Preparation of 2,5-diaminoterephthalic acid by the Hofmann degradation of pyromellitic di-imide (benzene-1,2,4,5-tetracarboxylic 1,2:4,5-di-imide) in the presence of metal salts

Hofmann degradation of pyromellitic di-imide gave a mixture of 4,6-diaminoisophthalic acid and 2,5-diminoterephathalic acid. Degradation of the copper of cobalt chelates of pyromellitic di-imide, or of pyromellitic di-imide in the presence of cupric or cobaltic salts, gave 2,5-diaminoterephthalic acid only. This is interpreted in terms of the structure of the chelates.