Prins cyclization of isoprenol with various aldehydes using MoO₃/SiO₂ as a catalyst

Abstract

MoO₃/SiO₂ was used as a catalyst of the Prins cyclization of isoprenol with various aldehydes, with isovaleraldehyde chosen as a model substance. Two catalyst preparation methods, impregnation and sol–gel, were applied and the differences between their structure and catalytic activity were studied. The prepared catalysts were characterized by available methods (XRD, XRF, N₂ adsorption, SEM and TGA). The catalyst prepared by sol–gel has a better dispersion of molybdenum oxide on the support and contains a lower amount of MoO₃ crystallites compared to the impregnation method. A higher yield of the desired product (substituted tetrahydropyranol) was achieved using the catalyst prepared by sol–gel (51%) in comparison with the impregnation method (45%). Changing the molybdenum oxide amount in the catalyst had no effect on the activity or selectivity but an increase of the total catalyst amount in the reaction mixture increased the reaction rate. The addition of water had a positive effect on the selectivity of the desired product (a yield up to 60%) but decreased the reaction rate. The prepared catalyst can be reused at least four times in this reaction without any loss of activity or selectivity and it can also be used in the Prins cyclization of isoprenol with various aldehydes. The advantages of MoO₃/SiO₂ are its heterogeneous state in the reaction, simple preparation, availability and low cost of raw materials, reusability and activity. The activity is comparable with other heterogeneous catalysts used previously in this reaction.