Ti-MCM-41 materials synthesised at room temperature as catalysts for cyclisation of (±)-citronellal

Citronellal can be cyclised to produce isopulegol, which is an intermediate in the synthesis of menthols. These chemicals are all used in the fragrance industry and menthol is also an important product used as a flavour, a pharmaceutical and in oral care. The cyclisation of citronellal proceeds readily with various homogeneous catalysts, but the catalyst frequently cannot be recovered and reused. Several heterogeneous catalysts have also been found to be active with, for instance, Sn-Beta zeolite being highly active and diastereoselective [1]. Ordered mesoporous materials have stimulated an enormous interest in the scientific community, principally in the fields of heterogeneous catalysis and materials science, since their disclosure in 1992. The MCM-41 material is the most widely studied among the numerous mesoporous materials due to the structural simplicity. Catalytic activity can be generated by modification of the siliceous framework by heteroelements such as Ti. In previous work we have demonstrated that well structured Ti-MCM-41 materials, with good thermal and mechanical stability in air and catalytically active in the oxidation of cyclohexene, could be synthesised at ambient temperature and pressure [2,3]. In the present work we extend the applicability of those Ti-MCM-41 materials, as heterogeneous catalysts, to produce an important intermediate, isopulegol, from the cyclisation of citronellal. The use of this kind of materials appears to be a good option over homogeneous catalysts, because they offer the advantage of recovery and, consequently, contribute to environmentally friendly processes.