A practical method for alcohol oxidation with aqueous hydrogen peroxide under organic solvent- and halide-free conditions

A catalytic system consisting of sodium tungstate and methyltrioctylammoniu m hydrogensulfate effects oxidation of simple secondary alcohols to ketones using 3-30% H2O2 Without any organic solvents. The oxidation can be conduc ted under entirely halide-free, mildly acidic conditions. A combination of tungstic acid and an appropriate quaternary ammonium salt also effects the alcohol dehydrogenation. The organic/aqueous biphasic reaction allows easy product/catalyst separation. The turnover number, defined as mols of produc t per mol of catalyst, approaches 77700 (2-octanol) or 179000 (1-phenyletha nol), two orders of magnitude higher than any previously reported. Eater, a lkyl and t-butyldimethylsilyl ether, epoxy, carbonyl, N-alkyl carboxamide, and nitrile groups are tolerated under the reaction conditions. Secondary a lcohols are preferentially oxidized over terminal olefins. Primary alkanols are oxidized directly to carboxylic acids in a moderate to high yield. Ben zylic alcohols are selectively oxidized to benzaldehydes or benzoic acids u nder suitable conditions. This method is high-yielding, clean, safe, operat ionally simple, and cost-effective, and therefore suitable for practical or ganic synthesis. The mechanistic origin of the catalytic efficiency is disc ussed.