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The catalytic performances of a series of multi-SO 3 H functionalized ionic liquid catalysts during synthesis of methyl caprylate under microwave irradiation condition were investigated. The physicochemical properties of these Bronsted acidic ionic liquids were characterized by a variety of different analytical and spectroscopic techniques such as TGA, NMR, FT-IR, and UV–vis. Among various ionic liquids examined, [Tshx][HSO 4 ] 4 ( i.e., N,N ′, N ″, N ‴ -tetrapropane sulfonic hexamethylenetetramine tetrahydrosulfate) showed the highest catalytic activity and superior recyclability. Process variables during esterification of caprylic acid and methanol, viz. amount of catalyst, methanol/ n -caprylic acid molar ratio, microwave temperature, microwave power and time were explored and optimized by the response surface methodology (RSM). Accordingly, an optimum methyl caprylate yield of 96.2% was achieved over [Tshx][HSO 4 ] 4 catalyst under the optimized conditions: catalyst amount 0.3 mmol, methanol/ n -caprylic acid molar ratio 7:1, temperature 80 °C, microwave power 400 W and reaction time 35 min. |
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