Hydrogen/deuterium reaction with platinum

The earliest attempts to prepare deuterated steroids were carried out by exchange reactions of aliphatic hydrogens with deuterium in the presence of a surface catalyst. Cholesterol, for example, has been treated with platinum in a mixture of deuterium oxide and acetic acid-OD, and was found to yield... 

The comparison of the catalytic performances of metals and their alloys is sometimes hampered by the different degree of deactivation by carbonaceous residues (107, 67). Therefore, it seems appropriate to start with a discussion of the exchange reactions of the hydrogen isotopes protium and deuterium on platinum and Pt-Au films (31). A comparison of this reaction on platinum and its alloy shows that of the two reaction paths possible on platinum in the temperature region studied, one remains unchanged on the alloy but the other, which prevails on platinum except at very low temperatures, seems... 

Modification of selectivity induced by sulfur adsorption has been widely studied (41, 90, 75) and can be evaluated by comparison of the initial toxicides (see Table VI) for different parallel reactions. As an example, sulfur on platinum does not inhibit similarly benzene hydrogenation and the exchange with deuterium reactions. The H/D exchange is less deactivated than the hydrogenation. For instance, one sulfur atom (introduced as H2S) poisons five accessible platinum atoms for benzene hydrogenation, whereas it poisons only two platinum atoms for exchange. The mechanism of selectivity modification induced by sulfur adsorption is far from being explained. 

Tanaka has recently reviewed the hydrogenation of ketones with an emphasis on the mechanistic aspects of the reaction.233 Numerous references related to this subject can be found in his article. Deuteration of cyclohexanones and an application of NMR spectroscopy to the analysis of deuterated products have revealed that on ruthenium, osmium, iridium, and platinum, deuterium is simply added to adsorbed ketones to give the corresponding alcohols deuterated on the Cl carbon, without any deuterium atom at the C2 and C6 positions, while over palladium and rhodium the C2 and C6 positions are also deuterated.234 A distinct difference between rhodium and palladium is that on rhodium deuterium is incorporated beyond the C2 and C6 positions whereas on palladium the distribution of deuterium is limited to the C2 and C6 carbons.234,235 From these results, together with those on the deuteration of adamantanone,236 it has been concluded that a Tt-oxaallyl species is formed on palladium while deuterium may be propagated by an a, 3 process237 on rhodium via a staggered a, 3-diadsorbed species. 

Figure 8. The hydrogen-deuterium exchange on the stepped and flat platinum surfaces. The reaction probability is much higher on the stepped metal surface. (Reproduced with permission from ref. 20. Copyright 1977 American Physical Society.)...

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. ... 

We may start by considering the results obtained with platinum catalysts the reactions of the -butenes with hydrogen and or deuterium have been studied using Pt/AbOs, on catalysts prepared from reverse micelles (Section 2.32), and on platinum foil and various single crystal surfaces. There are a number of common features (i) orders of reaction, where measured, are either accurately or close to first in hydrogen and zero in the butene (ii) activation energies for the macroscopic forms are between 33 and 43 kJ moD for both 1-butene and Z-2-butene, but lower for the latter on Pt/AlaOs (21 kJ mol ) (iii) rates of reactant removal for each butene appear to be structure-insensitive and all three isomers react at about the same rate. A notable characteristic of platinum catalysts prepared conventionally or in macroscopic form is the slow rate of... 

As was the case with ethene and other alkenes, replacing hydrogen by deuterium and analysis of reaction products reveals hitherto hidden aspects of reaction mechanism. Early work with platinum and nickel indicated that neither... 

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