Process for the hydroformylation of olefinically unsaturated compounds in a non-aqueous ionic solvent

A process for the hydroformylation of an olefinically unsaturated compound in the liquid phase by reaction, in a reaction section, with carbon monoxide and hydrogen in the presence of a polar phase comprising:a non-aqueous ionic liquid which is at least partly miscible with the reaction products and comprises a salt of general formula Q+A-, in which Q+ represents a quaternary ammonium and/or phosphonium and A- represents an anion;and a catalyst comprising a compound or a complex of a transition metal of groups 8, 9 and 10, optionally co-ordinated with a ligand containing at least one atom of phosphorus, arsenic, antimony or nitrogen,comprises addition to the medium, after the reaction section, of an organic solvent in a manner such as to improve the separation by demixing of the crude reaction products from the said polar phase, which is recycled to the reaction section.