CoCl2(TPPTS)(2) catalyzed hydroformylation of 1-hexene was studied in an aqueous biphasic medium. The effect of temperature, pressure, and concentration of cobalt catalyst on the reaction was studied. At elevated temperatures and pressures, it gave >90% conversion with 68% selectivity for aldehyde and n/iso ratio of 3.0 for the aldehyde. (C) 2003 Elsevier B.V. All rights reserved.