Thermal studies on some substituted aminobenzoic acids

The thermal behaviour of various substituted aminobenzoic acids (3-aminobenzoic acid (3-ABA), 4-aminobenzoic acid (4-ABA), 3-aminosalicylic acid (3-ASA), 4-aminosalicylic acid (4-ASA), and 5-aminosalicylic acid (5-ASA), as well as the 'parent' benzoic acid (BA) and salicylic acid (SA) as reference substances, and possible decomposition products: 2-aminophenol (2-AP), 3-aminophenol (3-AP) and 4-aminophenol (4-AP) in the solid state has been examined. The various sets of isomers studied showed considerable and interesting differences. Most sublimed well before melting, generally with an increasing rate of mass loss beyond their very different melting points. The differences in behaviour of 4-ASA and 5-ASA were the most remarkable, with 5-ASA being far more stable and apparently not decarboxylating readily, while 4-ASA sublimed at temperatures below the melting point, becoming less stable and decarboxylating in the liquid form.