Activity and stability of mesoporous molecular sieves modified with vanadium in the oxyfunctionalization of alpha-pinene

Abstract

Selective oxyfunctionalization of terpenes is an interesting route to utilize these inexpensive natural products for numerous industrial applications. Thus, the oxygenated derivates obtained from the α-pinene oxidation in liquid phase (campholenic aldehyde, verbenol, verbenone) are important as flavor chemicals and precursors of fine chemicals, including sandalwood fragrance, taxol and vitamins A and E [1]. Traditionally, the high aggregated value chemicals are frequently produced by classic organic chemistry, focusing only on the desired product instead of considering the synthesis route, which leads to generate significant amounts of contaminated effluents that cause a great environmental impact. Thus green chemistry appears as a practical approach to achieve clean technologies and sustainable developments, providing the catalysis as a fundamental tool to minimize the process steps and allow the use of mild reaction conditions. In addition, a catalytic process to be economically and environmentally viable, it is essential that the catalyst can be recovered and regenerated. However a particular problem associated with the use of solid catalysts in the liquid phase, as opposed to the gas phase, is the leaching of the metal ion into solution. Mesoporous molecular materials with V contents varying from 0.035 wt% to 1.21 %wt were prepared by hydrothermal synthesis [2] to be used as potential catalysts in the reaction of α-pinene oxidation with H2O2. The major products observed were: verbenone, verbenol and campholenic aldehyde which are used in the pharmaceutical, perfume and cosmetics industry. The material with lower V content (0.035% w/w) was selected for a further study due to its high activity, TON and selectivity to allylic oxidation products. In this way, the effect of the nature of protic solvent: ethanol (EtOH), isoamyl alcohol (iAOH), and nonprotic solvent: acetonitrile (AcN), methyl ethyl ketone (MEK), on the α-pinene activity and products distribution were studied. The best results were obtained with AcN. Finally, the stability of the catalyst to the leaching of the active species and the possibility of recycling were checked. The experiments confirm that the V active species are not leached during the reaction. Thus the heterogeneous catalyst can be recovered and reused many times without loss in catalytic activity and selectivity.