GENERAL METHOD: 3,4-Dichlorobenzaldehyde (1.0 mmol; 1.0 eq.) and 4molecular sieves (300 mg) were added to a mixture of DMF (3.0 mL) and ethanol (3.0 mL). Sodium cyanide (1.5 mmol; 1.5 eq.) was added to the above solution. The reaction mixture was stirred in an open flask at 50 °C and the progress of the reaction was monitored by TLC. After complete consumption of 3,4-dichlorobenzaldehyde, the mixture was poured into water (25 mL) and extracted with ether (5 x 10 mL). The organic layers were combined, dried with anhydrous magnesium sulfate and concentrated. The crude product was further purified by silica gel column chromatography using ethyl acetate/hexane as eluent to give ethyl 3,4-dichlorobenzoate. The aqueous layer was acidified with HCl to pH < 2, extracted with ether (3 x 10 mL), the organic layers were combined and concentrated to give 3,4-dichlorobenzoic acid, which was of sufficient purity not to require further purification.
