Exchange Reactions deuterium-butene

J. Turkevich I was in error in the statement that hydrogen-deuterium exchange reaction is the only reaction that takes place with the help of acid sites, for we have found that butene-1 to butene-2 transformation is catalyzed by both Bronsted and Lewis acid sites. The Bronsted sites, however, give a marked stereospecificity in producing nonequilibrium mixtures of cis and trans, while the Lewis acid sites give an equilibrium mixture of the geometric isomers. 

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). 

It was found that by treating either n-butane or isobutane with 10 mole % deuterium bromide-aluminum bromide catalyst for 20 hours at 25°, no isomerization of the butanes occurred and only 6 and 9.5% of the deuterium exchanged with n-butane and isobutane, respectively. When, however, 0.1 mole % butenes was added to n-butane and the isomerization reaction was carried out under the same experimental conditions, over 40% of the butane isomerized to isobutane and 92% of the deuterium underwent an exchange reaction. These results indicate clearly that olefins take an active part in isomerization. The results obtained are in agreement with the proposed mechanism of isomerization. 

TABLE 8.7. Reaction of 1,3-Butadiene with Deuterium on Metals of Groups 9 to 11 Butadiene Exchange and Deuterium Content of Butenes ... 

Deuterium KIE in the reaction of 3-metyl-l-butene, 378, with CF3COOH-D (TFA-D), providing 3-methyl and 2-methylbutyl trifluoroacetate, 389, in about 53 47 ratio both in TFA-H and in TFA-D, was 6.8 (at 26.5 °C)434. In the similar reaction with 2-methyl-l-butene 379, and 2-methyl-2-butene, 380, with TFA-D, the D KIEs have been found434 to be 5 (379, —18 °C). and 3.9 (380, —18 °C). 378 reacts by carbocationic mechanism and undergoes a Me shift. Extensive H/D exchange between the solvent and the ester 381 took place. 

The explanation given above recalls earlier speculations presented by Ledoux et al. (22, 23). The authors assigned a different role to various surface centers on a palladium film in the reactions of isomerization, hydrogenation, and deuterium exchange of butenes. The authors defined... 

A comparable study of the Ni-catalyzed reactions of isobutene, 1-butene, and cis-butene-2 in the presence of H2 and D2 has revealed a very complex series of chemical reactions that take place, including induced isomerization of 1-butene to 2-butene, deuterium exchange, induced cis-trans isomerization of butene-2, and finally, addition to the double bond. Below 200 mm Hg pressure, the rates of exchange, addition, and isomerization are about equal for 1-butene and are about % order in olefin and order in H2. With increasing excess of H2 this approaches zero order in olefin and % order in H2, while for large excess of 1-butene, all reactions become inhibited (30 to 150°C). Although the authors have attempted to discuss mechanisms in connection with the data, the lack of information on the isotherms makes that of dubious value. 

In the experiments with deuterium, a deuterium/l-butene ratio of 2 was employed. When deuterium oxide was used, the catalyst was allowed to pre-adsorb a small, controlled amount of D2O (normally approximately one molecule per cage) prior to the admission of the 1-butene. These reaction systems were examined over the least and the highest exchanged forms of the zinc and the cerium zeolites. 

Only three studies of the reaction of higher olefins with deuterium over nickel catalysts have been reported in which mass-spectrometric analysis of the products was performed (32, 48, 49). There have been other separate studies of the isomerization reactions, to be described in the next section, but no simultaneous studies of both exchange and isomerization. Thus when results have been given for the deuterated butenes formed by olefin exchange (48), it is uncertain to what extent deuterated isomerized olefins are contributing to the total effect. There is room here for much further work. 

A remarkable effect was observed when sintered iron films were used. The multiple exchange process disappears and a normal distribution is obtained (see Pig. 7b). The use of sintered films also enabled a course of reaction to be followed (cyclohexene at 0°, cyclopentene at —35°) stepwise olefin exchange was observed, slightly more marked with cyclopentene than with cyclohexene, and the results bear a marked resemblance to those shown for the reactions of ethylene and of 1-butene with deuterium over nickel in Figs. 5 and 6. Sintering also removes the ability of iron films to catalyze the disproportionation of cyclohexene to cyclohexene and benzene, and for this reason it was... 

The effect of temperature is peculiar (see Fig. 13). The deuterium content of the reactant olefin, in this case 1-butene, at about 10% conversion falls with increasing temperature, paralleling its behavior in isomerization. However, the deuterium content of the isomerized 2-butenes rises rapidly, as does also the deuterium number of the butane. This tells us (1) intramolecular hydrogen transfer becomes less important with rising temperature and is perhaps replaced by reactions involving adsorbed deuterium atoms (step 1. ii), and (2) butane is probably formed through the same intermediates as those which yield 2-butenes, viz., 2-butyI radicals. The same kind of behavior is shown by the other butenes. Partial pressure variation has no remarkable effect on the course of exchange and isomerization. 

In the reactions of 1-butene with deuterium at 30-60°, the two 2-butenes are almost equally deuterated but in each case 2-butene-do constitutes 50-60yo of the product. The isomerized butenes are rather less deuterated at higher temperatures. The general pattern of the high-temperature exchange results is very similar to that described for palladium in Section II, G, 2. Hydrogen exchange is, however, much more marked. 

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