2-chloromethylthiophene

2-Chloromethylthiophene is used as an intermediate to 1-(2-thienyl)-2-Propanone. In a 2-l. beaker surrounded by an ice-salt bath , and fitted with a mechanical stirrer and a thermometer, are placed 420 g. (392 ml., 5 moles) of thiophene and 200 ml. of concentrated hydrochloric acid. A rapid stream of hydrogen chloride is passed continuously into the mixture with vigorous stirring. When the temperature reaches 0°, 500 ml. of 37% formaldehyde solution is added at a rate that will permit the temperature to remain below 5°. The addition requires about 4 hours. When all the formaldehyde solution has been added, the mixture is extracted with three 500-ml. portions of ether. The ether extracts are combined, washed successively with water and saturated sodium bicarbonate solution, and then dried over anhydrous calcium chloride. The solvent is removed by distillation, and the product is distilled under reduced pressure through a 50-cm. fractionating column. The product boiling at 73–75°/17 mm. is collected. The yield is 257–267 g. (40–41%) of a colorless oily liquid.