Exchange Reactions deuterium-methane

Coillet, D. W., and G. M. Harris Exchange Reactions of Methane and Monodeuteromethane with Atomic Deuterium. J. Amer. chem. Soc. 75, I486 (1953.). 

Utiyama, M. Hattori, H. Tanabe, K. Exchange reaction of methane with deuterium over solid base catalysts. J. Catal. 1978, 53, 237-242. 

The exchange reaction of methane with deuterium has been found to show a decrease in specific activity upon alloying of palladium with gold (82), reflecting the decrease in number of reactive surface metal atoms upon alloying. 

The exchange reactions of methane with deuterium over several metals (21, 39,146,147,195, 215, 216, 229) exhibited compensation behavior (Table III, G), as has been pointed out previously (3). No such relationship was found in the data available for exchange reactions of C2-C6 hydrocarbons. This is consistent with discussion given above (see Section III, B, 4) in which it was concluded that the differences in the kinetic behavior of the exchange reactions between methane and the other hydrocarbons varied with the individual metals concerned. 

B. Schools, J. A. Martens, P. A. Jacobs, R. A. Schoonheydt, Kinetics of hydrogen-deuterium exchange reactions of methane and deuterated acid FAU- and MFI-type zeolites, J. Catal., 1999, 183, 355-367. 

Similar results have been obtained for methane 12) and for ethane 19). The values quoted in Table II also illustrate the point that the distribution of deuterium between hydrogen and propane differs from the value expected for a random distribution. With the ratio of pressures used, the expected percentage for the mean deuterium content of the hydrocarbon would be 33.3, which is substantially less than the experimental value of 40.9 %. This type of deviation is also found with other hydrocarbons, but it does not affect the validity of using classical theory for the calculation of the interconversion equilibrium constants in studies of mechanism of exchange reactions. More accurate values for these equilibrium constants are necessary, however, if one is interested in the separation of isotopes by chemical processes. 

In most cases the slow step of the reaction is not simply the activation or chemisorption of hydrogen, but involves other chemisorbed species. Thus, the exchange of deuterium with methane and with other saturated hydrocarbons is much slower than with hydrogen and probably proceeds through dissociative adsorption of the hydrocarbon. 

The production of hot radicals and molecules by chemical reaction was recognized by early workers.4 Two important instances were the deuterium-methane exchange mechanism of Taylor and co-workers,5 and the atomic-cracking degradation reaction of hydrocarbons, suggested by Steacie and co-workers.2 Equation (I), in which one of the radicals, Ri and R2, may be a hydrogen atom, generalizes the possibilities in these two processes ... 

Studies of the photochemical formation of benzyl carbanions have been reported for two systems this year. Ultra-violet light irradiation of (420) in aqueous acetonitrile resulted in formation of (421) exchange of the benzylic hydrogens of (420) was also observed when heavy water was used in the solvent. Compound (421) was shown to arise by two pathways a di-7r-methane rearrangement, and a 1,7-hydrogen shift followed by electrocyclic closure. The deuterium exchange reaction is presumed to occur due to... 

The equilibrium constant for the third, deuterium exchange, reaction is around 2 at the temperature at which the second, water-gas shift, reaction is carried out. Because an excess of water is used to convert CO completely to COj, the deuterium content of hydrogen will be less than that of the methane and water fed, unless the excess water is fully recycled. Because water recycle is usually not practiced at ammonia synthesis plants, the deuterium content of synthesis gas at operating plants is sometimes as low as 0.009 percent [M7]. If the ammonia plant were specifically designed for deuterium recovery from its synthesis gas, the deuterium content could be increased to the average of the methane and water feeds by recycling aU water and preventing losses. 

Activation studies for methane carried out by isotopic experiments may be considered the first indicator of catalytic activation for the exchange reaction. The reaction investigated was the exchange of methane with deuterium. 

Other investigations of methane activation by Sehested [415] showed a strong impact of alkali on the methane/deuterium exchange reaction as illustrated in Table 6.2. 

As an example we discuss predictions for the rate constant of the proton-deuterium exchange reaction between deuterated methane and the zeolite cluster of Figure 6.17... 

Fio. 20. Geometrical relationships for the simple exchange of methane with deuterium involving adjacent surface atoms each of which has available two octahedral bonding directions suitable for the reaction. 

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