The involvement of perruthenate in the RuCl3-catalysed oxidation of alcohols in base in the presence of peroxodisulphate

Abstract

It has been observed that the perruthenate formed on addition of ruthenium trichloride to peroxodisulphate solution in base decomposes, with loss of oxygen, to form ruthenate. Contrary to thermodynamic prediction, the latter species appears to be highly stable in the presence of excess of peroxodisulphate providing reactive organic species such as alcohols are not present. Addition of alcohols to the ruthenate–peroxodisulphate mixture at high pH affords a perruthenate–alcohol complex, the latter acting as an effective catalyst for the homogeneous oxidation of primary or secondary alcohols by the peroxodisulphate. A mechanism based on α-hydride abstraction has been proposed for the latter reaction, and the simultaneous formation of the insoluble dioxide RuO₂·xH₂O attributed to further reaction of the two products, ruthenate and aldehyde. Although there have been several claims to the contrary, ruthenate (RuO₄^2–) species do not directly oxidize alcohols (other than methanol); they are, however, capable of readily oxidizing aldehydes.