OXIDATION OF OCTYL ALPHA-D-GLUCOPYRANOSIDE TO OCTYL ALPHA-D-GLUCURONIC ACID, CATALYZED BY SEVERAL RUTHENIUM COMPLEXES, CONTAINING A 2-(PHENYL) AZOPYRIDINE OR A 2-(NITROPHENYL)AZOPYRIDINE LIGAND

The oxidation of octyl alpha Lu-D-glucopyranoside by NaBrO3, catalyzed by a number of ruthenium polypyridyl complexes was investigated. Both [Ru(azpy)(2)(H2O)(2)](2+) (azpy = 2-(phenyl)azopyridine, system I) and [Ru(naz)(2)(H2O)(2)](2+) (naz = 2-(p-nitrophenyl)azopyridine, system II) proved to be active catalysts yielding octyl glucuronic acid (in acidic medium) and a 2, 3-glycol cleavage product (in basic medium) from octyl alpha-D-glucopyranoside (OGP). A major side-reaction is the hydrolysis of OGP, at the C-1 position. System II appears to be more reactive than system I, which has been explained by the redox properties of the complex. Especially at pH 3 a considerable amount of 1-O-octyl alpha-D-glucuronic acid is formed without the formation of hydrolysis products. Mechanistic studies, using results from reactions with cyclobutanol in combination with spectroscopic data, indicate that a Ru(IV) = O species is the active catalytic species. Two new complexes were synthesized, [Ru(terpy)(azpy)(H2O)](ClO4)(2) (terpy = terpyridine, system III) and [Ru(terpy) (naz) (H2O)](ClO4)(2) (system IV). Both complexes are less active than system I and II. The origin of the reduced activity can Lie in the fact that the ruthenium site is sterically less accessible, or because of oxidative instability of the complex, as indicated by electrolysis experiments.