Hydrogen-deuterium exchange reactions mechanism

In discussing the mechanism of the para hydrogen conversion or the hydrogen deuterium exchange reaction, Eley (117) suggested that it could occur at a single metal atom. Two orbitals are needed to bind the activated complex and these can be provided easily by the d orbitals of... 

Studies of hydrogen-deuterium exchange reactions of some of these iridium hydrides show that two mechanisms are apparently exhibited, one possibly involving seven- or eight-coordinate intermediates. 

Which of the following best describes what happens in the first step in the mechanism of the hydrogen-deuterium exchange reaction shown ... 

The reaction takes place extremely rapidly, and if D2O is present in excess, all the alcohol is converted to ROD. This hydrogen-deuterium exchange can be catalyzed by either acids or bases. If D30 is the catalyst in acid solution and DO the catalyst in base, write reasonable reaction mechanisms for the conversion of ROH to ROD under conditions of (a) acid catalysis and (b) base catalysis. 

Recent studies have shown that the reaction, as described by Eq. (11), also requires Pt(II) as a necessary catalyst (29, 84). A range of substituted benzenes has been examined, and by studying concurrent hydrogen-deuterium exchange, it was concluded that the two reactions had common intermediates (29). In this work aqueous acetic acid was used as the solvent, and reactions were followed by measuring the concentration of the chlorobenzene product. Of the several possible mechanisms for the oxidation that have been given (29), only one will be considered here this is the one that has received substantial support from the most recent work (84). In this study, the loss of reactant benzene, the formation of product chlorobenzene, and the formation of platinum(II) were monitored as the reaction proceeded. Also aqueous trifluoroacetic acid was used as the solvent, as it is known that acetic acid is oxidized to chloroacetic acid by platinum(IV) (18). 

Many organic anions have been found to undergo hydrogen/deuterium exchange in the presence of deuterated reagents, such as p,0 and CH,OD. Such exchange reactions have proved to be a valuable method of probing mechanisms of ion/molecule reactions and structures of ions in the gas phase. 

It should be pointed out that this mechanism accounts for the observed first order kinetics (based on the sum of all deuterated products), since the rate of the hydrogen transfer step (8) depends on the first power of the concentration of isobutane in the gas phase, i.e., the rate of adsorption of isobutane. Probably the hydrogen transfer step (8) is the slow step in the overall reaction, since the activation energy of the overall deuterium exchange reaction is not affected by the initiating step involving olefin. 

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