Highly selective synthesis of campholenic aldehyde over Ti-MWW catalysts by α-pinene oxide isomerization

Abstract

Campholenic aldehyde is a highly valuable fine chemical that can be obtained by multistep synthesis from monoterpene α-pinene isolated from turpentine oil. Therefore, economical and environmentally benign synthesis of this aldehyde is of great interest. In this study, different titanosilicates were prepared and tested in selective campholenic aldehyde synthesis via isomerization of α-pinene oxide. Titanosilicates with MWW zeolitic structure were synthesized directly and compared with Ti impregnated SBA-15 and commercial titanium silicalite-1. The catalysts were thoroughly characterized and compared in terms of their catalytic activity and selectivity toward the desired aldehyde in isomerization reactions performed either in toluene as a solvent at 70 °C or in N,N-dimethylacetamide at 140 °C. Ti-MWW catalysts showed very high catalytic activity with total conversion of α-pinene oxide. The highest selectivity to campholenic aldehyde, being 96% at the total conversion, was reached over the Ti-MCM-22 catalyst in toluene at 70 °C. This result substantially exceeds any other results published so far in the literature. The great catalytic performance of Ti-MCM-22 was attributed to the combination of the presence of isolated tetrahedrally coordinated Ti species, which act as crucial Lewis acid centres, the absence of undesired Brønsted acidity, and the MWW architecture that facilitates the formation of the target aldehyde.