Tuning selectivity among acetalization, pinacol coupling, and hydrogenation reactions of benzaldehyde by catalytic and photochemical pathways at room temperature

Abstract

Benzaldehyde is one of the industrially most useful feedstocks, and its transformation to high-value chemicals is very attractive. Different transformations of benzaldehyde, such as acetalization, pinacol coupling, and hydrogenation, have been achieved herein by adjusting pH, light source, and selection of a catalyst. Consequently, the corresponding products have been obtained with excellent yields (e.g. 92% yield for acetalization, 96% yield for pinacol coupling, and 85% yield for hydrogenation). The mechanisms behind each transformation were studied, and it revealed that pinacol coupling reaction was achieved through a photochemical process under 365 nm irradiation at pH 12, where the introduction of the TiO2 (P25) catalyst would completely shift the selectivity toward benzyl alcohol through a photocatalytic pathway and to benzaldehyde dimethyl acetal via low-temperature thermal catalysis.