Process for the hydroformylation of olefinically unsaturated compounds

Hydroformylation of olefinically unsaturated compounds is carried out as follows. (a) The olefinic compounds are reacted in a heterogeneous reaction system with an aqueous solution containing water-soluble complexes of rhodium compounds and organic phosphorus (III) compounds as catalysts, at 0.4-10 MPa; and (b) the exhaust gas produced is subjected to a second reaction, in which residual olefinically unsaturated compounds still present in the gas are converted in a homogeneous reaction system in the presence of complex compound of Rh with organic P(III) compounds as catalysts at 15-40 MPa.