Ammonia deuterium exchange

The log—log plot of the adsorption isotherm, which can possibly be correlated to the pressure-dependency of the catalytic reaction rate, is very flat. The adsorption of ethylene on nickel increases only by 10% for an increase of the equilibrium pressure by a factor of 10, although the surface is still far from being covered by a monolayer. The work of Laidler et al. (3), who studied the ammonia-deuterium exchange reaction on a promoted iron catalyst by means of the microwave method, also throws doubt on the zero-order kinetics with respect to observations made by Farkas (4). 

Schuit, van Reijen, and Sachtler (470) have also calculated the volcanoshaped curves for other reactions according to the data of a number of authors the ammonia-deuterium exchange [Fig. 64, Kemball (471)], the hydrogenation of ethylene [Fig. 65, Schuit and van Reijen (472)-, Beeck... 

Analogous parahydrogen conversion and deuterium exchange reactions, catalyzed by NH2, have been observed in liquid ammonia (Wilmarth and Dayton, 61). The kinetics are of the same form as those of the OH -cat-alyzed reaction in water and the mechanism is open to similar interpretations. The NH2 -catalyzed reaction is much faster, its rate constant at —50° being 10 times that of the OH -catalyzed reaction at 100°. The assumption of equal frequency factors for the two reactions leads to a calculated activation energy for the NH2 -catalyzed reaction of about 10 kcal. This low value has been attributed to the much greater base strength of NH2 relative to OH . The results provide some support for the hydride ion mechanism. 

Deuterio-ammonia was synthesized by means of the reaction between heavy water and magnesium nitride, with subsequent drying by potassium amide (Landsberg et al., 1956). Compounds containing deuterium in a specific position were obtained either by deuterium exchange or by organic synthesis (Shatenshtein and Izrailevich, 1957). 

The amides of alkali and alkaline-earth metals catalyse hydrogen exchange in hydrocarbons even in the absence of liquid ammonia. For example, the heterogeneous deuterium exchange of benzene and 2-methylbutene-l occurs with a considerable velocity on solid KND2 and Ca(ND2)2 at 70°. This gives rise to the isomerization of 2-methyl-butene-1 to 2-methylbutene-2 (Shatenshtein et al., 1958a). 

Rate Constants for Deuterium Exchange in Liquid Ammonia and in Amines at 120°... 

The acid properties of hydrocarbons, deduced from deuterium exchange with liquid ammonia, will be discussed in detail in the following sections. 

Using the fact that the rate of anionic polymerization of a-methyl-styrene, initiated by potassium amide in liquid ammonia, is smaller than the rate of hydrogen exchange, it was possible to establish (Shatenshtem et al., 1962b) that hydrogen-deuterium exchange occurs... 

Table 10 gives the partial rate factors for deuterium exchange of aromatic compounds with a KNH2 solution in liquid ammonia (Hall et al., 1955 Shatenshtein and Izrailevich, 1962 Shatenshtein and Ranneva, 1961 Shatenshtein and Vedeneev, 1958a, b Shatenshtein et al., 1960 Yurygina et al., 1960). 

Chloro-l-methylpyrazinium ion with liquid ammonia reacted by addition at the 2-position to give 2-amino-3-chloro-l-methyl-1,2-dihydropyrazine (24) (609). The hexafluoroantimonate salt of perfluoropyrazine has been prepared and F n.m.r. measurements used to determine the relative order of its base strength with other perfluoroheterocycles (914). Hydrogen-deuterium exchange rates of Hj and Hg in 3-chloro(and other substituted)pyrazine l-oxide(s) have been correlated with a-constants, and the logs of the H2 exchange rates have been shown to be linearly related to the pK values (745). The pK value of 3-chloropyrazine 1-oxide is - 1.05 (745). 

Proton magnetic resonance techniques have been used for the measurement of rates of hydrogen-deuterium exchange of pyrazine (in CHsOD-CHsONa at 164.6") (591) for a study of protonation of pyrazine (1472) for analysis of the reaction mixture from quatemization of 2-substituted pyrazines with methyl iodide (666) for elucidation or confirmation of the structures of alkylpyrazines obtained by alkylation of pyrazines with aldehydes and ketones in the presence of a solution of an alkali or alkaline earth metal in liquid ammonia, or a suspension of these metals in other solvents (614) for a study of changes in chemical shifts produced on ionization of 2-methyl and 2-amino derivatives of pyrazine in liquid ammonia (665) for characterization of methoxymethylpyrazines (686) for the determination of the position of the A -oxide function in monosubstituted pyrazine V-oxides and the analysis of V-oxidation reactions (838) for a study of the structure of the cations of fV-oxides of monosubstituted pyrazines (1136) and for the determination of the structure of the products of peroxyacetic and peroxysulfuric acid iV-oxidation of phenyl- and chlorophenylpyrazines (733b). 

Deuterium exchange between ammonia and hydrogen does not proceed spontaneously. Wilmarth, Dayton, and Flournoy found that potassium amide catalyzed this exchange. Further studies showed that the rate of exchange is proportional to solubility of both hydrogen and catalyst in ammonia, which can be increased by intimate mixing of the liquid and gas phases. ... 

The monothermal NH3-H2 process was developed in France. Deuterium exchange takes place between liquid NH3 and gaseous H2. KNH2 is the catalyst, obtained by dissolving potassium metal in liquid ammonia. A schematic diagram of the process is given in Fig. 4. 

Another process that has been used to extract deuterium from ammonia synthesis gas is the deuterium-exchange reaction between liquid ammonia and gaseous hydrogen ... 

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. 

All other plants that for primary concentration use water electrolysis (WE), steam-hydrogen exchange (SH), synthesis gas distillation (SD), hydrogen distillation (HD), or ammonia-hydrogen exchange (AH) are parasitic to a synthetic ammonia plant. Heavy water is a by-product of these plants, and its production rate is limited by the amount of deuterium in the ammonia plant feed. 

The deuterium exchange reaction between water and ammonia, water and hydrogen sulfide, or water and the hydrogen halides proceeds rapidly in the liquid phase without catalysis, because of ionic dissociation. In the case of a mixture of water and hydrogen sulfide, for example, the ionic equilibria... 

Figure 1323 illustrates the principle of enriching deuterium by monothermal ammonia-hydrogen exchange in conjunction with a synthetic ammonia plant. The flow quantities have been developed from partial information reported for the Mazingarbe plant [LI, El, N2]. Feed, at point (1), consists of ammonia synthesis gas, SHj/lNj, which has been purified to reduce its content of water, CO, and COj to less than 1 ppm and compressed to the pressure of ammonia... 

To cause the deuterium exchange reaction between hydrogen and ammonia to take place at a useful rate, it is necessary to have 1 to 2 m/o (mole percent) of potassium amide, KNH2, dissolved in the liquid phase to serve as a homogenous catalyst [C2]. Presence of potassium amide complicates the process for three reasons ... 

It remains in deuterium exchange equilibrium with ammonia ... 

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