PMGB

Case 1: Esterification of an aromatic carboxylic acid  

To a suspension of the carboxylic acid (1 mol) in 120 mL anhydrous ethanol was added 1.2 mL concentrated sulfuric acid at room temperature. The resulting mixture was stirred at reflux for two days (48 h) until the suspension became a clear solution. The solvent was evaporated. The residue was diluted with dichloromethane and washed with saturated aqueous NaHCO₃ solution, dried (MgSO₄) and evaporated. The residue was triturated with ether to give the corresponding ethyl ester (white solid, 83% yield).

¹H NMR (400 MHz, CDCl₃): d 1.38 (t, J = 7.2 Hz, 3H); 2.66 (t, J = 8.0 Hz, 2H); 3.02 (t, J = 8.0 Hz, 2H); 4.37 (q, J = 7.2 Hz, 2H); 7.22 (d, J = 8.0 Hz, 1H); 7.48 (s, 1H); 7.67 (dd, J = 1.6, 8.0 Hz, 1H); 8.59 (broad s, 1H).

Case 2: Coupling of a benzylic alcohol with an aliphatic carboxylic acid

A mixture of the benzyl alcohol (0.0008 mol), aliphatic carboxylic acid (0.0008 mol), dicyclohexylcarbodiimide (DCC) (0.001 mol), 4-(dimethylamino) pyridine (DMAP) (0.001 mol) in 30 mL tetrahydrofuran was stirred at room temperature for 6 hours. The reaction mixture was evaporated; the residue was diluted with dichloromethane, and filtered to remove the white solid (dicyclohexyl urea) precipitated. The filtrate and washings was washed with saturated aqueous sodium bicarbonate solution (to remove the unreacted carboxylic acid) and water (to remove DMAP), dried (MgSO₄) and evaporated to give the corresponding ester which was purified by silica gel column chromatography using a gradient of hexane and ethyl acetate followed by triturating with ether (white solid, 50% yield).