Wasco, and Kenneth C. Kauer, Midland, Michassignors to The Dow Chemical Company, Midland, Mich., a corpo ration of Delaware No Drawing. Application March 14, 1949, Serial No. 8,402 3 Claims. (CI. 260-650) 2 This invention relates to a method for the con per cent of its weight, of anhydrous aluminum version of hexachlorocyclohexane (also known chloride at a temperature which is preferably as benzene hexachloride) to trichlorobenzenes, between 125° C. and 225° C. Hydrogen chloride and of higher chlorinated cyclohexanes to the is given off and may be utilized as desired. At correspondingly higher chlorinated benzenes. reaction temperatures below 200° C., the trichlo It is known that, when chlorine is added to robenzene produced remains in the reaction ves benzene, a mixture of isomeric forms of benzene sel, while at reaction temperatures oetween 205 hexachloride is obtained. It is also known that, and 225 C., the trichlorobenzene boils away from of the various isomers so-produced, only the so the reaction mixture. The catalyst tends to sub called gamma isomer has significant utility as an O line, and more should be added to replace it. insecticide. The other isomers appear to be mere The method is adapted to continuous operation, diluents of the insecticidal activity of the gamma at the higher reaction temperatures, benzene isoner. Methods have been developed to sepa hexachloride being fed into the hot reaction ves rate the active gamma-benzene hexachloride Sel together with a Small amount of aluminum from the relatively inactive isomers. Accord 15 chloride, while hydrogen chloride and trichloro ingly, there has arisen the problem of utilizing benzene are distilled from the Wessel. the relatively large amount of insecticidally in Experience has shown that from 85 to 95 per active benzene hexachloride. It is known, of cent of the theoretical amount of hydrogen chlo course, that benzene hexachloride reacts slowly ride will be recovered from the process, while with caustic alkalies at elevated temperatures to 20 from 80 to 90 per cent of the theoretical amount form trichlorobenzene. This is a valuable prod of trichlorobenzene is recovered, in batch opera uct, and one which can be made in purer form tion. from benzene hexachloride than by the direct In a specific example, a mixture of 125 grams substitution chlorination of benzene. Since, of the alpha isomer of benzene hexachloride and however, the reaction of benzene hexachloride 25 1 gram of anhydrous aluminum chloride was with alkali hydroxide forms three moles of salt heated in a flask fitted with a thermometer and (by the neutralization of three moles of the hy a reflux condenser, from the upper end of which droxides) for each mole of benzene hexachloride a tube was provided to conduct hydrogen chlo treated and each mole of trichlorobenzene pro ride to water in an absorbing tower. When the duced, the process is not economical. If the chlo 30 temperature in the reaction vessel reached 170° rine removed from the benzene hexachloride C., hydrogen chloride was being generated, and could be recovered in a chemically active form, at 210-220 C. the trichlorobenzene refluxed. and without destruction of other chemical values, There was absorbed in the scrubber 39 grams of this would be the practical Way of making tri hydrogen chloride, or about 85 per cent of the chlorobenzene, free from dichloro- and tetrachlo 35 theoretical yield. The reaction mixture was robenzenes. Analogously, if such a process can cooled, water was added to the flask, and 64 be developed, it should be applicable to the pro grams of trichlorobenzene was recovered by duction of tetrachlorobenzene from heptachloro steam distillation. This is 81 per cent of the cyclohexane (monochlorobenzene hexachloride) theoretical yield. A small amount of black tarry or to the production of pentachlorobenzene from 40 material remained in the reaction vessel. octachlorocyclohexane (dichlorobenzene hexa In a similar manner, each of the beta, gamma, chloride). and delta isomers of benzene hexachloride was It is the object of this invention to provide a heated with a catalytic amount of anhydrous method whereby hexachlorocyclohexane (ben aluminum chloride, and in each instance the Zene hexachloride) may be converted catalyti 45 cally to trichlorobenzene. A related object is to yield of hydrogen chloride and of trichloro provide such a method whereby mono- and di benzene was comparable with that reported chlorobenzene hexachlorides may be converted above. The trichlorobenzene in each case con to tetra- and pentachlorobenzene. sisted of from 81 to 85 per cent 1,2,4-trichloro We have found that the chlorine values in ben benzene and from 15 to 19 per cent 1,2,3-tri zene hexachloride need not be lost, and that they chlorobenzene.found. No 1,3,5-trichlorobenzene was can be recovered in a chemically active form, 100 grams of the hexachloride of monochloro ... while converting benzene hexachloride to tri benzene was mixed with 1 gram of anhydrous tehlorobenzene by heating benzene hexachloride aluminum chloride and heated at temperatures with a catalytic amount, usually from 0.5 to 5 s of 100-160° C. for 2 hours. There was recovered 2,569,54 d 4. 29.9 grams of hydrogen chloride and 69 grams heating benzene hexachloride with from 0.5 to 5 of a mixture of all the isomeric tetrachloro per cent of its weight of anhydrous aluminum benzenes. There was no trichlorobenzene in the chloride at a temperature of from 125° to 225 C., product. until the evolution of hydrogen chloride is sub When a crude mixture of heptachlorocyclo stantially complete, and recovering trichloro hexane and octachlorocyclohexane was heated in benzene from the reaction mixture, free from like manner with per cent of anhydrous alumi lower chlorobenzenes and from 1,3,5-trichloro num chloride, the chlorobenzene product, after benzene. the dehydrochlorination reaction was complete, 3. The method which consists essentially in was a mixture of tetrachlorobenzenes and penta 10 heating monochlorobenzene hexachloride with chlorobenzene. from 0.5 to 5 per cent of anhydrous aluminum No practical rate of reaction is found at ten chloride at a temperature of from 100° to 220° C., peratures below 90° C., and no, advantage is found until evolution of hydrogen chloride is substan in operating at temperatures above 250° C. The tially complete, and recovering tetrachloroben most generally useful temperatures have been 15 Zene from the reaction mixture. found between 125 and 225 C. Any such tem FRANCIS N. ALQUIST. perature may be used, at which the particular JOSEPH L. WASCO. mixture of hexachloride and catalyst gives off KENNETB C. KAUER. hydrogen chloride at a practical rate. We claim: 20 REFERENCEs CITED 1. The method which consists essentially in heating a compound from the group consisting The following references are of record in the of benzene hexachloride, monochlorobenzene file of this patent: hexachloride and dichlorobenzene hexachloride UNITED STATES PATENTS with from 0.5 to 5 per cent of its weight of an 25 Number Name Date hydrous aluminum chloride at a temperature 2,467,123 Fleck et al. ------Apr. 12, 1949 above 90° C. at which hydrogen chloride is liber ated, until about 3 moles of hydrogen chloride is OTHER REFERENCES liberated per mole of feed, and recovering the re Wan der Linden: "Ber. der deut. chem. Gesell." Sultant polychlorobenzenes. 30 vol. 45, pages 244-7 (1912). 2. The method which consists essentially in