3,4,5-Trichlorothiophene-2-carbonyl chloride synthesis: A mixture of 3,4,5-trichloro-2-thiophenecarboxylic acid (20.4 g, 0.088 mol), SOCl2 (7.3 mL, 0.1 mol), and DMF (0.2 mL) in 80 mL of 1,2-dichloroethane was heated at reflux temperature for 3 h. The reaction mixture became homogeneous after 1 h of heating. The solution was cooled to 25℃, concentrated and placed under high vacuum to remove residual solvent, giving 22.0 g (98% wt.) of 3,4,5-trichloro-2-thiophenecarbonyl chloride as an oil which solidified on standing to an off-white powder; m.p. 37-41℃, having a GC area % purity > 99%.
