Acetylene, kinetics cations

In less-coordinating solvents such as dichloromethane or benzene, most of the cationic rhodium catalysts [Rh(nbd)(PR3)n]+A (19) are less effective as alkyne hydrogenation catalysts [21, 27]. However, in such solvents, a few related cationic and neutral rhodium complexes can efficiently hydrogenate 1-alkynes to the corresponding alkene [27-29]. A kinetic study revealed that a different mechanism operates in dichloromethane, since the rate law for the hydrogenation of phenyl acetylene by [Rh(nbd)(PPh3)2]+BF4 is given by r=k[catalyst][alkyne][pH2]2 [29]. 

The temperatures reported in the kinetic studies range from 260 to 350°C. In most of the investigations, the hydration rates were found to be of the first order with respect to acetylene [300,302—304]. With zinc phosphate [303], cadmium—calcium phosphate [300] and cation-exchanged zeolites [304], the rates were independent of the concentration of water. Thus the simple kinetic equation... 

With cation-exchanged zeolites [304], the first-order kinetics [eqn. (18)] is explained by the degeneration of the Langmuir—Hinshelwood equation for monomolecular transformation of adsorbed acetylene in the rate-determining step... 

Cations 76 underwent quantitative reactions with acetylene to give 1,3,2-dithiazole cations 78 and 79 (Equation 22). The results are consistent with the expectation that the lower energy of the completely delocalized 671 HCSNSCH+ 78 (relative to that of the partially delocalized 4ji 76) renders reaction thermodynamically favorable. Cations 76 did not react with MeCN (ionization potential (MeCN) = 12.2 eV, (acetylene) = 10.5 eV) probably due to a higher kinetic barrier, although the reaction is thermodynamically favorable. 

The kinetics of the reaction of cyclohexanone oxime (1) with acetylene (Equation (1)) in MOH-DMSO under atmospheric pressure was studied and quantitative data on the effect of alkaline cations on the yields of 4,5,6,7-tetrahydroindole (2) and its N-vinyl derivative 3 as well as on the reaction selectivity were obtained (08DOC(423)66). 

The kinetics of the reaction between cyclohexanone oxime and acetylene in the systans MOH/DMSO (M=Li, Na, K, Cs) under atmospheric pressure has been studied, and the quantitative data about the effect of alkali metal cation on the yields of 4,5,6,7-tetrahydroindole and its vinyl derivative as well as on the reaction selectivity have been obtained [197],... 

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