Rate constants for addition of triethylsilyl radicals to spin traps

Conclusions The rate constants for the addition of triethylsilyl radicals to -phenyl-N-tert-butylnitrone (k_add=(11±5)·10⁶ liter/mole·sec) and 2,4,6-tri-tert-butylnitrosobenzene (k_add= (1.5±0.3)·10⁹ liter/mole·sec) at 20°C were determined by the EPR method.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 938–941, April, 1984.     

Pulse radiolysis studies of the quenching processes of Xe* excited atoms

The time resolved fluorescence of Xe ₂ ^* excimers in pure xenon and Xe-M (M=H₂,N₂,N₂O,CO₂) mixtures has been observed. The formation rate constant of Xe ₂ ^* , k₂=(1.1±0.1)·10^–30 cm⁶/s and the lifetime of the excimer precursors, ₀(100 ± 40) ns were evaluated. The quenching rate coefficients of Xe(6p) states by M have been found to be in the range of (0.5–1.3)·10^–9 cm³/s. The basic parameters and operating characteristics of the newly constructed pulse radiolysis set up based on SINUS-5 electron accelerator are also presented.     

A study by pulse radiolysis of the radiation-chemical transformation of aqueous solutions of hydrazine in the presence of oxygen

It is shown by pulse radiolysis that in aqueous solutions of hydrazine containing oxygen the radical N₂H₃ reduces oxygen to O₂ ^– at pH > 7 (k 3·10⁹ dm³· mole^–1·sec^–1), while this reaction does not occur for the protonated form N₂H₄ ⁺ at pH < 7 (k, 5·10⁶ dm³·mole^–1·sec^–1). The rate constants for the disappearance of O₂ ^– have been determined in the pH range from 4 to 12. Rate constants have been calculated for the reaction of O^– with N₂H₄ [k=(1.6 ±0.2)·10⁹ dm³·mole^–1·sec^–1] and of O₃with N₂H₄ [k=(1.2 ±0.2)·10⁶ dm³· mole^–1·sec^–1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 341–345, February, 1991.     

The aggregation in dodecyltrimethylammonium hydroxide aqueous solutions

The aggregation of dodecyltrimethylammonium hydroxide (DTAOH) aqueous solutions has been studied by several methods. It is stepwise and four critical points were found. AtC _T=(2.51±0.10)×10^–4 mol · dm^–3 the surface excess becomes zero, atC _T=(1.300±0.041)×10^–3 mol · dm^–3 small aggregates from, which grow with concentration. AtC _T=(1.108±0.010)×10^–2 mol · dm^–3 true micelles form (CMC) and at (3.02±0.28)×10^–2 mol · dm^–3 the structure of micelles probably changes affecting their properties. The DTAOH micelles are highly ionized (=0.8) at the CMC, and decreases to reach very small values when the total concentration increases.     

The kinetics of the oxidation-reduction reaction between uranium(VI) and titanium(III) in HCl solution

The oxidation-reduction reaction between U(VI) and Ti(III) in HCl solution was studied spectrophotometrically. The reaction is second-order at all concentrations of reactants, HCl, ferrous chloride and mannitol used in this work. In 5M HCl the rate constantk increases with increasing Ti(III) concentration, whereas it decreases with increasing U(VI) concentration, with increasing HCl concentration from 1.00M to 7.17M and increases thereafter from 7.17M to 11.79M. The addition of mannitol causes a consistent decrease in the rate of reaction, whereas ferrous chloride has no effect. The activation energy for this oxidation-reduction reaction was 47.90±0.11 kJ·mol^–1. The values of H , G and S were 45.40±0.11 kJ·mol^–1, 72.50±0.17 kJ·mol^–1 and –91.10±0.22J·k^–1·mol^–1, respectively. The mode of reaction is discussed in the light of kinetic results.     

The use of3H- and14C-labelled tyrosines and product analysis to measure the mono- to diiodination rate constant ratio for iodination by molecular iodine and chloramine-T/I−

The observed rate constant ratio,^k ₁obs/^k ₂ obs, for the sequential iodination of L-tyrosine was determined in the concentration range 1.84·10^–3 to 1·10^–6 M by the use of³H- and¹⁴C-labels and product analysis by HPLC. Iodinations by chloramine-T/I^– gave (^k ₁ obs/^k ₂ obs)· values (=the pH dependent factor) in the range 72±3 to 55±2 and molecular iodine iodinations gave values in the range 64±5 to 39±10. It is concluded that molecular iodine is the iodinating species in both cases.     

Kinetic Spectrophotometric Determination of Chromium (VI) by Oxidation of Sodium Pyrogallol-5-sulphonate by Hydrogen Peroxide

Summary. A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437nm within 1min after addition of H₂O₂. The optimum reaction conditions are PS (1.32·10^–3mol·dm^–3), H₂O₂ (0.32mol·dm^–3), HClO₄ (2.6·10^–3mol·dm^–3) at 25°C. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25ng·cm^–3 and a detection limit of 0.024ng·cm^–3, based on the 3 criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples.     

Kinetics of the thermal and photochemical decomposition of aquapentacyanoferrate(III) in aqueous solution

Summary The kinetics of the thermal and photochemical decomposition of aquapentacyanoferrate(III) ion in aqueous solution in the presence ofo-phenanthroline was studied spectrophotometrically. The first-order rate constant (k ) at 30° C [I=1 M(NaCl)] for the thermal reaction is (1.49±0.13)×10^–6 s^–1 with H =(158±7)kJ mol^–1 and S=(42±4) JK^–1 mol^–1. The initial quantum yield for the photochemical reaction at pH=7 is independent of the light intensity and is (1.49±0.33)×10^–2 mol einstein^–1.A communication on this subject was presented at the XVI Latinamerican Chemistry Congress held at Rio de Janeiro. Brasil, October 14–20, 1984.     

Kinetic Spectrophotometric Determination of Chromium (VI) by Oxidation of Sodium Pyrogallol-5-sulphonate by Hydrogen Peroxide

A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437nm within 1min after addition of H₂O₂. The optimum reaction conditions are PS (1.32·10^–3mol·dm^–3), H₂O₂ (0.32mol·dm^–3), HClO₄ (2.6·10^–3mol·dm^–3) at 25°C. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25ng·cm^–3 and a detection limit of 0.024ng·cm^–3, based on the 3 criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples.     

Separation of cerium and europium by extraction with tributyl phosphate and di(2-ethylhexyl)phosphoric acid in n-alkane from nitrate solutions

The following extraction systems have been studied: (Ce³⁺+Eu³⁺) (NO₃)-(EDTA, DCTA, DTPA)/TBP in n-alkane and (Ce³⁺+Eu³⁺)(NO₃)/DEHPA in n-alkane at concentration ratios as follows: [Ce³⁺]=trace –1 mol·dm^–3, [Eu³⁺]=trace –0.1 mol·dm^–3. [TBP]=(0.183–1.83) mol·dm^–3, [DEHPA]=(5·10^–3–0.1) mol·dm^–3, [(H, Na)NO₃]=(0.1–6) mol·dm^–3, [Eu³⁺]: [EDTA, DCTA, DTPA]=11–110. The initial concentration of Eu³⁺ in aqueous phase in the extraction system containing a mixture of Ce³⁺ and Eu³⁺ was trace, 1% and 10% compared with the Ce³⁺ concentration. The distribution of the elements between the phases was observed radiometrically using¹⁴¹Ce,¹⁵²Eu and¹⁵⁴Eu. The results are documented by the distribution ratios D_Ce, D_Eu and separation factor =D_Eu/D_Ce as functions of variable parameters of the systems.     

Kinetics and mechanism of the reaction between bis 4-(2-pyridylazo) resorcinol ferrate(II) complex and cyanide ion

Summary Cyanide ion reacts with [Fe(Par)₂]^2–,i.e. Par=4-(2-pyridylazo)resorcinol to form a 113 mixed cyanocomplex. The reaction has been studied spectrophotometrically at 720 nm _max, pH=11.5±0.02, and I=0.1 M (NaClO₄) at 25±0.1°C. The order with respect to cyanide varies from one to two at high and low cyanide concentrations respectively. The rate constants for respective reactions are k₁=(6.1±0.3)×10^–2 M^–1 s^–1, k₂=(12.6±1.0) M^–2 s^–1. The reverse reaction does not occur at a measurable rate even in presence of a large excess of Par. These observations suggest that [Fe(Par)₂]^2– forms a mixed [FePar(CN)₃]^3– complex in presence of an excess of cyanide ion. The activation parameters for the reaction have been calculated and used to support a three step mechanism consistent with these results. The effect of ionic strength tends further support to the mechanism.     

Determination of the formation rate constant of carrier-free111In(III) with EDTA

The kinetics of reaction of indium(III)ion with EDTA (H₄ edta) has been studied in aqueous acidic solutions using carrier-free¹¹¹In and low concentrations of EDTA. The reaction takes place predominatly between indium(III) and H₃ edta. The rate constant k₃ is determined to be k₃=(1.3±0.1)·10⁵ dm³ mol^–1 s^–1 (25 °C).     

The kinetics of vapor-phase nitration of cellulose 2. Nitration with nitric acid under static conditions

The regularities of vapor-phase nitration of cellulose with HNO₃ under conditions of natural convection and hindered heat removal in the absence of air were studied using the nonisothermal kinetic method. It was established that the nitration rate at the depth of conversion of 0.08 to 0.7 is described by the kinetic law d/dt =k ₁ p/(1+), wherek ₁ = 10^4.49±0.6 exp(–A/RT) s^–1 atm^–1, = 10^{–35.5±15.7}exp(B/RT),A = 36.6±3.8 kl mol^–1, andB = 203±88 kJ mol^–1. The diffusion mechanism of vapor-phase nitration of cellulose, which explains the high value of activation energies, is discussed. The effective diffusion coefficient of HNO₃ in cellulose at 25 °3.7 · 10^–7 cm² s^–1) and the activation energy of diffusion (38.3±4.2 kJ mol^–1) were estimated.For Part 1, see Ref. l.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1981–1985, August, 1996.     

Experimental Evidence for Acceleration of Reaction between Iodine Monoxide and Chlorine Monoxide at the Reactor Surface

The reaction of iodine monoxide with chlorine monoxide resulting in atom escape to the gas phase is studied at T = (303 ± 5) K and P = 2.5 Torr using a flow setup for measuring the resonance fluorescence signals of atomic iodine and chlorine. The heterogeneous reaction between chlorine monoxide and iodine monoxide occurring at the reactor surface covered with an F32-L Teflon-like compound and treated by the reaction products is characterized by the rate constant k = (4.9 ± 0.2) × 10^–11 cm³ molecule^–1 s^–1. This value is substantially higher than the rate constant for the homogeneous reaction IO^· + ClO^· (k ₁ 1 × 10^–12 cm³ molecule^–1 s^–1).     

Spectral and kinetic characteristics of the α-propionic acid methyl ester radical in cyclohexane and water

The -propionic acid methyl ester radical was produced in dissociative electron capture reaction of 2-chloropropionic acid methyl ester. The absorption maxima of the radical are at 310 and 300 nm in cyclohexane and water with extinction coefficients of 440±50 and 400±50 mol^–1 dm³ cm^–1. The second order decay rate parameter in water is (2.3±0.5)×10⁹ mol^–1 dm³ s^–1. The peroxy radicals have the characteristics: _max=265–270 nm, _max=700–900 mol^–1 dm³ and 2k=(7±2)·10⁸ mol^–1 dm³ s^–1.     

An equilibrium and calorimetric investigation of the hydrolysis of L-tryptophan to (indole + pyruvate + ammonia)

Apparent equilibrium constants and calorimetric enthalpies of reaction have been measured for the reaction L-tryptophan(aq) + H₂O(l) = indole(aq) + pyruvate(aq) + ammonia(aq) which is catalyzed by L-tryptophanase. High-pressure liquid-chromatography and microcalorimetery were used to perform these measurements. The equilibrium measurements were performed as a function of pH, temperature, and ionic strength. The results have been interpreted with a chemical equilibrium model to obtain thermodynamic quantities for the reference reaction: L-tryptophan(aq) + H₂O(l) = indole(aq) + pyruvate^–(aq) + NH ₄ ⁺ (aq). At T=25°C and I_m=O the results for this reaction are: K^o=(1.05±0.13)×10^–4, G°=(22.71±0.33) kJ-mol^–1, H°=(62.0±2.3) kJ-mol^–1, and S°=(132±8) J-K^–1-mol^–1. These results have been used together with thermodynamic results from the literature to calculate standard Gibbs energies of formation, standard enthalpies of formation, standard molar entropies, standard molar heat capacities, and standard transformed formation properties for the substances participating in this reaction.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

Kinetics and mechanism of the interaction of azide with [(H2O)(tap)2RuORu(tap)2-(H2O)]2+ ion at physiological pH

The title reaction has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand], pH and temperature at constant ionic strength. At the physiological pH (7.4) the interaction with azide shows two distinct consecutive steps, i.e., it shows a non-linear dependence on the concentration of N₃ ^–; both processes are [ligand]-dependent. The rate constant for the processes are: k ₁10^–3 s^–1 and k ₂10^–5 s^–1. The activation parameters calculated from Eyring plots are: H ₁ = 14.8 ± 1 kJ mol^–1, S ₁ = –240 ± 3 J K^–1 mol^–1, H ₂ = 44.0 ± 1.5 kJ mol^–1 and S ₂ = –190 ± 4 J K^–1 mol^–1. Based on the kinetic and activation parameters an associative interchange mechanism is proposed for the interaction process. From the temperature dependence of the outersphere association equilibrium constant, the thermodynamic parameters calculated are: H ₁ ⁰ = 4.4 ± 0.9 kJ mol^–1, S ₁ ⁰ = 64 ± 3 J K^–1 mol^–1 and H ₂ ⁰ = 14.2 ± 2.9 kJ mol^–1, S ₂ ⁰ = 90 ± 9 J K^–1 mol^–1, which gives a negative G ⁰ value at all temperatures studied, supporting the spontaneous formation of an outersphere association complex.     

An NMR study of proton exchange in the system p-nitrosophenol—p-quinone monooxime

The solvent used was dimethylformamide at neutral and alkaline pH. The equilibrium constants are determined by spectrophotometry. The rate of proton exchange has been measured as a function of temperature and concentration. The rate constants and activation energies have been measured; for uncatalyzed exchange k_n=(1.5±0.5) ·· 10³ M^–1 sec^–1, E=8±1 kcal/mole, while base-catalyzed exchange has k=(0.3±0.1) · 10⁶ M^–1 sec^–1 and E=6±1 kcal/mole.We are indebted to A. I. Brodskii for assistance in this work, and to V. I. Oshkaderov and L. A. Kichakova for recording the NMR spectra.     

On the reliability of equilibrium data of the charge-transfer complex between 2,3-dichloro-1,4-naphthoquinone and hexamethylbenzene

In view ofHammond's warning⁶ about the Conspiracy of errors, found in the case of low values of equilibrium constants of charge-transfer complexes a case is made out for redetermining the values for the system hexamethylbenzene—2,3-dichloro-1,4-naphthoquinone. Uncertainties in the parameters were estimated using theLiptay ⁸ matrix procedure. The solvent used was dichloromethane. The following data were obtained at 25°C: vC T = 22,220 cm^–1;E _A=0.99 eV;K =2599±57 l²·cm^–1·mol^–2. _max= 1020 ± 148 cm^–1··1;K=2.55±0.37 l·mol^–1; –H=2.7±0.3 kcal·mol^–1.With 1 Figure     

Radical chain mechanism of the oxidation of α-terpinene by molecular oxygen

The oxidation of -terpinene by molecular oxygen is shown to occur by a radical chain mechanism involving hydroperoxy radicals. The principal molecular reaction products are H₂O₂ and 1-methyl-4-isopropylbenzene. The rate constants for chain propagation and chain breaking measured at 35–70°C are (liter/mol·s) lgk₃ = 7.10– (6700±400)/4.57T and lgk₅ = 9.80– (2700±300)/4.57T respectively.Translated from Teoreticheskaya Éksperimental'naya Khimiya, Vol. 30, No. 3, pp. 143–146, May–June, 1994The authors thank the Ukraine National Committee for the Basic Research Fund for financing this work.