With a newly developed analytical technique, i.e. high temperature/pressure IR cell coupled to the reactor, it was possible to study the mechanism of hydroformylation at reaction conditions. It has been conclusively found that the hydrogenolysis of the aeyl cobalt, complex is performed by HCo(CO)4 and not by molecular H2, as proposed by Hect~ and Breslow. Therefore the formation of HCo(CO)4 from C02(CO)s is an intermediate step in the sequence of hydroformylation reaction steps. The rate of hydroformylation of any of the olefins is smaller than the rate of formation of HCo(CO)4 from C02(CO)s. The Ig spectra reveal that always more than 30% of the cobalt is in the form of tICo(CO)4 under the reaction conditions. It is found that the formation of tICo(CO)4 from C02(CO)s is the slowest and most temperature-dependent step of the hydroformylation reaction. Also the reaction between olefin and HCo(CO)4 is slower than the hydrogenolysis of the aeyl complex. The experiments were carried out under industrial oxo conditions. The diffusional effects were eliminated.

The kinetics and the position of the equilibrium of the reaction Co2(CO)sd-H2 <~ 2 I-ICo(CO)4 were studied in the range of 80-160 ~ and 50-100 arm. by means of in situ IR spectroscopy.The reaction is reversible first order with respect to Co2(CO)s and HCo(CO)4 and the energies of activation of the forward and the reverse reaction are found to be 17,3 cal/mole, and 11.0 keal/mole resp. The reaction is slightly endothermic with A H ~ 6.6 kcal/ mole and A S = 14.6 e.u. The heat of formation of HCo(CO)4 and the bond strength between hydrogen and cobalt in ttCo (CO)4 were found to be --146.1 kcal/mole and 54.7 kcal/mole resp.

By in situ ir spectroscopic techniques it was found that the cobalt carbonyl catalyst in hexane, after preforming at conditions of hydroformylation (temperatures of 101 and 124OC, Pc0 = 11 and 30 bars, PH2 = 20 and 49 bars, cobalt concentration = 2.0 and 4.2 mmolll.) consisted of more than 80% HCO(CO)~, the rest being C02(C0)8. Injection of octene-I, in order to start the hydroformylation, caused HCO(CO)~ to decrease (although not to zero concentration) in favor of an increasing CO~(CO)~ concentration. This reverted as the conversion of octene-1 increased. As intermediate complexes, only acyl cobalt carbonyl species were detected in very low concentrations. A catalyst composed of cobalt carbonyl and tributylphosphine in a phosphorus-to-cobalt ratio of 5, of a considerable amount of catalytically inactive CO~(CO),PBU~, while of all hydridocobalt carbonyls present only a minor part was liganded by PBu3 at the previously mentioned reaction conditions. Accordingly, in the hydroformylation of octene-I, the catalyst decreased only the octene conversion rate and left the yield of unbranched products unaffected.

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Several types of cells have been used for in situ studies of chemical reactions a t elevated temperature and pressure. Nearly all the cells can be characterized as small au-window support plugs. The seal between windows and cell body consists of four Frenzelite-Multi (phenol formalde-'hyde resin reinforced with asbestos) packing rings of 0.5 toclaves equipped with windows, that is to say the cell itself acts as the reactor in which the reaction is carried out.