Kinetic features of the reduction of 1,4-diamino-substituted anthraquinones with sulfur-containing reductants

The kinetics of reduction of anthraquinone dyes with thiourea dioxide and sodium hydroxymethanesulfinate under aerobic and anaerobic conditions was studied spectrophotometrically. Two induction periods were revealed in the kinetic curves of aerobic reduction, the first of which is due to the presence of dissolved oxygen in the reaction mixture and the second, due to accumulation in the solution of products of oxygen reduction (superoxide and peroxide) and to nonequivalence of quinone groups in the dye molecules, as one of these groups is involved in intramolecular hydrogen bonding with the proton of the substituted amino group.