Kinetic studies on the isotopic exchange of calcium ion and calcium carbonate

The heterogeneous exchange reaction of calcium carbonate in calcium chloride solution has been studied using ⁴⁵Ca as a tracer. The results of this study indicate that the rate is controlled by the surface reaction at the solid-liquid interface. It is found that the exchange rate increases as CaCl₂ concentration decreases for a fixed mole ratio of the exchange ion on the solid surface and in the solution. The activation energy is calculated to be 8·45 kcal/mole. The results show that the longer the solid is immersed in CaCO₃ saturated water, the higher the rate constant is obtained. The rate constant is also affected by the condition of the calcium carbonate preparation.     

Isotope effects in the hydrogen exchange reaction

The PODSs of the H₃ system and its isotopic derivatives are used for computing exact adiabatic barriers. We find good agreement with experimentally measured ground and vibrationally excited activation energies. The theoretical results should stimulate further measurements of activation energies of vibrationally excited species.     

Kinetic isotope effect in hydrogen isotope exchange between water and phosphines

The kinetic parameters of the tritium exchange between^*H₂O(^*D₂O) and (CH₃)₂PH in the gas phase and between^*H₂O(^*D₂O) and (C₆H₅)₂PH in liquid were measured. Both reactions appeared to be heterogeneous ones. The^*HH/^*DD kinetic isotope effects were estimated and compared with the results of exchange between methanol and phosphines. The differences in isotope effects are explained by the change of the symmetry of the four center cyclic transition complex resulting from the various type of solvation of this complex.     

Basic isotopic hydrogen exchange of heteroaromatic compounds (review)

Research on basic isotopic hydrogen exchange of the methyl groups and aromatic ring CH bonds in various classes of five- and six-membered heterocyclic compounds is examined. Principal attention is directed to the problem of the applicability of correlation and quantumchemical approaches to the establishment of the interrelationship between CH acidity and the peculiarities of the electronic structures of the molecules. The effect of a solvent on the change in the kinetic characteristics of the deuterium exchange of nitrogen-containing heterocycles is discussed.     

Kinetic solvent effects on hydrogen abstraction reactions

Kinetic solvent effects on hydrogen abstractions, namely, acceleration in nonpolar solvents, have been presumed to be restricted to O-H hydrogen donors. We demonstrate that also abstractions from C-H and even Sn-H bonds by cumyloxyl radicals and n,pi*-excited 2,3-diazabicyclo[2.2.2]oct-2-ene are fastest in the gas phase and nonpolar solvents but slowest in acetonitrile. Accordingly, solvent effects on hydrogen abstractions are more general, presumably due to stabilization of the reactive oxygen or nitrogen species in polar solvents.     

Peculiarities of the isotopic exchange of the hydrogen of the hydroxyl groups of metal-zeolite catalysts

Conclusions The hydrogen of the hydroxyl groups of HY zeolite, existing in a mechanical mixture with the catalyst 0.5% Pt-NaY, is exchanged with deuterium at room temperature. The rate of the reaction of isotopic exchange is controlled by the migration of D₂, activated on platinum.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2670–2673, December, 1975.     

Protophilic isotopic hydrogen exchange of 1-ferrocenyl-2-(nitrophenyl)ethylenes

cis-1-Ferrocenyl-2-(4-nitrophenyl)ethylene enters into the protium/deuterium exchange in basic medium at the expense of hydrogens of the phenyl ring, at ortho positions in respect of the nitro group. The homoaromatic analogue, 4-nitrostilbene, under the same conditions, undergoes isotopic exchange occurring exclusively at the vinylic CH fragment attached to the nitrophenyl group. The difference is eliminated as a result of the shift of the nitro group from position 4 into position 2 of the phenyl ring: cis-1-ferrocenyl-2-(2-nitrophenyl)ethylene enters into H⁺/D⁺ exchange in the same manner as 4-nitrostilbene. Correspondence to: Professor Z.V. Todres.     

QCT study of isotopic effects in H + HBr abstraction and exchange reactions

The method of quasi-classical trajectories on an LEPS hypersurface was used for studying the influence of the exchange of one or both of the hydrogen atoms for deuterium in the reaction H¹ + H²Br. As expected, the reaction cross sections of the exchange and abstraction reactions were found to increase if H¹ was replaced by D and decrease if H² was replaced by deuterium. A similar change in the reaction cross sections have also been observed for vibrationally excited reactants. The distribution of vibrational (rotational) energy is related to the ω_e (B_e) values of the respective reactants and products.     

Kinetic isotope effect during acid hydrogen exchange in σ-benzyl-π-cyclopentadienyliron dicarbonyl

Conclusions The kinetic isotope effect K_D/K_T was measured during acid hydrogen exchange in -C₅H₅-(CO)₂Fe--CH₂C₆H₅. The obtained K_D/K_T value testifies in support of the generality of the mechanisms of hydrogen exchange in the benzene ring of this complex and in other derivatives of the benzene series.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 221–222, January, 1979.     

Kinetic study of the isotopic exchange of Na+ and Zn2+ ions on iron and chromium titanates

Iron(III) (FeTi) and chromium (III) titanates (CrTi) were prepared as cation exchange materials in a granular form. The rate of the isotopic exchange of Na⁺/*Na⁺ and Zn²⁺/*Zn²⁺ between aqueous solution and iron(III) and chromium(III) titanates in Na⁺ or Zn²⁺form has been carried out radiometrically in the 25-60 °C temperature range. The exchange rate is controlled by a particle diffusion mechanism and experimental and theoretical approaches have been used to obtain the rate of diffusion through the spherical particles of the exchangers. The values of self diffusion () of Na⁺ and Zn²⁺ ions were measured at different operation conditions, particle size, reaction temperatures and drying temperatures of the matrix. The values of kinetic and thermodynamic parameters were calculated and their significance discussed. This revised version was published online in July 2006 with corrections to the Cover Date.