Oxidation of Thioglycolic Acid by Nickel(IV) Oxime-Imine Complexes - A Kinetic and Mechanistic Approach

Abstract

Abstract The kinetics of oxidation of thioglycolic acid (H2A) by two nickel(IV) oxime-imine complexes, [NiIV(L1)2]2 + and [NiIV(L2)]2+ (where HL1 and H2L2 are 6-amino-3-methyl-4-azahex-3-ene-2-one oxime and 3,14-dimethyl-4,7,10,13-tetraazahexadeca-3,13- diene-2,15-dione dioxime respectively) were carried out by using stopped-flow technique in the pH range 3.0-8.0. Under pseudo-first-order conditions the reaction follows a general rate law: - (d/dt) [Ni(Lx)] =kobs [Ni(Lx)] = nk [Ni(Lx)] [H2A]T where n is the stoichiometric factor with 0.5 for NiIV → NIII reactions and 1 for each step of Ni IV→ NiIII → NiII biphasic conversions. The evaluation of rate and equilibrium constants of the reactants was achieved by employing suitable computer-fit programs. Both the reactions have been proposed to follow the inner-sphere mechanism through the formation of an associated species involving the sulfur atom of the thiol and the metal center of the oxidant.