Baeyer-Villiger oxidation of cyclohexanone with H2O2/acetonitrile over hydrotalcite-like catalysts: Effect of Mg/Al ratio on the ε-caprolactone yield

Abstract

Phase-pure magnesium-aluminium hydrotalcite-like compounds with molar ratios of Mg/Al ranging from 1.93 to 6.63 were synthesized and characterized with ICP OES, XRD, BET, and Raman spectroscopy. The materials were used as catalysts in the Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone with H2O2/acetonitrile oxidizing system in mild conditions (70°C, atmospheric pressure). Initial catalysts activity increased with growing Mg content/basicity, but after completion of the catalytic run best ε-caprolactone yield was obtained for the catalyst with Mg/Al=5.62. Poorer than expected performance of the material richest in magnesium was attributed to the enhanced leaching of Mg in the mildly acidic reaction environment. The occurrence of the homogeneous catalytic reaction involving leached magnesium has been excluded. Recycling experiments show that leaching of Mg causes partial deactivation, but the catalysts can be easily regenerated and regain the initial performance.