Chlorinative Coupling of Thiophene by the Action of Sulfuryl Chloride and Iron Powder

In the presence of iron powder, thiophene reacted with sulfuryl chloride at room temperature to give a mixture of chlorinated 2,2′-dithienyls as the main product in yields of up to 42%, while the reaction without a catalyst gave chlorothiophenes. The yield of the coupling product and the chlorine content in the product increase with an increase in the molar ratio of sulfuryl chloride to thiophene. 5,5′-Dichloro-, 3,5,5′-trichloro-, and 3,3′,5,5′-tetrachloro-2,2′-dithienyls were isolated from the reaction products. The reaction was also catalysed by Friedel-Crafts-type catalysts, the efficiency of the catalysts decreasing in the order: AlCl3>FeCl3>SnCl4>ZnCl2.