bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of solvent on the reactions of coordination complexes: Part 17. Kinetics and mechanism of base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt (III) in methanol + water and dimethylsulphoxide + water media
Authors: Dash Anadi C. , Das Prafulla K. 
Published: January 2005

AbstractThe base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt(III) has been investigated in MeOH + water and DMSO + water media (0–70% (v/v) cosolvents) at 20.0 ⩽ t°C ⩽ 35.0 and I = 0.10 mol dm−3 (ClO4−). The phenoxide species [(tetren)CoO2CC6H4O]+ undergoes both OH−‐independent and OH−‐catalyzed hydrolysis via SN1ICB and SN1CB mechanism, respectively. The OH−‐independent hydrolysis of the phenoxide species is catalyzed by both DMSO + water and MeOH + water media, the former exerting a much stronger rate accelerating effect than the latter. The OH−‐catalyzed reaction is strongly accelerated by DMSO + water medium but insensitive to the composition of MeOH + water medium up to 40% (v/v) MeOH beyond which it was not detectable under the experimental conditions. Data analysis has been attempted on the basis of the solvent stabilizing and destabilizing effects on the initial state and transition state of the concerned reactions. The nonlinear variation of the activation parameters, ΔH≠ and ΔS≠, with solvent compositions presumably indicates that the solvent structural effects mediate the energetics of solvation of the initial state and transition state of the concerned reactions. The linearity in ΔH≠ vs. ΔS≠ plot accomodating all data for k1 and k2 paths in DMSO + water and MeOH + water further suggests that the solvent effects on these parameters are mutually compensatory.
Pressure dependence of the reaction Cl + C2H2 over the temperature range 230 to 370 K
Authors: Kaiser E. W. 
Published: January 2005

AbstractThe pressure dependence of reaction (1), Cl + C2H2 + M → C2H2Cl + M, has been measured by a relative rate technique using the pressure independent abstraction reaction (2), Cl + C2H6 → C2H5 + HCl, as the reference. Values of k1/k2 were measured at pressures between 25 and 1300 torr at four temperatures ranging from 252 to 370 K, using air, N2, or SF6 diluent gases. Low pressure measurements (10–50 torr) were performed at 230 K. Assuming a temperature‐independent center broadening factor of 0.6 in the Troe formalism and using the established value of k2, these data can be used to determine the temperature dependent high and low pressure limiting rate constants over the range of conditions studied in air for reaction (1): k∞(1) = 2.13 × 10−10 (T/300)−1.045 cm3/molecule‐s; and k0(1) = 5.4 × 10−30 (T/300)−2.09 cm6/molecule2‐s. Use of these expressions yields rate constants with an estimated 20% accuracy including uncertainty in the reference reaction. The data indicate that the rate constant for a typical stratospheric condition at 30 km altitude is approximately 50% of that previously estimated.
Rate constants of the reactions of OH radicals with cyclopropane and cyclobutane
Authors: DóBé S. , Turányi T. , Iogansen A. A. , Bérces T. 
Published: January 2005

AbstractThe kinetics of the reactions of hydroxy radicals with cyclopropane and cyclobutane has been investigated in the temperature range of 298–492 K with laser flash photolysis/resonance fluorescence technique. The temperature dependence of the rate constants is given by k1 = (1.17 ± 0.15) × 10−16 T3/2 exp[−(1037 ± 87) kcal mol−1/RT] cm3 molecule−1 s1 and k2 = (5.06 ± 0.57) × 10−16 T3/2 exp[−(228 ± 78) kcal mol−1/RT] cm3 molecule−1 s−1 for the reactions OH + cyclopropane → products (1) and OH + cyclobutane → products (2), respectively. Kinetic data available for OH + cycloalkane reactions were analyzed in terms of structure‐reactivity correlations involving kinetic and energetic parameters.
CH and C‐atom time histories in dilute hydrocarbon pyrolysis: Measurements and kinetics calculations
Authors: Dean Anthony J. , Hanson Ronald K. 
Published: January 2005

AbstractCH and C‐atom concentration‐time histories were measured during pyrolysis of highly dilute mixtures (6 to 100 ppm) of ethane or methane in argon behind reflected shock waves over the temperature range 2500 to 3800 K and pressure range 0.5 to 1.3 atm. CH was detected using narrow‐linewidth laser absorption at 431 nm. C‐atom concentrations were measured using atomic resonance absorption spectroscopy (ARAS) at 156.1 nm. These data allow improved understanding of dilute hydrocarbon pyrolysis.A pyrolysis reaction mechanism was developed which fits essential characteristics of the CH and C‐atom profiles (time to peak, peak concentration, and 50% decay time) within ±25%. Critical reactions for which rate coefficient data were not previously available are:

equation image

Best‐fit rate coefficients, valid over the range 2500 to 3800 K, are: k4 = 5.0 × 1015 exp(−42800 K/T), k5 = 4.0 × 1015 exp(−41800 K/T), k6 = 1.3 × 1014 exp(−29700 K/T), and k7 = 1.9 × 1014 exp(−33700 K/T) cm3 mol−1 s−1
Mono‐complex formation kinetics of 2‐acetylcyclohexanonatochromium(III) in aqueous solution
Authors: Blanco Carlos A. , Hernando José M. , Mateo Manuel 
Published: January 2005

AbstractThe kinetics and mechanism of the reaction of complexation of chromium(III) with 2‐acetyl‐cyclohexanone has been investigated spectrophotometrically in aqueous solution at 50°C and ionic strength 0.5 mol dm−3 NaClO4. The equilibrium constants of the complex have been determined. The mechanism proposed to account for the kinetic data involves a double reversible pathway where both Cr3+ and Cr(OH)2+ react with the enol tautomer of the ligand with rate constants of 9.6 × 10−3 dm3 mol−1 s−1, and 3.69 × 10−2 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.
Kinetics of the solvolysis of [Co(3Rpy)4Cl2]+ ions (R = Me or Et) in Water + t‐butyl alcohol mixtures
Authors: El‐Subruiti Gehan M. , Wells Cecil F. , Sidahmed Ibrahim M. 
Published: January 2005

AbstractRates of solvolysis of complex ions [Co(3Rpy)4Cl2]+ with R = Me and Et have been determined in mixtures of water with t‐butyl alcohol over a range of temperatures. Extrema found in the enthalpy ΔH* and entropy ΔS* of activation are correlated with the physical properties of the solvent mixtures which are influenced by changes in the solvent structure and these extrema are compared with those found for the solvolysis of related complexes in water + alcohol mixtures. Isokinetic plots over wide ranges of ΔH* and ΔS* are compared for the solvolysis of CoIII complexed to a variety of ligands. The application of a free energy cycle shows that the emergent cobalt (III) cation in the transition state becomes increasingly stabilized in water‐rich mixtures relative to the cobalt (III) cation in the initial state as the mol fraction of t‐butyl alcohol increases.
Kinetics of formation, dissociation, and redox reactions of the benzyl radical‐Cu(II) ion complex in a 10% acetonitrile‐90% water mixture
Authors: Mayouf Ahmed , Lemmetyinen Helge , Sychttchikova Irina , Koskikallio Jouko 
Published: January 2005

AbstractThe rate constant of formation, dissociation, and redox reaction of the benzyl radical‐copper(II) ion complex have been determined at temperatures from 274 K to 333 K by laser flash photolysis of 1,3‐diphenyl‐2‐propanone (DBK) in a 10% acetonitrile‐90% water mixture containing copper(II)perchlorate. Rate constants were calculated from time resolved absorbances of both benzyl radicals (Bz) at 315 nm and benzyl‐copper complexes (BzCu2+) at 375 nm. Values of the rate constants of the formation of BzCu2+ complex were fitted to the equation

and the rate constant of the reverse reaction of BzCu2+ complex to the equation

The rate constant of the redox reaction of BzCu2+ complex to benzyl alcohol and copper(I) ion can be described by the equation

The first order rate constant of dissociation of phenylacetyl radical formed initially in the flash photolysis of DBK is given by the equation
The unimolecular decomposition and isomerization of chemically activated 1‐methyl‐2,2,3,3‐tetrafluorocyclopropane
Authors: Arbilla G. , Ferrero J. C. , Staricco E. H. 
Published: January 2005

AbstractThe reaction of CH2(1A1) with 1,1,2,2‐tetrafluorocyclopropane was studied at 300 K and at pressures between 9.0 and 365.0 torr. Chemically activated 1‐methyl‐2,2,3,3‐tetrafluorocyclopropane was formed and two competitive reaction paths, namely decomposition and isomerization, were observed. By fitting the experimental results to calculated values from RRKM theory, we estimated the Arrhenius parameters for both reaction processess as well as the heat of formation of 1‐methyl‐2,2,3,3‐tetrafluorocyclopropane. © John Wiley & Sons, Inc.
Kinetics and mechanism of oxidation of hydroxylamine by peroxomonosulphate
Authors: Sharma Madhu , Prasad D. S. N. , Gupta K. S. 
Published: January 2005

AbstractThe kinetics of the reaction (1) obey the rate law (2) in acetate buffered solutions. A comparison with H2O2 and S2O82− shows the reactivity order to be H2O2 < HSO5− > S2O82−. © John Wiley & Sons, Inc.

equation image
Reactions of the nitrate radical with a series of reduced organic sulphur compounds in air
Authors: Jensen N. R. , Hjorth J. , Lohse C. , Skov H. , Restelli G. 
Published: January 2005

AbstractA 480 L evacuable reaction chamber, equipped with FT‐IR spectroscopy on‐line and ion chromatography off‐line, has been used to study the gas phase reaction between the nitrate radical, NO3, and the reduced organic sulphur compounds CH3CH2SH, (CH3CH2)2S, (CH3CH2)2S2, and CH3CH2SCH3 in air. The products CH3CH2SO3H, SO2, H2SO4, CH3CHO, and CH3CH2ONO2 were identified and quantified in the reactions of the first three compounds, CH3CH2SH, (CH3CH2)2S, and (CH3CH2)2S2. The reaction products were CH3CH2SO3H, CH3SO3H, SO2, H2SO4, CH3CHO, and CH2O in the reaction of CH3CH2SCH3. On the basis of identified reaction products and intermediates observed in the infrared spectra, mechanisms are proposed for the reactions between the NO3 radical and the four reduced organic sulphur compounds. The results of this study, together with those from previous experiments performed in this laboratory on CH3SCH3, CH3SH, and CH3SSCH3 lead to the conclusion that all these species, in the reaction with the NO3 radical, follow a similar degradation mechanism producing SO2, H2SO4, RSO3H, RCHO, and RCH2ONO2, as the main reaction products. The inital step of the reaction of NO3 with RSR and RSH type (R = CH3, CH2CH3) reduced organic sulphur compounds was found to be H‐atom abstraction, probably after the formation of an initial adduct. For the reaction between NO3 and RSSR type compounds, evidence for an addition‐decomposition reaction, as the initial steps, was obtained. RS·, RS(O)·, and RS(O)2· appear to be formed as intermediates in all the reactions. © John Wiley & Sons, Inc.
Kinetics and mechanism of sulfite oxidation by permanganate in basic medium
Authors: Ernst Teresa , Cyfert Maria , Wilgocki Michal 
Published: January 2005

AbstractThe kinetics of the permanganate‐sulfite redox reaction has been studied in the alkaline medium using a stopped‐flow technique. In the pH range 10 to 12 the reaction was found to obey the rate expression: −½d[MnO4−]/dt = (k1 + k2[OH−]) [MnO4−] [SO32−]. Mechanisms for the two paths involving the formation of a (O3MnOSO3)3− complex prior to the rate‐determining step are consistent with the data. © John Wiley & Sons, Inc.
Enzymic oxidation of dopamine by polyphenol oxidaze
Authors: Tan T. C. , Chen Y. 
Published: January 2005

AbstractThe kinetics of the enzymic oxidation of dopamine (A) by polyphenol oxidaze (E) was studied by spectrophotometrically monitoring the concentration of the reaction product, 2,3‐dihydroindole‐5, 6 quinone, at 470 nm. The kinetics model proposed for the reaction and the effect of pH agreed with the experimental data and the resulting rate equation is given by

where [A] is the concentration of dopamine (mM), [Eo] the concentration of polyphenol oxidaze (mg/1) and [H+] the concentration of hydrogen ion (M) in the reaction mixture. © John Wiley & Sons, Inc.
Oxidation with permanganate in strong alkaline medium. Oxidation of pyruvic and lactic acids
Authors: Jáky Miklós , Kozhevnikov Ivan V. , HÖFt Eugen 
Published: January 2005

AbstractThe reaction of permanganate ion with pyruvic acid and lactic acid has been studied in aqueous solutions containing 0.10–2.0 mol dm−3 alkali. In this range of HO− concentration the reaction

is followed slowly by the reduction of manganate, thus, the above process can be studied separately. In the case of lactic acid (LA), the reactive species is alkoxy anion, and the deprotonation constant could be calculated from the kinetic data. A mechanism based on electron abstraction from the alkoxy anion has been proposed. In the case of pyruvic acid (PA) oxidation may proceed with participation of enolate anion, or hydrate anion, or an adduct. These three possibilities have been investigated. © John Wiley & Sons, Inc.
Chlorine initiated photooxidation studies of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs): Results for HCFC‐22 (CHClF2); HFC‐41 (CH3F); HCFC‐124 (CClFHCF3); HFC‐125 (CF3CHF2); HFC‐134a (CF3CH2F); HCFC‐142b (CClF2CH3); and HFC‐152a (CHF2CH3)
Authors: Edney E. O. , Driscoll D. J. 
Published: January 2005

AbstractData on the tropospheric degradation of proposed substitutes for ozone depleting CFCs were obtained by conducting photochemical oxidation studies of HCFCs and HFCs using long path Fourier transform infrared spectroscopy. The hydrogen abstraction reactions were initiated using Cl radicals rather than OH radicals because of the rather unreactive nature of the compounds. The experimental product yields at T = 25 ± 3°C and 700 Torr of dry air were: CHClF2 (1.11 ± 0.06 C(O)F2); CClFHCF3 (1.00 ± 0.04 CF3C(O)F); CF3CHF2 (1.09 ± 0.05 C(O)F2); CClF2CH3 (0.98 ± 0.03 C(O)F2); CHF2CH3 (1.00 ± 0.05 C(O)F2); CF3CH2F (0.16 ± 0.03 CF3CF(O), and 0.83 ± 0.22 HFC(O)), where all standard deviations are 2σ. For each compound, the critical step in determining the oxidation products was the decomposition of a halogenated alkoxy radical. For HCFC‐22 and HCFC‐124, the major alkoxy radical decomposition route was Cl elimination. The HFC‐125 product data were consistent with CC cleavage of a two carbon alkoxy radical as the major decomposition route whereas both CC cleavage and H abstraction by O2 were significant contributors to the decomposition of the HFC‐134a alkoxy radical. Secondary Cl reactions in the HCFC‐142b and HFC‐152a experiments prevented an unambiguous determination of the decomposition modes; the data are consistent with both CC bond scission and Cl reactions with halogenated aldehydes producing the oxidation product C(O)F2. With the exception of the HFC‐134a and HFC‐125 data, the proposed mechanisms can account for the major oxidation products. For HFC‐134a and HFC‐125, a number of product bands could not be identified. The bands are likely due to products from reactions involving the CF3O2 radical. © John Wiley & Sons, Inc.
Study of the kinetics of the reactions of NO3 with HO2 and OH
Authors: Mellouki A. , Talukdar R. K. , Bopegedera A. M. R. P. , Howard Carleton J. 
Published: January 2005

AbstractThe Absolute rate constants for the gas‐phase reactions of NO3 with HO2 and OH have been determined using the discharge flow laser magnetic resonance method (DF‐LMR). Since OH was found to be produced in the reaction of HO2 with NO3, C2F3Cl was used to scavenge it. The overall rate constant, k1, for the reaction, HO2 + NO3 → products, was measured to be k1=(3.0 ± 0.7)×10−12 cm3 molecule−1 s−1 at (297 ± 2) K and P=(1.4 – 1.9) torr. This result is in reasonable agreement with the previous studies. Direct detection of HO2 and OH radicals and the use of three sources of NO3 enabled us to confirm the existence of the channel producing OH:HO2+NO3→OH+NO2+O2 (1a); the other possible channel is HO2+NO3→HNO3+O2 (1b). From our measurements and the computer simulations, the branching ratio, k1a/(k1a + k1b), was estimated to be (1.0). The rate coefficient for the reaction of OH with NO3 was determined to be (2.1 ± 1.0) × 10−11 cm3 molecule−1 s−1. © 1993 John Wiley & Sons, Inc.
Extrapolating H‐atom transfer rate constants via thermochemical kinetics: The effect of tunneling
Authors: Rodgers Alan S. 
Published: January 2005

AbstractOne of the important applications of chemical kinetics is the attempt to understand complex processes through kinetic modeling. This process frequently requires that rate constants be obtained by extrapolation of data either to higher or lower temperatures than the experimental, or by estimation or correlation with such data. Thermochemical kinetics combined with conventional transition state theory forms a framework from which this may be done. However, rate data for H transfer reactions may have a significant contribution from tunneling. In this work, a one dimensional approach to tunneling, consistent with conventional transition state theory, is taken to show how tunneling affects the extrapolation and correlation of rate constants in thermochemical kinetics. It is concluded that extrapolation and correlation are both quite good even when tunneling comprises 80% of the reaction. However, this is not without limitations, which are discussed. © 1993 John Wiley & Sons, Inc.
A relative rate study of the reaction of chlorine atoms (Cl) and hydroxyl radicals (OH) with a series of ethers
Authors: McLoughlin Peter , Kane Rosaleen , Shanahan Imelda 
Published: January 2005

AbstractRate constants for the gas phase reactions of hydroxyl radicals and chlorine atoms with a number of ethers have been determined at 300 ± 3 K and at a total pressure of 1 atmosphere. Both OH radical and chlorine atom rate constants were determined using a relative rate technique. Values for the rate constants obtained are as follows.

compound
kOH×1012(cm3 molecule−1 s−1)
kC1×1011(cm3 molecule−1 s−1)

Hexane
5.53 ± 1.55
—

2‐Chloro ethyl methyl ether
4.92 ± 1.09
14.4 ± 5.0

2,2‐Dichloro ethyl methyl ether
2.37 ± 0.50
4.4 ± 1.6

2‐Bromo ethyl methyl ether
6.94 ± 1.38
16.3 ± 5.4

2‐Chloro,1,1,1‐trifluoro ethyl ethyl ether
<0.3
0.30 ± 0.10

Isoflurane
<0.3
<0.1

Enflurane
<0.3
<0.1

Di‐i‐propyl ether
11.08 ± 2.26
16.3 ± 5.4

Diethyl ether
—
25.8 ± 4.4

The above relative rate constants are based on the values of k(OH + pentane)=[3.94 ± 0.98]×10−12 and k(OH + diethyl ether)=[13.6 ± 2.26] × 10−12 cm3 molecule−1 s−1 in the case of the hydroxyl reactions. In the case of the chlorine atom reactions, the above rate constants are based on values of k(Cl + ethane)=[5.84 ± 0.88] × 10−11 and k(Cl + diethyl ether)=[25.4 ± 8.05] × 10−11 cm3 molecule−1 s−1. The quoted errors include ±2σ from a least squares analysis of our slopes plus the uncertainty associated with the reference rate constants.Atmospheric lifetimes calculated with respect to reaction with OH radicals are based on a tropospheric OH radical concentration of (7.7 ± 1.4) × 105 radicals cm−3, and lifetimes with respect to reaction with Cl atoms are based on a tropospheric Cl atom concentration of 1 × 103 atoms cm−3. Observed trends in the relative rates of reaction of hydroxyl radicals and chlorine atoms with the ethers studied is discussed. The significance of the calculated tropospheric lifetimes is also reviewed. © 1993 John Wiley & Sons, Inc.
Rate constants for reactions of SO4˙− radicals in acetonitrile
Authors: Padmaja S. , Alfassi Z. B. , Neta P. , Huie R. E. 
Published: January 2005

AbstractRate constants have been measured for the reactions of the sulfate radical, SO4˙−, with alkanes, alkenes, alcohols, ethers, and amines in 95% acetonitrile solution. The rate constants were in the range of 106 L mol−1 s−1 for the abstraction reactions and 107−109 L mol−1 s−1 for the addition and electron transfer reactions. These values are 20 to 80 times lower than those measured in aqueous solutions. Furthermore, the rate constants for the reactions of SO4˙− with the primary alcohols increase with the number of carbon atoms and then level off, in contrast to the behavior observed in aqueous solution, where the rate constant increases more sharply for the larger alcohols. © 1993 John Wiley & Sons, Inc.
A kinetic study of the oxidation of L‐ascorbic acid by chromium(VI)
Authors: Perez‐Benito Joaquin F. , Arias Conchita 
Published: January 2005

AbstractThe reaction between chromium(VI) and L‐ascorbic acid has been studied by spectrophotometry in the presence of aqueous citrate buffers in the pH range 5.69–7.21. The reaction is slowed down by an increase of the ionic strength. At constant ionic strength, manganese(II) ion does not exert any appreciable inhibition effect on the reaction rate. The rate law found is

where Kp is the equilibrium constant for protonation of chromate ion and kr is the rate constant for the redox reaction between the active forms of the oxidant (hydrogenchromate ion) and the reductant (L‐hydrogenascorbate ion). The activation parameters associated with rate constant kr are Ea = 20.4 ± 0.9 kJ mol−1, ΔH≠ = 17.9 ± 0.9 kJ mol−1, and ΔS≠=−152 ± 3 J K−1 mol−1. The reaction thermodynamic magnitudes associated with equilibrium constant Kp are ΔH0 = 16.5 ± 1.1 kJ mol−1 and ΔS0 = 167 ± 4 J K−1 mol−1. A mechanism in accordance with the experimental data is proposed for the reaction. © 1993 John Wiley & Sons, Inc.
Kinetic isotope effect for hydrogen/deuterium abstraction by chlorine atoms from (CH3)2NNO2 and (CD3)2NNO2
Authors: Lazarou Yannis G. , Papagiannakopoulos Panos 
Published: January 2005

AbstractThe kinetic isotope effect for the abstraction of hydrogen/deuterium from dimethylnitramine and dimethylnitramine‐d6 by chlorine atoms has been studied in the temperature range 273–353 K. The rate constant ratio kH0/kD is given by the Arrhenius expression, kH/kD=(0.92 ± 0.07)exp(286 ± 250/RT), where R is expressed in cal mol−1 K−1. The absolute rate constant for the deuterium abstraction reaction is extrapolated as kD=(1.50 ± 0.90) × 10−10 exp(−1,486 ± 370/RT) cm3 molecule−1 s−1. The temperature dependence of the kinetic isotope effect was calculated using the conventional transition‐state theory, and the obtained values for kH/kD and ΔEH, D are in good agreement with the experimental value for a bent transition state geometry, with two new vibrational frequencies of 340 cm−1 (272 cm−1) corresponding to the in‐plane and out‐of‐plane motions of hydrogen (deuterium) atoms in the Cl…H…C arrangement. © 1993 John Wiley & Sons, Inc.
CO2 laser‐induced decomposition of ethanol
Authors: Holbrook K. A. , Oldershaw G. A. , Shaw C. J. 
Published: January 2005

AbstractThe multiple photon absorption and decomposition of ethanol irradiated by pulsed 9P18 infrared radiation (1048.7 cm−1) from a TEA CO2 laser has been studied in the fluence range 15 to 5 J cm−2. The absorption cross‐section is pressure‐dependent due to rapid collisional rotational hole‐filling. At low pressures the only important decomposition channel following absorption is molecular dehydration of ethanol to yield ethene, but at higher pressures hydrogen, methane, carbon monoxide, ethane, and ethyne are also produced. In the irradiation of pure ethanol under ‘collision‐free’ conditions, thermal decomposition following collisional redistribution of energy makes only a small contribution to the overall decomposition yield at fluences above 3.5 J cm−2 but may become more significant at lower fluences. Modelling using RRKM calculations has been employed to link measured absorbed energies to extents of decomposition of ethanol. Both these calculations and the absorption measurements indicate that at low pressures only a fraction of the irradiated ethanol molecules absorb the 9P18 radiation. © 1993 John Wiley & Sons, Inc.