Ferricyanide Oxidation of Butanol Homogeneously Catalysed by Chlororuthenium Complexes

Abstract

The oxidation of butan-1-ol by ferricyanide ion in alkaline aqueous solution is catalysed by solutions of ruthenium trichloride hydrate. The kinetics of the reaction has been reinvestigated and the data are consistent with the rate law

-d[Fe^III]/dt = [Ru](2k₁k₂ [BuOH] [Fe^III])/(2k₁ [BuOH]+k₂ [Fe^III])

This rate law is interpreted by a mechanism involving oxidation of butanol by the catalyst (k₁) followed by reoxidation of the catalyst by ferricyanide (k₂). The non-linear dependence of the rate on the butanol concentration is ascribed to the rate-determining, butanol-independent reoxidation of the catalyst, rather than to the saturation of complex formation between butanol and the catalyst as previously claimed. Absolute values of the rate constants could not be determined, because some of the ruthenium precipitates from basic solution. With K₃RuCl₆ as the source of a homogeneous catalyst solution, estimates were obtained at 30·0ºC of k₁ = 191. mol^-1 s^-1 and k₂ = 1·4 × 10³ l. mol^-1 s^-1.