Cholinium ionic liquids as cheap and reusable catalysts for the synthesis of coumarins via Pechmann reaction under solvent-free conditions

Abstract

A cheap cholinium ionic liquid N,N′-dimethylaminoethanol hydrosulfate ([N₁₁₂OH][HSO₄]) was found to be an efficient and reusable catalyst for the Pechmann condensation under solvent-free conditions. The coumarin products can be simply separated and the ionic liquid catalyst can be recycled and reused for at least six runs without noticeable decrease in the catalytic activity. The UV-vis studies suggested that the increase of the acidity and the introduction of a hydroxyl group to the cation benefit the existence of the keto tautomer of ethyl acetoacetate, which then leads to the excellent performance of [N₁₁₂OH][HSO₄].