Propylene-deuterium exchange reaction

A preliminary study of the propylene-deuterium reaction over palladium-pumice (55) showed extensive olefin exchange the reaction has since been re-examined using palladium-alumina 31). The progress of the exchange reaction at — 20° is shown in Fig. 8, from which it appears... 

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). 

Katzer (28) observed that counterdiffusion of benzene and cumene within the pores of H-mordenite does not occur at low temperatures. However, H-mordenite shows activity for the alkylation of benzene with propylene to form cumene under the liquid phase conditions used for the diffusion studies, and he has suggested that reaction must occur on the external crystallite surface, or just within the pore mouth. In earlier studies on the isomerization of 2,3-dimethylbutene-l at 0°-20°C over a deuterated Y-type faujasite (62), we observed that the extent of isomerization (2,3-dimethylbutene-2) was far greater than the extent of deutera-tion only a fraction of the total deuterium on catalyst OD groups was exchanged. One possible explanation—assuming a protonic isomerization mechanism—is that, because of lowered intracrystalline diffusion rates... 

In earlier work (52) we found that reaction between ethylene and deuterium on catalysts activated at high temperatures led to detectable formation of neither ethylene-d nor ethane-ds. Under similar conditions propylene-d and propane-da were formed in reaction between deuterium and propylene. We will assume for the moment that this situation would also obtain on chromias activated at lower temperatures. On this assumption, reversal of monoadsorbed alkane to adsorbed olefin is not a significant process. If it were, one would get exchanged ethylene. 

The presence of a variety of reaction intermediates described above can be clearly demonstrated by detailed tracer studies in the case of deuterium exchange of propylene, which is dosely related to double-bond isomerization of olelins. ... 

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