Ethylene deuterium reaction

It should be noted that the correlations being discussed here are far from perfect and exceptions can be found in nearly each of the reaction series. (For the ethylene-hydrogen and deuterium-ammonia reactions, the correlation between catalytic activity and per cent d-character is nearly quantitative.) This is to be expected in view of the experimental difficulties involved in preparing clean and reproducible metal surfaces, particularly where different metals are being compared. In any attempt to correlate catalytic properties with work functions, it should also lie recognized that the work function is affected by adsorption, and therefore that the work functions of metals under catalytic conditions, or even their relative order, may be somewhat different than those of the clean metals. 

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). 

There are two recent investigations that nicely illustrate the dilemma. As already noted, Nickon and Werstiuk (1966) found the same product, nortrioyclene (50) for the reaction of norhornan-3-one tosylhydrazone (49) in both ethylene glycol and its dimethyl ether. They further found that for the tosylhydrazone, specifically deuteriated in the exo- or ewdo-6-positions, reaction in the aprotic solvent occurs without loss of deuterium, whereas reaction in the protic solvent leads to the loss of 19 and 52% deuterium from the exo and endo substrates, respectively. 

A study of the effect of the ratio of the reactants on the course of the addition and exchange reactions was carried out using 40, 20, and 10 mm. of deuterium for 10 mm. of ethylene. It was found that the rate decreased with decrease in deuterium-ethylene ratio, the times necessary for 30% addition reaction being 40, 55, and 180 min., respectively. If, however, the rate of exchange and the appearance of the various deuteroethanes is plotted in terms of per cent addition reaction, it was found that the individual rates for all the processes of formation of the seven deuteroethanes and the four deuteroethylenes were the same. 

C2H6D. At —78° the presence of ethylene did not affect the hydrogen-deuterium equilibrium reaction rate. 

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 mechanism of the hydration of ethylene is discussed here based on experimental results of the effect of the molar ratio of H2O/C2H4 on the reaction rate and of the deuterium exchange reaction of ethylene with heavy water. 

C-C bond cleavage reactions of titanacyclopentanes and titanacyclohexane were independently studied by Grubbs [10] and Whitesides [11]. In the case of titanacyclopentane, ethylene was eliminated via a titanocene-bis(ethylene) complex as shown in Eq. 8. According to the deuterium labeling reaction, the real mechanism is more complicated, since scrambling of D was observed (Eq.9)[10]. 

Extensive studies on the Wacker process have been carried out in industrial laboratories. Also, many papers on mechanistic and kinetic studies have been published[17-22]. Several interesting observations have been made in the oxidation of ethylene. Most important, it has been established that no incorporation of deuterium takes place by the reaction carried out in D2O, indicating that the hydride shift takes place and vinyl alcohol is not an intermediate[l,17]. The reaction is explained by oxypailadation of ethylene, / -elimination to give the vinyl alcohol 6, which complexes to H-PdCl, reinsertion of the coordinated vinyl alcohol with opposite regiochemistry to give 7, and aldehyde formation by the elimination of Pd—H. 

Oxidation of ethylene in alcohol with PdCl2 in the presence of a base gives an acetal and vinyl ether[106,107], The reaction of alkenes with alcohols mediated by PdCl2 affords acetals 64 as major products and vinyl ethers 65 as minor products. No deuterium incorporation was observed in the acetal formed from ethylene and MeOD, indicating that hydride shift takes place and the acetal is not formed by the addition of methanol to methyl vinyl etherjlOS], The reaction can be carried out catalytically using CuClj under oxygen[28]. 

At least for ethylene hydrogenation, catalysis appears to be simpler over oxides than over metals. Even if we were to assume that Eqs. (1) and (2) told the whole story, this would be true. In these terms over oxides the hydrocarbon surface species in the addition of deuterium to ethylene would be limited to C2H4 and C2H4D, whereas over metals a multiplicity of species of the form CzH D and CsHs-jD, would be expected. Adsorption (18) and IR studies (19) reveal that even with ethylene alone, metals are complex. When a metal surface is exposed to ethylene, selfhydrogenation and dimerization occur. These are surface reactions, not catalysis in other words, the extent of these reactions is determined by the amount of surface available as a reactant. The over-all result is that a metal surface exposed to an olefin forms a variety of carbonaceous species of variable stoichiometry. The presence of this variety of relatively inert species confounds attempts to use physical techniques such as IR to char-... 

Over zinc oxide it is clear that only a limited number of sites are capable of type I hydrogen adsorption. This adsorption on a Zn—O pair site is rapid with a half-time of less than 1 min hence, it is fast enough so that H2-D2 equilibration (half-time 8 min) can readily occur via type I adsorption. If the active sites were clustered, one might expect the reaction of ethylene with H2-D2 mixtures to yield results similar to those obtained for the corresponding reaction with butyne-2 over palladium That is, despite the clean dideutero addition of deuterium to ethylene, the eth-... 

This means that the ionization and rearrangement need not be concerted and that symmetrical protonated ethylene can not be a major intermediate in the reaction. A similar experiment with isobutylamine and nitrous acid in heavy water gave products that contained no carbon-deuterium bonds. Since it is known that the -complex formed from isobutylene and acid is in rapid equilibrium with protons from the solvent, none of this can be formed in the nitrous acid induced deamination. This in turn makes it probable that the transition state for the hydrogen migration is of the sigma rather than the -bonded type.261... 

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