A new method for the preparation of 1-amino-4-bromo-2-anthraquinonesulphonic acid (bromamine acid) directly from anthraquinone

Abstract

Bromamine acid (1-amino-4-bromo-2-anthraquinonesulphonic acid) is one of the most important intermediates in the synthesis of acid dyes. Apart from quinizarin and leucoquinizarin, more acid dyes have been produced from bromamine acid by replacement of the bromine atom with aryl amino groups than from any other anthraquinone intermediate. This paper presents a new method for the preparation of 1-amino-4-bromo-2-anthraquinonesulphonic acid in high yield and good quality economically. In most of the methods of nitration of anthraquinone, about 30% anthraquinone is converted to by-product such as dinitroanthraquinones which can be separated only with great difficulty and used as a reagent of reaction and in the end must be discarded and these methods are not economical. Due to the formation of about 35–45% 1-nitroanthraquinone, diffusion of product such as 1-nitroanthraquinone in solvent of nitration is more than anthraquinone, consequently 1-nitroanthraquinone is quickly nitrated from anthraquinone, and the factor of diffusion in nitration is very important. With due attention to analyses of formation of nitroanthraquinones from anthraquinone which are obtainable by high pressure chromatography and from Ref. [Hohmann Walter, Wunderlich Klaus. Process for the mononitration of anthraquinone. U.S.Pat. 4203885; May 20, 1980], nitration of anthraquinone is stopped in about 35–45% conversion of anthraquinone to 1-nitroanthraquinone because the formation of by-product at this point is minimal, and at the end of manufacture of bromamine acid, the unreacted anthraquinone is returned to step of nitration.