OXIDATION OF METHYL-ALPHA-D-GLUCOPYRANOSIDE AND OCTYL-ALPHA-D-GLUCOPYRANOSIDE, CATALYZED BY HIGH-VALENT RUTHENIUM SPECIES - RUO4, RUO4(-) AND RUO4(2-)

The oxidation of two alkyl glucopyranosides (OGP and MGP) by NaBrO3, catalyzed by three different high-valent ruthenium species, ruthenium tetroxide, perruthenate and ruthenate, is reported. At pH 4.5, RuO4 appears to catalyze the oxidation of the alkyl glucopyranosides quite fast and produces alkyl glucuronic acid as the main product. Analysis of the kinetic and thermodynamic data suggests a hydride-transfer mechanism. At pH 10, perruthenate appears to catalyze the oxidation of the alkyl glucopyranoside by NaBrO3, albeit with a lower reaction rate and a lower selectivity for the alkyl glucuronic acid. The kinetic data, activation parameters and UV-Vis, spectroscopy experiments all point towards a radical mechanism. At pH 14, ruthenate seems to be unable to catalyze the oxidation of an alkyl glucopyranoside by NaBrO3. Product inhibition of these homogeneous catalysts eventually results in the deactivation. Re-oxidation of the lower-valent ruthenium species appears to be prevented by coordination of the glucuronic acid to the lower-valent ruthenium species, as deduced from electronic absorption studies.