bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of a simplex technique and contour diagrams for the determination of the reaction rate constants between glutathione and thiram in the presence of NADPH
Authors: Elskens Marc , Penninckx Michel J. , Vandeloise Robert , Donckt Emile Vander 
Published: January 2005

AbstractThe Modified Simplex Method (MSM) coupled with contour diagrams is used to determine the rate constants of a kinetic scheme involving three sequential second order processes.Reaction between glutathione and the dithiocarbamate fungicide tetramethylthiuram disulfide produces the oxidized form of glutathione which is then reduced in the presence of NADPH. The concentration of the reducing agent is monitored as a function of time. In the absence of simplifying assumption a closed form solution of the rate equations does not exist. Computed curves of NADPH concentration versus time were generated using the software SIMULCIN.The rate constant values are optimized by the MSM procedure to obtain the best agreement between calculated and experimental data. The significance, validity limits of the estimated rate constants and the relevance of these in vitro data to previous in vivo studies are discussed.
Gas phase reaction of Cl atoms with a series of oxygenated organic species at 295 K
Authors: Wallington Timothy J. , Skewes Loretta M. , Siegl Walter O. , Wu Ching‐Hsong , Japar Steven M. 
Published: January 2005

AbstractThe relative rate technique has been used to determine the rate constants for the reaction of chlorine atoms with a series of oxygenated organic species. Experiments were performed at 295 ± 2 K and atmospheric pressure of synthetic air or nitrogen. The decay rates of the organic species were measured relative to that of ethane or n‐butane. Using rate constants of 5.7 × 10−11 cm3 molecule−1 s−1, and 2.25 × 10−10 cm3 molecule−1 s−1 for the reaction of Cl with ethane and n‐butane respectively the following rate constants were derived, in units of 10−11 cm3 molecule−1 s−1: propane, (16.0 ± 0.4);i‐butane, (15.1 ± 0.9) n‐pentane, (31.0 ± 1.6); n‐hexane, (34.5 ± 2.3); cyclohexane, (36.1 ± 1.5); methanol, (4.57 ± 0.40); ethanol, (8.45 ± 0.91); n‐propanol, (14.4 ± 1.2); t‐butylalcohol, (3.26 ± 0.19); acetaldehyde, (8.45 ± 0.79); propionaldehyde, (11.3 ± 0.9); dimethylether, (20.5 ± 0.8); diethylether, (35.6 ± 2.8); and methyl‐t‐butylether, (16.6 ± 1.2). Quoted errors represent 2σ, and do not include any errors due to uncertainties in the rate constants used to place our relative measurements on an absolute basis. The results are discussed with respect to the mechanisms of these reactions and to previous literature data.
Kinetics and mechanism for the reactions of H atoms with CH3SH and C2H5SH
Authors: Martin D. , Jourdain J. L. , Le Bras G. 
Published: January 2005

AbstractA kinetic study of the reactions of H atoms with CH3SH and C2H5SH has been carried out at 298 K by the discharge flow technique with EPR and mass spectrometric analysis of the species. The pressure was 1 torr. It was found: k1 = (2.20 ± 0.20) × 10−12 for the reaction H + CH3SH (1) and k2 = (2.40 ± 0.16) × 10−12 for the reaction H + C2H5SH (2). Units are cm3 molecule−1 s−1. A mass spectrometric analysis of the reaction products and a computer simulation of the reacting systems have shown that reaction (1) proceeds through two mechanisms leading to the formation of CH3S + H2 (1a) and CH3 + H2S (1b).
Yields of O2(1Σg+) and O2(1Δg) in the H + O2 reaction system, and the quenching of O2(1Σg+) by atomic hydrogen
Authors: Michelangeli Diane V. , Choo Kuang‐Yul , Leu Ming‐Taun 
Published: January 2005

AbstractThe generation of metastable O2(1Σg+) and O2(1Δg) in the H + O2 system of reactions was studied by the flow discharge chemiluminescence detection method. In addition to the O2(1Σg+) and O2(1Δg) emissions, strong OH(v = 2) → OH(v = 0), OH(v = 3) → OH(v = 1), HO2(2A′000) → HO2(2A″000), HO2(2A′001) → HO2(2A″000), and H O2(2A″200) → HO2(2A″000) emissions were detected in the H + O2 system. The rate constants for the quenching of O2(1Σg+) by H and H2 were determined to be (5.1 ± 1.4) × 10−13 and (7.1 ± 0.1) × 10−13 cm3 s−1, respectively. An upper limit for the branching ratio to produce O2(1Σg+) by the H + HO2 reaction was calculated to be 2.1%. The contributions from other reactions producing singlet oxygen were investigated.
Rate constants for abstraction of hydrogen from ethylene by methyl and ethyl radicals relative to abstraction from propane and isobutane
Authors: Ahonkhai S. I. , Lin X‐H. , Back M. H. 
Published: January 2005

AbstractA method is described for the measurement of relative rate constants for abstraction of hydrogen from ethylene at temperatures in the region of 750 K. The method is based on the effect of the addition of small quantities of propane and isobutane on the rates of formation of products in the thermal chain reactions of ethylene. On the assumption that methane and ethane are formed by the following reactions,
equation image
measurements of the ratio of the rates of formation of methane and ethane in the presence and absence of the additive gave the following results:

Values for k2 and k3 obtained from these ratios are compared with previous measurements.
Effect of solvent on the reactions of coordination complexes part VII: Kinetics of solvolysis of cis‐(bromo) (imidazole) bis‐(ethylenediamine)cobalt (III) and cis‐(bromo) (N‐methyl imidazole)bis‐(ethylenediamine) cobalt(III) in methanol‐water media
Authors: Dash Anadi C. , Dash Neelamadhab 
Published: January 2005

AbstractThe kinetics of the solvolytic aquation of cis‐(Bromo) (imidazole) bis(ethylenediamine) cobalt (III) and cis‐(Bromo) (N‐methylimidazole) bis(ethylenediamine) cobalt(III) have been investigated in aqueous methanol media with methanol content 0–80% by weight and at temperatures 40–55°C. The pseudo‐first order rate constant decreases with increasing methanol content. Plots of log k vs. D (where Ds is the bulk‐dielectric constant of the solvent mixture) and log k vs. the Grunwald‐Winstein Y‐solvent parameter are nonlinear, the curvature of the plots is relatively more significant for the imidazole complex. The plots of log k vs. molfraction of methanol (XMeOH) for both the substrates also deviate from linearity, the deviation being less and less marked, particularly for the N‐methyl imidazole complex, as the temperature is increased. Hence preferential solvation phenomenon appears to be less significant when the N‐H proton of imidazole is replaced by ‐CH3 group. The plots of calculated values of the transfer free energy of the dissociative transition state, cis‐{[(en)2Co(B)]3+}* (B = imidazole, N‐methylimidazole), relative to that of the initial state, cis‐[Co(en)2(B)Br]2+, for the transfer of the ions from water to the mixed solvent, against XMeOH exhibit maxima at XMeOH = 0.06, 0.27, and 0.12, 0.36 and minima at XMeOH = 0.12 and 0.19 for cis‐[(en)2Co(imH)Br]2+ and its N‐methylimidazole analogue respectively which are in keeping with the solvent structural changes around the initial state and transition state of these substrates as the solvent composition is varied.Plots of activation enthalpy and entropy against molfraction of the solvent mixtures exhibit maxima and minima. This type of variations of the activation parameters, ΔH≠ and ΔS≠, with XMeOH speaks of the enthalpy and entropy changes associated with the solvent‐shell reorganization of the complex ions both in the initial and in the transition states which contribute appreciably to the overall activation enthalpy and entropy of the aquation reaction.
Pyrolysis of Propyne/2‐Methylbut‐1‐ene‐3‐yne mixtures between 350 and 450°C
Authors: Harper Charles , Heicklen Julian 
Published: January 2005

Abstract2‐Methylbut‐1‐ene‐3‐yne and Propyne mixtures were pyrolyzed at 350–450°C in the absence and presence of O2 and NO. The major product of the reaction is a polymer, but m‐xylene and p‐xylene are also produced and were studied as the species of interest. The C8H10 formation rate is first‐order in C3H4 and C5H6. The rate coefficient is best fitted by

though it is not inconsistent with

where R is the ideal gas constant in kJ/mol‐K. Experiments in the presence of NO show that m‐xylene and p‐xylene formation occur by two processes: a concerted molecular mechanism (≃ 41%) and a singlet diradical mechanism (≃ 59%).
Very low‐pressure pyrolysis (VLPP) of methyl‐ and ethynyl‐cyclopentanes and cyclohexanes
Authors: Brown Trevor C. , King Keith D. 
Published: January 2005

AbstractStudies of the kinetics of thermal unimolecular decomposition of methylcyclopentane, methylcyclohexane, ethynylcyclopentane, and ethynylcyclohexane have been carried out at temperatures in the range 861–1218 K using the technique of very low‐pressure pyrolysis (VLPP). Multiple reaction pathways and secondary decomposition of primary products results in a complex array of reaction products. VLPP rate data (fall‐off regime) were obtained for the overall decompositions and interpreted via the application of RRKM theory. The data for methylcyclopentane and methylcyclohexane were interpreted in terms of ring‐opening bond fission pathways and bond fission to methyl and cycloalkyl radicals. By selecting Arrhenius parameters consistent with the analogous pathways in open‐chain alkanes, a good fit to the overall decomposition is obtained. The data for ethynylcyclopentane and ethynylcyclohexane were interpreted in terms of ring‐opening bond fission and alkyne to allene isomerization. The A factors for ring opening were based on known values for C‐C fission in open‐chain alkynes and the Arrhenius parameters for isomerization were chosen to be consistent with previously reported alkyne to allene isomerizations. The VLPP data are consistent with the following high‐pressure rate expressions (at < T > = 1100 K) for the dominant primary reaction channel of ring opening adjacent to the substitutent group:

where θ = 2.303RT kJ mol−. Comparison of the activation energies for the ethynyl‐cycloalkanes with those for the methyl‐cycloalkanes shows that the effect of the ethynyl substituent is consistent with the propargyl resonance energy. This evidence supports the assumption of a biradical mechanism for ring opening in these cycloalkanes.
Association reactions of atoms and radicals
Authors: Pilling Michael J. 
Published: January 2005

AbstractThe pressure and temperature dependences of association reactions involving atoms and/or radicals is discussed and illustrated by reference to the reactions CH3 + CH3 → C2H6, CH3 + O2 → CH3O2, CH3 + H → CH4, and H + C2H4 → C2H5. Recent experimental measurements of the rate coefficients, k([M], T) are described, particular attention being paid to experiments designed to measure the rate coefficient over wide ranges of pressure and temperature. Methods of fitting the experimental data, to obtain estimates of the limiting rate coefficients, k0 and k∞, and to permit extrapolation to regions beyond the experimental range, are discussed. These methods include the Troe factorization technique, a combination of master equation and variational RRKM theory, and recent calculations by Wagner and Wardlaw using the technique developed by Wardlaw and Marcus to describe loose transition states.
Kinetics of partly diffusion‐controlled reaction XXI: A simple algorithm for computing the apparent rate of reaction
Authors: Andre J. C. , Baros F. , Sousa A. T. Reis E. 
Published: January 2005

AbstractStarting from Smoluchowski's hypothesis, a simple algorithm is developed in order to obtain the apparent rate constant at large values of time, t, with some physical and chemical processes, as in the case of diffusion controlled reactions. Some practical examples are illustrated, assuming nonuniform distribution function, space‐dependent diffusion coefficient or short‐range interaction leading to an asymptotic analytical expression of the form α + β/√t, where α and β are constants function of the system of interest.
Stability of N‐chloro‐3‐aminopropanol in aqueous solution. Kinetics of decomposition and disproportion of N‐chloro‐3‐aminopropanol
Authors: Antelo Juan M. , Arce Florencio , Franco Julia , Barro P. Rodriguez , Varela Angel 
Published: January 2005

AbstractN‐chloro‐3‐aminopropanol was obtained in aqueous solution by mixing the amine with the hypochlorite. The first order decomposition kinetics of the N‐chloramine in strongly alkaline media are explained by a mechanism in which the rate controlling step is the formation of an imine which is subsequently hydrolyzed. Spectrophotometry of the reaction in acid media showed that under these conditions dichloramines are formed: the second order experimental kinetics of this process are explained by a mechanism in which the rate‐controlling step is a reaction between the protonated and free forms of the N‐chloramine.
Micellar hydrolysis of hydroxamic acids. Michaelis‐menten kinetics
Authors: Berndt Donald C. , Angus Jill E. , Wood Michael J. , Atkinson Richard F. , Qureshi Tanveer A. , Shay Brian J. , Provancher Aura I. 
Published: January 2005

AbstractRates of reaction for the alkaline hydrolysis of various hydroxamic acids in the presence of cetyltrimethylammonium bromide have been determined. Empirical reaction orders of zero, one‐half, and one were found for the hydroxamic acids depending upon reaction conditions and substrate structure. N‐methylhydroxamic acids exhibited only first‐order kinetics. The results are consistent with the Michaelis‐Menten rate equation.
Importance of steric effect and evaluation of quantitative structure reactivity relationship (QSRR) in the quaternization reaction of benzothiazoles and phenacyl bromide
Authors: Mishra Bijay Kumar , Sharma Arabinda , Behera Gopabandhu 
Published: January 2005

AbstractThe kinetics of reaction of substituted 2‐aminobenzothiazoles and phenacyl bromide have been followed conductometrically and in some cases, argentometrically. Both the methods produced almost the same rate constants. Substituents at position 5 of the benzothiazole nucleus behave like para substituents of the benzene ring. A correlation with Hammett σp substituent constants has been obtained with a rho value of −1.04. The rate data of quaternization reaction of 4, 5, and 6 substituted 2‐aminobenzothiazoles with phenacyl bromide have been correlated with Fk, Rk, and Vw values by multiple regression analysis with the equation suggested by Williams and Norrington and modified by us. The values are found to correlate well with the equation, log k = −4.4979 − 0.4815fjFk + 0.5933rjRk − 0.0277Vw.
Mechanistic studies with positive iodine: Kinetics of oxidation of thiocyanate ion by iodine monochloride and aqueous iodine in perchloric acid medium
Authors: Gowda B. Thimme , Bhat J. Ishwara 
Published: January 2005

AbstractKinetics of oxidation of thiocyanate ion (NCS−) by iodine monochloride and iodine has been studied in aqueous perchloric acid medium. The rates of oxidations followed the rate laws:

Variations in ionic strength and dielectric constant of the medium had little effects on the rates of reactions with both the oxidants. Mechanisms consistent with the observed rate laws have been suggested. Rate limiting steps have been identified and the constants of some of these steps have been evaluated by varying [NCS−] at each temperature. Activation parameters were computed from the Arrhenius plots. The rate constants predicted from the rate law as [NCS−], and [H+], varied in iodine monochloride oxidation, are in good agreement with the experimental values providing support to the proposed mechanism.
Quenching of I (2P1/2) by halogen cyanides
Authors: Badini Raúl G. , Pasteris Leonor E. , Argüello Gustavo A. , Staricco Eduardo H. 
Published: January 2005

AbstractRelaxation rate constants for the collisional deactivation of I (2P1/2) by halogen cyanides were measured by time resolved atomic absorption. The values obtained were (1.2 ± 0.1) × 10−15, (5.2 ± 0.7) × 10−15, and (2.6 ± 0.4) × 10−14 cm3 molecule−1 s−1 for ClCN, BrCN, and ICN, respectively. Quenching efficiencies are discussed in view of the stability of linear molecules to form the transient complex as well as the similarities assumed between halogen cyanides and interhalogen diatomic molecules.
Study of the reaction of MoOS2(S2CNR2)2 with PPh3 in 1,2‐dichloroethane: Part II. Detection of reaction intermediate pentavalent molybdenum using ESR method at low temperature
Authors: Xiaoqing Song , Huixing Yang , Degang Han 
Published: January 2005

AbstractIntermediate product of the reaction of MoOS2(S2CNR2)2 and PPh3 in dichloroethane has been detected by ESR spectroscopy. Two ESR signals have been observed at low temperature in the reaction system which was stopped by quenching it in liquid nitrogen. The g values are 2.020 ± 0.001 and 1.972 ± 0.001 respectively. The signal at g = 2.020 is attributed to a reaction intermediate with pentavalent molybdenum. A reaction mechanism has been proposed which is consistent with the observation of pentavalent molybdenum as the intermediate in the process of reaction.
Cation, solvent, and substituent effects on the decay kinetics of alkali metal salts of diaryl disulfide radical anions in nonaqueous solutions
Authors: Miyashita Tokuji , Matsuda Minoru 
Published: January 2005

AbstractThe transient diaryl disulfide radical anions (RSSR−) were produced in nonaqueous solutions at room temperature by the flash photolysis of a solution of arylthiolate ion pair in the presence of the excess corresponding disulfide. The transient spectra were almost identical with those obtained from γ‐radiolysis of the disulfides in 77 K 2‐methyl‐tetrahydrofuran (MTHF) glassy matrix. The spectra of disulfide radical anions in nonaqueous solutions were changed by cations, solvents, and para‐substituents depending on the ion pair properties. The tighter ion pairs showed a shift of absorption band to the shorter wavelength. The disulfide radical anions decay by a unimolecular dissociation reaction to yield thiolate anion and thiyl radical. The decay kinetics were first‐order in the initial time region. The rate constants obtained were changed by the counter cations in the order Na+ > K+ > Cs+ > Li+, and by solvents. The tighter ion pairs of the disulfide radical anions showed faster dissociation reaction. This is due to stabilization of a transition state with the counter cation.
Vibrational relaxation and collision‐induced dissociation of xenon fluoride by neon
Authors: Wilkins Roger L. 
Published: January 2005

AbstractRate coefficients were calculated for vibrational relaxation and collision‐induced dissociation of ground state xenon fluoride in neon at temperatures between 300 and 1000 K for each of nine vibrational levels. These coefficients were calculated using a pairwise additive potential energy surface, which consists of a Morse function for the XeF interaction and Lennard–Jones functions for the NeXe and NeF interactions. Rate coefficients are provided for both temperature and v‐ dependences. The vibrational relaxation and dissociation processes occur by multiquanta transitions. Dissociation can take place from all v‐levels provided that the internal energy of the XeF molecule is close to the rotationless dissociation limit. The order of increase effectiveness of the various forms of energy in promoting dissociation in XeF was found to be translation–rotation‐vibration. At room temperature, neon atoms were found to be more efficient than helium atoms in the dissociation processes; helium atoms were found to be more efficient than neon atoms in the vibrational relaxation of XeF. Strong vibration–rotation coupling in both vibrational relaxation and in the dissociation processes is demonstrated.
Rate constants for abstraction of hydrogen from ethylene by methyl and ethyl radicals over the temperature range 650–770 K
Authors: Zhang H‐X , Back M. H. 
Published: January 2005

AbstractMeasurements rate constants for abstraction of hydrogen from ethylene by methyl and ethyl radicals relative to the corresponding rate constants for abstraction from hydrogen, over the temperature range 650–770 K, are reported. The methodis based on the effect of the addition of small quantities of hydrogen on the rates of formation of methane and ethane in the thermalchain reactions of ethylene. On the assumption that methane and ethane are formed by the following reactions:
equation image
measurements of the relative rates of formation of methane and ethane in the presence and absence of hydrogen gave the following ratios of rate constants: (R = 8.314 Joule mol−1 K−1)

With values from the literature for 𝓀1 and 𝓀3 the following values were obtained for 𝓀2 and 𝓀4:
Identification of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) pyrolysis products by simultaneous thermogravimetric modulated beam mass spectrometry and time‐of‐flight velocity‐spectra measurements
Authors: Behrens Richard 
Published: January 2005

AbstractThe pyrolysis products formed during the isothermal decomposition of HMX at 211°C are H2O, HCN, CO, CH2O, NO, N2O, methylformamide, C2H6N2O, octahydro‐1‐nitroso‐3,5,7‐trinitro‐1,3,5,7‐tetrazocine, and a nonvolatile residue. The temporal behaviors of these products during the decomposition are presented. The method for using time‐of‐flight (TOF) velocity spectra to assist mass‐spectrometry measurements in identifying the different gaseous products formed from the pyrolysis of a material by determining the approximate molecular weights of the different gaseous products contributing to the different m/z values in the mass spectrum of the mixture is described. The ion fragmentation of HMX as a function of electron energy shows complete fragmentation of the HMX molecular ion for electron energies ≥ 12.4 eV. No fragments from the pyrolysis of HMX other than those mentioned above are observed.
The photolysis of trans‐3,4‐dimethylcyclopentanone. II. Short Wavelengths
Authors: Becerra Rosa , Frey H. Monty 
Published: January 2005

AbstractThe photolysis of trans‐3,4‐dimethylcyclopentanone has been investigated in the gas phase at 100°C using light of 206 and 193 nm. The photolytic products are propene, 1,2‐dimethylcyclobutane, and the butene isomers. Small quantities of 3,4‐dimethylpent‐4‐enal were also detected. Relative yields of these products were determined as a function of the ketone pressure and also of that of added nitrogen. A mechanism for the photochemical decomposition based on that suggested for the photolysis of cyclopentanone using short wavelength radiation, is consistent with the experimental results and is simpler than that required to account for the long wavelength photolysis reported earlier.