Kinetics and mechanism of oxidation of aurate(I) by peroxydisulphate in aqueous hydrochloric acid

The reaction between Au(I), generated by reaction of thallium(I) with Au(III), and peroxydisulphate was studied in 5 mol dm^?3 hydrochloric acid. The reaction proceeds with the formation of an ion‐pair between peroxydisulphate and chloride ion as the Michealis–Menten plot was linear with intercept. The ion‐pair thus formed oxidizes AuCl₂^? in a slow two‐electron transfer step without any formation of free radicals. The ion‐pair formation constant and the rate constant for the slow step were determined as 113 ± 20 dm^?3 mol^?1 and 5.0 ± 1.0 × 10^?2 dm³ mol^?1 s^?1, respectively. The reaction was retarded by hydrogen ion, and formation of unreactive protonated form of the reductant, HAuCl₂, causes the rate inhibition. From the hydrogen ion dependence of the reaction rate, the protonation constant was calculated to be as 0.6 ± 0.1 dm³ mol^?1. The activation parameters were determined and the values support the proposed mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 589–594, 2002     

The enthalpy of formation of tungsten azide pentafluoride

The enthalpy of hydrolysis of solid tungsten azide pentafluoride in alkaline aqueous solution (1.O mol dm^?3 KOH; 298.2K) is ?578 kJ mol^?1. Hence its enthalpy of formation is ?1170 kJ mol^?1.     

Kinetics of acrylamide/glutathione binding by fast atom bombardment and thermospray mass spectrometry

The kinetics of the binding of the neurotoxin acrylamide to the cysteine residue of glutathione has been studied. At 37 °C and pH 7.3 the second order rate constant has been determined to be 0.72 ± 0.06 mol^?1 dm³ min^?1 by thermospray mass spectrometry. The critical energy at pH 11.5 measured over the temperature range 10–37°C by fast atom bombardment mass spectrometry was measured as 24.6 kJ mol^?1.     

Interconversion of the Tautomers of 2-Benzylidene-4-Methyl-3-Oxo-Pentanoic Acid Phenylamide During Gas Chromatography

Tautomerization of 2-benzylidene-4-methyl-3-oxo-pentanoic acid phenylamide has been studied by NMR and GC-MS. The two tautomers were separated on an HP-5 column, which enabled the kinetic and the thermodynamic behavior of on-column interconversion to be investigated. The enol-to-imide tautomerization was found to occur primarily in the stationary phase. By treating the column as a reactor, the interconversion was investigated as a function of retention time and oven temperature. This enabled determination of the rate constant (0.0605 s^?1) by monitoring the increase of the less gas stable tautomer at a constant temperature of 260 °C and determination of the activation energy of the reaction for the net tautomerization (52.0 kJ mol^?1), because it was found that the reaction obeyed pseudo first-order kinetics. The enthalpy and the entropy changes (?H=1.68 kJ mol^?1, ?S=3.54 J K^?1 mol^?1) for the enol-to-imide reaction in the stationary phase were also obtained.     

IONIC STRENGTH EFFECTS ON THE GROUND STATE COMPLEXATION and TRIPLET STATE ELECTRON TRANSFER REACTION BETWEEN ROSE BENGAL and METHYL VIOLOGEN

Abstract— The equilibrium constants, K_c, for complexation between methyl viologen dication (MV²+) and Rose Bengal, or Eosin Y, decrease with increasing ionic strength. At zero ionic strength K_c is 6500 (± 500) mol^?1 dm³ for Rose Bengal and 3200 (± 200) mol^?1 dm³ for Eosin Y, and these values decrease to 1500 (± 100) and 680 (± 40) mol^?1 dm³, respectively, at an ionic strength of 0.1 mol dm^?3. K_c is independent of pH between 4.5 and 10. ΔH is -25 (± 1) kJ mol^?1 for complexation with either dye, whereas ΔS is -15 (± 3) J K^?1 mol^?1 for Rose Bengal, and - 23 (± 3) J K^?1 mol^?1 for Eosin Y. The complexation constant for Rose Bengal and the neutral viologen, 4,4'-bipyridinium-N, N'-di(propylsulphonate), (4,4'-BPS), is 420 (± 35) mol^?1 dm³, and independent of ionic strength. No complexation could be observed for either Rose Bengal or Eosin with another neutral viologen, 2,2'-bipyridinium-N,N'-di(propylsulphonate), (2,2'-BPS). MV²+ quenches the triplet state of Rose Bengal with a rate constant of 7 × 10⁹ mol^?1 dm³ s^?1, and this rate constant decreases slightly as ionic strength increases. The cage escape yield following quenching, Φ_cc is very low (Φ_cc= 0.02 (± 0.005), and independent of ionic strength. 4,4'-BPS quenches the triplet state of Rose Bengal with a rate constant of 2.2 (± 0.1) × 10⁹ mol^?1 dm³ s^?1, and gives a cage escape yield of 0.033 (± 0.006). 2,2'-BPS quenches the Rose Bengal triplet with a rate constant of 6 (± 1) × 10⁸ mol^?1 dm³ s^?1 and gives a cage escape yield of 0.07 (± 0.01). Conductivity measurements indicate that MV²+(Cl^?)₂ is completely dissociated at concentrations below 2 × 10^?2 mol dm^?3.     

Catalytic Adsorptive Stripping Voltammetry of Molybdenum: Redox Kinetic Measurements

The electrode mechanism of Mo(VI) reduction was studied under catalytic adsorptive stripping mode by means of square‐wave voltammetry (SWV). Mo(VI) creates a stable surface active complex with mandelic acid. The electrode reaction of Mo(VI)‐mandelic acid system undergoes as one‐electron reduction, exhibiting properties of a surface electrode process. In the presence of chlorate, bromate, and hydrogen peroxide, the electrode reaction is transposed into a catalytic mechanism. The experimental results are compared with the recent theory for surface catalytic reaction, enabling qualitative characterization of the electrode mechanism in the presence of different catalytic agents. Utilizing both the method of “split SW peaks” and “quasireversible maximum” the standard redox rate constant of Mo(VI)‐mandelic acid system was estimates as k_s=150±5 s^?1. By fitting the experimental and theoretical results, the following catalytic rate constants have been estimated: (8.0±0.5)×10⁴ mol^?1 dm³ s^?1, (1.0±0.1)×10⁵ mol^?1 dm³ s^?1, and (3.2±0.1)×10⁶ mol^?1 dm³ s^?1, for hydrogen peroxide, chlorate, and bromate, respectively.     

Aspects of the Chemistry of Poly (Ethylene Terephthalate). IV. Hydrolysis of Poly(Ethylene Terephthalate) in the Melt Phase

The effect of water vapor pressure on the molecular weight of molten poly (ethylene terephthalate) has been followed by measurement of the changes which occur in the intrinsic viscosity and the end-group concentrations upon hydrolysis. It was found that phosphoric acid is highly effective as a stabilizer; the hydrolysis rate constant (K_h) decreasing from 7.6 × 10^?7 mol^?1s^?1 for nonstabilized to 2.5 × 10^?7 mol^?1s^?1 for the stabilized polyester at 290°C and water vapor pressure of 20 mmHg.     

Investigation of the kinetics of formation of 1 : 1 complex between chromium(III) with 1,3-propanediamine-N,N′-diacetate-N,N′-di-3-propionate ion in aqueous acidic media

The kinetics of formation of the 1?:?1 complex of chromium(III) with 1,3-propanediamine-N,N′-diacetate-N,N′-di-3-propionate (1,3-pddadp) were followed spectrophotometrically at λ _max?=?557?nm. The reaction was first-order in chromium(III). Increasing the 1,3-pddadp concentration from 2.2?×?10^?2 to 0.11?mol?dm^?3 accelerated the reaction rate. Increasing the hydrogen ion concentration from 1.995?×?10^?5 to 6.31?×?10^?4 mol?dm^?3 retarded the reaction rate. The reaction rate was also retarded by increasing ionic strength and dielectric constant of the reaction medium. A mechanism was suggested to account for the results obtained which involves ion-pair formation between the various reactants. Values of 22?kJ?mol^?1 and ?115?J?K^?1 mol^?1 were obtained for the energy and the entropy of activation, respectively, which indicate an associative mechanism. The logarithm of the formation constant of the 1?:?1 complex formed was 11.3.     

Estimation of activation parameters for the propagation rate constant of styrene

For a temperature range of −11.8–92.6°C, the propagation rate constant k_p of styrene has been determined with the use of pulsed-laser polymerization (PLP). The temperature dependency of the obtained k_p data was evaluated using the Arrhenius equation. The NLLS error-in-variables method (EVM) is recommended for this fit. The resulting activation energy is 32.6 kJ mol⁻¹ and the pre-exponential factor is 10^7.66 dm³ mol⁻¹ s⁻¹. A joint confidence interval for these parameters is given. © 1996 John Wiley & Sons, Inc.     

PRIMARY INTERMEDIATES IN THE PULSED IRRADIATION OF RETINOIDS

Abstract Laser flash photolysis and pulse radiolysis have led to the characterisation of several shortlived intermediates formed after irradiation of retinoic acid and retinyl acetate in hexane or methanol. For retinoic acid, the triplet state, wavelength maximum 440 nm, extinction coefficient 7.3 × 10⁴ dm³ mol^?1 cm^?1, decay constant 6.2 × 10⁵ s^?1, is formed with a quantum yield of 0.012 for 347 nm excitation. The radical cation, absorption maximum 590 nm, extinction coefficient ～7 × 10⁴ dm³mol^?1 cm^?1, is formed in a biphotonic process. The radical anion, absorption maximum 510nm in hexane, 480 nm in methanol where its extinction coefficient is 1.2 × 10⁵ dm³mol^?1 cm^?1, appears to decay partially in methanol into another longer-lived neutral radical, wavelength maximum 420 nm, by loss of OH^?. For retinyl acetate, the triplet state, absorption maximum 395 nm, extinction coefficient 7.9 × 10⁴dm³mol^?1 cm^?1, decay constant 1.2 × 10⁶s^?1 is formed with a quantum yield of 0.025 for 347 nm excitation. Monophotonic photoelimination of OCOCH₃? in methanol produces the retinylic carbenium ion, wavelength maximum 590 nm, whose decay is enhanced by ammonia, k ～ 2 × 10⁶ dm³ mol^?1 s^?1 and retarded by water. The radical cation also has a wavelength maximum at 590 nm, its extinction coefficient being ～ 1.0 × 10⁵ dm³mol¹ cm^?1. The long-lived transient absorption with maximum at 385 nm, extinction coefficient 1.0 × 10⁵ dm³mol^?1 cm^?1, obtained from the reaction of the solvated electron with retinyl acetate in methanol may be due to either the radical anion itself or more likely the radical resulting from elimination of OCOCH₃? from this anion. These results suggest that skin photosensitivity caused by retinyl acetate might be greater than that due to retinoic acid.     

The Kinetics of Ferrocene Volatilisation from an Ionic Liquid

The volatilisation of ferrocene (Fc), dissolved in the ionic liquid N‐butyl‐N‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C₄mpyrr][NTf₂], to the gas phase has been indirectly monitored by cyclic voltammetry and chronoamperometry. Simulation of the observed trends in concentration with time using a simple model allowed quantification of the process. Volatilisation of dissolved Fc under flowing wet and dry dinitrogen gas (N₂) was found to be kinetically limited with a rate constant in the region of 2×10^?7 cm s^?1. The activation energy of diffusion for Fc was found to be 28.2±0.7 kJ mol^?1, while the activation energy of volatilisation of Fc from [C₄mpyrr][NTf₂] to dry N₂ was found to be 85±2 kJ mol^?1.     

Kinetics and Mechanism of the Interaction of Di-μ-hydroxobis(1,10-phenanthroline)dipalladium(II) Perchlorate with Thioglycolic Acid and Glutathione in Aqueous Solution

The kinetics of interaction between di-μ-hydroxobis(1,10-phenanthroline)dipalladium(II) perchlorate and thioglycolic acid and with glutathione has been studied spectrophotometrically in aqueous medium as a function of the complex concentration as well as the ligand concentrations, pH, and temperature at constant ionic strength. The observed pseudo-first-order rate constants k _obs (s^?1) obeyed the equation k _obs = k ₁[Nu] (Nu = nucleophile). At pH = 6.5, the interaction with thioglycolic acid shows two distinct consecutive steps and both steps are dependent on the concentration of thioglycolic acid. The rate constants for the process are: k ₁ ≈ 10^?5 s^?1 and k ₂ ≈ 10^?3 dm³ · mol^?1 · s^?1. The association equilibrium constant (K _E) for the outer sphere complex formation has been evaluated together with the rate constants for the two subsequent steps. The other bio-active ligand, glutathione, showed a single step reaction depending on [ligand] with a second-order anation rate constant: the 10² (k ₂) values are (61.72, 79.20, 109.24 and 154.33) dm³ · mol^?1 · s^?1 at 20, 25, 30 and 35 °C, respectively. On the basis of the kinetic observations and evaluated activation parameters, plausible associative mechanisms are proposed for both interaction processes.     

Spectrocoulometric study of the hydrolysis of the tris (1,10-phenanthroline)iron(III) complex ion

The spectrocoulometric technique reported earlier is applied to verify the mechanism and to evaluate the contributions k_Bi of the individual bases to the total rate constant k of the hydrolysis of the tris (1,10-phenanthroline) iron(III) complex, Fe (phen)³⁺₃. Both normal and “open-circuit” spectrocoulometric experiments are used. Partial rate constants for four bases in the acetate-buffered solutions are k_H2O=(3.4±1.2) × 10^?4s^?1 (k_H2O includes the H₂O concentration), k_OH=(1.20±0.06)×10⁷ mol^?1dm³s^?1, k_phen=(1.4±0.2) mol^?1dm³s^?1, k_Ac=(3.8±0.3)×10^?2 mol^?1dm³s^?1, at 25°C and ionic strength 0.5 mol dm^?3. The Fe(phen)³⁺³ hydrolysis, with (phen)₂ (H₂O) Fe-O-Fe (H₂O) (phen)⁴⁺² formation, is first order with respect to Fe (phen)³⁺³ and the bases present in the solution. The rate-determining step in the hydrolysis is the entry of a base to the coordinating sphere of the complex, as in the hydrolysis of the analogous 2,2′-bipyridyl complex.     

Reaction rates for nucleophiles with cyanogen chloride: Comparison with two other digonal carbon compounds

The hydrolysis kinetics of CICN have been reinvestigated from pH 0.0–10.5 and from 18–40°C. In the pH range from 1–5, the hydrolysis rate is invariant and the activation parameters (ΔH? = 84 kJ mol^?1 and ΔS? = ?84 J mol^?1 K^?1) are consistent with water attack. In basic solution the rate is first order each in CICN and OH^? concentrations with parameters ΔH? and ΔS? equal to 82 kJ mol^?1 and + 54 J mol^?1 K^?1, respectively. The rate constants with 20 other donors have been measured. Nitrogen nucleophiles are more reactive than oxygen donors, and an alpha-effect is seen. The constants follow a pattern indicative of attack at carbon. Cyanate in its acid form reacts with nucleophiles. Further points on the cyanate rate–pH profile have been obtained. A chromate-catalyzed hydrolysis can contribute between pH 5–10. Some studies were made of the reaction of cyanate with hydrogen peroxide. Free energy correlations are presented.     

Electroanalytical,kinetic, and mechanistic investigations of coordination-inspired electron transfer between Fe(II)/Cu(II)

Herein, we report that the thermodynamic barrier for solution-phase electron transfer (ET) between Cu(II) and Fe(II) in aqueous acidic media can be overcome through the addition of 2,9-dimethyl-1,10-phenanthroline (Neocuproine [NC]) to the reaction mixture. A detailed discussion of the kinetic and mechanistic aspects of this coordination-inspired ET is presented. We attribute the observed change in the thermodynamic feasibility to the change in the reduction potential of Cu(II)–Cu(I) couple on its ligation with NC. The reaction was found to be slow, following first-order kinetics with respect to each Cu(II) and Fe(II). In the presence of excess NC, the reaction was observed to proceed with a pseudo-second-order rate constant of 3.37?±?0.05?dm³?mol^?1?s^?1 at 298?K, with an activation barrier of ca. 26.22?kJ?mol^?1. The slow reaction is attributed to the significant reorganization energy associated with large-scale changes in the coordination sphere of the oxidant. A two-step mechanism that explains the experimental observations is proposed for the investigated reaction.     

The kinetics of complex formation between Ti(IV) and hydrogen peroxide

The kinetics of the formation of the titanium‐peroxide [TiO²⁺₂] complex from the reaction of Ti(IV)OSO₄ with hydrogen peroxide and the hydrolysis of hydroxymethyl hydroperoxide (HMHP) were examined to determine whether Ti(IV)OSO₄ could be used to distinguish between hydrogen peroxide and HMHP in mixed solutions. Stopped‐flow analysis coupled to UV‐vis spectroscopy was used to examine the reaction kinetics at various temperatures. The molar absorptivity (ε) of the [TiO²⁺₂] complex was found to be 679.5 ± 20.8 L mol^?1 cm^?1 at 405 nm. The reaction between hydrogen peroxide and Ti(IV)OSO₄ was first order with respect to both Ti(IV)OSO₄ and H₂O₂ with a rate constant of 5.70 ± 0.18 × 10⁴ M^?1 s^?1 at 25°C, and an activation energy, E_a = 40.5 ± 1.9 kJ mol^?1. The rate constant for the hydrolysis of HMHP was 4.3 × 10^?3 s^?1 at pH 8.5. Since the rate of complex formation between Ti(IV)OSO₄ and hydrogen peroxide is much faster than the rate of hydrolysis of HMHP, the Ti(IV)OSO₄ reaction coupled to time‐dependent UV‐vis spectroscopic measurements can be used to distinguish between hydrogen peroxide and HMHP in solution. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 457–461, 2007     

Kinetics and electron spin resonance study of the radical polymerization of n‐butyl acrylate mediated by a nitroxide precursor: C‐phenyl‐N‐tert‐butylnitrone

The C‐phenyl‐N‐tert‐butylnitrone/azobisisobutyronitrile pair is able to impart control to the radical polymerization of n‐butyl acrylate as long as a two‐step process is implemented, that is, the prereaction of the nitrone and the initiator in toluene at 85 °C for 4 h followed by the addition and polymerization of n‐butyl acrylate at 110 °C. The structure of the in situ formed nitroxide has been established from kinetic and electron spin resonance data. The key parameters (the dissociation rate constant, combination rate constant, and equilibrium constant) that govern the process have been evaluated. The equilibrium constant between the dormant and active species is close to 1.6 × 10^?12 mol L^?1 at 110 °C. The dissociation rate constant and the activation energy for the C? ON bond homolysis are 1.9 × 10^?3 s^?1 and 122 ± 15 kJ mol^?1, respectively. The rate constant of recombination between the propagating radical and the nitroxide is as high as 1.2 × 10⁹ L mol^?1 s^?1. Finally, well‐defined poly(n‐butyl acrylate)‐b‐polystyrene block copolymers have been successfully prepared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6299–6311, 2006     

Mono-complex formation kinetics of iron(III) with nonsubstituted octane and nonane 2,4-dicarbonyl ligands in aqueous solution

The kinetics and mechanism of the reaction of complexation of iron(III) with 2,4-octanedione and 2,4-nonanedione have been investigated spectrophotometrically in aqueous solution at 10°C and ionic strength 0.5 mol dm^?3 NaClO₄. The equilibrium constants of the mono-complexes have been determined. The mechanism proposed to account for the kinetic data involves a double reversible pathway where both Fe³⁺ and Fe(OH)²⁺ react with the enol tautomer of the ligand. 2,4-Octanedione reacts with Fe³⁺ and Fe(OH)²⁺ with rate constants of 0.65 dm³ mol^?1 s^?1, and 14.07 dm³ mol^?1 s^?1, respectively. For 2,4-nonanedione complexation the rate constants determined are 0.49 dm³ mol^?1 s^?1, and 11.39 dm³ mol^?1 s^?1, respectively. Some discussions are made on the basis of Eigen-Wilkins theory considering the effect of solvent exchange on the complex formation. © 1993 John Wiley & Sons, Inc.     

Surface segregation measurements of In and S impurities from a dilute Cu(In,S) ternary alloy

The surface segregation of In and S from a dilute Cu(In,S) ternary alloy were measured using Auger electron spectroscopy coupled with a linear programmed heater. The alloy was linearly heated and cooled at constant rates. Segregation data of a linear heat run showed surface segregation of In that reached a maximum surface coverage of 25% followed by S, which reached a coverage of 30%. It was found that after In had reached a maximum surface coverage, it started to desegregate as soon as the S enriched the surface until In was completely replaced by S. The segregation parameters, namely, the pre‐exponential factor (D₀), activation energy (Q), segregation energy (ΔG?) and interaction energy (Ω) were extracted from the measured segregation data for both In and S segregation in Cu by simulating the measured segregation data with a theoretical segregation model (modified Darken model). The segregation parameters obtained for In segregation in Cu are D₀ = 1.8 ± 0.5 × 10^?5 m² s^?1, Q = 184.3 ± 1.0 kJ.mol^?1, ΔG? = ?61.4 ± 1.4 kJ.mol^‐1, Ω_Cu?In = 3.0 ± 0.4 kJ.mol^?1; for S segregation in Cu the parameters are D₀ = 8.9 ± 0.5 × 10^?3 m² s^?1, Q = 212.8 ± 3.0 kJ.mol^?1, ΔG? = ?120.0 ± 3.5 kJ.mol^?1, Ω_Cu?S = 23.0 ± 2.0 kJ mol^?1 and the In and S interaction parameter is Ω_In?S = ?4.0 ± 0.5 kJ.mol^?1. The initial parameters used for the Darken calculations were extracted from fits performed with the Fick's and Guttmann model. Copyright © 2013 John Wiley & Sons, Ltd.     

Kinetics and mechanism of oxidation of glycine,alanine, and threonine by fluoride coordinated bismuth(V) in aqueous HClO4–HF medium

The kinetics of oxidation of amino acids viz. glycine, alanine, and threonine with bismuth(V) in HClO₄–HF medium have been studied. The kinetics of the oxidation of all these amino acids exhibit similar rate laws. The second-order rate constants were calculated to be 2.04 × 10^?2 dm³ mol^?1 and 2.72 × 10^?2 dm³ mol^?1 s^?1 for glycine and alanine, respectively, at 35°C and 5.9 × 10^?2 dm³ mol^?1 s^?1 for threonine at 25°C. All the possible reactive species of both bismuth(V) and amino acids have been discussed and a most probable kinetic model in each reaction has been envisaged. © 1994 John Wiley & Sons, Inc.