N,N-diethyl-N-sulfoethanaminium hydrogen sulfate as an effective catalyst for the preparation of 14-aryl-14H-dibenzo[a,j]xanthenes

The aim of this study is development of a novel SO3H-containing Brønsted acidic ionic liquid as catalyst for organic transformations. Therefore, initially, N,N-diethyl-Nsulfoethanaminium hydrogen sulfate {[Et3N-SO3H]HSO4} (as a novel member of this family of ionic liquids) was synthesized, and characterized using 1H and 13C NMR,FT-IR and mass spectral data[1]. Afterward, its catalytic activity was checked for promotion of one class of useful organic transformations under solvent-free conditions, including the condensation reaction of arylaldehydes with 2-naphthol to give 14-aryl-14Hdibenzo[ a,j]xanthenes(Scheme1).The ionic liquid efficiently catalyzed the reaction,and the product were obtained in excellent yields within short reaction times. Ionic liquids are of importance because they have been extensively used as solvent,catalyst and reagent in organic synthesis. These attractive compounds have various unique properties including non-flammability, non-volatility, wide liquid-state temperature range, high thermal and chemical stability, large electrochemical window, favorable salvation behavior and enhanced reactivity.[2] Xanthene derivatives, especially benzoxanthenes are of importance since they have various biological activities such as antibacterial, antiviral, and anti-inflammatory , properties. Furthermore, some other benzoxanthenes have found applications in industries, such as fluorescent materials for visualization of biomolecules, and as dyes in laser technology.[3].