THE EFFECT OF SALT ON SELECTIVITY IN WATER-SOLUBLE HYDROFORMYLATION CATALYSTS

The hydroformylation of octene-1 under two-phase reaction conditions with rhodium catalysts derived from TPPTS (trisulfonated triphenylphosphine) or the new water soluble phosphines, P[C6H4-p-(CH2)(x)C6H4-p-SO3Na](3), x = 3, 6, is salt concentration dependent. Both reaction rate and reaction selectivity are affected by the ionic strength of the aqueous reaction medium. Reaction selectivity increases with increased ionic strength while activity is dependent on whether the phosphine is capable of forming micelles. Reaction rate increases with increased ionic strength with the new surface active phosphines. The concentration of all components, free ligand, rhodium complex and salt affect the activation barrier to ligand exchange in HRh(CO)(TPPTS)(3) as determined by dynamic P-31 NMR spectroscopy. At low concentration with no added salt the barrier to exchange is estimated to be 22.4 kcal mol(-1) whereas at high ligand and complex concentration the barrier is estimated to be 30.6 kcal mol(-1). It is proposed that high ionic strength stabilizes the complex, HRh(CO)(TPPTS)(3), in aqueous solution.