Tungsten oxide-based materials as effective catalysts in isopulegol formation by intramolecular Prins reaction of citronellal

Several types of mixed WO3/SiO2/Al(2)O(3)materials were prepared using sol-gel and wet impregnation methods. Four different loadings of WO3(1, 10, 25 and 40 wt%) were prepared. Materials were characterized usingX-ray diffraction,X-ray fluorescence spectroscopy, and their acidity was measured by temperature programmed desorption of pyridine. Catalytic activity of these materials was tested in Prins reaction-intramolecular cyclization of citronellal. Influence of reaction conditions (temperature 70-90 degrees C, catalyst amount 1-10 wt%, catalyst type) on citronellal conversion and selectivity of isopulegol formation was monitored. The best result (90% of isopulegol, 97% selectivity of isopulegol formation, 24 h) was obtained using W25 IMP catalyst (10 wt%, 50 degrees C). Possibility of catalyst reuse was confirmed.