Ruthenium catalysed oxidation of cyclohexanol

Abstract

The oxidation of cyclohexanol by ferricyanide in alkaline aqueous solution is catalysed by micromolar concentrations of K₃RuCl₆. The rate law at 25.0ºC in pH 11.9 phosphate buffer containing 0.50 M NaCl is

-d[Fe^III]/dt = [Ru](2k_lk₂[alcohol][Fe^III])/(2k_l[alcohol] + k₂[Fe^III])

with k_l 12 ± 2 mol^-1 1. s^-1 and k2 (2.5 ± 0.2) × 10² mol^-1 1. s^-1. A deuterium isotope effect of about 4 is observed when (D₁₂)cyclohexanol is used. A mechanism consistent with these observations involves reduction of the Ru^III catalyst by hydride transfer from the alcohol followed by reoxidation by ferricyanide to the original Rul^III state.