Theoretical study of the michael addition of acetylacetone to methyl vinyl ketone catalyzed by the ionic liquid 1-butyl-3-methylimidazolium hydroxide

摘要

By performing density functional theory calculations, we have investigated the Michael addition of acetylacetone to methyl vinyl ketone in the absence and presence of the ionic liquid 1-butyl-3-methylimidazolium hydroxide ([bmIm]OH). In the absence of ionic liquids, acetylacetone is firstly tautomerized to enol form and then takes place Michael addition to methyl vinyl ketone. As in the catalyzed Michael addition reaction, a bmIm~+- OH~- ion pair is introduced into the reaction system to model the effect of the ionic liquid environment on the reactivity. The calculated results show that the anion enhances nucleophilic ability of acetylacetone since the OH~- anion captures a proton to form an acetylacetone anion-H_2O complex, and the cation improves the electrophilic ability of methyl vinyl ketone by forming intermolecular hydrogen-bonds. Both the remarkable effects of the cation and anion on the reactivity of reactants promote this reaction, which take place more easily compared with uncatalyzed reaction. The calculated results show that the main product of the Michael addition is in its ketone form. Our study provides a detailed reaction mechanism of Michael addition catalyzed by basic ionic liquid [bmIm]OH and clearly reveal the catalytic role of ionic liquid in important chemical reaction.