The active sites in the heterogeneous Baeyer-Villiger oxidation of cyclopentanone by hydrotalcite catalysts

The active sites of hydrotalcites, [View the MathML source, A″n−; CO32−, Cl−, etc., were studied in the heterogeneous Baeyer-Villiger oxidation of cyclopentanone to δ-valerolactone with a combination oxidant system of molecular oxygen and benzaldehyde (O2/benzaldehyde) in a 1,2-dichloroethane solvent. The hydrotalcites with different basicity were prepared by changing element ratios of Al3+ to Mg2+ in the Brucite-like layer and by changing anionic compounds (CO32−, Cl−, and SO42−) in the interlayer. The basicities of hydrotalcites were evaluated by measuring the calorimetric heats of benzoic acid adsorption and the zeta-potential of potassium chloride and by the indicator titration method. Yields of δ-valerolactone were almost proportional to the basicities of hydrotalcites, i.e., the heats of benzoic acid adsorption on hydrotalcites, which suggests that basic sites of hydrotalcites are active sites for the oxidation. Yields of δ-valerolactone were also dependent on the basicities of hydrotalcites using m-chloroperbenzoic acid (m-CPBA) as an oxidant instead of O2/benzaldehyde. Basic sites of hydrotalcites play an important role in the oxygen transfer from perbenzoic acid to ketone.