Kinetics of the oxidation of DL-1-phenylethanol by tris(2,2′-bipyridine)nickel(III) ions in aqueous perchlorate media

Abstract

The product of the oxidation of DL-1-phenylethanol by [Ni(bipy)₃]³⁺ is acetophenone, and it is found that the ratio |Δ[Ni^III]|/|Δ[acetophenone]|= 2, analogous to the stoichiometry found for the oxidation of secondary alcohols by aqua-cations. The rate of the oxidation is first-order in [Ni(bipy)³⁺₃] and first-order in [alcohol] with the second-order rate constant independent of acidity. It is concluded that the oxidation is an outersphere reaction not involving the preliminary removal of a bipyridine molecule from the Ni^III and that none of the alcohol is converted to an oxidatively inert form via a solvent-sorting equilibrium involving protons. The values found kinetically for the equilibrium constant K_c for this solvent-sorting involving phenylethanols are compared with K_c values for other alcohols. The enthalpy and entropy of activation are compared with values for ΔH* and ΔS* for the oxidation of a range of substances by [Ni(bipy)₃]³⁺.