2-Chloro-5-hydroxy:toluene-5-sulphonic acid prepn. - by sulphonation of 2-chloro-5-hydroxy-toluene in an aliphatic chloro:hydrocarbon solvent with relatively small amts. of sulphur tri:oxide

摘要

Prepn. of 2-chloro-5-hydroxytoluene-4-sulphonic acid (I) comprises sulphonation of 2-chloro-5-hydroxytoluene (II) in an inert organic solvent with SO3; and (i) the solvent used is a chlorinated aliphatic hydrocarbon in which (I) is insol.; (ii) liq. SO3 and solvent-dissolved (II) are alternatingly fed in at a mol. ratio SO3:(II) of 1.2-2:1 at a low temp. preventing sulphone formation and oxidn.; and (iii) the (I) prod. is sepd. off using suction. USE/ADVANTAGE - (I) is used as an intermediate for 2,6-dichloro-4-nitro-5-hydroxytoluene which is used in the synthesis of photographic colour couplers. High yields of (I) are obtd. in a process which uses a reduced amt. of sulphonation agent (cf the 7 mols. per mol. (II) of H2SO4 used in prior-art) and so produces waste water of reduced salt loading.