bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anomalous kinetic hydrogen isotope effect in the oxidation of formate by bromine: Tunneling via an intermediate
Authors: Brusa M. A. , Colussi A. J. 
Published: January 2005

AbstractRates of oxidation of XCOO− (X = H, D) by Br2 in acid aqueous media were measured between 274 and 332 K. The derived Arrhenius parameters for both reactions

where θ = 4.575T × 10−3 kcal/mol, with (kH/kD)298K = 2.85, reveal a primary isotope effect, but the difference (ED ‐ EH) = 3.29 kcal/mol and the ratio AD/AH = 91 fall beyond the limits imposed by semiclassical transition‐state theory, suggesting tunneling or a multiple‐stage mechanism. However, it can be shown that either tunneling in a single step or a three‐step, internal return mechanism can be ruled out as alternative models, since both require unreasonable kinetic parameters to fit the data. The simplest scheme accounting for the present observations involves tunneling in the decomposition of a charge transfer complex in equilibrium with the reactants.
Reactions of isopropylperoxy radicals with NO and NO2
Authors: Adachi Hiroyuki , Basco Norman 
Published: January 2005

AbstractThe rate constants for the reactions magnified image have been measured directly by flash photolysis and kinetic spectroscopy. At room temperature, k3 = (3.4 ± 0.1) × 109 L/mol·s, independent of pressure in the range of 55–400 torr, and k6 = (2.1 ± 0.2) × 109 L/mol·s.
Free‐energy correlation for catalysis of outer sphere electron‐transfer reactions by noncoordinated pyridine derivatives
Authors: Fanchiang Yueh‐Tai 
Published: January 2005

AbstractRecent experimental data concerning the rate constants and their free energy of the outer sphere electron‐transfer reactions, as catalyzed by noncoordinated pyridine derivatives in aqueous solution, are examined for possible correlation. For the electron transfer reactions between V or Eu and the bipyridyl derivatives, such as N,N'‐dimethyl‐4,4′‐bipyridyl (paraquat) or diquat, the data are correlated quite well by the Marcus equation. The electron exchange rate constant, 5 × 107M−1·s−1, for an organic radical ion and its parent molecule obtained from semiquinones or their related compounds can be applied to these pyridine derivatives. However, in some cases such as electron transfer from paraquat or diquat cation radical to Co(en), positive departures from the Marcus model are observed. These positive departures are interpreted in terms of interaction between the molecular orbitals of electron donors and electron acceptors in the transition state.
The use of transition‐state theory to extrapolate rate coefficients for reactions of oh with alkanes
Authors: Cohen N. 
Published: January 2005

AbstractA method is described for extrapolating existing experimental data on the reactions of OH radicals with alkanes to higher temperatures using conventional transition‐state theory. Expressions are developed for the estimation of the structural properties of the activated complex necessary for calculating ΔS± and ΔH±. The vibrational frequencies and internal rotations of the activated complex are given by those of the reacting alkane or the analogous alcohol and a set of additional internal modes that is the same for all OH + alkane reactions considered. Differences between primary, secondary, and tertiary hydrogen attack are discussed, and the validity of representing the activated complexes of all OH + alkane reactions by a fixed set of vibrational frequencies and other internal modes is evaluated. Calculations are presented for the reaction of OH with CH4, C2H6, C3H8, n‐C4H10, i‐C4H10, c‐C4H8, c‐C5H10, c‐C6H12, (CH3)2CHCH(CH3)2, (CH3)3CCH(CH3)2, (CH3)4C, and (CH3)3CC(CH3)3, and the results are compared with experiments.
Kinetics of oxidation of some meta‐ and para‐substituted phenyl methyl sulfoxides by chloramine‐T in buffered ethanol–water
Authors: Ganapathy K. , Jayagandhi P. 
Published: January 2005

AbstractThe kinetics of oxidation of methyl phenyl sulfoxide by chloramine‐T (CAT) has been studied in buffered ethanol–water (1:1 v/v) of pH 7.0. The reaction was found to follow no simple‐order kinetics. A possible mechanism is suggested involving three rate‐controlling steps: (1) the reaction between RNHCl (R = CH3C6H4SO2) and the sulfoxide, (2) the disproportionation of RNHCl, and (3) the reaction between RNCl2 and the sulfoxide. A mixed‐order rate law is derived as rate/[C][SO] = k1 + Kdk2[C]/[SA]. The rate law is found to be obeyed for the meta‐ and para‐substituted phenyl methyl sulfoxides also. The ρ value is obtained using Hammett's σ constants. The ρ values obtained for the attack of both RNHCl and RNCl2 with the sulfoxides are almost the same, showing that both are converting the sulfoxide to the same intermediate. A chlorinium ion transfer is suggested.
A novel kinetic and mechanistic study of the oxidation of pinacol by acid bromate—homogeneous catalysis of maganous ions
Authors: Reddy Ch. Sanjeeva , Sundaram E. V. 
Published: January 2005

AbstractA detailed kinetic study of the Mn(II)‐catalyzed and ‐uncatalyzed oxidation of pinacol by bromate has been carried out in aqueous acetic acid media containing Hg(II) ions. The uncatalyzed reaction exhibits 1.5 order that is, 0.5 order in [pinacol] and 1.0 in [bromate]. A decrease in k1 by increasing [bromate] has been accounted for due to the formation of Br2O5, which is inactive toward reduction. Mn(II)‐catalyzed oxidation follows first order in [oxidant], 0.5 order in [manganous ion], and variable order with respect to [pinacol]. At lower [pinacol] (0.005–0.025M) the order is 0.5, but at higher concentration (0.03–0.15M) it becomes negative (−1.0). These observations can be accounted for qualitatively by the formation of 1:1 and 1:2 Mn(II)–pinacol complexes of which only 1:1 is active toward bromate oxidation. At higher [pinacol] the ratio of 1:2 and 1:1 complexes reached 98.2. All reactions were accelerated with acidity, and the rate constant follows the h0 function. Participation of H2O in the rate‐limiting step and a free‐radical mechanism were proposed for the manganous‐ion‐catalyzed reaction, whereas for the uncatalyzed reaction this was not true. The effects of NaClO4, Na4P2O7, and the dielectric constant of the media are also in accordance with the proposed mechanism.
Theoretical rate constant calculations for O(3P) with saturated hydrocarbons
Authors: Michael J. V. , Keil D. G. , Klemm R. B. 
Published: January 2005

AbstractTheoretical rate constants have been calculated for O(3P) with five saturated hydrocarbons, CH4, C2H6, C3H8, iso‐C4H10, and neo‐C5H12. The method of choice is bond energy–bond order (BEBO) with activated complex theory (ACT). Because the BEBO method is empirical, O(3P) + CH4 is evaluated first, and the theoretical results are compared to more rigorous calculations and to the empirical transition state method. Comparisons are also made between predictions and experimental results. All of these comparisons show that the BEBO‐ACT method gives results which are consistent with experiment and other theory. Because the method is successful, the other four cases are then considered. Ambiguity arises for the higher hydrocarbons from the problem of internal rotations in the activated complexes, and three cases are evaluated. Best agreement with experiment is obtained if the primary rotor(s) in the complexes are considered to be free. Predictions of rate constants are made from 500 to 2500 K. Throughout the discussion issues of theory which are common to any ACT calculation from any method of potential energy evaluation (LEP, LEPS, or ab initio quantum mechanics) are featured.
Kinetic and mechanistic studies of oxidation of alanine and phenylalanine by sodium N‐chlorobenzene sulfonamide (chloramine‐B) in hydrochloric acid medium
Authors: Mahadevappa D. S. , Ahmed M. Sayeed , Gowda N. M. Made , Gowda B. Thimme 
Published: January 2005

AbstractThe kinetics of oxidation of alanine and phenylalanine by sodium N‐chlorobenzene sulfonamide (CAB) has been investigated at 30°C in two ranges of acid concentrations. The reactions follow identical kinetics for both amino acids. At low acid concentration (0.03–0.10M), simultaneous catalysis by H+ and Cl− ions is noted. The rate shows a first‐order dependence on [CAB], but is independent of [substrate]. A variation of the ionic strength or the dielectric constant of the medium or the presence of the added reaction product benzene sulfonamide (BSA) has no pronounced effect on the rate.At [HCl] > 0.2M, the rate is independent of [H+], but shows a first‐order dependence on [CAB] and a fractional‐order dependence on [amino acid]. The addition of BSA or Cl− ions, or a change in the ionic strength of the medium has no influence on the rate. Upon decreasing the dielectric constant of the medium, the rate increased, indicating positive ion–dipole interaction in the rate‐determining step. The reaction was studied at different temperatures, and activation parameters have been computed. Rate laws in agreement with experimental results have been derived. Suitable mechanisms to account for the observed kinetics are proposed. The rate constants obtained from the derived rate laws as [H+], [Cl−], and [substrate] vary are in excellent agreement with the observed rate constants, thus justifying the proposed rate laws and hence the suggested mechanistic schemes.
Studies in nickel(IV) chemistry. Electron transfer kinetics of the reaction between tris(dimethylglyoximato)nickelate(IV) and hexacyanoferrate(II) in aqueous medium
Authors: Sahu R. , Neogi G. , Acharya S. , Panda R. K. 
Published: January 2005

AbstractThe kinetics of electron transfer from hexacyanoferrate(II) to tris(dimethylglyoximato)‐nickelate(IV), Ni(dmg)32−, to produce Fe(CN)63− and Ni(dmgH)2, follows a pseudo‐first‐order disappearance in the Ni(IV). The pseudo‐first‐order rate constants kobs are linearly dependent on [Fe(CN)64−]0 in a fiftyfold range of 2 × 10−4−1 × 10−2M, and the average values of kobs/[Fe(CN)64−]0 range from 194M−1·s−1 at pH = 5.20 to 0.2M−1·s−1 at pH = 9.07 in aqueous medium at 35°C and μ = 0.57M. Results are interpreted in terms of a probable mechanism involving rate‐determining outer sphere one‐electron transfer steps from the reductant and one‐protonated reductant species to the unprotonated and one‐protonated Ni(IV) species present in solution. The more electrophilic one‐protonated reductant species apparently reacts several orders of magnitude faster than the unprotonated one.
Kinetic and mechanistic studies on the oxidation of nitrite by peroxomonophosphoric acid
Authors: Panigrahi Ganesh Prasad , Nayak Ramanando 
Published: January 2005

AbstractThe kinetics of oxidation of nitrite to nitrate by peroxomonophosphoric acid in aqueous acid medium have been studied. The observed monotonic fall in rate with increasing pH of the medium has been rationalized on the basis of proton‐dissociation equilibria of the substrate as well as the oxidant species. It is found that only HNO2 reacts with the different PMPA species.
Disproportionation reactions between alkyl and fluoroalkyl radicals. II. Fluoro‐ and trifluoromethyl with ethyl radicals
Authors: Pritchard G. O. , Nilsson W. B. , Marchant P. E. , Case L. C. , Parmer J. F. , Youngs R. F. 
Published: January 2005

AbstractCross‐disproportionation/combination ratios for CFH2 and CF3 with C2H5 radicals have been determined to be Δ = 0.032 ± 0.012 and δ = 0.098 ± 0.020, respectively, over the temperature range 25–75°C. For the pathway that yields CFH and C2H6, δ = 0.020 ± 0.005 at 25°C.
Pseudo‐phase ion‐exchange model for micellar catalysis in the acid hydrolysis of vinyl ethers
Authors: Velázquez Maria Mercedes , García‐Mateos Inmaculada , Herraez Miguel A. , Rodriguez Licesio J. 
Published: January 2005

AbstractThe rate of the perchloric acid hydrolysis of aqueous ethyl and butyl vinyl ethers at 25.0°C, in the presence of micellar aggregates [anionic, sodium dodecyl sulfate (SDS); cationic, cetyl trymethyl ammonium bromide (CTAB); and nonionic, polyoxyethylen23dodecanol, (Brij 35)], has been studied. Negligible effects were observed in the cases of cationic and nonionic micelles. Anionic micelles produce an enhancement in the reaction velocity, and the rate constants go through maxima with increasing SDS concentration. These maxima disappear in the presence of excess sodium perchlorate. All these facts are interpreted quantitatively by means of the pseudo‐phase ion‐exchange model.
Kinetic characteristics of chloride‐assisted oxidative dealkylation of alkylcobalamins
Authors: Fanchiang Yueh‐Tai 
Published: January 2005

AbstractThe recent experiments on the chloride‐assisted dealkylation of alkylcobalamins by a variety of oxidants (IrCl, AuCl, Fe(H2O)5Cl2+, and PtCl), which are scattered in several previous publications, and their general kinetic characteristics are summarized. The kinetic studies are also extended to include the dealkylations of (methylaquo)−3,5,6‐trimethylbenzimidazolylcobamide and protonated base‐off ethylcobalamin by IrCl (1.0M Cl−) and by Fe(III) ions at 0.1M Cl−, and the demethylation of (methylaquo)−3,5,6‐trimethylbenzimidazolylcobamide by AuCl (1.0M Cl−). This extension is in an effort to substantiate the general mechanism which has been previously proposed for these oxidative dealkylations. The general kinetic characteristics are described in terms of a preassociation of the reactants, followed by a rate‐determining electron‐transfer process to yield the R‐B radical, which then undergoes further reactions to produce the products observed. The overall reactions are discussed within the framework of chlorine‐bridging inner sphere electron‐transfer reactions.
Kinetics of tetrachloroethylene photochlorination
Authors: Ledakowicz S. , Nowicki L. , Perkowski J. 
Published: January 2005

AbstractPhotochlorination of tetrachloroethylene has been studied in a homogeneous liquid system. Kinetic parameters such as reaction orders for chlorine, tetracholoroethylene and light intensity, preexponential factor, and activation energy were evaluated from experimental data. The following kinetic equation was obtained by parameter estimation following the Marquardt procedure:
Kinetics of recombination, dismutation, and disproportionation reactions involving neutral ketyl radicals and radical anions
Authors: Koroli L. L. , Kuzmin V. A. , Khudyakov I. V. 
Published: January 2005

AbstractThe kinetics of fast elementary recombination of neutral ketyl radicals of benzophenone and its four derivatives (BPH⋅),
equation image
the dismutation of benzophenone radical anions,
equation image
the disproportionation between BPH⋅ and stable nitroxyl radicals, (magnified image), magnified image and the electron transfer magnified image have been investigated in both individual solvents and binary mixtures of different viscosities. Reaction (1) for unsubstituted BPH in water, water glycerol, and n‐hexane is controlled by diffusion with 2k1 ≃ kdiff. In aliphatic alcohols and toluene, which form solvation complexes with BPH⋅, reaction (1) is diffusion‐enhanced and activation‐controlled, respectively, with 2k1 < kdiff. In a viscous solvent such as 1‐propanol–glycerol mixture (100 ≲ η ≲ 450 cP) reaction (1) is diffusion‐controlled. Reaction (2) in alkaline 1‐propanol and alkaline 1‐propanol–glycerol mixture is activation controlled. The rates of reactions (3) and (4) for benzophenone radicals and nitroxyl radicals of the imidazoline series decrease as the viscosity of the water–glycerol and 1‐propanol–glycerol mixtures is increased. The reactions are molecular mobility limited; nevertheless, the numerical values of k3 (k4) are 2–6 times as small as the corresponding kdiff values due to the low steric factor of the reactions (therefore called pseudodiffusion‐controlled reactions). The theoretical estimates of k3 (k4) are in good agreement with the experimental results. The elimination of spin forbiddance in the process of radical recombination in viscous solvents is discussed.
Liquid‐phase autooxidation of retinyl polyenes
Authors: Finkelshtein E. I. , Rubchinskaya Yu. M. , Kozlov E. I. 
Published: January 2005

AbstractThe autooxidation of retinyl acetate and methyl retinoate was investigated in chlorobenzene at 45°C. The rates of thermal initiation in the retinyl acetate solutions were measured, and a value was determined of the rate constant for the reaction of oxygen with retinyl acetate (RH + O2→ R· + HO2·):kio= (1.3 ± 0.2) × 10−5L/mol · s. The number of moles of oxygen absorbed per mole of polyene depends on the substrate concentration. A kinetic scheme for the methyl retinoate autooxidation was proposed which takes into account the isomerization of primary peroxy radicals, and the rate constants for different elementary reactions were estimated. The partial rate constant for “allylic” hydrogen abstraction from retinyl acetate was estimated to be ≥ 1.65 × 103L/mol · s. A probable propagation sequence was proposed for the autooxidation of retinyl acetate.
Kinetics of rich ammonia flames
Authors: Dean Anthony M. , Chou Mau‐Song , Stern David 
Published: January 2005

AbstractWe report laser absorption measurements of NH3 decay within the flame front region of rich, atmospheric pressure ammonia flames. These data are combined with earlier OH, NH, and NH2 measurements to obtain new estimates for the oscillator strength of NH2. This value, fi = 6.4 × 10−5 for the PQ1,7 line in the (0,9,0) ← (0,0.0) vibrational band of the A2A1 ← X2B1 transition, suggests ΔH(NH) ≅ 87 kcal/mol. The ammonia profiles were also combined with previous data on NO, NH, NH2, and OH to provide an extensive database at fuel equivalence ratios (ø) of 1.28, 1.50, and 1.81 for comparison to our kinetic model predictions. This modeling used a one‐dimensional flame code which explicitly accounts for the diffusional component in our flame experiments. Modeling results using a conventional mechanism predicted concentration profiles which deviated markedly from our observations. It was possible to obtain much more satisfactory fits by postulating reactions between various NHi (i = 1, 2) species to form N—N bonds. The N2Hj (j = 1–3) species could then lose H atoms via dissociation to ultimately form N2. Inclusion of these reactions in the mechanism allowed us to predict concentration—distance profiles for five different species at three different equivalence ratios that are in good agreement with experiment. The most important component of this mechanism is the recognition that the NHi + NHi reactions dominate the kinetics in rich flames. A most satisfying aspect of these calculations is that the key rate constants in the NHi + NHi sequence were estimated using simple RRK theory.
High temperature study of the reactions of O and OH with NH3
Authors: Salimian S. , Hanson R. K. , Kruger C. H. 
Published: January 2005

AbstractMixtures of NH3 and N2O dilute in Ar were heated behind incident shock waves in the temperature range 1750–2060 K. A cw ring dye laser, tuned to the center of an OH absorption line in the ultraviolet, was used to monitor OH concentration profiles by absorption spectroscopy. Infrared emission was used to follow N2O (at 4.5 μm) and NH3 (at 10.5 μm) concentration—time histories. The early‐time NH3 and OH concentration profiles were sensitive to the rate constants of the reactionsmagnified imageleading to the following best‐fit expressions for k2 and k3:k2 = 1013.34±0.3 exp(−4470/T) and k3 = 1013.91±0.2 exp(‐4230/T) cm3 mol−1 s−1. The results of this study combined with previous low‐temperature data suggest a significant non‐Arrhenius behavior for both k2 and k3.
Kinetics of OH reactions with furan, thiophene, and tetrahydrothiophene
Authors: Wine P. H. , Thompson R. J. 
Published: January 2005

AbstractThe kinetics of OH reactions with furan (k1), thiophene (k2), and tetrahydrothiophene (k3), have been investigated over the temperature range 254–425 K. OH radicals were produced by flash photolysis of water vapor at λ > 165 nm and detected by timeresolved resonance fluorescence spectroscopy. The following Arrhenius expressions adequately describe the measured rate constants as a function of temperature (units are cm3 molecule−1 S−1): k1 = (1.33 ± 0.29) × 10−11 exp[(333 ± 67)/T], k2 = (3.20 ± 0.70) × 10−12 exp[(325 ± 71)/T], k3 = (1.13 ± 0.35) × 10−11 exp[(166 ± 97)/T]. The results are compared with previous investigations and their implications regarding reaction mechanisms and atmospheric residence times are discussed.
Rate constants for the reactions of OH radicals with alkyl substituted olefins
Authors: Ohta Tomohiro 
Published: January 2005

AbstractRelative rate constants for the reactions of hydroxyl radicals with a series of alkyl substituted olefins were measured by competitive reactions between pairs of olefins at 298 ± 2 K and 1 atmospheric pressure. Hydroxyl radicals were produced by the photolysis of H2O2 with 254‐nm irradiation. The obtained rate constants were (× 10−11 cm3 molecule−1 s−1): 2.53 ± 0.06, propylene; 5.49 ± 0.17, cis‐2‐butene; 5.47 ± 0.1, isobutene; 6.46 ± 0.13, 2‐methyl‐1‐butene; 6.37 ± 0.16, cis‐2‐pentene; 6.23 ± 0.1, 2‐methyl‐1‐pentene; 8.76 ± 0.14, 2‐methyl‐2‐pentene; 6.24 ± 0.08, trans‐4‐methyl‐2‐pentene; 10.3 ± 0.1, 2,3‐dimethyl‐2‐butene; 9.94 ± 0.1, 2,3‐dimethyl‐2‐pentene; 5.59 ± 0.07, trans‐4,4‐dimethyl‐2‐pentene. A trend in alkyl substituent effect on the rate constant was found, which is useful to predict kOH on the basis of the number of alkyl substituents on the double bond.
Kinetics of the gas‐phase reactions of NO3 radicals with a series of aromatics at 296 ± 2 K
Authors: Atkinson Roger , Carter William P. L. , Plum Christopher N. , Winer Arthur M. , Pitts James N. 
Published: January 2005

AbstractRate constants have been determined at 296 ± 2 K for the gas phase reaction of NO3 radicals with a series of aromatics using a relative rate technique. The rate constants obtained (in cm3 molecule−1 s−1 units) were: benzene, <2.3 × 10−17; toluene, (1.8 ± 1.0) × 10−17; oxylene, (1.1 ± 0.5) × 10−16; mxylene, (7.1 ± 3.4) × 10−17; pxylene, (1.4 ± 0.6) × 10−16; 1,2,3‐trimethylbenzene, (5,6 ± 2.6) × 10−16; 1,2,4‐trimethylbenzene (5.4 ‐ 2.5) × 10−16; 1,3,5‐trimethylbenzene, (2.4 ± 1.1) × 10−16; phenol, (2.1 ± 0.5) × 10−12; methoxybenzene, (5.0 ± 2.8) × 10−17; o‐cresol, (1.20 ± 0.34) × 10−11; m‐cresol, (9.2 ± 2.4) × 10−12; p‐cresol, (1.27 ± 0.36) × 10−11; and benzaldehyde, (1.13 ± 0.25) × 10−15. These kinetic data, together with, in the case of phenol, product data, suggest that these reactions proceed via H‐atom abstraction from the substituent groups. The magnitude of the rate constants for the hydroxy‐substituted aromatics indicates that the nighttime reaction of NO3 radicals with these aromatics can be an important loss process for both NO3 radicals and these organics, as well as being a possible source of nitric acid, a key component of acid deposition.
The high temperature oxidation of the methyl side chain of toluene
Authors: Brezinsky K. , Litzinger T. A. , Glassman I. 
Published: January 2005

AbstractFrom the results of order of magnitude analyses, it is concluded that during the oxidation of toluene, radical‐atom and radical‐radical reactions (1) and (3) play an unusually important and approximately equal role in the formation of benzaldehyde, an intermediate that leads eventually to the complete removal of the side chain.
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An additional radical‐radical system, reaction (2), is shown to be the most likely source of benzyl alcohol observed during toluene oxidation.
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