Cu(II) catalyzed reaction between phenyl hydrazine and toluidine blue - Dual role of acid

The detailed kinetics of Cu(II) catalyzed reduction of toluidine blue (TB+) by phenyl hydrazine (Pz) in aqueous solution is studied. Toluidine white ( TBH) and the diazonium ions are the main products of the reaction. The diaz onium ion further decomposes to phenol (PhOH) and nitrogen. At low concentr ations of acid, H+ ion autocatalyzes the uncatalyzed reaction and hampers t he Cu(II) catalyzed reaction. At high concentrations, H+ hinders both the u ncatalyzed and Cu(II) catalyzed reactions. Cu(II) catalyzed had stoichiomet ry similar to the uncatalyzed reaction, Pz + 2 TB+ + H2O = PhOH + 2 TBH + 2 H+ + N-2, Cu(II) catalyzed reaction occurs possibly through ternary comple x formation between the unprotonated toluidine blue and phenyl hydrazine an d catalyst. The rate coefficient for the Cu(II) catalyzed reaction is 2.1 X 10(4) M-2 s(-1). A detailed 13-step mechanistic scheme for the Cu(il) cata lyzed reaction is proposed, which is supported by simulations, (C) 1999 Joh n Wiley & Sons, Inc.