Process for the hydroformylation of olefins in homogeneous phase

The present invention relates to a process for the preparation of aldehydes by hydroformylation of olefins by means of synthesis gas over a transition metal complex catalyst, wherein within a first process step the olefins are reacted by means of a water-soluble transition metal complex catalyst consisting of a metal and ligands bound thereto in the presence of a water-miscible solvent, the pressure, temperature and proportions of the solvent and aqueous catalyst solution being controlled so that the hydroformylation is carried out in a homogeneous single-phase reaction solution and within a second process step, by lowering the temperature and/or reducing the pressure, the homogeneous reaction solution obtained from the first reaction step is converted into a two-phase process solution and at least part of the organic phase is separated from the aqueous phase.