THE ACTIVE-SITES IN THE HETEROGENEOUS BAEYER-VILLIGER OXIDATION OF CYCLOPENTANONE BY HYDROTALCITE CATALYSTS

The active sites of hydrotalcites, [Mg1-x2+Alx3+(OH)(2)](x+)[A(x/n)(n- ).mH(2)O](x-), A(n-); CO32-, Cl-, etc., were studied in the heterogene ous Baeyer-Villiger oxidation of cyclopentanone to delta-valerolactone with a combination oxidant system of molecular oxygen and benzaldehyd e (O-2/benzaldehyde) in a 1,2-dichloroethane solvent. The hydrotalcite s with different basicity were prepared by changing element ratios of Al3+ to Mg2+ in the Brucite-like layer and by changing anionic compoun ds (CO32-, Cl-, and SO42-) in the interlayer. The basicities of hydrot alcites were evaluated by measuring the calorimetric heats of benzoic acid adsorption and the zeta-potential of potassium chloride and by th e indicator titration method. Yields of delta-valerolactone were almos t proportional to the basicities of hydrotalcites, i.e., the heats of benzoic acid adsorption on hydrotalcites, which suggests that basic si tes of hydrotalcites are active sites for the oxidation. Yields of del ta-valerolactone were also dependent on the basicities of hydrotalcite s using m-chloroperbenzoic acid (m-CPBA) as an oxidant instead of O-2/ benzaldehyde. Basic sites of hydrotalcites play an important role in t he oxygen transfer from perbenzoic acid to ketone. (C) 1997 Elsevier S cience B.V.