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The thermal reaction of HNCO at moderate temperatures
Authors: He Y. , Liu Xiaoping , Lin M. C. , Melius C. F.
Published: January 2005

The thermal reaction of HNCO has been studied in a static cell at temperatures between 873 and 1220 K and a constant pressure of 800 torr under highly diluted conditions. The reaction was measurable above 1000 K by FTIR spectrometry. The products detected include CO, CO2, HCN, NH3, and the unreacted HNCO. In this moderate temperature regime, the rates of product formation and HNCO decay cannot be accounted for by a previously established high‐temperature mechanism, assuming HNCO → NH + CO (1) as the initiation process. Instead, a new bimolecular reaction, 2HNCO → CO2 + HNCNH (2), has been invoked to interpret the disappearance of HNCO as well as the formation of various products, most importantly CO2.

The concentration profiles of all measured species can be quantitatively modeled, throughout the temperature range analyzed, by varying k2 using a modified mechanism. The kinetically modeled values of k2 can be effectively represented by

This result agrees closely with that computed with the conventional transition‐state theory using the TST parameters predicted by the BAC‐MP4 method:

The bimolecular reaction takes place via a stable 4‐membered ring intermediate which is isoelectronic with diketene; viz. magnified image
Kinetics studies of reactions of OH radicals with four haloethanes part I. Experiment and BEBO calculation
Authors: Xing Shi‐Ben , Shi Su‐Hao , Qiu Lian‐Xiong
Published: January 2005

The rate constants for reactions of OH with ClCH2CH2Cl, Cl2CHCHCl2, BrCH2CH2Br, CH3CH2Br have been measured by using a discharge flow‐resonance fluorescence (DF‐RF) technique over the temperature range 293–418 K. The rate constants as a function of temperature were fitted to the Arrhenius expression as follows: (k's units are 10−12 cm3 molecule−1 s−1, and Ea's units are cal/mol)

The experimental data have been compared with theoretical calculations of the semi‐empirical BEBO‐transition state method. Life‐times of the four haloethanes in the troposphere have been estimated.
Kinetics and mechanism of the iodine oxidation of hydroxylamine
Authors: Wang Robert T. , Rábai Gyula , Kustin Kenneth
Published: January 2005

Studies of the stoichiometry and kinetics of the reaction between hydroxylamine and iodine, previously studied in media below pH 3, have been extended to pH 5.5. The stoichiometry over the pH range 3.4–5.5 is 2NH2OH + 2I2 = N2O + 4I− + H2O + 4H+. Since the reaction is first‐order in [I2] + [I3−], the specific rate law, k0, is k0 = (k1 + k2/[H+]) {[NH3OH+]0/(1 + Kp[H+])} {1/(1 + KI[I−])}, where [NH3OH+]0 is total initial hydroxylamine concentration, and k1, k2, Kp, and KI are (6.5 ± 0.6) × 105 M−1 s−1, (5.0 ± 0.5) s−1, 1 × 106 M−1, and 725 M−1, respectively. A mechanism taking into account unprotonated hydroxylamine (NH2OH) and molecular iodine (I2) as reactive species, with intermediates NH2OI2−, HNO, NH2O, and I2−, is proposed.
Microemulsions as a medium in chemical kinetics, II. The I− + S2O8= and crystal Violet + OH− reactions in different surfactant/oil/water microemulsions
Authors: Izquierdo Carmen , Casado Julio , Rodriguez Amalia , Moyá Maria Luisa
Published: January 2005

A kinetic study of the reactions I− + S2O8= and CV+ + OH− (CV = 4, 4′, 4″‐tris(dimethylamino)triphenylmethyl chloride or crystal violet) in different water in oil microemulsions is reported. The dependence of the rate constants on the nature of the surfactant as well as on the molar ratio R = [H2O]/[Surfactant] has been investigated. The results are interpreted on the basis of the electrostatic interactions between the reactants and the surfactant polar heads and considering the water properties inside the aqueous core of the droplets.
Evidences on the intermediacy of furoxan in the flash vacuum thermolysis of some 4‐Nitroisoxazoles
Authors: Wunderlin Daniel A. , Davico Gustavo E. , Perez Jorge D.
Published: January 2005

The kinetic measurements in the Flash Vacuum Thermolysis (FVT) of 3,5‐Dimethyl‐ and 5‐Methyl‐ 4‐Nitroisoxazole confirm the already suggested intermediacy of the isomer 2H‐Azirine in the formation of 1‐ Cyano‐1‐Nitroacetone. Moreover, theoretical calculations of the stabilization energy (Es), at the transition state, using second order perturbation suggest that this azirine is formed through the isomer furoxan rather than directly from the starting isoxazole.
Atmospheric photooxidation of isoprene part I: The hydroxyl radical and ground state atomic oxygen reactions
Authors: Paulson Suzanne E. , Flagan Richard C. , Seinfeld John H.
Published: January 2005

The OH reaction with isoprene is studied. Methyl nitrite photolysis experiments were carried out in an outdoor smog chamber in an attempt to identify as completely as possible OH‐isoprene product distribution. Emphasis was placed on identification and quantification of oxygenated products. A Tenax‐based cryo‐trap thermal desorber used to trap, concentrate, and dry chamber samples for identification on a GC/MS is described. Analysis of the products revealed that O(3P) can form in reaction systems designed to study OH reactions that include high concentrations of NO, and consequently NO2, hence, this reaction is also examined. The yields of methacrolein and methyl vinyl ketone are determined as 25 ± 3 and 35.5 ± 4%, respectively, with an additional 4 ± 2% as 3‐methyl furan, totaling 65 ± 4%. These results, combined with those of previous studies allow 80% of isoprene's products to be explicitly identified, and the general structure of the remaining products to be ascertained. The O(3P) reaction produces 84 ± 8% epoxides, and 8 ± 3% species which result in production of HO2, and subsequently, OH. A heretofore unidentified product of the O(3P) reaction, 2‐methyl 2‐butenal, is identified. The rate constant of the NO2‐isoprene reaction is measured.
Atmospheric photooxidation of isoprene part II: The ozone‐isoprene reaction
Authors: Paulson Suzanne E. , Flagan Richard C. , Seinfeld John H.
Published: January 2005

A series of experiments have been performed to study the ozone‐isoprene reaction in a smog chamber by adding externally produced O3 to the hydrocarbon in the dark. A chemical tracer, methyl cyclohexane, was added to probe the OH formation in the system. O(3P) formation was also examined using the known distribution of products that are unique to the O(3P)‐isoprene reaction (part I). The results provide clear evidence that both OH and O(3P) are produced by the O3‐isoprene reaction directly in large quantities; about 0.68 ± 0.15 and 0.45 ± 0.20 per O3‐isoprene reaction, respectively. These additional radicals severely complicate the analysis of the O3 reaction, hence, computer kinetic modeling was necessary to ascertain the products of the O3 reaction itself, corrected for OH and O(3P) reactions. The product distribution, which differs dramatically from that published previously, is: 67 ± 9% methacrolein, 26 ± 6% methyl vinyl ketone, and 7 ± 3% propene, accounting for 100 ± 10% of the reacted isoprene. Applicability of these results to the gas‐phase O3 reaction with other unsaturated hydrocarbons is briefly discussed.
Kinetics and mechanism of the atmospheric oxidation of Ethyl tertiary butyl ether
Authors: Smith D. F. , Kleindienst T. E. , Hudgens E. E. , McIver C. D. , Bufalini J. J.
Published: January 2005

Ethyl tertiary butyl ether (ETBE) is being proposed as an additive for use in reformulated gasolines. In this study, experiments were performed to examine the kinetics and mechanism of the atmospheric removal of ETBE. The kinetics of the reaction of ETBE with OH radicals were examined by using a relative rate technique with the photolysis of methyl nitrite to generate OH radicals. With n‐hexane as the reference compound, a value of (9.73 ± 0.33) × 10−12 cm3 molecule−1 s−1 was obtained for the rate constant. The OH rate constant for t‐butyl acetate, a product of the oxidation of ETBE, was (4.4 ± 0.4) × 10−13 cm3 molecule−1 s−1 at 298 K.

The primary products and molar yields for the OH reaction with ETBE in the presence of NOx were t‐butyl formate (0.64 ± 0.03), t‐butyl acetate (0.13 ± 0.01), ethyl acetate (0.043 ± 0.003), acetaldehyde (0.16 ± 0.01), acetone (0.019 ± 0.002), and formaldehyde (0.53 ± 0.04). Under the described reaction conditions, the formation of t‐butyl nitrite was also observed. From these molar yields, approximately 98% of the reacted ETBE could be accounted for by paths leading to these products. Chemical mechanisms to explain the formation of these products are presented.
The chain mechanism of ozone destruction by CFCl3 in the 214 nm photolysis of its mixtures with oxygen
Authors: Horowitz A. , Schuster G. , Moortgat G. K.
Published: January 2005

The effect of CFCl3 (0.025–0.200 mbar) addition on the formation of ozone in 214 nm photolysis of oxygen (800–2000 mbar) was investigated. Kinetic analysis of the drastic reduction in ozone formation in the presence of CFCl3 shows that it proceeds by a chain mechanism with a chain length of 5.07 ± 0.21(2σ). This chain length is independent of CFCl3 and O2 pressures as well as incident light intensity and the mechanism of the chain reaction is governed by the Cl generating reactions of ClO radicals. A mechanism based only on the self reaction of these radicals: ClO + ClO → Cl2 + O2 (7), Cl + ClO2 (8), and Cl + OClO (9), followed by fast decomposition of ClO2 into Cl and O2, predicts a chain length which is considerably lower than the observed value. Incorporation of the reaction CFCl2O2 + ClO → CFCl2O + ClO2 (11) in the mechanism satisfactorily accounts for the observed chain length. A lower limit of 3 × 10−12 cm3 molecule−1 s−1 for k11 is estimated.
On the reaction of CH with CO studied in high temperature CH4/Ar + CO mixtures
Authors: Markus Michael W. , Roth Paul
Published: January 2005

In this study a ring dye laser spectrometer was employed for in‐situ measurements of CH concentrations in the reaction zone behind shock waves. The time dependent absorption in the Q‐branch of the A2Δ — X2Π band of CH at 431.1311 nm caused by the formation and consumption of CH radicals during the shock induced pyrolysis of a few ppm methane in argon was recorded. The CH concentration could directly be calculated from the measured absorption by applying the Lambert‐Beer law. By adding a few percent CO to the initial mixtures, the CH concentration profiles were significantly perturbed. Both the perturbed and unperturbed CH concentration profiles have been compared with those calculated from reaction kinetic simulations. A reaction mechanism describing the CH concentration history in the CH4/Ar and CH4/CO/Ar systems between 2900 K and 3500 K was developed. By a fitting procedure, a value of k1 = 1.85 × 1011 cm3 mol−1 s−1 was obtained for the most important perturbation reaction CH + CO → C2O + H.
Kinetics of solvolysis of 1‐acetyl‐4‐(1‐ethoxycarbonyl‐1‐cyano) methylene‐1,4‐dihydroquinoline in undried DMSO‐d6· formation of Acetic Anhydride as an intermediate
Authors: Klemm Leroy H. , Lu Jennifer J. , Klemm Richard A.
Published: January 2005

The kinetics of solvolysis of the title compound (QAc) in undried DMSO‐d6 to give 4‐(1‐ethoxycarbonyl‐1‐cyano)methylquinoline (QH) and HOAc at ambient temperature were investigated by 1H nmr spectrometry. With a limited excess of water the solvolysis follows a three‐step process of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm QAc} + {\rm H}_2 {\rm O}\mathop \to \limits^{k_1} {\rm QH} + {\rm HOAc}, $\end{document} , and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Ac}_{\rm 2} {\rm O} + {\rm H}_2 {\rm O}\mathop \to \limits^{k_3} {\rm 2\,HOAc}, $\end{document} where k2 > k1 and k3 < k1. Addition of pyridine‐d5 to the reaction mixture markedly catalyzes the overall solvolysis, while addition of CF3CO2D to the reaction mixture simplifies the kinetics to pseudo first‐order in [QAc] with k = 4.3 × 10−3 min−1.
Kinetics of a second order reaction involving two intermediate second order reactions
Authors: Klemm Richard A. , Klemm Leroy H.
Published: January 2005

We have studied the kinetics of a reaction in which starting materials A and B react to form the products C and D directly, as well as by way of two additional intermediate reactions. In the first intermediate reaction, A and C react to form D and E, and in the second intermediate reaction, B and E react to form 2C. There are three conservation laws, which effectively reduce the number of variables to two, resulting in nonlinear coupled first order differential equations for [A](t) and [B](t). These equations are readily solved by standard numerical procedures, for various values of the relative reaction rates and starting concentrations. Our results are used to fit experimental data for the case in which A and B are 1‐acetyl‐4‐(1‐ethoxycarbonyl‐1‐cyano)methylene‐1,4‐dihydroquinoline and water, for which the first and third reverse reactions can be neglected.
Gas‐phase reactions of azulene with OH and NO3 radicals and O3 at 298 ± 2 K
Authors: Atkinson Roger , Arey Janet , Aschmann Sara M.
Published: January 2005

Azulene, which is isomeric with naphthalene, was studied to determine whether it behaves like a polycyclic aromatic hydrocarbon or an alkene in its gas‐phase reactions with OH and NO3 radicals and O3. Using relative rate methods, rate constants for the reactions of azulene with OH and NO3 radicals and O3 of (2.73 ± 0.56) × 10−10 cm3 molecule−1 s−1, (3.9) × 10−10 cm3 molecule−1 s−1, and <7 × 10−17 cm3 molecule−1 s−1, respectively, were obtained at 298 ± 2 K. The observation that the NO3 radical reaction did not involve NO2 in the rate determining step indicates that azulene behaves more like an alkene than a polycyclic aromatic hydrocarbon in this reaction. No conclusive evidence for the formation of nitroazulene(s) from either the OH or NO3 radical‐initiated reaction of azulene (in the presence of NOx) was obtained.
The mechanism of O(3P) atom reaction with ethylene and other simple olefins
Authors: Knyazev V. D. , Arutyunov V. S. , Vedeneev V. I.
Published: January 2005

Reactions of oxygen atoms with ethylene, propene, and 2‐butene were studied at room temperature under discharge flow conditions by resonance fluorescence spectroscopy of O and H atoms at pressures of 0.08 to 12 torr. The measured total rate constants of these reactions are K = (7.8 ± 0.6)·10−13cm3s−1,K = (4.3 ± 0.4) ± 10−12 cm3 s−1, K = (1.4 ± 0.4) · 10−11 cm3 s−1. The branching ratios of H atom elimination channels were measured for reactions of O atoms with ethylene and propene. No H‐atom elimination was found for the reaction of O‐atoms with 2‐butene. A redistribution of reaction O + C2 channels with pressure was found. A mechanism of the O + C2 reaction was proposed and the possibility of its application to other olefins is discussed. On the basis of mechanism the pressure dependence of the total rate constant for reaction O + C2 was predicted and experimentally confirmed in the pressure range 0.08–1.46 torr.
Investigation of the reaction order for nucleophilic substitution of dialkyl methylphosphonates by alkoxides
Authors: Leslie D. R. , Long G. J. , Pantelidis S.
Published: January 2005

The rate of nucleophilic substitution at the phosphorus centre of dialkyl methylphosphonates by methoxide and ethoxide has been studied to investigate the possible involvement of hexacoordinated phosphorus species in this reaction. For alkoxide concentrations less than ca. 1.5 M the rate increases with the square of alkoxide concentration. However, consideration of the activity of the alkoxides, represented by an appropriate acidity function, reveals that only one equivalent of alkoxide is involved in the rate‐determining step. Thus, there is no requirement to invoke the intermediacy of a hexacoordinated species in the reaction pathway. © John Wiley & Sons, Inc.
The retro‐aldol mechanism in the pyrolysis kinetics of primary, secondary, and tertiary β‐hydroxy ketones in the gas phase
Authors: Rotinov Alexandra , Chuchani Gabriel , Machado Ruben A. , Rivas Carlos , Quijano Jairo , Yepes Maria Del Socorro , Restrepo Iliana
Published: January 2005

The pyrolysis kinetics of primary, secondary, and tertiary β‐hydroxy ketones have been studied in static seasoned vessels over the pressure range of 21–152 torr and the temperature range of 190°–260°C. These eliminations are homogeneous, unimolecular, and follow a first‐order rate law. The rate coefficients are expressed by the following equations: for 1‐hydroxy‐3‐butanone, log k1(s−1) = (12.18 ± 0.39) − (150.0 ± 3.9) kJ mol−1 (2.303RT)−1; for 4‐hydroxy‐2‐pentanone, log k1(s−1) = (11.64 ± 0.28) − (142.1 ± 2.7) kJ mol−1 (2.303RT)−1; and for 4‐hydroxy‐4‐methyl‐2‐pentanone, log k1(s−1) = (11.36 ± 0.52) − (133.4 ± 4.9) kJ mol−1 (2.303RT)−1. The acid nature of the hydroxyl hydrogen is not determinant in rate enhancement, but important in assistance during elimination. However, methyl substitution at the hydroxyl carbon causes a small but significant increase in rates and, thus, appears to be the limiting factor in a retroaldol type of mechanism in these decompositions. © John Wiley & Sons, Inc.
Kinetics of dissociation of tris‐2,2′‐bipyridyl‐iron(II) cation in aqueous acetic acid solutions
Authors: Sriramam K. , Sreelakshmi J. , Ramadevi L. , Ramakrishna Ch.
Published: January 2005

The kinetics of dissociation of tris‐2,2′‐bipyridyl‐iron(II) complex ion have been examined in aqueous acetic acid solutions. The reaction is first order in the complex ion; the dependence of rate on H+ is somewhat like that observed in aqueous solutions approaching a limiting value at higher H+ concentrations. The influence of solvent composition on the reaction rate under acid‐dependent and acid‐independent conditions shows an initial retardation by acetic acid. The argument of ion‐pair formation based on decrease of dielectric constant proposed to explain the kinetics in other aqueous solvent media was found useless to explain the behavior in acetic acid solutions. Other solvent parameters also did not provide satisfactory correlation with the kinetic results, thus, indicating the operation of more complex microscopic solute‐solvent and solvent‐solvent interactions. While solvent effects play some part in the rate process, the rate of reaction would tend to zero in the absence of H2O and H+. This interesting observation proved useful in proposing a reaction mechanism that is consistent with the rate behavior over the entire range of solvent composition. The activity of water in the reaction medium is controlled by the content of acetic acid which can effect the structure of water through operation of hydrophobic forces and formation of hydrates. While acetic acid cannot possibly fulfill the role of water in occupying the vacated coordination position, the anomalous rise in rate even under some water deficient conditions seems to be related to the coordinating ability of HSO4− derived from H2SO4 present in the solution.
Kinetics and mechanism of oxidation of some para‐, meta‐, and ortho‐substituted ethyl S‐phenylmercaptoacetates by chloramine‐B(CAB)
Authors: Gurumurthy R. , Sathiyanarayanan K. , Gopalakrishnan M.
Published: January 2005

The kinetics of oxidation of ethyl S‐phenylmercapto acetate and several para‐, meta‐, and ortho‐substituted ethyl S‐phenylmercaptoacetates by chloramine‐B have been studied in 50% (V/V) aqueous ethanol medium containing phosphate buffer. This oxidation is of first order with respect to substrate and zero order with respect to oxidant. A catalytic effect of mercury is observed and the order with respect to mercury is fractional (0.74). The increase in pH decreases the rate of oxidation and the order with respect to H+ is 0.05. In general electron‐releasing substituents accelerate the rate while electron‐attracting groups retard the rate. A good correlation is found to exist between log k
1 and Hammett constants. Susceptibility of the reaction to the steric effect of ortho‐substituents has been analyzed in the light of application of Taft's steric energy parameters. © John Wiley & Sons, Inc.
Kinetics and mechanism of oxidation of aspartic acid by bismuth(V) in HClO4‐HF medium
Authors: Rao Indu , Jain Seema , Sharma P. D.
Published: January 2005

The kinetics of oxidation of Aspartic acid by bismuth(V) studied in HClO4‐HF mixture iodometrically exhibit complex dependence with respect to aspartic acid (AA). The rate law (i) accounts for all the experimental observations.

equation image

where [Bi(V)] and [AA] are the gross analytical concentration of all fluorobismuth(V) species and the equilibrium concentration of aspartic acid, respectively. The oxidation product of the amino acid was identified to be an aldehyde. HF and F− do not affect the rate of the reaction. © John Wiley & Sons, Inc.
Implications of the HCN → HNC process to high‐temperature nitrogen‐containing fuel chemistry
Authors: Lin M. C. , He Yisheng , Melius C. F.
Published: January 2005

We have found in our recent kinetic study of the oxidation of HCN by NO2 in the temperature range 623–773 K that HNCO and CO2 are very important early products. The measured kinetic data cannot be accounted for by a “conventional” mechanism involving HCN reactions with NO2, O, and OH. However, the introduction of the isomerization reaction HCN → HNC, followed by the rapid oxidation of HNC by NO2, O, and OH, can quantitatively simulate all measured kinetic data. A similar study of the NO2 + HCN reaction in shock waves at temperatures between 1500 and 2400 K also required the inclusion of HNC reactions in order to quantitatively account for measured product distributions. The effects of the HNC molecule on the high temperature HCN chemistry are discussed in terms of the predicted rate constants for HNC reactions with O and OH employing the BAC‐MP4 method. © John Wiley & Sons, Inc.
In situ separation of heterogeneous and homogeneous reaction components in flow experiment
Authors: Orkin V. L. , Khamaganov V. G. , Larin I. K.
Published: January 2005

A method is suggested for the determination of the character (homogeneous or heterogeneous) of the material transformation in the investigation of gas‐phase reactions under tubular flow conditions. The method provides the estimation of the error in the rate constant of a gas‐phase reaction due to the possible parallel occurrence of a heterogeneous process. © 1993 John Wiley & Sons, Inc.
Temperature dependence of the self‐decay rate constants of some phenoxyl radicals in aqueous solution
Authors: Alfassi Z. B. , Shoute L. C. T.
Published: January 2005

The Arrhenius parameters of the bimolecular rate constants for the decay of several phenoxyl radicals in aqueous solution were measured. The p‐halophenoxyl radicals (F, Cl, and Br) decay in a diffusion controlled reaction as the activation energies are the same as that of diffusion of water (16 ± 1.5 kJ · mol−1). The A factors are 1012.2 ± 0.2. For alkyl and alkoxy substituted phenoxyl, slightly higher activation energies were found (19.5 − 21.9 kJ · mol−1). © 1993 John Wiley & Sons, Inc.
Kinetic study of the electrophilic reaction of trialkyltin chlorides and iodine monochloride
Authors: Verbiest P. , Verdonck L. , Van Der Kelen G. P.
Published: January 2005

The kinetics of the electrophilic substitution of several trialkyltin chlorides by iodine monochloride are presented. Rate constants have been determined at four different temperatures and the activation parameters A, Ea, and ΔS°= are calculated. A mechanism is proposed involving charge‐transfer as the driving force for the substitution. © 1993 John Wiley & Sons, Inc.
“Surprising kinetics” or the major role of trace quantities in radical chain mechanisms
Authors: Olbregts Jean
Published: January 2005

Although hydrogen abstraction from 1,1,1,2‐tetrachloroethane should produce only one kind of radical, CCl3CHCl, the presence of small amounts of trichloroethene, as impurity as well as product of reaction, induces the formation of the a priori unexpected CHCl2CCl2 radicals. The importance of this radical in the reaction pathways of the chlorination and the chlorine induced dehydrochlorination of CCl3CH2Cl, under different experimental conditions, is computed and discussed. For example, at 380 K, and for small partial pressures of chlorine (2 torr), the CHCl2CCl2 radicals account for more than 70% of the formation of the reaction products after only 2% reaction. The major role of trace quantities in long chain radical reactions is emphasized. © 1993 John Wiley & Sons, Inc.
Solvent effects on the rate of reaction of Cl2˙− and SO4˙− radicals with unsaturated alcohols
Authors: Alfassi Z. B. , Padmaja S. , Neta P. , Huie R. E.
Published: January 2005

Rate constants have been measured in several aqueous/organic solvent mixtures for the addition reaction of Cl2˙− radicals with 2‐propen‐1‐o1 and 2‐buten‐1‐o1 as a function of temperature and with 2, 3‐dimethyl‐2‐butene at room temperature. The rate constants were in the range of 106–109 L mol−1 s−1, the activation energies were relatively low (1–10 kJ mol−1), and the pre‐exponential factors varied over the range log A = 7.9 to 9.4. The rate constants (k) decreased (by up to a factor of 30) upon increasing the fraction of organic solvent and log k correlated linearly with the dielectric constant for a given water/organic solvent system, but the lines for the different solvent systems had different slopes. A better correlation of log k was found with a combination of the solvatochromic factor, ET(30), and the hydrogen‐bond donor acidity factor, α. This suggests that the rate of reaction is influenced by the solvent polarity and also by specific solvation of the ionic reactant and product. Solvent effect on the reaction of SO4˙− with 2‐propen‐1‐o1 was studied for comparison. © 1993 John Wiley & Sons, Inc.
Rate constants for some hydrogen abstraction reactions of the carbonate radical
Authors: Clifton Carol L. , Huie Robert E.
Published: January 2005

Rate constants have been measured in aqueous solutions for the reactions of the carbonate radical, CO3˙−, with several saturated alcohols and one cyclic ether as a function of temperature. Arrhenius pre‐exponential factors ranged from 2×108 to 1×109 𝓁 mol−1 s−1 and activation energies ranged from 16 to 29 kJ mol−1. The results suggest that the reactions are not pure hydrogen abstraction, but involve an additional interaction of the radical with the OH or O linkage. © 1993 John Wiley & Sons, Inc.
Rate constants for the addition of the 2‐cyano‐2‐propyl radical to alkenes in solution
Authors: Hėberger K. , Fischer H.
Published: January 2005

Absolute rate constants for the addition of the 2‐cyano‐2‐propyl radical to 26 alkenes CH2=CXY at 315 K were determined in solution by time‐resolved electron‐spin‐resonance spectroscopy. They vary with the alkene substituents from 30 M−1 s−1 to 7′010 M−1 s−1. For styrene the temperature dependence is given by log k/M−1 s−1 = 7.7 − 26.1/Θ where Θ = 2.303 RT in kJ/mol. An analysis of the substituent effects in terms of polar and enthalpic factors reveals a dominant influence of the overall reaction enthalpy. © 1993 John Wiley & Sons, Inc.
On the kinetics and mechanism of Nb(V) hydrolysis
Authors: Bottecchia Otávio L. , Boodts Julien F. C.
Published: January 2005

Kinetics of Nb(V) hydrolysis in MgCl2, Mg(ClO4)2 mixtures has been investigated by electroanalytical methods and the rate constants determined. A hydrolysis model based on species postulated in the literature is proposed. Resolution of the corresponding differential equations led to results consistent with experimental data obtained from polarographic current vs. time curves. © 1993 John Wiley & Sons, Inc.
New substrates in the ferroin‐catalyzed bromate system in aqueous‐organic mixed media
Authors: Lalitha P. V. , Ramaswamy R.
Published: January 2005

A large number of substrates have hitherto been employed in the Belousov‐Zhabotinsky (B‐Z) oscillatory system in pure aqueous medium. A systematic study of aromatic bromate oscillators is limited by solubility problem relating to the compounds and the brominated derivatives. The use of aqueous‐organic mixed media for the oscillatory study is found to be highly useful for the study of water insoluble substances. A comparative study of the oscillatory behavior of gallic acid as substrate in pure aqueous as well as in a number of mixed media have been made in order to ascertain the suitability of mixed media in oscillatory systems. The alteration of oscillatory characteristics in the presence of organic solvent can be understood in terms of the Field‐Koros‐Noyes (FKN) mechanism. The oscillatory behavior of seventeen new substrates in the ferroin‐catalyzed bromate system in 20% (v) acetonitrile is also presented and discussed in this communication. The reactivity of structurally related substrates has been correlated to the structure in terms of the relevant oscillatory parameters. The use of aqueous‐organic mixed media in oscillatory systems would enable the investigation of new classes of substrates since getting them into the solution phase would no longer be a limitation. © 1993 John Wiley & Sons, Inc.
A kinetic study of the reaction of fluorine atoms with CH3F, CH3Cl, CH3Br, CF2H2, CO, CF3H, CF3CHCl2, CF3CH2F, CHF2CHF2, CF2ClCH3, CHF2CH3, and CF3CF2H at 295 ± 2 K
Authors: Wallington Timothy J. , Hurley Michael D. , Shi Jichun , Maricq M. Matti , Sehested Jens , Nielsen Ole J. , Ellermann Thomas
Published: January 2005

A variety of relative and absolute techniques have been used to measure the reactivity of fluorine atoms with a series of halogenated organic compounds and CO. The following rate constants were derived, in units of cm3 molecule−1 s−1: CH3F, (3.7 ± 0.8) × 10−11, CH3Cl, (3.3 ± 0.7) × 10−11; CH3Br, (3.0 ± 0.7) × 10−11; CF2H2, (4.3 ± 0.9) × 10−12; CO, (5.5 ± 1.0) × 10−13 (in 700 torr total pressure of N2 diluent); CF3H, (1.4 ± 0.4) × 10−13; CF3CCl2H (HCFC‐123), (1.2 ± 0.4) × 10−12; CF3CFH2 (HFC‐134a), (1.3 ± 0.3) × 10−12, CHF2CHF2 (HFC‐134), (1.0 ± 0.3) × 10−12; CF2ClCH3 (HCFC‐42b), (3.9 ± 0.9) × 10−12, CF2HCH3 (HFC‐152a), (1.7 ± 0.4) × 10−11; and CF3CF2H (HFC‐125), (3.5 ± 0.8) × 10−13. Quoted errors are statistical uncertainties (2σ). For rate constants derived using relative rate techniques, an additional uncertainty has been added to account for potential systematic errors in the reference rate constants used. Experiments were performed at 295 ± 2 K. Results are discussed with respect to the previous literature data and to the interpretation of laboratory studies of the atmospheric chemistry of HCFCs and HFCs. © 1993 John Wiley & Sons, Inc.
Kinetics and mechanism of the formation of CO2 hydrate
Authors: Shindo Yuji , Lund Per Christer , Fujioka Yuichi , Komiyama Hiroshi
Published: January 2005

This article proposes a mechanism of CO2 hydrate formation taking into account both diffusion and reaction, and gives an analysis of its kinetics. The most important assumptions on the model are that water dissolves into liquid CO2 and reacts to form CO2 hydrate, and that the hydrate blocks the dissolution and diffusion of water. Computational simulations were conducted, and the model proposed explains well the many observations on the CO2 hydrate formation in previous articles. It is concluded that liquid CO2 disposed in a deep ocean will form a very thin film of CO2 hydrate, and this will greatly control the CO2 diffusion in the ocean. © 1993 John Wiley & Sons, Inc.
The flash photolysis of aqueous solutions of rhodizonic and croconic acids
Authors: Zhao B. , Back M. H.
Published: January 2005

The flash photolysis of aqueous solutions of rhodizonic and croconic acids has been studied in the presence and absence of electron acceptors. No transient absorption which could be identified with an excited state was observed with either anion. The rate of recovery of the ground state in the absence of additives was a first‐order process with both acids and gave rate constants for deactivation of the excited state, kD, of 2.4 × 105 s−1 for rhodizonate and 2.8 × 105 s−1 for croconate. With croconate dianion in the presence of three acceptors, 4‐nitrobenzylbromide, methylviologen, and biacetyl, a transient absorption was detected, with a maximum absorbance at 500 nm, and was tentatively identified with the monoanion radical, formed following electron transfer to the acceptor. From the rate of growth of the transient, rate constants for the rate of electron transfer to the acceptor were measured as follows: 4‐nitrobenzylbromide: 2.8 × 109 M−1 s−1; methyl viologen: 3.7 × 1010 M−1 s−1; and biacetyl: 2.0 × 108 M−1 s−1. The significance of the measurements is discussed in relation to the mechanism proposed for the photochemical reactions of these dianions. © 1994 John Wiley & Sons, Inc.
Structure–reactivity correlations for gas‐phase thermal Diels‐Alder reactions of cyclohexa‐1,3‐diene with substituted ethenes and reverse reactions
Authors: Huybrechts G. , Van Mele B.
Published: January 2005

Structure–reactivity correlations are developed and used to test a biradical mechanism for gas‐phase thermal Diels‐Alder reactions of cyclohexa‐1,3‐diene with substituted ethenes and reverse reactions. © 1994 John Wiley & Sons, Inc.
Complex dynamical behavior in the oxidation of hydroxylamine by bromate
Authors: Adamˇíková Lubica , Vranová Tamara , Valent Ivan
Published: January 2005

Complex dynamical behavior has been observed in the oxidation of hydroxylamine by bromate in acidic sulfate medium. The reaction shows clock type kinetics in closed conditions and an aperiodic oscillations if gaseous products are removed from the system with a constant flow‐rate. The reduction kinetics of bromate ions with excess hydroxylamine has been studied in the presence of allyl alcohol. The observed pseudo‐first‐order rate constant kobs has been found to follow the expression

where [hydroxylamine] is total initial hydroxylamine concentration, K1 = 0.5 M−1, K2 = 106 M−1, and k = 2.57 × 103 M−1 s−1 at 298.15 K and I = 2.0 M.

The rate constant for the bromine oxidation of hydroxylamine in sulfuric aqueous solution has been determined. © 1994 John Wiley & Sons, Inc.
Hydrolysis of 2‐aminoethanethiolsulfate ions
Authors: Zheng Z. B. , Littlejohn D. , Chang S. G. , Zhuang Y. H.
Published: January 2005

The kinetics of the acid catalyzed hydrolysis of 2‐aminoethanethiolsulfate (AETS) ions were investigated. The dependence of the hydrolysis rate constant on acidity and temperature was determined. The hydrolysis rate equation can be expressed as

where Ho is the Hammett acidity function. The rate constant, k, can be expressed as
equation image
The pKa's for the compound were measured and literature value of pKa was found to be in error. The values determined in this study are pKa1 < −0.5 and pKa2 = 9.1 ± 0.1. General acid catalysis of the hydrolysis reaction was found not to proceed to a significant degree. © 1994 John Wiley & Sons, Inc.

This article is a US Government work and, as such, is in the public domain in the United States of America.
Vacuum ultraviolet photolysis of CClF2CH2Cl
Authors: Minamikawa Tadahiro , Ogura Seido , Sakka Tetsuo , Ogata Yukio , Iwasaki Matae
Published: January 2005

Photolysis of CClF2CH2Cl was studied by 147 nm vacuum ultraviolet irradiation. In the presence of NO; CF2CH2, CF2CHCl, and CClF2CN were produced. These products represent three different reaction paths; the molecular dechlorination, molecular dehydrochlorination, and chlorine radical elimination reactions. The reactant pressure and the addition gas (He or NO) pressure effects upon the product yield were studied. © 1994 John Wiley & Sons, Inc.
Kinetics and mechanism of oxidation of glycine, alanine, and threonine by fluoride coordinated bismuth(V) in aqueous HClO4–HF medium
Authors: Devra Vijai , Jain Seema , Sharma P. D.
Published: January 2005

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.
Photoactivated α‐ketocarbenes: Formation and isomerization reactions. RRKM calculations with semi‐empirical parameters (AM1, MNDOC)
Authors: Bachmann Christian , N'Guessan Thomas Yao
Published: January 2005

The dynamical aspects of some α‐diazoketones (DZ) photolysis are investigated within the framework of statistical theories (RRKM formulation). On the whole, the results agree satisfactorily with the gas‐phase experimental observations (quantum yields). In particular, the reactions DZ + hv → α‐ketocarbene (KC) + N2, appear to be mainly governed by statistical behavior. The two channel isomerizations KC → ketene (KE), i.e, the Wolff Rearrangement, and KC → α,β‐unsaturated ketone (ON) are also considered. It is suggested that the trapping of the α‐ketocarbenes and oxirenes (OX) species would be favored under appropriate conditions (among them the irradiation wavelength and the relaxation processes involved in the reactive medium). The parametrization of the model relies on semi‐empirical quantum calculations and is improved by some adjustments with experimental data. © 1994 John Wiley & Sons, Inc.
The IR multiphoton decomposition of CF3I. The effect of inert and reactive gases
Authors: Rinaldi Carlos A. , Lane Silvia I. , Ferrero Juan C.
Published: January 2005

The multiphoton decomposition of CF3I with a pulsed CO2 laser has been studied at incident fluences of 0.6 and 1.2 J/cm2. The effect of pressure on the reaction probability for dissociation of CF3I was measured in the presence of added isobutane, Ar and CO2. In the experiments with isobutane, the CF3 radicals generated by the decomposition of excited CF3I react to yield CF3H in competition with the recombination to C2F6. The laser absorption cross section was also measured as a function of fluence at a pressure of 0.1 torr of CF3I and with 0.5–2.0 torr of added isobutane. The experimental results were modeled with a master equation in order to obtain information on the energy transferred by collisions of excited CF3I with the bath molecules. An energy dependent value of 〈ΔE〉d produces the best fit to the experimental data. Integration of the rate equations to account for the fractional product yield, [CF3I]/[C2F6], allowed for the calculation of the specific rate constant for hydrogen abstraction from isobutane by CF3 radicals. The value obtained is dependent on the total pressure and higher than expected at room temperature. From these results, an effective temperature for the reaction mixture was calculated. © 1994 John Wiley & Sons, Inc.
Pulsed laser powered homogeneous pyrolysis: A computational analysis
Authors: Swihart Mark T. , Carr Robert W.
Published: January 2005

The use of the pulsed laser powered homogeneous pyrolysis technique for measuring unimolecular decomposition rate constants under unambiguously homogeneous conditions is investigated by numerical simulation of the experiment. The coupled partial differential equations which govern the gas dynamics and chemical kinetics are solved numerically and the results analyzed. Conditions under which rate constants can be extracted from the experimental data using a simplified analysis are determined. The effects of five sources of error in the simplified analysis are computed. A correlation is presented which may be used to correct for overestimation of the rate constant which is inherent in the simple analysis. Conditions under which the other four sources of error become negligible are presented. Overall, it is expected that this technique will be capable of routinely measuring rate constants within a factor of 2, and will do much better when a high power laser with a uniform beam profile is used and/or a well characterized thermal monitor molecule is available which decomposes with kinetic parameters close to that of the reactant being investigated. © 1994 John Wiley & Sons, Inc.
Kinetics of the DS‐radical reactions with CINO and NO2
Authors: Fenter Frederick F. , Anderson James G.
Published: January 2005

The rate constants for the reactions of the DS radical with NO2 (reaction 1) and ClNO (reaction 2) have been measured using the discharge‐flow technique at 2 torr total pressure of helium. The DS radical was monitored by laser‐induced fluorescence. The reactions were found to have the following bimolecular rate constants (95% confidence level, in units of cm3 molecule−1 s−1):

This expression for k1 is found to be in excellent agreement with one of several previous studies. The magnitude of k2 is examined within the framework of a well‐established reactivity trend. © 1994 John Wiley & Sons, Inc.
Kinetics of oxidation of heterocyclic secondary alcohols by N‐chloro‐r‐2,c‐6‐diphenyl‐t‐3 methyl piperidin‐4‐one (NCP) in perchloric acid medium
Authors: Selvaraj Kuppusamy , Venkateswaran Vinayagam , Ramarajan Krishnasamy
Published: January 2005

An investigation of the kinetics of oxidation of epimeric piperidin‐4‐ols, oxan‐4‐ols, and cyclohexanol by N‐chloro‐r‐2, c‐6‐diphenyl‐t‐3‐methylpiperidin‐4‐one (NCP) in aqueous acetic acid in the presence of perchloric acid shows that the reaction is first‐order each in substrate and oxidant. Both H3O+ and Cl− which catalyze the reaction, exhibit a fractional order kinetics. While increase in ionic strength increases the rate slightly, an inverse dependence is observed between rate and solvent polarity. Addition of r‐2‐c‐6‐diphenyl‐t‐3‐methylpiperidin‐4‐one, one of the reaction products, did not influence the rate. Also, no kinetic isotope effect has been observed. A plausible mechanism consistent with these observations is proposed and the relative reactivities of the substrates are explained on conformational grounds. © 1994 John Wiley & Sons, Inc.
Products of the gas‐phase reactions of aromatic hydrocarbons: Effect of NO2 concentration
Authors: Atkinson Roger , Aschmann Sara M.
Published: January 2005

The formation yields of selected products of the OH radical‐initiated reactions of toluene, o‐xylene, and 1,2,3,‐trimethylbenzene have been measured in the absence of NOx and in the presence of varying concentrations of NO and NO2. The formation yield of o‐cresol from toluene increased from 0.123 ± 0.022 in the absence of NOx to 0.160 ± 0.008 for an average NO2 concentration of 1.7 × 1014 molecule cm3. The formation yield of 2,3‐butanedione from o‐xylene was 0.092 ± 0.013 in the absence of NOx, and in the presence of NOx decreased from 0.16 at an average NO2 concentration of (7–8) × 1012 molecule cm−3 to 0.09 at an average NO2 concentration of ca. 7 × 1013 molecule cm−3. The formation yield of 2,3‐butanedione from 1,2,3‐trimethylbenzene increased from 0.18 in the absence of NOx to 0.444 ± 0.053 in the presence of ca. (0.16–3.6) × 1013 molecule cm−3 of NO2. These product data are consistent with literature kinetic data showing that the hydroxycyclohexadienyl radicals formed by OH radical addition to the aromatic ring react with both O2 and NO2 and with the NO2 reaction rate constants being ca. 105 higher than the O2 reaction rate constants at room temperature. Under typical tropospheric conditions the reactions of the hydroxycyclohexadienyl radicals with O2 will dominate over their reactions with NO2. © 1994 John Wiley & Sons, Inc.
Formation yields of epoxides and O(3P) atoms from the gas‐phase reactions of O3 with a series of alkenes
Authors: Atkinson Roger , Aschmann Sara M. , Arey Janet , Tuazon Ernesto C.
Published: January 2005

Reactions of ozone with propene, 1‐butene, cis‐2‐butene, trans‐2‐butene, 2,3‐dimethyl‐2‐butene, and 1,3‐butadiene were carried out in N2 and air diluent at atmospheric pressure and room temperature and, by monitoring the formation of the epoxides and/or a carbonyl compound formed from the reactions of O(3P) atoms with these alkenes, the formation yields of O(3P) atoms from the O3 reactions were investigated. No evidence for O(3P) atom formation was obtained, and upper limits to O(3P) atom formation yields of <4% for propene, <5% for 1.3‐butadiene, and <2% for the other four alkenes were derived. The reaction of O3 with 1,3‐butadiene led to the direct formation of 3,4‐epoxy‐1‐butene in (2.3 ± 0.4)% yield. These data are in agreement with the majority of the literature data and show that O(3P) atom formation is not a significant pathway in O3—alkene reactions, and that epoxide formation only occurs to any significant extent from conjugated dienes. © 1994 John Wiley & Sons, Inc.
Kinetics and mechanism of H2O2 decomposition by Cu(II)‐, Co(II)‐, and Fe(III)‐Amine complexes on the surface of Silica‐Alumina (25% Al2O3)
Authors: Salem Mohamed A. , Salem Ibrahim A. , Gemeay Ali H.
Published: January 2005

The kinetics of the H2O2 decomposition by Cu(II)‐, Co(II)‐, and Fe(III)‐amine complexes supported on the surface of silica‐alumina (25% Al2O3) catalyst have been investigated. The decomposition process proceeded with first‐order kinetics for the substrate concentration. With copper complexes, in particular, the rate of reaction decreased in the sequence: ethylenediamine (en) > monoethanolamine (mea) > triethanolamine (tea). With ethylenediamine as aligand, the rate has also decreased in the order: Cu(II) > Co(II) > Fe(III). Both of the energy and entropy of activation were found to decrease as: en > mea > tea and for one ligand (en) and different metal ions the sequence was Cu(II) > Co(II) > Fe(III). The decomposition reaction involved the formation of an intermediate active species, which converts into a peroxo‐metal‐complex of brown or faint red color. The rate of reaction was directly proportional to the [complex], [H2O2], and [H]−1. A mechanism describing the decomposition process is proposed. © 1994 John Wiley & Sons, Inc.
The oscillating reaction of Hydrogen Peroxide and Iodate with Butanone as substrate
Authors: Love Ian
Published: January 2005

The system iodate‐peroxide‐manganese(II)‐butanone is a member of the Briggs–Rauscher set of oscillators. The stoichiometry and variation of the oscillation period with concentration for each component is studied under batch conditions. The system is simulated using the skeleton mechanism of earlier workers and reproduces the observed variation in oscillation period. Examination of the roles of the reaction steps shows that there are significant differences from those found using malonic acid. Iodine is stored during the low iodide regime and utilized during the high iodide regime, and different overall reactions occur during the two regimes. © 1994 John Wiley & Sons, Inc.
Kinetics of solvolysis of trans‐dichlorotetra (t‐butylpyridine)‐cobalt(III) ions in mixtures of water with ethane‐1,2‐diol and with 2‐methoxyethanol. A contrast with the effect of hydrophobic co‐solvents
Authors: Halawani Kamal H. , Wells Cecil F.
Published: January 2005

The kinetics of the solvolysis of the hydrophobic ion, Co(4‐t‐Bupy)4Cl2+, have been followed in mixtures of water with co‐solvents having a hydrophilic tendency, ethane‐1,2‐diol and 2‐methoxyethanol. The variation of In(rate constant) with the reciprocal of the dielectric constant is nonlinear for both co‐solvents. The enthalpy and the entropy of activation are rather insensitive to changes in the solvent composition in both mixtures, but low maxima may exist at mol fractions of co‐solvent Ca. 0.10–0.20. The application of a Gibbs energy cycle to the process of the initial state going to the transition state suggest that, in water‐rich conditions, the increase in the stability of the emergent solvated CoIII ion in the transition state relative to the increase in the stability of Co(4‐t‐Bupy)4Cl2+ in the initial state as the co‐solvent content rises is greater for 2‐methoxyethanol than for ethane‐1,2‐diol. © 1995 John Wiley & Sons, Inc.