Propene, reaction with deuterium

The reaction has been studied on copper catalysts " on Cu/Si02 prepared by ion exchange, reaction with deuterium produces propyne-1-rfi and propenes containing deuterium only in the vinylic positions (CH3—CX=CX2, where X may be H or D). ... 

Distribution of products from the reaction of propene with deuterium... 

The reaction of propene with deuterium has been studied over a variety of catalysts [92,103,105,118]. Some typical deuteropropane and deutero-propene distributions are shown in Table 8. Values of j3e as defined in Sect. 3.3 and a (Sect. 3.4) are also quoted. 

The reactions of the n -butenes with deuterium have been studied over alumina-supported platinum and iridium [103] and palladium [124]. In general, the results obtained are similar to those discussed above for ethylene—deuterium and propene—deuterium reactions. A comparison of the deuteroalkane distributions over platinum is shown in Fig. 17. 

Fig. 17. Deuteroalkane distributions observed in the reactions of deuterium with ethylene at 54°C (0)> propene at 73°C ( ) and but-l-ene at 67°C ( ) over platinum-alumina [103],...

The purpose of this section is to provide an overview of the principal kinetic features of the hydrogenation of ethene and of propene, as providing a framework (or at least part of one) within which discussion of mechanisms must be conducted. Their reactions with hydrogen (and with deuterium) are quite comparable the addition of the methyl group leads to somewhat higher reactivity, due to weaker chemisorption as might be predicted from its lower heat of hydrogenation (Table 7.1). Relative rates for other alkenes will be considered later. The problem of deactivation by carbon deposition has already been mentioned, but quantitative... 

This section is concerned with the reactions of ethene and of propene with deuterium on forms of metal catalyst other than single crystals, which are covered in the next section. A fuller discussion of reaction mechanisms is reserved to Section 7.2.6. 

Rapid exchange of ethene and propene on iron and nickel films appears to proceed in this way. Very detailed studies by Japanese scientists using microwave spectroscopy have identified the structure of propene-di formed in reaction of propene with deuterium over metals of Groups 10 and 11, either supported on silica or as powders. Interpretation of the results is somewhat difficult because although addition and exchange show very similar kinetics, and are therefore thought to have the same intermediates, the locations of the deuterium atom in the propene-di are not entirely as expected by the alkyl reversal mechanism. Except on palladium and platinum, the major initial product was propene-2-di " this could arise if... 

There are few reports of alkene-deuterium reactions on bimetallic catalysts, but those few contain some points of interest. On very dilute solutions of nickel in copper (as foil), the only product of the reaction with ethene was ethene-di it is not clear whether the scarcity of deuterium atoms close to the presumably isolated nickels inhibits ethane formation, so that alkyl reversal is the only option, or whether (as with nickel film, see above) the exchange occurs by dissociative adsorption of the ethene. Problems also arise in the use of bimetallic powders containing copper plus either nickel, palladium or platinum. Activation energies for the exchange of propene were similar to those for the pure metals (33-43 kJ mol ) and rates were faster than for copper, but the distribution of deuterium atoms in the propene-di clearly resembled that shown by copper. It was suggested that the active centre comprised atoms of both kinds. On Cu/ZnO, the reaction of ethene with deuterium gave only ethane-d2. as hydrogens in the hydroxylated zinc oxide surface did not participate by reverse spillover. ... 

Selective trapping of alkyl radicals from the alkyl halide component during the course of the catalytic disproportionation is the same as the previous observation with silver, and it indicates that the prime source of radicals in the Kharasch reaction lies in the oxidative addition of alkyl halide to reduced iron in Equation 47. Separate pathways for reaction of i-propyl groups derived from the organic halide and the Grignard reagent are also supported by deuterium labelling studies which show that they are not completely equilibrated.(49) Furthermore, the observation of CIDNP (AE multiplet effect) In the labelled propane and propene... 

Naito et al. studied hydrogenation with use of adsorption measurements, mass spectrometry, and microwave spectroscopy for product analysis. In the room temperature deuteriation of propene, butene, and 1,3-butadiene, the main products were [ H2]-propane, [ H2]-butane, and l,2-[ H2]-but-l-ene, respectively. They showed, using mixtures of H2 and D2, that deuterium was added in the molecular form and at a rate proportional to the partial pressure of D2, as opposed to D surface coverage the reaction rates were zero order in hydrocarbon. They proposed, therefore, in contrast to the model of Dent and Kokes for ethene (but note in this case that reaction rate was 0.5 order in hydrogen pressure and proportional to ethene surface coverage), that hydrogenation proceeded by interaction of adsorbed hydrocarbon with gas-phase D2, that is by an Eley-Rideal mechanism. 

When alkene is in excess, the reaction in a constant volume system stops when the deuterium is used up, and the deuterium alkene ratio decreases continuously as the reaction proceeds. Unreacted but partially exchanged alkene remains at the end, and the deuterium number of the alkanes M is less than two, the alkane-d<, becoming a major product (see Figure 7.9 for the propene-deuterium reaction on Pt/pumice ). Contrarily when deuterium is in excess, the final alkane deuterium number is greater than two, the alkene-rfo falls to near zero, and the alkane-d2 becomes the major product (see also Figure 7.9). Similar but less complete results were seen with propene ° and ethene on a variety of supported platinum catalysts. 

Other metals of Groups 8 to 10 have very different characteristics in respect of reactions of the butenes with hydrogen and deuterium as might be expected from the way they behave in the ethene- (and propene-) deuterium reactions, nickel, palladium, ruthenium, rhodium and osmium are able under some conditions to exhibit much higher values of r,/rfc, so that the butenes are able to achieve their equilibrium concentrations before their hydrogenation is finished. 

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