Hydroformylation of olefinic compounds

A process for hydroformylating an olefinic compound in an organic solvent to obtain the corresponding aldehyde, which comprises treating said olefinic compound with gaseous carbon monoxide and hydrogen in the presence of a rhodium complex, 10 to 500 equivalents per gram-atom of rhodium in said rhodium complex of a trisubstituted phosphine and 0.20 to 5.0 equivalents per gram-atom of rhodium in said rhodium complex of at least one diphosphino compound of the general formula (I) ##STR10## wherein A.sup.1 and A.sup.2, respectively, are aryl groups;

• R.sup.1 and R.sup.2, respectively, are an aryl group or a saturated hydrocarbon residue containing 1 or more carbon atoms;
• and ##STR11## represents a substituted or unsubstituted alicyclic hydrocarbon group containing 3 to 6 carbon atoms in the main ring, said aryl group, in each instance, being selected from the group consisting of phenyl, naphthyl, tolyl and xylyl, which may be unsubstituted or substituted by lower alkyl or lower alkoxy.