Multistep process for the preparation of butanedicarboxylic acid by the hydrogenation of carbon monoxide under pressure in the presence of a cobalt carbonyl catalyst, the improvement of heating at a temperature of 250.degree. to 350.degree. C. under superatmospheric pressure the resulting aqueous solution of cobalt carbonyl hydride that has been extracted with butadiene or with mixtures thereof before using in a subsequent step of the multistep process.