Epoxidation with hydrotalcite-intercalated organotungstic complexes

Abstract W(VI)-based catalysts for epoxidation were incorporated into hydrotalcite either by anionic exchange or by complexation with phosphonic acids previously incorporated between the sheets. Phenyl- and dodecylphosphonic acids and peroxotungstic salts were intercalated into hydrotalcite as attested by the expansion of the lamellar lattice and the complexation of phosphonic acids with W-peroxo species was made possible when using a lipophilic quaternary ammonium peroxotungstic salt [W(VI)-Aliquat] which maintains the layered structure. These catalysts were checked in the epoxidation of cyclohexene with hydrogen peroxide or terbutylhydroperoxide as external oxidants. The materials prepared by anionic exchange gave only epoxycyclohexane but with moderate yields, whereas those prepared from previously incorporated phosphonic acids gave rather high selectivity (50–72%) in allylic oxidation products.