Baeyer–Villiger oxidation of cyclohexanone with hydrogen peroxide/benzonitrile over hydrotalcites as catalysts

Abstract

Various Mg/Al, Mg/Al/Sn and Mg/Al/Zr hydrotalcite-like compounds (HTs) were prepared for use as catalysts in the Baeyer–Villiger (BV) oxidation of cyclohexanone with H 2O 2/benzonitrile as oxidant and benzonitrile itself as the solvent. The reaction gave water and benzamide as byproducts, the latter can be recycled in an appropiate process. Analysis of the solids revealed that tin and zirconium are in fact incorporated into the HT structure. The solids containing Mg/Al and Mg/Al/Sn and their calcination products (viz. Mg/Al and Mg/Al/Sn mixed oxides) were found to be effective catalysts for the BV oxidation of cyclohexanone. The Sn solids exhibited a higher activity than a more conventional catalyst obtained from an HT containing Mg and Al only (17% in the best case). Also, the catalyst containing tin was active when we used H 2O 2/acetonitrile system as oxidant. The solids containing Zr were found to promote the decomposition of the hydrogen peroxide and hence to adversely influence the oxidation reaction. A mechanism accounting for the experimental results is proposed. The reaction was conducted under very mild conditions (viz. atmospheric pressure and a temperature of 70 °C), and conversions obtained were higher than 80% in some cases and 100% selectivity after 6 h. The most active catalyst, which was that containing the largest amount of tin, retained full activity after three reuses.