MoO₃-MCM-41 materials as effective catalysts in Prins reaction of isoprenol with butanal followed by esterification in one-pot reaction arrangement

Prins reaction of isoprenol with butanal provides important intermediate 4-methyl-2-propyltetrahydro-2H-pyran-4-ol, which can be esterified to 4-methyl-2-propyltetrahydro-2H-pyran-4-yl acetate. This desired fragrance with fruity and rose scent is known, e.g., as Clarycet®. Molybdenum-modified MCM-41 materials were obtained by a wet impregnation method using a water solution of ammonium molybdate. We prepared several materials with different MoO₃ loadings. These materials were thoroughly characterized (nitrogen physisorption, acidity—temperature-programmed desorption, elemental composition, etc.). The activity of prepared materials was tested in Prins reaction of isoprenol with butanal in batch arrangement. The influence of various reaction conditions (catalyst type, solvent, and water addition) was tested. We showed that modification of MCM-41 with MoO₃ led to a significant increase of catalytic activity (butanal conversion at 4 h of reaction: 7% for nonmodified MCM-41 compared to 93% for material 5 wt% of MoO₃-MCM-41). Water addition to the reaction mixture positively influenced the selectivity of the desired substituted tetrahydropyranol (selectivity > 70%). Mo-modified materials were also active in the esterification of 4-methyl-2-propyltetrahydro-2H-pyran-4-ol with acetanhydride to 4-methyl-2-propyltetrahydro-2H-pyran-4-yl acetate providing desired product after 5 h with 100% selectivity and total conversion. Reaction in the “one-pot” arrangement was also performed.