Hydroformylation of olefins

In a process for producing aldehydes by hydroformylating a lower olefin which comprises ethylene, propylene, 1-butene, isobutene, 1-pentene, allyl alcohol or allyl methyl ether at a temperature within the range of from about room temperature to 130.degree. C., in an organic solvent in the presence of a rhodium complex having the general formula

• HRh(CO)(PR.sub.3).sub.3
• wherein R is alkyl or aryl, or a rhodium carbonyl cluster, employed at a concentration of from 0.1 to 25 mg atoms/1 of reaction mixture, and a trisubstituted phosphine in an amount of from 10 to 500 equivalents per rhodium atom, while maintaining a carbon monoxide partial pressure within the range of 0.1 to 2.5 atmospheres during the progress of the reaction and a ratio of hydrogen partial pressure to that of the carbon monoxide within the range of 1:2 to 5:1, the improvement which comprises adding to the reaction system a diphosphino alkane represented by the general formula ##STR16## in an amount of 0.20 to 2.5 equivalents per gram atom of the rhodium present in said rhodium complex, wherein, in the formula, A.sup.1 and A.sup.2 are each aryl, R.sup.1 and R.sup.2 are each aryl or a saturated hydrocarbon residue containing one or more carbon atoms, the aryl groups being selected from the group consisting of unsubstituted phenyl and napthyl groups and phenyl and napthyl groups substituted with lower alkyl groups, and Z is an alkylene radical whose principal chain contains 2 to 5 carbon atoms, said alkylene radical being selected from the group consisting of unsubstituted alkylenes and alkylenes substituted with at least one lower alkyl radical.