Process for the hydroformylation of an olefin in a two-phase medium

A process for the hydroformylation of an olefin by a CO/H.sub.2 gas mixture in a two-phase medium, comprising the steps of:

• placing in contact (i) an aqueous solution containing a catalytic system comprising a water-soluble transition metal complex and a water-soluble phosphine, and (ii) an olefin to form a reaction mixture,
• heating the reaction mixture obtained with stirring, after it has been placed under a pressure of the CO/H.sub.2 gas mixture,
• introducing a modified cyclodextrin into the aqueous solution containing the catalytic system, said modified cyclodextrin comprising .alpha.-cyclo-dextrins, .beta.-cyclodextrins or .gamma.-cyclodextrins including, respectively 6, 7 or 8 glucose units and bearing one or more substituents, which may be identical or different, comprising alkyl radicals which may or may not be functionalized, hydroxyalkyl radicals, carboxyl, carboxylate, nitro, amino, sulfonate, sulfate, phosphate, ether, polyether and ammonium radicals or radicals comprising an ester function.