This invention relates to the preparation of 2-amino-6-nitrobenzothiazole which is useful in azo dye synthesis.
Various processes for the preparation of 2-amino-6-nitrobenzothiazole are known. For example Pubbl. ist. chim. univ. Bologna No. 2, 3-10 (1943); Chemical Abstracts 41:754 discloses the chlorination of 2-mercaptobenzothiazole to give 2-chlorobenzothiazole which is then treated with nitric and sulfuric acids to give 2-chloro-6-nitrobenzothiazole. The 2-chloro-6-nitrobenzothiazole is then treated with alcoholic ammonia under pressure at 140.degree. to give 2-amino-6-nitrobenzothiazole. No yields are stated in the English abstract.
It has also been reported [see J. Amer. Chem. Soc. 49, 1748 (1927)] that treatment of 2-mercapto-6-nitrobenzothiazole with concentrated aqueous ammonia under pressure at 160.degree. C. followed by crystallization from alcohol and treatment with bone black gives 2-amino-6-nitrobenzothiazole in small yield.
According to the process of this invention, 2-amino-6-nitrobenzothiazole is obtained in good yield and without the use of extreme reaction conditions which the prior art processes require. The compound is obtained according to the process of my invention by contacting 2-mercapto-6-nitrobenzothiazole in the presence of ammonia with hydrogen peroxide. While hydrogen peroxide has previously been used in the preparation of hydroxybenzothiazole from mercaptobenzothiazole (see J. Pharm. Soc. Japan 58, 29-37 (1938); Chemical Abstracts 32:3759), its usefulness in the preparation of 2-amino-6-nitrobenzothiazole from 2-mercapto-6-nitrobenzothiazole has heretofore been undisclosed.