Studies on the effect of the cation nature on the kinetics of the isotopic exchange reaction between chloride ion and O,O-diphenylphosphorochloridothionate in acetonitrile

Rate constants and activation parameters for the isotopic exchange reactions between (PhO)₂PSCl and M³⁶Cl (M = Me₄N⁺, Et₄N⁺, n-Bu₄N⁺, Et₃HN⁺, EtH₃N⁺, Li⁺) in acetonitrile were measured in order to find the effect of the cation nature onthe kinetics of the reaction. The rate constants measured for a range of concentrations of Et₃HN³⁶Cl, EtH₃N³⁶Cl, and Li³⁶Cl were analyzed using the Acree equation. The equivalent conductance of LiCl in acetonitrile was determined. The nature of the cation has no effect on the mechanism of the reaction. The cation changes only the experimental rate constant proportionally to the dissociation degree of the salt. Smaller values of the rate constant and smaller activation parameters ΔH? and ΔS? for the reaction with Li³⁶Cl indicate the existenceof the intermolecular interaction between lithium ions and O,O-diphenylphosphorochloridothionate.     

Kinetics of isotopic exchange between chloramine-B and radioactive chloride

The kinetics of chlorine isotope exchange between chloramine-B /CAB/ and chloride has been studied using ion-exchange separation and tracer technique. McKay's plot are linear. The exchange reaction is fast in acidic medium, very slow in neutral medium and does not take place in alkaline medium. In the acidic range the exchange is maximum at pH 3.3. The rate of exchange decreases at pH >3.3 and <3.3. The order with respect to CAB and chloride is unity. The order with respect to [H⁺] is unity at pH>5. Addition of neutral salt or parent compound has no effect on the rate of exchange. Activation energy and activation entropy for this exchange reaction have been calculated.     

离子交换纤维的交换动力学研究

本文研究了VS-1型强酸性阳离子交换纤维的交换动力学.在有限浴条件下,用放射性示踪法,研究了温度,搅拌速度,溶液浓度及pH 值对该离子交换纤维的异相同位素交换反应的影响.并推导出离子交换纤维的交换动力学方程,计算出不同条件下的粒内扩散系数D及液膜中的传输系数D/δ.从机理上明确了交换纤维的交换反应速率远比球形树脂快的原因     

Preparation of radioactive chloramine-B by isotopic exchange with radioactive chlorine

The exchange between chloramine-B and radioactive chlorine has been carried out in various media. The exchange is slow in strong acid and very weak acid media. Its maximum is at pH 3.3. There is no exchange in alkaline media. Optimum conditions for the preparation of radiochloramine-B with high specific activity are reported.     

The kinetics of the15N/14N isotopic exchange between nitric oxide and nitric acid

The rate of the¹⁵N/¹⁴N isotopic exchange between NO−HNO₃ at high nitric acid concentration (2–10M) have been measured. The experimental data were obtained by contacting nitric oxide at atmospheric pressure with nitric acid solution labelled with¹⁵N, in a glass contactor.     

Effect of chloride ion on the kinetics and mechanism of the reaction between chlorite ion and hypochlorous acid

The effect of chloride ion on the chlorine dioxide formation in the ClO 2 (-)-HOCl reaction was studied by following .ClO 2 concentration spectrophotometrically at pH 5-6 in 0.5 M sodium acetate. On the basis of the earlier experimental data collected without initially added chloride and on new experiments, the earlier kinetic model was modified and extended to interpret the two series of experiments together. It was found that the chloride ion significantly increases the initial rate of .ClO 2 formation. At the same time, the .ClO 2 yield is increased in HOCl but decreased in ClO 2 (-) excess by the increase of the chloride ion concentration. The two-step hydrolysis of dissolved chlorine through Cl 2 + H 2O left harpoon over right harpoon Cl 2OH (-) + H (+) and Cl 2OH (-) left harpoon over right harpoon HOCl + Cl (-) and the increased reactivity of Cl 2OH (-) compared to HOCl are proposed to explain these phenomena. It is reinforced that the hydrolysis of the transient Cl 2O 2 takes place through a HOCl-catalyzed step instead of the spontaneous hydrolysis. A seven-step kinetic model with six rate parameters (constants and/or ratio of constants) is proposed on the basis of the rigorous least-squares fitting of the parameters simultaneously to 129 absorbance versus time curves measured up to approximately 90% conversion. The advantage of this method of evaluation is briefly outlined.     

H/D isotopic exchange between water molecules at ice surfaces

H/D isotopic exchange between H(2)O and D(2)O molecules was studied at the surface of ice films at 90-140 K by the technique of Cs(+) reactive ion scattering. Ice films were deposited on a Ru(0001) substrate in different compositions of H(2)O and D(2)O and in various structures to study the kinetics of isotopic exchange. H/D exchange was very slow on an ice film at 95-100 K, even when H(2)O and D(2)O were uniformly mixed in the film. At 140 K, H/D exchange occurred in a time scale of several minutes on the uniform mixture film. Kinetic measurement gave the rate coefficient for the exchange reaction, k(140 K)=1.6(+/-0.3) x 10(-19) cm(2) molecule(-1) s(-1) and k(100 K)< or =5.7(+/-0.5) x 10(-21) cm(2) molecule(-1) s(-1) and the Arrhenius activation energy, E(a)> or =9.8 kJ mol(-1). Addition of HCl on the film to provide excess protons greatly accelerated the isotopic exchange reaction such that it went to completion very quickly at the surface. The rapid reaction, however, was confined within the first bilayer (BL) of the surface and did not readily propagate to the underlying sublayer. The isotopic exchange in the vertical direction was almost completely blocked at 95 K, and it slowly occurred only to a depth of 3 BLs from the surface at 140 K. Thus, the proton transfer was highly directional. The lateral proton transfer at the surface was attributed to the increased mobility of protonic defects at the molecularly disordered and activated surface. The slow, vertical proton transfer was probably assisted by self-diffusion of water molecules.     

Oxygen isotopic exchange between carbon dioxide and some molybdates or rare-earth elements

The oxygen exchange between C¹⁸O₂ and the normal molybdates of cerium, lanthanum, praseodymium and neodymium has been studied within the temperature interval 300–500°C. The specific rates and activation energies of exchange for these molybdates were found to have similar values. The reactivity of oxygen in the molybdates studied was shown to be close to the reactivity of oxygen in MoO₃     

Study of kinetics,equilibrium and isotope exchange in ion exchange systems. II

The kinetics of isotope exchange in the²³⁸U(VI)-²³³U(VI)-strongly acidic cation exchanger Ostion KS system was studied in the temperature range 275–307K and for total uranium concentration 2.94·10⁻⁴–1.75·10⁻² mol·l⁻¹ in UO₂(NO₃)₂ solution. The experimental results were evaluated by means of the “two-film mass-transfer model” and by the use of Fick's diffusion equations which have been proved more suitable for the system studied than McKay's equation. The influence of the temperature was evaluated using the Arrhenius equation. The diffusion character of the process follows also from the value of the activation energy (15.12 kJ·mol⁻¹). In comparison with the UO ₂ ²⁺ ↔H⁺ ion exchange⁶ the isotope exchange studied is faster and less dependent on temperature (the activation energy is substantially lower).     

Kinetics of chlorine isotope exchange reaction between sodium chloride-36 and triphenyltin chloride in mixed solvents

Fluorine is an important trace element for life and human well-being. Food, in general, provides about 40 percent of the fluorine intake in the human body. In order to measure fluorine levels in human diet samples, Instrumental Neutron Activation Analysis (INAA) and Proton Induced Gamma-ray Emission (PIGE) analysis were used. Reactions¹⁹F(n,)²⁰F and¹⁹F(n, p)¹⁹O were employed for determination of the fluorine concentration using a reactor neutron spectrum and epithermal neutrons. Corrections were made for the sodium matrix interference caused by the²³Na(n, )²⁰F threshold reaction in the case of reactor neutron cyclic activation analysis and for the oxygen interference via¹⁸O(n, )¹⁹O reaction when using the epithermal cyclic NAA method. The fluorine content of the diet samples was also determined by PIGE analysis making use of the resonance reaction¹⁹F(p, )¹⁶O at 872 keV. Cyclic Neutron Activation Analysis (CNAA) when combined with mass fractionation was found to be the most suitable for determination of low concentration of fluorine, through the¹⁹F(n, )²⁰F reaction with a detection limit of 2.2 ppm in Bowen's Kale elemental standard.     

Kinetics of chlorine isotope exchange reaction between sodium chloride-36 and triphenyltin chloride in mixed solvents

Isotope exchange reaction between NaCl-36 and triphenyltin chloride in dioxane-water (8020% w/w) and ethanol-water (9010% w/w) mixed solvents has been studied at 25, 35 and 50 °C. The exchange reaction was found to proceed via a bimolecular S_N2, limiting mechanism with reaction rates depending on the solvent used. Inhibition of the exchange in ethanol-water is probably due to solvation of chloride ion through hydrogen bond formation. The rate laws for the exchange reactions are: R_e=3.24×10⁹ e^–65550/RT [Rh₃SnCl] [NaCl] in dioxanewater and R_e=6.61×10⁸ e^–69600/RT [Ph₃SnCl] [NaCl] in ethanol-water, where is the degree of dissociation of NaCl and R_e is the rate of exchange in mol l^–1 s^–1. The activation parameters H^*, S^* and G^* are reported.     

Substitution kinetics of chelate complexes as studied by isotopic exchange

The fact that isotopic exchange reactions take place at chemical equilibirum makes this type of reaction useful for kinetic studies. In the case of chelate complexes [M(chel)_n] isotopic exchange reactions can be classified as metal exchange reactions. [M(chel)_n]+^*M⇆[^*M(chel)_n]+M and ligand exchange reactions [M(chel)_n]+^*chel⇆[M(chel)_n−1 ^*chel]+chel The literature on type (a) and type (b) reactions of mainly transition metal complexes is reviewed with respect to the kinetic information obtained. The value and the limitations of isotopic exchange studies as a kinetic technique are discussed.     

Diffusion kinetics of the ion exchange of benzocaine on sulfocationites

The theory of the ion exchange kinetics on strong acid cationites with the participation of weak electrolytes is discussed. The kinetics of desorption of benzocaine in the protonated and molecular forms from strong acid cationites, sulfonated polycalixarene, and KU-23 30/100 sulfocationite, is studied experimentally. It is shown that the flow of protonated benzocaine from cationite upon desorption proceeding by the ion-exchange mechanism is more intense than upon desorption of nonionized benzocaine molecules. It is established that the diffusion coefficient of benzocaine cations is (1.21 ± 0.23) × 10^?12 m²/s in KU-23 30/100 sulfocation and (0.65 ± 0.06) × 10^?13 m²/s in sulfonated polycalixarene, while the diffusion coefficient of benzocaine molecules is (0.65 ± 0.15) × 10^?14 m²/s in sulfonated polycalixarene.     

The kinetics of tritium-hydrogen exchange between xanthine,theophylline,caffeine and water

Isotopic hydrogen exchange at C-8 of xanthine, theophylline and caffeine in water has been studied at several temperatures and constant pH. The rates of detritiation of these compounds have been determined over a pH range at constant temperature. The rate-pH profiles for theophylline and caffeine are interpreted in terms of rate determining attack by hydroxide ion on protonated substrate. For caffeine and xanthine at high pH an additional mechanism involving hydroxide catalysed exchange of the neutral compound is suggested.     

Study of kinetics,equilibrium and isotope exchange in ion exchanger systems

An automatic, rapid combustion method has been developed for the determination of tritium and¹⁴C in singly or doubly labelled organic materials by liquid scintillation counting. The sample is burned in a stream of oxygen. The water formed and its tritium content are retained from the gas stream in an absorber containing a small amount of diethyleneglycol monoethyl ether. Radioactive carbon dioxide, if included in the combustion products, is transferred into 3-methoxypropylamine. The final solutions ready for counting are obtained in less than three minutes. Quantitative collection recoveries for both tritium and¹⁴C are achieved and no cross-contamination occurs.     

The kinetics of cation exchange reaction of europium propylenediaminetetraacetate with ytterbium ion

The kinetics of cation exchange reaction of Eu(III) propylenediaminetetraacetate with Yb(III) has been studied in an aqueous solution by the polarographic procedure. The measurements were made at 25°C and at an ionic strength of 0.5 M KCl. The dissociation of the europium complex has been found to be catalyzed by hydrogen ions. The influences of the inductive effect and the steric hindrance of a C-methyl group on the ethylene of PDTA are discussed by comparing it to analogous EDTA and CyDTA system.