New Sn-Mg-Al hydrotalcite-based catalysts for Baeyer-Villiger oxidation of β-cyclocitral

Abstract

This study focuses on the Baeyer-Villiger (BV) oxidation of β-cyclocitral using tin-modified mixed oxides based on hydrotalcites as catalysts. Hydrotalcite-like compounds modified with tin were found to be promising catalysts capable of catalyzing both BV oxidation and subsequent hydrolysis of formed formate. The testing of catalytic activity and optimization of reaction conditions for achieving high conversion and selectivity to the desired product, 2,6,6-trimethylcyclohexanone, was carried out. The effects of the Mg/Al ions molar ratio, tin amount, catalyst amount, and form (hydrotalcite or mixed oxide) on the reaction course and selectivity to 2,6,6-trimethylcyclohexanone were studied. Optimal reaction conditions (temperature, reactant ratio, solvent type and amount) were determined. Additionally, different dosing methods, amounts and types of oxidizing agents were tested. The reaction was successfully scaled up, and the possibility of reusing the catalyst at least three times was confirmed. Gradual dosing of 6.4 molar equivalents of 50% hydrogen peroxide in 24 doses during 5-minute intervals over 115 min was determined as the most suitable method. The temperature of 115 °C, cyclohexanol in a mass ratio of 2:1 to the starting material as a solvent, and 15 wt% of the catalyst to the starting material was identified as optimal for the BV oxidation of ß-cyclocitral. The mixed oxide with a Mg/Al molar ratio of 2 impregnated with 3 wt% tin at room temperature (3Sn-MO2imp25) exhibited the highest activity and selectivity towards 2,6,6-trimethylcyclohexanone. Under these reaction conditions, total conversion and a 60% selectivity to the desired product were achieved after 5 h of reaction.