The general procedure for the synthesis of 5-methylthiophene-2-carbonitrile from 5-methyl-2-thiophenecarboxaldehyde is as follows: In a 50 mL three-necked round-bottomed flask equipped with a magnetic stirrer, a reflux condenser tube, and a thermometer, 6.3 g (50 mmol) of 5-methyl-2-thiophenecarboxaldehyde, 3.0 g (20 mmol) of sodium bromate, 10 mL (174 mmol) of acetic acid, and 5 g (74 mmol) of 25% ammonia solution. The reaction mixture was stirred at 80°C for 4 hours. Upon completion of the reaction, the mixture was diluted by adding 30 mL of water and 50 mL of ether to the mixture. Subsequently, the pH was adjusted to above 11 by slow dropwise addition of 23% aqueous sodium hydroxide solution. The organic phase was separated and washed sequentially with water and saturated aqueous sodium chloride solution. The organic layer was dried over anhydrous sodium sulfate and the ether was removed by distillation under reduced pressure to give 6.5 g of oily crude product. The crude product was purified by Kugel-rohr distillation to obtain 5.9 g of the colorless oily target product 5-methylthiophene-2-carbonitrile. The product was analyzed by high performance liquid chromatography (HPLC) with a purity of 94.0% (area percentage) and a yield of 96.0%. The structure of the target compound was further verified by liquid chromatography-mass spectrometry (LC-MS) analysis confirming that the molecular ion peak [M-1]+ of the product was 122.
