Oxidation of different sugar residues catalyzed by [Ru(azpy)2(H2O)2]2+; A comparative study

Abstract The oxidation of several sugars by NaBrO 3 catalyzed by [Ru(azpy) 2 (H 2 O) 2 ] 2+ , is reported and compared with earlier oxidation results with octyl α‐D‐glucoside (α‐OGP). The sugars studied were 1‐octyl β‐D‐glucoside (β‐OGP), 1‐octyl β‐D‐galactoside (β‐OGaP), 1‐phenyl β‐D‐glucoside (β‐PGP), 1‐methyl α‐D‐glucoside, 1‐methyl β‐D‐glucoside and 1‐decyl β‐D‐maltoside (β‐DMP). The results with β‐DMP are compared with previously reported oxidation results with β‐DMP heterogeneously catalyzed over platinum. The structure of the sugar substrate appears to have a significant effect on the activity and selectivity of the oxidation reaction. The main conclusions from this study are that β‐isomers are in general less reactive than α‐isomers; β‐PGP in particular is very unreactive. The kind of substitution (phenyl versus alkyl, octyl versus methyl) on the anomeric centre has considerable effect on the reactivity of the sugar. The oxidation of β‐DMP catalyzed by [Ru(azpy) 2 (H 2 O) 2 ] 2+ results in a number of different oxidation products. The C 6 ‐primary hydroxy groups of both glucose units of β‐DMP can be oxidized to carboxylic groups, in contrast to the previously reported heterogeneous catalyzed oxidation of β‐DMP by dioxygen. However, the main reaction is the splitting of the decyl chain from the maltose unit. The α‐1,4‐O link between the glucose units appears to be quite stable under the catalytic oxidation conditions used. Based on the results obtained, possible reaction mechanisms are discussed.