Ethyl Acetoacetate → 3-Chloro-but-2-enoic acid ethyl ester

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To a stirred mixture of ethyl acetoacetate (15.0 g, 0.12 mol) in petroleum ether (30 mL) under a nitrogen atmosphere was added phosphorus pentachloride (12.7 g, 0.06 mol) gradually. After addition was complete the mixture was stirred at 25° C. for 1 h. Upon completion of the reaction water (50 mL) was added in small portions, transferred to a separatory funnel and the layers separated, followed by washing the aqueous layer with petroleum ether (2×50 mL). The combined petroleum ether extracts were washed with a 20% potassium carbonate solution, followed by a saturated sodium chloride solution and dried over magnesium sulfate. The combined organic layers were concentrated to give a yellow oil. Distillation of the residue yielded 3-chloro-but-2-enoic acid ethyl ester (7.4 g 43%) as a clear oil: LR-ES-MS m/z calculated for C6H9ClO2 [M]+ 148, observed [M+H]+ 149.

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