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

Several types of mixed WO 3 /SiO 2 /Al 2 O 3 materials were prepared using sol–gel and wet impregnation methods. Four different loadings of WO 3 (1, 10, 25 and 40 wt%) were prepared. Materials were characterized using X -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 °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 °C). Possibility of catalyst reuse was confirmed.