Starting from 4-nitro-o-toluidine, a commercially available dyestuff intermediate, 4-aminosalicylic acid has been prepared in an overall yield of 60 per cent. New derivatives of the acid are described. 3∶3′-Dihydroxyazobenzene-4∶4′-dicarboxylic acid has been obtained from 4-nitrosalicylic acid, an intermediate in the synthesis of 4-aminosalicylic acid. This azo salicylic acid and its O-acetyl derivative are of interest on account of theirin vivo reducibility to 4-aminosalicylic acid and 4-aminoaspirin.

3∶5-Diiodosalicylic acid, 4-amino-O-acetylsalicylic acid (aminoaspirin), and a series of ethers of 4-aminosalicylic acid have been prepared.

The behaviour of 4-aminosalicylic acid towards diazonium salts has been investigated.