KINETICS AND MECHANISM OF THE OXIDATION OF SOME CARBOXYLATES BY A NICKEL(III) OXIME-IMINE COMPLEX

The kinetics of the oxidation of formate, oxalate, and malonate by [Ni -III(L(1))](2+) (where HL(1) = 1 ino-7-methyl-4,7,10,13-tetraazapentad ec-3-en-2-one oxime) were carried out over the regions pH 3.0-5.75, 2. 80-5.50, and 2.50-7.58, respectively, at constant ionic strength and t emperature 40 degrees C. All the reactions are overall second-order wi th first-order on both the oxidant and reductant. A general rate law i s given as - d/dt[ Ni-III(L(1))(2+)] = k(obs)[Ni-III(L(1))(2+)] = (k(d ) + nk(s)[R])[Ni-III(L(1))(2+)], where k(d) is the auto-decomposition rate constant of the complex, k(s) is the electron transfer rate const ant, M is the stoichiometric factor, and R is either formate, oxalate, or malonate. The reactivity of all the reacting species of the reduct ants in solution were evaluated choosing suitable pH regions. The reac tivity orders are: k(HCOOH) > k(HCOO-) > k(H2OX) > k(OX2-) and k(H2mal ) > k(Hmal-) < (mal2-) for the oxidation of formate, oxalate, and malo nate, respectively, and these trends were explained considering the ef fect of hydrogen bonded adduct formation and thermodynamic potential. (C) 1996 John Wiley & Sons, Inc.