Combination of a Dual-Site Phase-Transfer Catalyst and an Ionic Liquid for the Synthesis of Benzyl Salicylate

Abstract

The green synthesis of benzyl salicylate was investigated using a dual-site phase transfer catalyst and an ionic liquid in a triliquid system. The dual-site phase-transfer catalyst 4,4′-bis(tripropylammonium methyl)-1,1′-biphenyl dichloride (BTPAMBC) synthesized from 4,4′-bis(chloromethyl)-1,1′-biphenyl and tripropylamine was used to form the third-liquid phase for catalysis, and the ionic liquid tributyl(tetradecyl)phosphonium methanesulfonate (TBTDPMS) was used to enhance the reaction rate. The yield of the product was only 0.1% without using a catalyst and an ionic liquid in a liquid–liquid system and increased to 31% using BTPAMBC in a triliquid system. The yield of the product greatly increased to 94% with BTPAMBC and TBTDPMS at a short reaction time of 15 min. The apparent rate constant (pseudo-first-order) at 60 °C using BTPAMBC and TBTDPMS (0.177 min–1) was much larger than that using BTPAMBC alone (0.0231 min–1), demonstrating significant enhancement by TBTDPMS in the BTPAMBC-catalyzed system. An efficient and environmentally benign method for synthesizing esters was developed.