MECHANISMS OF ANTIOXIDANT ACTION - ROLE OF MERCAPTOBENZTHIAZOLE AND ITS DERIVATIVES AS ANTIOXIDANTS

Mercaptobenzthiazole (MBT) and its zinc complex (ZMBT) are compared as antioxidants for paraffin oil at 140°. The latter is much more effective than the former at comparable molar concentrations. Autoxidation studies at lower temperatures indicate that MBT is superior to ZMBT both as a hydroperoxide decomposer and as a chain-breaking antioxidant. However, products formed from them by reaction with hydroperoxides are much more effective than either MBT or ZMBT. Both are oxidised to bis-2-benzthiazole disulphide (MBTS) are benthiazole sulphinic acid (BTS) which decomposes to give benzthiazole (BT) and sulphur dioxide. In addition, MBT gives benzthiazole sulphonic acid (BTSO) and ZMBT gives the very stable zinc benzthiazole sulphimate (ZBTS) which also behaves as a reservoir for sulphur oxides. The difference in behaviour at 140° appears to be associated with the relative instability of BTSO compared with ZBTS. © 1979.