Abstract: | The kinetics and mechanism of reduction of aqueous toluidine blue (TB+) by phenyl hydrazine (Pz), which exhibits nonlinear behavior, is studied spectrophotometrically at 630 nm. Typical kinetic curves exhibited autocatalytic characteristics. The role of H+ as an autocatalyst is established. Rate constants for the uncatalyzed and acid catalyzed reactions are determined. The forward rate constants for the uncatalyzed and acid catalyzed reactions were 1.4 × 10?2 M?1 s?1 and 60 M?1 s?1. Reaction products are toluidine white, phenol, and an azo dye. From the stoichiometric ratios, the major reaction is Pz + 2 TB+ + H2O = PhOH + 2 TBH + 2 H+ + N2. The rate expression and a detailed 12‐step reaction mechanism supported by simulations are proposed. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet: 31: 83–88, 1999 |