Exchange Reactions deuterium-propene

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... 

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). ... 

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-... 

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. 

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. ... 

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