Versatile etherification of alcohols with allyl alcohol by a titanium oxide-supported molybdenum oxide catalyst: gradual generation from titanium oxide and molybdenum oxide

Abstract

Etherification using allyl alcohol to produce allyl ether via dehydration is a fundamental technique for producing fine chemicals that can be applied to electronic devices. We demonstrate a sustainable method to synthesize allyl ethers from allyl alcohol with various alcohols up to a 91% yield, with water as the sole by-product. In this reaction, the active catalyst is gradually generated as the reaction proceeds through the simple mixing of TiO₂ and MoO₃. The dispersion of MoO₃ on the spent catalyst has been observed by XRD, HAADF-STEM, and STEM-EDS mapping. This catalyst shows excellent catalytic activity by virtue of the highly dispersed nature of MoO₃ supported on TiO₂, which is reusable at least five times. According to a mechanistic study including the measurement of XPS of MoO₃ on TiO₂ and control experiments using SiO₂ and Al₂O₃ supports, the suitable reducibility of MoO₃ to coordinate the allyl moiety on TiO₂ seems to be a key factor for high-yielding syntheses of various allyl ethers even under heterogeneous reaction conditions. The reaction mechanism is considered to be as follows: σ-allyl species are formed from dehydration of the allyl alcohol, followed by a nucleophilic attack by another alcohol against the σ-allyl carbon to give allyl ethers. The developed catalytic system should be suitable for easily handled syntheses of allyl ethers due to the employment of commercially available MoO₃ and TiO₂ with halide- and organic solvent-free reaction conditions.