[C:1]1(=[O:6])[O:5][CH2:4][CH2:3][CH2:2]1.[C:7]([Cl:10])(Cl)=[O:8].[ClH:11]>[Cl-].C[N+](C)(C)CC1C=CC=CC=1>[Cl:11][CH2:3][CH2:2][CH2:1][C:7]([Cl:10])=[O:8].[C:1]1(=[O:6])[O:5][CH2:4][CH2:3][CH2:2]1430 parts of 4-butyrolactone and 47 parts of trimethylbenzylammonium chloride are initially taken in a 1 l stirred reactor which is equipped with a thermometer, inlet tubes for phosgene and hydrogen chloride and 2 low-temperature coolers set at -20° C. and -70° C. respectively. The mixture is heated to 130° C. 560 parts of phosgene and 120 parts of hydrogen chloride are passed in over 5.5 hours. Thereafter, nitrogen is passed in until the reaction mixture no longer contains any phosgene. Working up by distillation gives 620 g of 4-chlorobutyryl chloride and 30.5 g of butyrolactone. The distillation residue of 75 g, which consists of the catalyst and chlorobutyroyloxybutyryl chloride, can be reused for further batches. The yield of 4-chlorobutyryl chloride is 88 mol %, based on butyrolactone used.
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