Aqueous-biphasic hydroformylation of alkenes promoted by "weak" surfactants

The aqueous-biphasic hydroformylation of higher alkenes catalyzed by Rh/TPPTS has been carried out in the presence of imidazolium, pyridinium and triethylammonium salts. High reaction rates are achieved with imidazolium and triethylammonium salts provided that their alkyl "tail" is >= C-8. Fast and complete phase separation, and good retention of the metal in the aqueous phase could be achieved with an octyl "tail". Imidazolium salts were found to give the highest rate enhancement. The nature of the anion showed a moderate influence on the reaction. Evidence suggests that the additive can act as weak surfactant allowing emulsions to be formed and broken by simply switching the stirring on and off.