In the laboratory, acyl chlorides are generally prepared by treating carboxylic acids with thionyl chloride (). The reaction is catalyzed by dimethylformamide and other additives.
Thionyl chloride⁠ is a well-suited reagent as the by-products (HCl, ) are gases and residual thionyl chloride can be easily removed as a result of its low boiling point (76 °C).