Deuterium exchange reactions

Two types of hydrogen replacement are discussed here (1) the base-induced hydrogen-deuterium exchange reactions and (2) the hydrogen-metal exchange reactions. 

The deuterium exchange reactions in the H2S/H2O process (the GS process) occur in the tiquid phase without the necessity for a catalyst. The dual-temperature feature of the process is illustrated in Figure la. Dual-temperature operation avoids the necessity for an expensive chemical reflux operation that is essential in a single-temperature process (11,163) (Fig. lb). 

The NMR spectra of pyrido[2,3-d]pyridazine Af-oxides reduced derivatives and quaternary salts have also been studied and alkaline deuterium exchange reactions investigated <77BSF919). 

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). 

Pyridin-4-one, 1 -hydroxy-2,6-dimethyl-hydrogen-deuterium exchange reactions, 2, 196 Pyridin-4-one, 1-methyl-hydrogen-deuterium exchange, 2, 287 pK 2, 150 Pyridin-2-one imine tautomerism, 2, 158 Pyridin-2-one imine, 1-methyl-quaternization, 4, 503 Pyridin-4-one imine tautomerism, 2, 158 Pyridinone methides, 2, 331 tautomerism, 2, 158 Pyridinones acylation, 2, 352 alkylation, 2, 349 aromaticity, 2, 148 association... 

Recently, other authors when studying the activation of hydrogen by nickel and nickel-copper catalysts in the hydrogen-deuterium exchange reaction concentrated for example only on the role of nickel in these alloys (56) or on a correlation between the true nickel concentration in the surface layer of an alloy, as stated by the Auger electron spectroscopy, and the catalytic activity (57). 

At Bayer CropScience, the use of a stable isotope IS has become common practice to eliminate the effects of matrix suppression on instrument signals. The stable isotopes are synthesized by deuterium exchange reactions on authentic native standards or the... 

A number of theoretical works have been devoted to the study of the hydrogen-deuterium exchange reaction. Hauffe (25) examined this reaction from the standpoint of the boundary layer theory of chemisorption. Dowden and co-workers (26) undertook a theoretical investigation of the hydrogen-deuterium exchange reaction from the viewpoint of the theory of crystalline fields. 

We shall consider the hydrogen-deuterium exchange reaction from the viewpoint of the electronic theory of chemisorption and catalysis (27),... 

A large number of works have been devoted to the effect of impurities on the rate of the hydrogen-deuterium exchange reaction. 

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). 

Investigations carried out on specimens of the same semiconductor, prepared by different methods, have shown that there is a correlation between the catalytic activity of a specimen in relation to the hydrogen-deuterium exchange reaction and its initial electrical conductivity. Electron... 

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. 

Kohn and Taylor (40) also studied the influence of illumination on the hydrogen-deuterium exchange reaction using specimens of barium, calcium, lithium, and sodium hydrides. If the specimens were annealed in the hydrogen atmosphere, the photocatalytic effect on these specimens was positive. And if the specimens of the same hydrides were preliminarily calcined in vacuum, the irradiation of these specimens retarded the reaction. 

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. 

The great majority of experimental data (see Section III.A) indicate that the hydrogen-deuterium exchange reaction belongs to the class of acceptor reactions (i.e., reactions that are accelerated by electrons and decelerated by holes). This means that the experimenter, as a rule, remains on the acceptor branch of the thick curve in Fig. 8a, on which the chemisorbed hydrogen and deuterium atoms act as donors. Here a donor impurity must enhance the catalytic activity, while an acceptor impurity must decrease it. This is what actually occurs, as we have already seen (see Section III.A). 

We see that the correlation between the electrical conductivity of a specimen and its catalytic activity established by the electronic theory (1) must show up distinctly and in fact reveals itself in the case of the hydrogen-deuterium exchange reaction. 

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. 

There is considerable evidence available which indicates that these surface Voh centers are the active sites for the irradiation induced catalytic activity of MgO for the hydrogen-deuterium exchange reaction (143). In particular, a correlation exists between the Voh center concentration and the induced catalytic activity (1) for samples degassed at different tem-... 

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... 

Masjedizadeh and coworkers have recently described similar microwave-promoted hydrogen-deuterium exchange reactions in a series of heterocydes using mixtures of deuterium oxide and deuteriomethanol (Scheme 6.173 b) [328], The rapid exchange method was applied to the deuteration of the anti-tumor antibiotic bleomycin A under catalyst-free conditions [328],... 

Deuterium Exchange Reaction of A a Pentenoic Acid. J. chem. Soc. [London] 1940, 1362. 

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