Continuous ion-exchange resin catalysed esterification of eugenol for the optimized production of eugenyl acetate using a packed bed microreactor

Abstract

A green scalable flow-synthesis process for the production of eugenyl acetate, an eugenol derivative with potential applications in food and medicinal chemistry, was developed. Through batch experiments, the anion-exchange resin Amberlyst A-21 was recognized as a suitable catalyst for the esterification of eugenol with acetic anhydride. Next, the process was switched from batch- to flow-mode by using a packed-bed microreactor integrated in an instrumental platform that permitted at the same time continuous control of the main process parameters (flow rate, feed mixture composition, temperature) and the on-line HPLC analysis of the reactor effluent. Thanks to this apparatus, a number of experiments with different reaction conditions have been easily performed to evaluate the effects of temperature and reagent molar ratios on eugenyl acetate production. The results have been used to carry out a central composite rotatable experimental design (CCRD) whose derived response surface model (RSM) suggested an optimal temperature and acetic anhydride to eugenol molar ratio of 95 °C and 3 : 1, respectively. The goodness of these theoretically deduced parameters has been experimentally confirmed obtaining, with a flow rate of 40 μL min⁻¹, a 95% conversion. The Amberlyst A-21 packed-bed microreactor also demonstrated good long-term stability ensuring, under the above optimized conditions, a high and stable conversion (over 93%) for prolonged reaction times.