Method of preparing malonic acid dialkyl esters

Process for producing malonic acid dialkyl ester which consists essentially of contacting the corresponding halogen acetic acid alkyl ester wherein said halogen is chlorine, bromine or iodine with carbon monoxide, an alkylol of 1-8 carbon atoms, and alkali alcoholate, alkali earth alcoholate or a solution of alkali hydroxide in said alkylol, said alcoholate moiety corresponding to said alkylol, at a pH of up to 8.5 in the presence of Co.sub.2 (CO).sub.8 as catalyst for the reaction, at a temperature of 0.degree. C. to 150.degree. C. and a carbon monoxide pressure of 0.1-50 atmospheres absolute.