Ethylene deuterium

In fact, MWD obtained at different deuterium-ethylene ratios are not influenced by the amount of the chain terminating agent Similar results have been found by Berger and Grieveson in ethylene polymerization, using different hydrogen concentrations. 

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. 

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]. 

Draw structural formulas for all the isomers of ethylene (QH ) in which two of the hydrogen atoms have been replaced by deuterium atoms. Label the cis and the irons isomers. 

This mechanism accounts for the fact, established by deuterium labeling, that the four hydrogens of the acetaldehyde all come from the original ethylene and none from the solvent. 

The main difficulty in obtaining the vinyl radical is that the species easily loses the hydrogen atom and is converted into acetylene. Nevertheless, a very low concentration of the radical H2C=CH has been achieved (Shepherd et al., 1988) by vacuum UV photolysis of ethylene frozen in an argon matrix, and a Fourier transform IR study of this intermediate has been carried out. A variety of and deuterium-substituted ethylene parent molecules were used to form various isotopomers of vinyl radical. On the basis of its isotopic behaviour and by comparison with ab initio... 

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-... 

Since deuterium addition to ethylene yields C2H4D2, both of the last steps are irreversible and (13) can be taken as the rate-determining step. Accordingly, if all prior steps are at equilibrium, we can write for the rate R of ethane formation ... 

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... 

The formation of acetaldehyde from the w-olefin complex was shown to involve intramolecular migration of a hydrogen atom from one carbon of the ethylene to the other, rather than 0H attack on a vinyl group generated by hydride abstraction with Pd (CH2=CH+ + OH -> CH2=CH0H) followed by rearrangement of the vinyl alcohol to acetaldehyde, since hydrolysis in DgO yielded acetaldehyde free of deuterium (59). 

The deuterium kinetic isotope effect (DKIE) for the electrophilic bromination of ethylene-/z4 and ethylene- 4 in methanol and dichloroethane at 25 °C has been... 

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