Esterification of lignin-derived phenolic compound eugenol to eugenol benzoate using acidic deep eutectic solvent as a catalyst

Eugenol is a lignin-derived aromatic model compound extracted from the lignin and has been used for various reactions. The eugenol esterification to eugenol benzoate with benzoic acid was studied using different deep eutectic solvents (DESs) as catalysts. DESs are a type of ionic liquid that is formed by combining a hydrogen bond donor with a hydrogen bond acceptor. In the current paper, carboxylic acids such as oxalic acid, acetic acid, p-toulenesulfonic acid (p-TSA) and tartaric acid were used as hydrogen bond donors to form choline-based DESs which were used as catalysts in esterification reactions. The catalysts were screened based on the conversion and p-TSA based DES was found to be best and used for further experiments. Effects of parameters (eugenol to benzoic acid ratio, reaction time, temperature, and catalyst loading) on the yield of eugenol benzoate were studied. The highest eugenol conversion was obtained as 90.42% (383 K, 0.02 g/cm³ catalyst, molar ratio of eugenol to benzoic acid = 1:5, 600 rpm, 3 h).