Mechanism of Ruthenium (III) Catalysis of Periodate Oxidation of Aldoses in Aqueous Alkaline Medium.

A general mechanism for Ru(III) catalysed oxidation of L(+) arabinose (Ara) and D(+) galactose (Gal) in aqueous alkaline medium is proposed. The most reactive species of the catalyst was found to be [RuCl₃(OH)₂H₂O]^2-. The reactions exhibit pseudo-first order kinetics with respect to Ru(III) and are first order with respect to lower [IO₄^-] and OH^-, but tend towards zeroth order to both higher [IO₄^-] and [OH^-]. The reactions are zero order with respect to each aldoses. Positive effect of Cl^- on the rate of reaction is also evident in the oxidation of both reducing sugars. A mechanism, involving the interaction of the reactive species of Ru(III) and [IO₄^-] leading to the formation of a complex, which in the rate determining step decomposes into another complex with the release of Cl^- ion, is proposed and the rate law is derived. [ABSTRACT FROM AUTHOR]