Hungarian journal of industrial chemistry, 1975
3. szám - Speier, G.: Kinetics and Mechanism of The Dimerization of Ethylene Using (Co(C2H4) (РРh3)3)2 as catalyst
1975 Kinetics of the i-zer ization of Ethylene 1*55 and becomes of first order if : [PPh3] + K2 » K2K3[C2Hu ] (8) Assuming K3 to be small (K2 can be determined) the first order dependence on ethylene is expected at small ethylene concentrations, which was actually found. According to Equation (6) there is a first order dependence on cobalt, however, the experimental data (Figures 2 and 3), show a more complicated picture. This apparent contradiction is resolved by considering the effect of phosphine ligands dissociated from the catalyst. The concentration of free phosphine is determined by Equation (9): [PPh3] = [Co(C2H4)(PPh3)2] + [Co(C2Hi*)2(PPh3)2] (9) If K3 is small (as assumed earlier) Equation (9) simplified to (10): [PPh3] « [Co(C2H<,) (PPh3)23 (10) and the total cobalt concentration can be expressed by Equation (11): [Co] = [Co(C2H<*) ( PPh3 ) 3 ] + ( PPh3 ) (11) Substituting (10) and (11) into (3), Equations (12) and (13) are obtained : [PPh3]2 К = (12) [Co] - [PPh3] 1 [PPh3] = (K2 {[Co] - [PPh3]})2 (13) If [PPh3] is not large the concentration of free phosphine, according to (12), is approximately proportional to the square root of the total cobalt concentration and thus [PPh3] in Equation (6) reduces the first order of dependence on the catalyst concentration, if no extra phosphine is added.