Hydrogen isotope exchange reaction rate in tritium and methane mixed gas

Hydrogen isotope exchange reaction rate in tritium and methane mixed gas, as induced by tritium decay and beta radiation, has been experimentally measured. Initially T₂ gas was filled to 40 kPa and 20 kPa of CH₄ gas was added. The mixed gas spectrum was analyzed periodically by laser Raman spectrometry. The first order HT and H₂ formation rates and T₂ and CH₄ decay rates by hydrogen isotope exchange reaction were observed between 2.9·10^–3 h^–1 and 4.8·10^–3 h^–1. Although the estimated hydrogen isotope exchange reaction rate was 1/20–1/10 slower than the rate of H₂+T₂ mixed gases, it was nearly equivalent to the ion formation rate by tritium beta radiation. This suggested that isotopic hydrogen radicals formed via ionization would disappear in the presence of methane.     

Synthesis of polyester by means of polycondensation of diol ester and dicarboxylic acid ester through ester–ester exchange reaction

Based on our finding that the ester-ester exchange reaction between butyl benzoate and ethyl 4-phenylbenzoate in the presence of a metal alkoxide is faster than the ester-alcohol exchange reaction of butyl benzoate and ethanol, we investigated the synthesis of polyester through ester-ester exchange reaction under various conditions. The polycondensation of diol formate and methyl dicarboxylate in the presence of a catalytic amount of potassium tert-butoxide (^tBuOK) in diglyme at 120 °C under reduced pressure (90–100 Torr) afforded high-molecular-weight polyesters. Methyl dicarboxylate containing an amino group could be used for this polycondensation, although the corresponding diacid chloride containing an amino group was not isolable. The ester-ester exchange reaction could proceed even at the polyester backbone, and the reaction of poly(1,12-dodecamethylene isophthalate) ( PEs ₁ ) with poly(ε-caprolactone) (PCL) in the presence of ^tBuOK at 140 °C afforded a copolymer PEs ₁ -stat-PCL, the structure of which was confirmed by ¹³C NMR spectroscopy and DSC thermal analysis. A similar copolymer was also obtained by the polycondensation of dodecane-1,12-diol formate and dimethyl isophthalate in the presence of PCL and ^tBuOK at 120 °C under reduced pressure.     

Heterogeneous isotope exchange reaction between SnCl2 and SnO2·xH2O in HCl medium

Heterogeneous isotope exchange between hydrated stannic oxide and stannous chloride in 0.1M HCl solution has been studied as a function of the stannic oxide, stannous chloride, and chloride ion concentrations, and temperature. The exchange process is a second-order reaction, which is independent of the chloride ion concentration, with a mean rate constant, k, of 2.31 dm³ mol^–1·min^–1. The activation energy of the isotope exchange process was found to equal 3.62 kcal·mol^–1. Possible use of this system, SnCl₂/SnO₂·xH₂O, as basis for a¹¹³Sn-^113mIn generator is suggested.     

A study of ion exchange equilibrium for some uni-univalent and uni-divalent reaction systems using strongly basic anion exchange resin Indion-830 (Type 1)

A study of the thermodynamics of ion exchange equilibrium for uni-univalent Cl⁻/I⁻, Cl⁻/Br⁻ and uni-divalent Cl⁻/SO ₄ ²⁻ , Cl⁻/C₂O ₄ ²⁻ reaction systems was carried out using ion exchange resin Indion-830 (Type 1). The equilibrium constant K was calculated by taking into account the activity coefficients of ions both in solution and in the resin phase. For uni-univalent ion exchange reaction systems, the equilibrium constants K′ were also calculated from the mole fraction of ions in the resin phase. The K values calculated for uni-univalent and uni-divalent anion exchange reaction systems increased as the temperature grew, indicating the endothermic character of the exchange reactions with enthalpies of 38.2, 32.3, 7.6, and 11.4 kJ/mol, respectively. The article is published in the original.     

Studies on the rate of isotopic oxygen exchange between [Re(py)4O2]+ and solvent water

The rate of oxygen exchange between trans-[Re(py)₄O₂]⁺ and solvent water in pypyH⁺ buffer solution follows simple first-order kinetics and both oxygens are equivalent. The half-life for isotopic oxygen exchange is about 12 h at a pH of 5.0, 25°C, and [py] = 0.10 M. The observed rate constant for exchange increases with acidity, in the pH range 4 to 6, decreases with [py], and is nearly independent of ionic strength. A small but significant increase of k_obs occurs with increasing complex concentration. The rate of exchange follows the rate equation k_obs/2 = k₀ + k₁/[py] with k₀ = 1.4 × 10^?5(2) s^?1 and k₁ = 4.7 × 10^?7(1) M, s^?1 at 25°C. The activation parameters for the reaction at pH = 7.15 (predominately the k₀ term) are: ΔH* = +137.(1) kJ/M and ΔS* = +126.(1) J/MK. The pH effect and complex concentration effect are discussed in mechanistic terms. These results are compared to those found for [Re(en)₂O₂]⁺ and [Re(CN)₄O₂]^3?.     

Ligand exchange reaction of Zn(II)-acetylacetonate complex with 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonic acid

Ligand exchange reaction of Zn(II)-acetylacetonate complex (Zn-acac₂) with 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonic acid (H₂TPPS) has been investigated spectrophotometrically and radiometrically. The exchange reaction was observed by spectral change from H₂TPPS to Zn-TPPS or activity of⁶⁵Zn(acac)₂ extracted into the chloroform phase. The 2nd order rate constants (k ₂) for the exchange reaction at 70 °C and at pH 7.8 were found to be 32.8±2.3 and 31.2±3.2 M^–1·s^–1 from the spectrometric and radiotracer experiments, respectively. For the direct complexation of Zn(II) with H₂TPPS, a similar 2nd order rate constant (k=32.4±4.7 M^–1·s^–1) was obtained as that in the ligand exchange reaction. The activation energies (E) for the exchange and the formation of Zn-TPPS were found to be 69.3±0.2 and 69.4±0.2 kJ·mol^–1, respectively, in the temperature range from 40 to 70 °C.     

Oxygen surface exchange kinetics of erbia-stabilized bismuth oxide

The surface oxygen exchange kinetics of bismuth oxide stabilized with 25 mol% erbia (BE25) has been studied in the temperature and pO₂ ranges 773–1,023 K and 0.1–0.95 atm, respectively, using pulse-response ¹⁸O–¹⁶O isotope exchange measurements. The results indicate that BE25 exhibits a comparatively high exchange rate, which is rate determined by the dissociative adsorption of oxygen. Defect chemical considerations and the observed pO₂^1/2 p{{\hbox{O}}_2}^{1/2} dependence of the rate of dissociative oxygen adsorption suggest electron transfer to intermediate superoxide ions as the rate determining step in surface oxygen exchange on BE25.     

On amide exchange reaction of polymide precursor

The reaction of poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and oxydianiline (ODA) with 1-aminopyrene (APy) in solution as a model of amide exchange reaction between PAAs was studied in the temperature range of 0–60°C using viscometry and light-scattering (LS) measurements. The decrease in the weight-average molecular weight (M?_w) of PAA in N,N-dimethylacetamide (DMAc) solution with time and the acceleration of M?_w drop due to the increase in storage temperature or the addition of APy into PAA solution were observed. Apparent activation energies (E_a) for scission of PAA chains were similar: about 13 kcal/mol in PAA/DMAc and PAA/APy/DMAc, respectively. When stored at 60°C for a week, the number of scissions per polymer chain in PAA/DMAc is about 2, but is about 5 in PAA/DMAc with a large amount of APy. The result indicates that the M?_w drop accelerated by the addition of APy is attributed to amide exchange reaction between PAA Chains and monofunctional APy. It was concluded from the dependence of M?_w drop on Apy concentration that the exchange reaction between different PAA molecules during storage of PAA/PAA solution may scarcely occur under the conditions (storage time and temperature) used for preparation of PAA/PAA blends.     

Studies on14CO2 exchange reaction with p-fluorophenyl acetic acid and microsynthesis of carboxyl-14C labelled p-fluorophenyl acetic acid

The exchange reaction between¹⁴CO₂ and sodium salt of p-fluorophenyl acetic acid was found to proceed with greater than 50% isotope incorporation when salt to CO₂ ratio was 61. The carboxyl-C-14 labelled p-fluorophenyl acetic acid was isolated in a pure form using small chemical concentrations of radioactive¹⁴CO₂ of high specific activity /30 mCi/mmol/.     

Isotope exchange study of the e lectrophilic replacement reaction in a saturated carbon atom

Summary A study of the isotope exchange of the ethyl esters of -brommercuryarylacetic acids with²⁰³Hg Br₂ and 70% aqueous dioxane at 60°, made it possible to arrange the substituents in the following series in order of decreasing reaction rate: p-I, Br, Cl > p-F >H > o-CH₃ > p-CH₃> p-typet. C₄H₉.     

Study of temperature effect on uni-univalent and uni-bivalent ion exchange reaction

Ion exchange equilibrium constant (K) for Cl⁻/Br⁻ and Cl⁻/C₂O₄²⁻ system was studied at different temperatures from 30 to 45°C. For both uni-univalent and uni-bivalent exchange systems, the value of K increases with rise in temperature i.e., from 1.16 at 30°C to 2.95 at 45°C for Cl⁻/Br⁻ system and 19.5 at 30°C to 30.0 at 45°C for Cl⁻/C₂O₄²⁻ system indicating the endothermic ion exchange reaction. The difference in K values at the same temperature for the two was related to the ionic charge of exchangeable ions in the solution. The article is published in the original.     

Base-catalyzed hydrogen isotope exchange and the aqueous acidity of toluene

Measurements of hydrogen isotope exchange of toluene-α-d and -α-t in aqueous sodium hydroxide are reported for temperatures of 150–200°C. The reaction shows essentially no primary isotope effect. The rate extrapolated to 24°C is combined with the rate constant for reaction of benzyl anion with water obtained earlier by Bockrath and Dorfman⁸ to derive the aqueous pk_a, of toluene as 39.6 (per hydrogen basis).     

Kinetics of reaction between acetic acid and Ag2+ in nitric acid medium

The reaction kinetics between acetic acid and Ag²⁺ in nitric acid medium is studied by spectrophotometry. The effects of concentrations of acetic acid (HAc), H⁺, NO^?₃, and temperature on the reaction are investigated. The rate equation has been determined to be –dc(Ag²⁺)/dt = kc(Ag²⁺)c(HAc)c^?1(H⁺), where k = (610 ± 15) (mol/L)^?1 min^?1 with an activation energy of about (48. 8 ± 3.5) kJ mol^?1 when the reaction temperature is 25°C and the ionic strength is 4.0 mol L^?1. The reduction rate of Ag²⁺ increases with the increase in HAc concentration and/or temperature and the decrease in HNO₃ concentration. However, the effect of NO^?₃ concentrations within 0.5–2.5 mol L^?1 on the reaction rate is negligible. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 47–51, 2013     

Isotope exchange between alkaline earth metal hydroxide and HTO water in the equilibrium state

In order to reveal to what extent tritium (³H or T) can be incorporated into hydroxides, the isotope exchange reaction (OT-for-OH exchange reaction) between each alkaline earth metal hydroxide (M(OH)₂), where M means alkaline earth metal (M=Ca, Sr or Ba) and HTO water was observed homogeneously at 30 °C under equilibrium after mixing. Consequently, the followings were obtained: (1) a quantitative relation between the electronegativity of each M ion and the ability (of the M ion) incorporating OT^– into the M hydroxide can be found and the ability is small when the temperature is high, (2) the exchange rate for the OT-for-OH exchange reaction is small when the electronegativity of the M ion in the M hydroxide in great, (3) as for the dissociation of HTO water, it seems that fomula (HTOT⁺+OH^–) is more predominant than the fomula (HTOH⁺+OT^–) when the temperature is high and (4) the method used in this work is useful to estimate the reactivity of a certain alkaline material.     

Effect of tritium on hydrogen isotope exchange reaction in a heterogeneous system

In order to reveal the effect of tritium (³H or T) on hydrogen isotope exchange, the exchange reaction between a certain compound (solid or liquid) and a tritiated one (gas or solid) was observed in gas-solid or liquid-solid systems. The reaction was analyzed using the data obtained and theA-McKay plot method, and it has been quantitatively clarified that the effect of T on the reactivity of a material is changed with (1) the degree of polymerization of the material, (2) the kind of functional groups in the material, and (3) the reaction system.     

Investigation of electrophilic substitution at a saturated carbon atom by isotope exchange

Summary The isotope exchange between ethyl-bromomercuriphenylacetate and mercuric bromide, labeled with Hg²⁰³, is a bimolecular reaction of the type S_E2.     

Mechanism of isotope exchange reaction between methane and deuterium

The rate of CH₄ disappearance in a shock-heated CH₄:D₂:Ar = 9.70:9.86:80.44 mixture was monitored by coincidence absorption of the 2948 cm^?1 He-Ne laser line over the shockfront temperature range of 1900–2300K. Comparison with CH₄ pyrolysis results by means of computer simulations suggested that atom and free radical chains are responsible for the homogeneous D/H exchange reaction on CH₄. Additional simulations for the experimental conditions of previous single-pulse shock tube experiments led to the recognition of a high sensitivity of the exchange rate to trace amounts of hydrocarbon impurity and to the dissociation rate of CH₄.     

The proton exchange reaction between indene and the indenyl anion

The proton exchange reaction between the indenyl carbanion and its parent compound indene has been studied by NMR as a function of temperature. The rate of this bimolecular reaction is very low and has been found to be strongly dependent on the polarity of the solvent. In solvents like dimethoxyethane (? = 7·2) and diglyme the reaction becomes manifest in the NMR spectrum only at elevated temperatures (T > 150°C). In hexamethylphosphortriamide (? = 30) the rate is much greater and line broadening may be observable at room temperature. The reaction in this solvent is characterised by a frequency factor f = 7 × 10⁷ 1 mol^?1 s^?1, an activation enthalpy ΔH ≠ = 9·5 kcal mol^?1 and an entropy of activation ΔS≠ = ?23 e.u. The low reaction rate and its solvent dependence are briefly discussed.     

Nitrogen isotope exchange between nitric oxide and nitric acid

The rate of nitrogen isotope exchange between NO and HNO₃ has been measured as a function of nitric acid concentration of 1.5–4M·1^–1. The exchange rate law is shown to beR=k[HNO₃]²[N₂O₃] and the measured activation energy isE=67.78kJ ·M^–1 (16.2 kcal·M^–1). It is concluded that N₂O₃ participates in¹⁵N/¹⁴N exchange between NO and HNO₃ at nitric acid concentrations higher than 1.5M·1^–1.     

Study on ion exchange equilibrium for some uni-univalent and uni-divalent reaction systems using strongly basic anion-exchange resin Duolite A-113

The study on thermodynamics of ion exchange equilibrium for uni-univalent Cl⁻/I⁻, Cl⁻/Br⁻, and uni-divalent Cl⁻/SO₄²⁻, Cl⁻/C₂O₄²⁻ reaction systems was carried out using ion-exchange resin Duolite A-113. The equilibrium constant K was calculated by taking into account the activity coefficient of ions both in solution as well as in the resin phase. The K values calculated for uni-univalent and uni-divalent anion exchange reaction systems were observed to increase with rise in temperature, indicating the endothermic exchange reactions having enthalpy values of 17.21, 36.60, 19.50, 18.43 kJ/mol respectively.