The hydroformylation of octene-1 and the removal of Co 2 (CO) 8 and HCo(CO) 4 from the reaction products including commercial C9 OXO-product were studied under biphasic conditions using an aqueous solution of different electrondonating sulfonated phosphine R n P(C 6 H 4 -m-SO 3 Na) 2 (n = 0, 1, 2; R = Me, Bu, Cp) ligands. Depending on the electronic and steric properties of the phosphines, 6−70 ppm residual cobalt concentrations could be achieved in the organic phase under 10 bar of CO/H 2 (1:1) at 75°C. The formation of several water-soluble-phosphine-substituted cobalt carbonyl species including Co 2 (CO) 6 (TPPTS) 2 , HCo(CO) 3 (TPPTS), HCo(CO) 2 (TPPTS) 2 , and [Co(CO) 3 (TPPTS) 2 ] + [Co(CO) 4 ] − were identified and monitored by in situ IR and NMR spectroscopy.