Synthesis of Benzoxanthene Derivatives Catalyzed by Multi-SO₃H acidic Ionic Liquids under Solvent-free Conditions

Four kinds of multi-SO₃H-acidic ionic liquids were synthesized with a two-step method and their catalytic properties were analyzed and compared with the condensation reaction of benzaldehyde and β-naphthol as the probe reaction. The preparation of benzoxanthene derivatives through the reaction of 4-substituted aromatic aldehydes, which had different types of functional groups and β-naphthol used N, N´, N´´, N´´´-tetrapropane sulfonic hexamethylenetetramine tetrahydrosulfate as a catalyst under solvent-free conditions was investigated. The results show that:the optimum reaction temperature, molar ratio of aromatic aldehyde to β-naphthol, catalyst amount are 110℃, 1:2 and 55% (based on the mass of aromatic aldehydes); N, N´, N´´, N´´´-tetrapropane sulfonic hexamethylenetetramine tetrahydrosulfate after removed water can be recycled and when reused for five times, its catalytic activity has no noticeably decreasing; 4-substituted aromatic aldehydes, whether the substituent is an electron-donating group or electron-withdrawing group, are beneficial to the condensation reaction.