Florol synthesis via Prins cyclization over hierarchical beta zeolites

A set of hierarchical beta zeolites with variable Si/Al ratios, nanoparticle sizes, textural and acidic properties was prepared using a hydrothermal treatment of a concentrated alkali metal-free protic acid-containing zeolite gel-precursor. The obtained catalysts were investigated in the Prins cyclization of isovaleraldehyde with isoprenol yielding a commercially valuable tetrahydropyranol (Florol). The highest yield of the desired product (55.4%) was achieved over a zeolite catalyst possessing moderate acidity, developed mesoporosity (V_meso 0.60 cm³/g) and a high external surface area (290 m²/g). Preferable formation of substituted tetrahydropyranol over weak- and medium-strength Brønsted acid sites, on the one hand, and generation of the undesired dehydration products mainly over strong Brønsted acid sites, on the other hand, occurring in parallel routes were supported by the kinetic analysis of the reaction network.