Deuterium exchange reaction with

To the best of our knowledge, there are no published data on the reactions of alkanes with H2 over palladium single crystals. Deuterium exchange reactions with various alkanes over palladium films were extensively investigated by Kemball et al. (39-42). Because those results were already discussed in several excellent review articles (43-46), we do not intend to dwell upon analyzing all the data at greater length. We only specify here the basic characteristics of Pd films exhibited in D2/alkane reactions ... 

B. Schools, J. Schuermans, R. A. Schoonheydt, Hydrogen-deuterium exchange reactions with isobutane over acid zeolites, Micropor. Mesopor. Mater., 2000, 35-36, 99-111. 

In theory two carbanions, (189) and (190), can be formed by deprotonation of 3,5-dimethylisoxazole with a strong base. On the basis of MINDO/2 calculations for these two carbanions, the heat of formation of (189) is calculated to be about 33 kJ moF smaller than that of (190), and the carbanion (189) is thermodynamically more stable than the carbanion (190). The calculation is supported by the deuterium exchange reaction of 3,5-dimethylisoxazole with sodium methoxide in deuterated methanol. The rate of deuterium exchange of the 5-methyl protons is about 280 times faster than that of the 3-methyl protons (AAF = 13.0 kJ moF at room temperature) and its activation energy is about 121 kJ moF These results indicate that the methyl groups of 3,5-dimethylisoxazole are much less reactive than the methyl group of 2-methylpyridine and 2-methylquinoline, whose activation energies under the same reaction conditions were reported to be 105 and 88 kJ moF respectively (79H(12)1343). 

The growth of the catalytic activity of Si02 with respect to the hydrogen-deuterium exchange reaction upon addition of a donor impurity to specimens has also been observed by Taylor and his colloborators (31). 

The same authors (41) working with specimens of silica gel observed a positive photocatalytic effect in the course of the hydrogen-deuterium exchange reaction. In this case the introduction of an acceptor impurity into a catalyst enhanced the action of irradiation. 

Boreskov and co-workers (45) point out that on y irradiation the specific catalytic activity of silica gel with respect to the hydrogen-deuterium exchange reaction first increases with increasing radiation dose and then attains saturation at a sufficiently large dose. 

As in the case of the hydrogen-deuterium exchange reaction, so far as K is positive, its value, as is evident from (84) (since the parameters ev and constant over fairly wide temperature ranges) falls with rise of temperature. This is what is observed in reality (53, 57). 

Let us now turn to a comparison of theory with experiment. Comparing (95), (84), and (68), we find that the dependence of the photocatalytic effect K on the position of the Fermi level at the surface s and in the bulk cv of an unexcited sample for the oxidation of water is the same as for the oxidation of CO or for the hydrogen-deuterium exchange reaction. For this reason, such factors as the introduction of impurities into a specimen, the adsorption of gases on the surface of the specimen, and the preliminary treatment of the specimen will exert the same influence on the photocatalytic effect in all the three reactions indicated above. The dependence of K on the intensity I of the exciting light must also be the same in all the three cases. 

The articles by J. R. Anderson, J. H. Sinfelt, and R. B. Moyes and P. B. Wells, on the other hand, deal with a classical field, namely hydrocarbons on metals. The pattern of modem wTork here still very much reflects the important role in the academic studies of deuterium exchange reactions and the mechanisms advanced by pioneers like Horiuti and Polanyi, the Farkas brothers, Rideal, Tw igg, H. S. Taylor, and Turkevich. Using this method, Anderson takes ultrathin metal films with their separated crystallites as idealized models for supported metal catalysts. Sinfelt is concerned with hydrogcnolysis on supported metals and relates the activity to the percentage d character of the metallic bond. Moyes and Wells deal with the modes of chemisorption of benzene, drawing on the results of physical techniques and the ideas of the organometallic chemists in their discussions. 

Apart from the preparation of radiotracers, microwave-assisted transformations have also been utilized to carry out simple hydrogen-deuterium exchange reactions. In the case of acetophenone, for example, simple treatment with deuterium oxide as solvent in the presence of molecular sieves at 180 °C for 30 min led to complete... 

Deuterium or tritium exchange reactions with in the absence of electron donors or acceptors... 

It is also possible to produce deuterium-labelled acetaldehyde by an exchange reaction with D2O and NaOD. This results in exchange of all three... 

Deuterium may be analyzed from density measurements of waters. A confirmation method recommended here is GC mass spectrometry. Deuterium is burned in oxygen (or air) to form D2O which may be separated with helium on a GC column (of intermediate polarity) and identified from its mass spectra. The mass to charge ratio of the molecular ion is 20. Additionally, deuterated products obtained by exchange reactions with hydrogen containing substances (other than those containing C—H bonds) may be separated on a capillary GC column and identified by mass spectrometry. 

It is important to understand why this apparent first-order behavior is found for the course of an exchange reaction with time whatever the true kinetics of the reaction. A failure to understand this feature of exchange reactions has sometimes led to unjustifiable statements about the ratedetermining step in such reactions. It is convenient to discuss a specific example—the exchange of ethane with deuterium. Suppose that the only adsorbed species taking part in the reaction are (a) physically adsorbed... 

F. Balza and A. S. Perlin, Some stereochemical characteristics of C-1H-C-2H exchange-reactions with Raney nickel catalyst in deuterium oxide, Carbohydr. Res., 107 (1982) 270-278. 

The superacidic properties of trichlorogermane are clearly manifested in the properties of its etherates (vide infra) and the ability of DGeCl3 to participate in a deuterium-hydrogen exchange reaction with methylbenzenes32 (Section VIII.E). 

It must be stressed, however, that the hydrogen-deuterium exchange reactions discussed earlier are extremely informative and most useful in assigning structures to a wide variety of anions. Although the specific examples of the (M — H) ions of 2,4- and 1,5-hexadiene, discussed above, cannot be distinguished by these reactions, the 1-phenylcyclopropyl and 2-phenylallyl anions are easily shown to be distinct, non-interconverting species by their differing reactions with D20 (Andrist et al., 1984 Squires et al., 1981). 

---