Synthesis, spectroscopic characterization and biological studies of esters from benzoic acid and three homologous alcohols

Abstract

This work reports the synthesis, characterization and antimicrobial screening of benzoate esters synthesized from benzoic acid and the three alcohols: methanol, ethanol, and isopropanol-by means of an acid-catalyzed Fischer esterification. The resulting compounds, namely methyl, ethyl, and isopropyl benzoate, were obtained in yields of 85%, 83%, and 78%, respectively. The compounds were subjected to spectroscopic structural studies using IR, NMR, and mass spectrometry. They confirmed the formation of ester functionalities, giving molecular identities  Antimicrobial screening of the esters against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans revealed that all esters exhibited inhibitory activities with Methyl, ethyl, and isopropyl benzoate having zones of inhibition between (8–18 mm zones), with isopropyl benzoate being the most effective. Though less potent than Ciprofloxacin (24 mm) activity but more than the others.  Activity increases with alkyl chain branching. Measurements of the diameters of zones of inhibition correlated well with MIC assay results, showing isopropyl benzoate to be superior, suggesting that higher hydrophobic interaction and molecular branching would enhance disruption of microbial membranes. SAR study indicated a strong correlation between esters and antimicrobial activities, with secondary alcohol derivatives performing better than others.