Preparation method for 5-chloro-2-methyl-1,4-phenylenediamine

The invention relates to a preparation method for 5-chloro-2-methyl-1,4-phenylenediamine. 5-chloro-2-methyl aniline is used as a raw material and subjected to coupled reaction with aniline diazonium salt prepared through diazotization of an aniline substance to prepare an azo-compound; the azo-compound is subjected to hydrazine hydrate normal-pressure reduction and hydrogenolysis with the existence of a catalyst; in the later period of reduction, after the aniline substance taken off by reaction is subjected to water steaming out while reduction is performed; a methanol lysate is added to remove the catalyst so as to obtain a methanol water solution of 5-chloro-2-methyl-1,4-phenylenediamine; the obtained methanol water solution is subjected to adsorption, decoloring and edulcoration, and then after-treatment technologies of cooling crystallization, filtering, water washing, drying and the like to prepare high-purity 5-chloro-2-methyl-1,4-phenylenediamine; a mixture of the aniline substance subjected to steam distillation and recovery and water is separated and rectified, and then recycled in preparation of aniline diazonium salt. The preparation method has the characteristics of novel route, easily accessible raw material, high atom utilization ratio, conventional equipment, simple and convenient operation, little pollution, capability of realizing circular economy and the like.