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

The hydroformylation of octene-1 under two-phase reaction conditions w ith rhodium catalysts derived from TPPTS (trisulfonated triphenylphosp hine) or the new water soluble phosphines, P[C6H4-p-(CH2)(x)C6H4-p-SO3 Na](3), x = 3, 6, is salt concentration dependent. Both reaction rate and reaction selectivity are affected by the ionic strength of the aqu eous reaction medium. Reaction selectivity increases with increased io nic strength while activity is dependent on whether the phosphine is c apable of forming micelles. Reaction rate increases with increased ion ic strength with the new surface active phosphines. The concentration of all components, free ligand, rhodium complex and salt affect the ac tivation 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) wher eas at high ligand and complex concentration the barrier is estimated to be 30.6 kcal mol(-1). It is proposed that high ionic strength stabi lizes the complex, HRh(CO)(TPPTS)(3), in aqueous solution.