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Some novel Brønsted acidic ionic liquids (TSILs) that bear an alkane sulfonic acid group in an acyclic trialkanylammonium cation were synthesized and their uses as dual solvent−catalysts for Fischer esterification reactions of acetic acid, metacetonic acid, and benzoic acid with ethanol, butanol, and benzyl alcohol were investigated. The reactions were completed smoothly at room temperature to 110 °C for 1.5−3.0 h with good yields of 88−95%. The results indicate that catalytic activity depends on anion acidity and the solubility of the starting material in TSILs. The increasing of the anion's acidity improves the catalytic activity of the TSILs. Furthermore, the produced esters could be separated by decantation after the reaction and the TSILs could be reused without noticeably decreasing the catalytic activity.

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Some dicationic ionic liquids, N,N,N′,N′-tetramethyl-N,N′-dipropanesulfonic acid ethylenediammonium hydrogen sulfate, N,N,N′,N′-tetramethyl-N,N′-dipropanesulfonic acid 1,3-propanediammonium hydrogen sulfate, N,N,N′,N′-tetramethyl-N,N′-dipropanesulfonic acid 1,6-hexanediammonium hydrogen sulfate, were prepared. These ionic liquids could be used as efficient and recyclable catalysts for the synthesis of biodiesel from free long-chain fatty acids or their mixtures with low-molecular-weight alcohols as substrates. the reaction was accomplished in a monophase at 70 °C for 6 h, while the products was separated from the catalyst system by liquid/liquid biphase separation at room temperature with good yields of 93−96%. The post processing was simple, and after removal of water, the catalysts could be reused at least six times and the decrease in the yield was 3%. The novel and clean procedure offers advantages including short reaction time, good yield, operational simplicity, and environmentally benign characteristics.

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