Functionalized Polyethylene Glycol as a Catalyst for Esterification of Salicylic Acid

In this work, two catalysts based on polyethylene glycol (PEG) containing sulfonic acid group and the −COOH group of citric acid (CA) were synthesized. Characterization of the −SO3H functionalized PEG and citric acid functionalized PEG has been carried out using FT–IR. The acidity of PEG–SO3H and PEG–CA has been explored to investigate their catalytic efficiency towards eco-friendly production of methyl salicylate via esterification of salicylic acid using methanol as a reactant as well as solvent. Methanol to acid molar ratios of 4:1, 6:1, 8:1, and 10:1 was applied. The sulfonated PEG is found to be a very active solid acid catalyst giving high yields (82%) under the optimized reaction conditions (10:1 M ratio of methanol to acid; reaction temperature, 65 °C; reaction time, 150 min with catalyst loading of 1.5%. In comparison with the catalytic activity of H2SO4, PEG–SO3H, and PEG-CA; the PEG–SO3H surpassed the catalytic activity of both H2SO4 and PEG–CA. The IEC of PEG–SO3H was 4 meq/g. And the maximum water uptake of PEG-SO3H was 8.25%.