The detailed kinetics of Cu(II) catalyzed reduction of toluidine blue (TB ϩ ) by phenyl hydrazine (Pz) in aqueous solution is studied. Toluidine white (TBH) and the diazonium ions are the main products of the reaction. The diazonium ion further decomposes to phenol (PhOH) and nitrogen. At low concentrations of acid, H ϩ ion autocatalyzes the uncatalyzed reaction and hampers the Cu(II) catalyzed reaction. At high concentrations, H ϩ hinders both the uncatalyzed and Cu(II) catalyzed reactions. Cu(II) catalyzed had stoichiometry similar to the uncatalyzed reaction, Cu(II) catalyzed2 2 reaction occurs possibly through ternary complex formation between the unprotonated toluidine blue and phenyl hydrazine and catalyst. The rate coefficient for the Cu(II) catalyzed reaction is A detailed 13-step mechanistic scheme for the Cu(II) catalyzed 4 Ϫ2 Ϫ12.1 ϫ 10 M s . reaction is proposed, which is supported by simulations.

The kinetics and mechanism of reduction of aqueous toluidine blue by ϩ (TB ) phenyl hydrazine (Pz), which exhibits nonlinear behavior, is studied spectrophotometrically at Typical kinetic curves exhibited autocatalytic characteristics.