Hydrogen Isotope Exchange Reactions Research Articles

Regioselective Hydrogen Isotope Exchange Reaction in Benzoic Acid and Its Alkali Metal Salts.

The hydrogen isotope exchange reaction of benzoic acid and its alkali metal salts with deuterium oxide was studied in the presence of RhCl3⋅3H2O. The products were analyzed by 1H-and 13C-NMR spectroscopies. High regioselectivity of the exchange at the ortho positions was established, and the extent of deuterium labeling and the distribution of d0, d1, and d2 were determined. The reaction mechanism was briefly discussed.

Hydrogen isotope exchange reactions involving C–H (D, T) bonds

Exchange reactions involving the displacement of hydrogen bonded to carbon by its heavier isotopes are of interest for both mechanistic and product-orientated research. This review surveys practical strategies for the preparation of isotopically labelled compounds, discusses recent progress made in developing mild and regioselective exchange protocols, and summarizes the mechanistic aspects of C–H bond activation under homogeneous and heterogeneous exchange conditions.

Theory, design, and characterization of a microdialysis flow cell for Raman spectroscopy

The theory, design, and application of a dialysis flow cell for Raman spectroscopy are described. The flow cell permits rapid collection of Raman spectra concurrent with the efflux of small solute molecules or ions into a solution of macromolecules and is well suited to acquisition of data during hydrogen-isotope exchange reactions of biological molecules. Kinetic parameters of the device are described by a diffusion model, which accounts satisfactorily for the observed rates of efflux of deuterium oxide (K2H = 0.30 min-1), calcium ions (KCa = 0.10 min-1) and EGTA (KEGTA = 0.07 min-1). Application to the kinetics of glutamate protonation in a peptide copolymer [poly(Glu, Lys, Tyr)] shows that pH-titration rates as high as 3.3 pH units/min can be monitored. It is also shown that one can extract first-order hydrogen-isotope exchange rate constants from measured second-order exchanges by taking into account the rate of entry of 2H2O effluent into the bulk H2O solution. Deuterium exchanges of the single-stranded polyribonucleotides poly(rA) and poly(rU) and of the double-stranded RNA genome from bacteriophage phi 6 have been investigated. The measured nucleotide base exchange rates are comparable with those determined previously by other methods. The results indicate that base exchanges as fast as approximately 2 min-1 can be determined reliably with the present design. Application of the Raman flow cell to hydrogen-isotope exchange of the basic pancreatic trypsin inhibitor confirms consistency with results obtained previously on this protein by tritiation and NMR techniques.

Temperature dependence of the reactivity of monosubstituted thiophenols by applying the hydrogen-isotope exchange reaction in a liquid-solid system

In order to reveal the reactivity of monosubstituted thiophenols, the hydrogen-isotope exchange reaction between T-labeled poly(vinyl alcohol) and each monosubstituted thiophenol (unlabeled) was studied in a liquid-solid system. Using both the data obtained and theA″-McKay plot method, the reaction was analyzed, and the rate constant (k) for the monosubstituted thiophenol has been obtained. Consequently, it has been found that (1) the higher the temperature is, the larger is the reactivity of monosubstituted thiophenols, (2) the temperature dependence of the effect of the substituent (in a monosubstituted thiophenol) on the reactivity of the monosubstituted thiophenol is weak, (3) the reactivity of monosubstituted thiophenols follows the Hammett rule, (4) the reactivity of monosubstituted thiophenols can be enhanced with one of the electron-attractive substituents.

Hydrogen isotope exchange reactions between hydrous minerals and molecular hydrogen: I. A new approach for the determination of hydrogen isotope fractionation at moderate temperatures

Molecular hydrogen was used as an exchange medium to make indirect determinations of hydrogen isotope fractionation factors between hydrous minerals (epidote, kaolinite, muscovite, biotite, and hornblende) and water at temperatures between 150 and 400°C. Hydrogen isotope exchange between hydrous minerals and H 2 is found to be unusually rapid at these temperatures and, in the absence of reducible iron, may represent true diffusive exchange. Two methods were used for the exchange: (1) the molecular hydrogen provided an “infinite” reservoir of H 2 and (2) the mineral provided an “infinite” reservoir of H 2. Results of these methods are in good agreement for epidote and kaolinite, suggesting that “surface effects” are not important for these experiments. Fractionation factors in the epidote-H 2 system, expressed as 1000 lnα, increase linearly with increasing 1 T 2 (or decreasing temperature) between temperatures of 150 and 400°C. This behavior is also true for epidote-water fractionation factors calculated from published H 2O (vapor) — H 2 and H 2O (vapor) — H 2O(liquid) fractionation factors. Values of 1000 lnα for kaolinite-H 2 and muscovite-H 2 fractionation factors are similar and also decrease linearly with increasing 1 T 2 between 200 and 275°C, and 200 and 400°C, respectively. There is a small departure from such linearity at temperatures of less than 200°C for the kaolinite-H 2 system. The trends of the calculated kaolinite-H 2O fractionation factors with temperature are similar to those previously published, with a maximum at about 200°C. Muscovite-H 2O fractionation factors also decrease with decreasing temperatures and become increasingly positive at temperatures lower than about 225°C. Problems of reduction of iron and a concomitant increase in the amount of water were encountered in exchange experiments involving biotite, hornblende, and, to a lesser extent, muscovite. The consequences of these reactions were the production of apparent relatively small mineral-H 2 and large mineral-H 2O equilibrium fractionation factors and support the hypothesis that hydroxyl groups are added to sites linked to iron and that there is indeed a compositional effect on hydrogen isotope fractionations in mineral-H 2O systems. The new equilibrium fractionation factors determined in this study do not unambiguously resolve serious conflicts in data published by previous workers, but do provide some important constraints on the direction and magnitude of the D H fractionation factors between water and the common rock-forming minerals.

ChemInform Abstract: Hydrogen Isotope Exchange, Alkylation and Acylation Reactions of Potentially Tautomeric Methyl and Methylidene Derivatives of Pyridine and Diazines

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Analysis of the reactivity of materials having two different kinds of functional groups using the A″-McKay plot method

The hydrogen-isotope exchange reaction between HTO vapor (as a gaseous material) andp-aminophenol (or α-alanine) (as a solid material) having two different kinds of functional groups, has been studied to reveal the reactivity of the compounds. The reaction has been analyzed by the A″-McKay plot method and the rate constants (k) for each group have been obtained. Comparison ofk leads to the following: (1) the effect of the NH2 group inp-aminophenol on the reactivity is greater than that in α-alanine, and (2) the reactivity of compounds having two different kinds of functional groups can be analyzed by the A″-McKay plot method only.

Effect of Anions in Ammonium Salts on the Reactivity of the Salts in Hydrogen-Isotope Exchange Reaction

Effect of Anions in Ammonium Salts on the Reactivity of the Salts in Hydrogen-Isotope Exchange Reaction

Comparison of the Reactivity of the Materials Having Two Different Kinds of Functional Groups by Applying Hydrogen-Isotope Exchange Reaction

Article Comparison of the Reactivity of the Materials Having Two Different Kinds of Functional Groups by Applying Hydrogen-Isotope Exchange Reaction was published on February 1, 1995 in the journal Radiochimica Acta (volume 68, issue 2).

Aromatic Hydrogen Isotope Exchange Reactions Catalyzed by Iridium Complexes in Aqueous Solution

Sodium hexachloroiridate (III) and sodium hexachloroiridate (IV) have been used as homogeneous catalysts for hydrogen isotope exchange between benzenoid compounds and water. The ideal solvent consisted of 50 mole % acetic acid/water, and the optimum temperature was found to be 160°C. Under these conditions the rate of incorporation of deuterium into benzene was significant (typically 15% D in 6 h), and reduction to iridium metal was minimized. The active catalytic species was identified as a solvated iridium(III) species, which is also postulated to be the active catalyst in solutions containing hexachloroiridate (IV). The kinetics of exchange in benzene catalysed by sodium hexachloroiridate (III) were elucidated, and found to be more complex than for the corresponding sodium tetrachloroplatinate (II) catalysed exchange, in that a two-term rate dependence was found for catalyst concentration and the reaction was inversely dependent on hydrogen ion concentration. The reaction was found to be independent of chloride ion concentration, this confirming that the active catalyst is a solvated species. Isotopic labelling in all compounds was confined to the aromatic ring, and most substituted benzenes exhibited deactivation of the ortho positions, indicating that a dissociative π-complex exchange mechanism was operating. This was confirmed by exchange into naphthalene, where it was found that labelling was predominantly in the β position. Facile exchange into nitrobenzene provided good evidence of homogeneous catalysis, and not catalysis by precipitated metal.

Adsorption characteristics of water vapor on Li 2ZrO 3

Lithium metazirconate (Li 2ZrO 3) is one of the probable candidates for the tritium breeding material because of its potential to give a fair tritium breeding ratio, stability at high temperature and stability in atmosphere containing water vapor. Investigation of the adsorption performances of water vapor on Li 2ZrO 3 is important for optimization of the way to recover bred tritium from Li 2ZrO 3, for estimation of tritium inventory in the breeding blanket and for quantification of the hydrogen isotope exchange reaction. The amount of water vapor captured on Li 2ZrO 3 was studied in the temperature range of 393–1073 K using the breakthrough method, and adsorption isobars and isotherms of water vapor on Li 2ZrO 3 were proposed based on the data obtained. The water capture phenomenon was attributed to the dissociative adsorption, and the apparent heat of adsorption was determined to be 10.7 kJ/mol. The tritium inventory due to sorption for Li 2ZrO 3 was compared with those for Li 20, LiA1O 2 and Li 4SiO 4. Furthermore, the tritium inventory in the blanket due to sorption was compared with that due to diffusion in the crystal grain.

Heterogeneous palladium‐catalyzed exchange labelling of representative organic compounds with tritium gas

AbstractA range of organic substrates was successfully exchanged with tritium gas using NaBH4‐reduced palladium oxide or chloride as catalyst. Exchange conditions involved a reaction temperature of 100 °C, a reaction time of 3 days, and products were analyzed by radio‐gas chromatography and 3H NMR spectroscopy. Both aromatic and aliphatic compounds underwent exchange, 18 of the 22 substrates incorporated > 35% of the available tritium, and most products showed high radiochemical purity. 3H NMR analyses showed that both alkanes and the alkyl chains of alkylbenzenes were rapidly and evenly labelled. Some aromatic compounds showed general ring exchange while others showed high specificity. These results for bulk palladium catalyst are strikingly different from those obtained with bulk platinum and supported palladium catalysts. The results are discussed in terms of currently accepted mechanisms of heterogeneous metal catalyzed hydrogen isotope exchange reactions.

Deactivation of a Hydrophobic Pt/SDBC Catalyst by Nitrogen Compounds for Hydrogen Isotopic Exchange Reaction.

水素同位体分離に用いられる疎水性Pt触媒の活性に対する硝酸, 硝酸塩および酸化窒素などの不純物の影響を評価するために, これらの窒素化合物を反応物に混入して同位体交換反応速度の経時変化を測定し, 触媒活性サイトの収支に基づいて活性劣化機構を検討した.その結果, HNO3は可逆的な被毒を示し, 硝酸被毒による触媒活性劣化速度はZeldovich速度式により解析することができた. Sr (NO3) 2のような中性の硝酸塩は触媒活性に殆ど影響せず, ZrO (NO3) 2のような加水分解により酸性を呈する硝酸塩はHNO3と類似な被毒挙動を示した. また, NO, NO2, NH3は何れも触媒を被毒せず, 逆にNOまたはNO2による H2/HDO 間の交換反応の促進効果が認められた. これはNO, NO2とH2間の発熱反応に伴う触媒表面の局部的な温度上昇に基づくものと推察された.

Comparison of the reactivity of ammonium halides using hydrogen-isotope exchange reaction in a gas-solid system

In order to reveal the behavior of the hydrogen atoms in an ammonium salt, the hydrogen-isotope exchange reaction between each of the three ammonium halides and tritiated water vapor was followed at 50–80°C. Analyzing the data obtained by theA″-McKay plot method, the following has been quantitatively clarified: both the reactivity of an ammonium halide and the temperature dependence of its reactivity increase when the electronegativity of the halogen element in the ammonium halide is larger.

Comparison of toluenethiols in reactivity using hydrogen isotope exchange reaction in a liquid-solid system

In order to reveal the reactivity of toluenethiols, the hydrogen isotope exchange reaction between one of three toluenethiols (o−,m−, andp−) and poly (vinyl alcohol) labeled with tritium was observed at 50 ≈ 90°C. The reaction was analyzed with both the data obtained and theA″-McKay plot method, and the following has been quantitatively clarified: (1) the reactivity order of toluenethiols is (o−>(m−)>(p−); (2) the temperature dependences of the reactivity of toluenethiols are nearly equal; (3) the reactivity of benzenethiol is considerably decreased by the CH3 group bonded to the ortho position.

Hydrogen isotope exchange reaction rates: Origin of water in the inner solar system

Rate constants for hydrogen isotope exchange between molecular hydrogen and water ( k( T) H 2- HDO ) and hydrogen and methane ( k( T) H 2- CH 3 D ) have been determined experimentally. The temperature dependence of the constants can be expressed by: with k( T) in cm 3/sec. Catalytic effects on charcoal, silica, phyllosilicates, and iron were found to be negligible. A model describing the evolution (with time) of the hydrogen isotopic composition of water in the solar nebula is proposed: while the temperature is decreasing in the gas, isotope exchange between H 2 and H 2O yields a deuterium enrichment in water. Using Cameron's numerical models (1972, 1978, 1985) of the solar nebula, we show that the observed difference between the protosolar and the carbonaceous chondrite D/H ratios (i.e., between 30 and 150 10 −6, respectively) is well accounted for by our model, provided that (1) water was accreted as ice at a temperature of ≤ 160 K. and (2) the hydrogen pressure was higher than 10 −5 atm somewhere between 1 and 3 AU. In such conditions, the calculations show that meteoritic phyllosilicates did not form in the gas phase, by reactions between water vapour and silicate grains, but by the subsequent circulation of liquid water, originally condensed as ice. Water on Earth ( D/ H = 155 · 10 −6) also results from such a cold nebula chemistry.

Tritiation of organic compounds by polymer‐supported acid catalysts

AbstractA range of organic compounds have been tritiated (and in some cases deuteriated) via hydrogen isotope exchange reactions using polymer supported acid catalysts. The extent and regiospecificity of labeling were investigated as a function of substrate and catalyst type. Although all the catalysts were found to be active in the tritiation of both aromatic and heterocyclic compounds, there was clear evidence that the extent of hydrogen isotope exchange was influenced by the nature of the polymer support matrix.

Diffusion Model of Solid-State Catalytic Hydrogen Isotope Exchange-Isotopomer Formation Kinetics and Reaction Mechanism

Using the diffusion model previously proposed for solid-state catalytic hydrogenation, it has been possible to show that for a hydrogen isotope exchange reaction resulting in the formation of two or more isotopomers the presence of spillover deuterium (or tritium) gradient in the organic phase induces qualitative alterations in the shape of the kinetic curves which can be used as a criterion of reaction mechanism. For gradient-controlled kinetics the shape of the time dependence plot of the isotopomer ratio Q RDD /Q RHD must be convex, whereas for uniform concentration distribution this function must be concave. An experimental study of the kinetics of isotopomer formation in the solid-state metal-catalyzed deuteration of glycine has been undertaken, and the results are consistent with gradient-controlled kinetics

Adsorption characteristics of water vapor on Li4SiO4

Lithium orthosilicate (Li4SiO4) is one of the probable candidates for tritium breeding material because of its potential to give a fair tritium breeding ratio, stability at high temperature and stability in atmosphere containing water vapor. Investigation of the adsorption performances of water vapor on Li4SiO4 is important for optimization of the way to recover bred tritium from Li4SiO4, for estimation of tritium inventory in the breeding blanket and for quantification of the hydrogen isotope exchange reaction. The amount of water vapor captured on Li4SiO4 was studied in the temperature range of 393–1073 K using the breakthrough method, and adsorption isobar and isotherm of water vapor on Li4SiO4 were proposed based on the data obtained. The water capture phenomenon was attributed to the dissociative adsorption, and the apparent activation energy was determined to be 13.8 kJ/mol. The tritium inventory by sorption for Li4SiO4 was compared with that for Li2O and LiAlO2.

Reactant Correlation Effects Study of Hydrogen Isotope Exchange Reaction on Supported Metal Catalysts

ABSTRACTNon-classical results due to reactant correlation effects have been observed in the study of Monte Carlo simulations of the A2 + B2 → 2AB reaction. These simulation results, interpreted by the Pair Density Analysis method and the experimental kinetic studies, may provide an explanation of the early time anomalous kinetic behavior of the catalytic hydrogen isotope exchange reaction exhibited for surface-diffusion limited conditions on alumina supported platinum islands.