Ethylene deuterium exchange

From the results we concluded that the dissociative mechanism originally suggested for the ethylene-deuterium exchange is valid and is responsible for the exchange involving other unsaturated, saturated and aromatic hydrocarbons and oxygenated compounds. 

Other systems for which the results cannot be explained by energy transfer include the ketone sensitized isomerization of / -methylstyrene, 1,2-dichloro-ethylene and 2-butene studied by Caldwell,147,148 deuterium exchange between acetone-d8 and tetramethylethylene reported by Japar, Pomerantz, and Abrahamson,149 and the acetone sensitized isomerization of 1-methoxy-l-butene examined by Turro and Wriede.71... 

Hydrogen is chemisorbed on a surface partially covered with ethylene and reacts rapidly with the ethylene at room temperature. This is not consistent with observations that hydrogen-deuterium exchange on nickel is strongly inhibited by the presence of chemisorbed ethylene. The latter effect may be due to fragmentation of ethylene which occurs only at higher temperatures. 

Whilst the use of deuterium allows a deeper insight into the mechanism of catalytic reactions than was previously possible, it nevertheless does not allow an absolutely rigorous analysis to be made. One of the major problems in ethylene—deuterium and propene—deuterium studies is that there is no method whereby the true fraction of olefin which has undergone an olefin—alkyl—olefin cycle and reappeared in the gas phase as olefin-d0 can be determined. This is especially true for reactions on metals such as palladium, ruthenium and rhodium where the olefin exchange results sug-... 

It has been concluded from deuterium exchange experiments, using ethylene and heavy water, that the addition of an adsorbed proton to adsorbed ethylene is the actual rate-determining step. It can be seen that the two schemes differ, mainly in that the latter includes dissociative adsorption of water on the surface of the catalyst and does not specify the adsorption of ethylene, but they are consistent in that they assume the formation of a carbonium ion as the rate-determining step. 

Deuterated thiazoles, mass spectra of, 347 Deuterium exchange, in thiazoles, 113 Deuterothiazoles, infrared absorption, 57 7V,A -Diacetyl V,A -bis (4-phenyl-2-thia-zolyhnethyl-ethylene diamine), synthesis of, 195... 

The log—log plot of the adsorption isotherm, which can possibly be correlated to the pressure-dependency of the catalytic reaction rate, is very flat. The adsorption of ethylene on nickel increases only by 10% for an increase of the equilibrium pressure by a factor of 10, although the surface is still far from being covered by a monolayer. The work of Laidler et al. (3), who studied the ammonia-deuterium exchange reaction on a promoted iron catalyst by means of the microwave method, also throws doubt on the zero-order kinetics with respect to observations made by Farkas (4). 

An interesting differentiation between reactions was observed on nickel. The hydrogen-deuterium exchange activity was not affected by a bombardment that altered the rate of ethylene hydrogenation by a factor of 100 (44). Evidently the defects responsible for the latter are... 

Deuterium exchange and kinetic analysis of ethylene electrogenerative hydrogenation on Pt black showed that, in the absence of pore diffusion, the rate is limited by surface addition of the second hydrogen to an adsorbed ethyl radical (25, 26) ... 

Schuit, van Reijen, and Sachtler (470) have also calculated the volcanoshaped curves for other reactions according to the data of a number of authors the ammonia-deuterium exchange [Fig. 64, Kemball (471)], the hydrogenation of ethylene [Fig. 65, Schuit and van Reijen (472)-, Beeck... 

Various reactions appeared to be very useful in this respect. Well-known examples are the hydrogen-deuterium exchange and the hydrogenation of ethylene on metals and oxides. Such studies deepened the understanding of hydrogenation reactions in general, while these reactions could at the same time serve as a means of comparing the activities of different catalysts. Other examples of reactions well suited for use in fundamental catalysis research, are the synthesis and decomposition of ammonia, and the decomposition of NaO. 

Catalysis of Ethylene Hydrogenation and Hydrogen-Deuterium Exchange by Dehydrated Alumina... 

These results seemed to be inconsistent with any simple electronic theory of hydrogenation catalysis they were, however, relevant to the general concept that dehydration of oxide catalysts should leave the surface in a strained, catalytically active condition ( , S). A systematic study was therefore undertaken of the activation of pure y-alumina for ethylene hydrogenation and hydrogen-deuterium exchange the effects of pretreatment, drying conditions, and rehydration were investigated. 

Effects of Radiation Quenching, Ion-Bombardment, and Annealing on Catalytic Activity of Pure Nickel and Platinum Surfaces. II. Hydrogenation of Ethylene (continued). Hydrogen-Deuterium Exchange f... 

On the basis of these results, it does not appear that there is any difference which can be attributed to a change in density of surface defects for the hydrogen-deuterium exchange. Hence, the results indicate that the rate-controlling factor for the hydrogen-deuterium reaction is not the same as that for the hydrogen-ethylene reaction. 

M. Salmerdn and G.A. Somoijai. Desorption, Decomposition, and Deuterium Exchange Reactions of Unsaturated Hydrocarbons (Ethylene, Acetylene, Propylene, and Butenes) on the Pt(lll) Crystal Face. J. Phys. Chem. 86 341 (1982). 

The planar bis(ethylene)-rhodium(I) complex (LXX) is the active catalyst. Oxidative addition of HCl to this unsaturated <7 complex affords the rhodium(Ill) hydride (LXXl) which rapidly yields the ethyl complex (LXXII). No direct evidence was found for the existence of the hydride (LXXI), but NMR evidence supports the existence of the ethyl complex (LXXII). These first two steps are rapid and reversible and provide a mechanism for deuterium exchange between the protons on ethylene and... 

Imidazolium salts, catalysts of the benzoin condensation 723 deuterium exchange in 705 Imines, from an azide and ethylene 725, 726 reduction of 68... 

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