Contribution to MoO₃–SiO₂ and WO₃–SiO₂ utilization—active catalysts in jasmine aldehyde, 2-hexyl-1,3-dioxolane and methyllaurate synthesis

Abstract

Several types of mixed molybdenum and tungsten oxide—SiO₂ materials were prepared using sol–gel and wet impregnation method. In all cases, four different loading of MoO₃ or WO₃ (1, 10, 25 and 40 wt%) were prepared. Materials were characterized using X-ray diffraction, X-ray fluorescence spectroscopy and its acidity was determined by temperature programmed desorption of pyridine. Catalytic activity of these materials was tested in three model reactions providing valuable fine chemicals—aldol condensation, acetalization and esterification. These reactions are usually catalyzed by homogenous catalysts. With increasing interest in environmental protection these catalysts are replaced by heterogeneous ones—offering easy separation from reaction mixture and a possibility of catalyst reuse. More specifically the chosen reactions were: aldol condensation of benzaldehyde with heptanal giving jasmine aldehyde (1), acetalization of heptanal by ethylene glycol giving 2-hexyl-1,3-dioxolane (2) and esterification of lauric acid by methanol giving methyllaurate (3). The prepared materials proved to be catalytically active in above mentioned reactions—in aldol condensation was the best result (78% heptanal conversion, 58% selectivity to jasmine aldehyde, 24 h) obtained using Mo 40 material prepared by impregnation. This material showed to be the best together with W 40 material prepared by sol–gel process in esterification (91 or 94% conversion, 24 h). Acetalization occurs very willingly, best results (heptanal conversion > 90% and selectivity > 90%, 5 h) was obtained using Mo and W 25 and 40 prepared by sol–gel and impregnation process.