Synthesis of 2, 3, 5, 6-tetrachlorotoluene. I.

Attempts have been made to synthesize 2, 3, 5, 6-tetrachlorotoluene, a starting compound for the preparation of 2, 3, 5, 6-tetrachlorophenylacetic acid, which has previously proved to be a potent hormonic herbicide. Since direct chlorination of toluene fails to introduce chlorine into the desired positions, 2, 3, 5, 6-tetrachlorotoluene has been synthesized from p-toluene sulf onylchloride through chlorination followed by hydrolysis. (1) Chlorination of p-toluene sulf onyl chloride proceeded with relative ease until three chlorine atoms had been introduced to the ring. Further chlorination was difficult due to increased viscosity of the reaction mixture. When the reaction temperature was raised, liberation of methyl and sulfonyl chloride groups started to occur to give highly chlorinated products such as pentachlorotoluene and hexachlorobenzene, the yield of desired product being lowered. (2) The by-products were separated from the product mixture by hydrolysis using steam with simultaneous steam distillation at a controlled temperature in the forms of 2, 3, 6-trichlorotoluene, pentachlorotolueue, and hexachlorobenzene. (3) Selective analysis of 2, 3, 5, 6-tetrachlorotoluene has been made possible by polarography, which serves as a simple and reliable means to detect the end point of the reaction.