A method for making .beta.-ketophosphonates by reacting a trialkyl phosphonocarboxylate (such as triethyl phosphonoacetate) with an acyl halide (such as acetyl chloride) in a reaction involving ester formation, followed by decarboxylation, followed by purification. The reaction is run in a single solvent, which is not removed from the reaction mixture until the purification stage. Suitable solvents for this purpose include halogenated aromatic hydrocarbons (such as mono-chlorobenzene).