One-pot sequential oxidation and aldol-condensation reactions of veratryl alcohol catalyzed by the Ru@ZIF-8 + CuO/basic ionic liquid system

Abstract

The development of green and efficient methods to transform lignin into fuels and high value-added chemicals is of great importance. In this work, we studied one-pot sequential oxidation and aldol-condensation reactions of veratryl alcohol in a basic ionic liquid (BIL) 1-butyl-3-methylimidazolium 5-nitrobenzimidazolide, which acted as the solvent and provided the basic conditions required for the reactions. The effects of different factors such as the type of catalyst, reaction time, reaction temperature, and the amount of BIL on the oxidation reaction were investigated. It was demonstrated that the catalytic performance of individual Ru@ZIF-8 (zeolitic imidazolate framework-8) or CuO was very poor for the oxidation of veratryl alcohol to veratryl aldehyde. Interestingly, Ru@ZIF-8 + CuO was very efficient for the oxidation reaction and a high yield of veratryl aldehyde could be obtained, indicating the excellent synergistic effect of the two catalysts in the BIL. The veratryl aldehyde generated by the oxidation of veratryl alcohol could react directly with acetone to form 3,4-dimethoxybenzylideneacetone by aldol-condensation reaction catalyzed by the BIL in high yield.