Showing papers in "International Journal of Chemical Kinetics in 2004"

An updated comprehensive kinetic model of hydrogen combustion

Abstract: A comprehensively tested H2/O2 chemical kinetic mechanism based on the work of Mueller et al. 1 and recently published kinetic and thermodynamic information is presented. The revised mechanism is validated against a wide range of experimental conditions, including those found in shock tubes, flow reactors, and laminar premixed flame. Excellent agreement of the model predictions with the experimental observations demonstrates that the mechanism is comprehensive and has good predictive capabilities for different experimental systems, including new results published subsequent to the work of Mueller et al. 1, particularly high-pressure laminar flame speed and shock tube ignition results. The reaction H + OH + M is found to be primarily significant only to laminar flame speed propagation predictions at high pressure. All experimental hydrogen flame speed observations can be adequately fit using any of the several transport coefficient estimates presently available in the literature for the hydrogen/oxygen system simply by adjusting the rate parameters for this reaction within their present uncertainties. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 566–575, 2004

A comprehensive modeling study of hydrogen oxidation

Abstract: A detailed kinetic mechanism has been developed to simulate the combustion of H2/O2 mixtures, over a wide range of temperatures, pressures, and equivalence ratios. Over the series of experiments numerically investigated, the temperature ranged from 298 to 2700 K, the pressure from 0.05 to 87 atm, and the equivalence ratios from 0.2 to 6. Ignition delay times, flame speeds, and species composition data provide for a stringent test of the chemical kinetic mechanism, all of which are simulated in the current study with varying success. A sensitivity analysis was carried out to determine which reactions were dominating the H2/O2 system at particular conditions of pressure, temperature, and fuel/oxygen/diluent ratios. Overall, good agreement was observed between the model and the wide range of experiments simulated. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 603–622, 2004

Collaborative data processing in developing predictive models of complex reaction systems

Abstract: The subject of this report is a methodology for the transformation of (experimental) data into predictive models. We use a concrete example, drawn from the field of combustion chemistry, and examine the data in terms of precisely defined modes of scientific collaboration. The numerical methodology that we employ is founded on a combination of response surface technique and robust control theory. The numerical results show that an essential element of scientific collaboration is collaborative processing of data, demonstrating that combining the entire collection of data into a joint analysis extracts substantially more of the information content of the data. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 57–66, 2004

Validation of a thermal decomposition mechanism of formaldehyde by detection of CH2O and HCO behind shock waves

Abstract: The thermal decomposition of formaldehyde was investigated behind shock waves at temperatures between 1675 and 2080 K. Quantitative concentration time profiles of formaldehyde and formyl radicals were measured by means ofsensitive 174 nm VUV absorption (CH 2 O) and 614 nm FM spectroscopy (HCO), respectively. The rate constant of the radical forming channel (1a), CH 2 O + M → HCO + H + M, of the unimolecular decomposition of formaldehyde in argon was measured at temperatures from 1675 to 2080 K at an average total pressure of 1 2 bar, k 1 a = 5.0 x 10 1 5 exp(-308 k] mol - 1 /RT) cm 3 mol - 1 s - 1 . The pressure dependence, the rate of the competing molecular channel (1b), CH2O + M → H 2 + CO + M, and the branching fraction β = k 1 a /(k 1 a + k 1 b ) was characterized by a two-channel RRKM/master equation analysis. With channel (1b) being the main channel at low pressures, the branching fraction was found to switch from channel (1b) to channel (1a) at moderate pressures of 1-50 bar. Taking advantage of the results of two preceding publications, a decomposition mechanism with six reactions is recommended. which was validated by measured formyl radical profiles and numerous literature experimental observations. The mechanism is capable of a reliable prediction of almost all formaldehyde pyrolysis literature data, including CH 2 O, CO, and H atom measurements at temperatures of 1200-3200 K, with mixtures of 7 ppm to 5% formaldehyde. and pressures up to 15 bar. Some evidence was found for a self-reaction of two CH 2 O molecules. At high initial CH 2 O mole fractions the reverse of reaction (6), CH 2 OH + HCO ⇄ CH 2 O + CH 2 O becomes noticeable The rate of the forward reaction was roughly measured to be k 6 = 1.5 x 10 1 3 cm 3 mol - 1 s - 1 .

Analysis of gas–solid noncatalytic reactions in porous particles: Finite volume method

Abstract: Gas–solid noncatalytic (GSNC) reactions in porous particles are analyzed employing volume reaction model (VRM). Both single-stage and two-stage models have been used in the work. Earlier analysis for such reactions was mostly restricted to the first-order reactions with respect to the gaseous component. The present work has used a range of reaction orders with respect to both gaseous and solid reactants. Front tracking method was employed for solving the moving boundary problem. Finite volume method (FVM) has been used for the first time for the analysis of GSNC reactions in porous particles, based on moving boundary zone models. The discretized equations are solved by tridiagonal matrix algorithm. The results for the first-order reaction agree well with the analytical solution. FVM solution compares well with other numerical method (integral transformation followed by orthogonal collocation). Numerical results have also been validated with reported experimental data for reduction of Magnetite by CO. FVM is thus established to be a suitable numerical method to solve GSNC reactions in porous particles employing VRM. The effects of different process parameters on the progress of reaction have also been assessed.© 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 1–11, 2003

Rate coefficients for the gas‐phase reaction of NO3 radicals with selected dihydroxybenzenes

Abstract: Using a relative kinetic technique, rate coefficients have been determined at (298 ± 2) K and atmospheric pressure for the gas-phase reactions of the NO3 radical with three vicinal dihydroxy aromatic compounds. The experiments were carried out in a 1080-l quartz glass reactor at the Bergische Universitat Wuppertal and in the European Photoreactor (EUPHORE), Valencia, Spain. The rate coefficients obtained (in units of cm3 molecule−1 s−1) using 2,3-dimethyl-2-butene as the reference hydrocarbon were kNO3(1,2-dihydroxybenzene) = (9.8 ± 5.0) × 10−11, kNO3(1,2-dihydroxy-3-methylbenzene) = (17.2 ± 5.6) × 10−11, and kNO3 (1,2- dihydroxy-4-methylbenzene) = (14.7 ± 6.5) × 10−11. This study represents the first kinetic investigation of the reactions of the NO3 radical with dihydroxybenzenes. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 577–583, 2004

Rate constants for reaction of 1,2‐dimethylimidazole with benzyl bromide in ionic liquids and organic solvents

Abstract: The rate constant for the Menschutkin reaction of 1,2-dimethylimidazole with benzyl bromide to produce 3-benzyl-1,2-dimethylimidazolium bromide was determined in a number of ionic liquids and molecular organic solvents. The rate constants in 12 ionic liquids are in the range of (1.0–3.2) × 10−3 L mol−1 s−1 and vary with the solvent anion in the order (CF3SO2)2 N− < PF6− < BF4−. Variations with the solvent cation (butylmethylimidazolium, octylmethylimidazolium, butyldimethylimidazolium, octyldimethylimidazolium, butylmethylpyrrolidinium, and hexyltributylammonium) are minimal. The rate constants in the ionic liquids are comparable to those in polar aprotic molecular solvents (acetonitrile, propylene carbonate) but much higher than those in weakly polar organic solvents and in alcohols. Correlation of the rate constants with the solvatochromic parameter ET(30) is reasonable within each group of similar solvents but very poor when all the solvents are correlated together. Better correlation is obtained for the organic solvents by using a combination of two parameters, π* (dipolarity/polarizibility) and α (hydrogen bond acidity), while additional parameters such as δ (cohesive energy density) do not provide any further improvement. © 2004 Wiley Periodicals, Inc.* Int J Chem Kinet 36: 253–258, 2004

Inorganic reactions of iodine(+1) in acidic solutions

Abstract: We present a thorough analysis of the former works concerning the hydrolysis of iodine and its mechanism in acidic or neutral solutions and recommend values of equilibrium and kinetic constants Since the literature value for the reaction H2OI+ ⇌ HOI + H+ appeared questionable, we have measured it by titration of acidic iodine solutions with AgNO3 Our new value, K(H2OI+ ⇌ HOI + H+) ∼ 2 M at 25°C, is much larger than accepted before It decreases slowly with the temperature We have also measured the rate of the reaction 3HOI IO3− + 2I− + 3H+ in perchloric acid solutions from 5 × 10−2 M to 05 M It is a second order reaction with a rate constant nearly independent on the acidity Its value is 25 M−1 s−1 at 25°C and decreases slightly when the temperature increases, indicating that the disproportionation mechanism is more complicated than believed before An analysis of the studies of this disproportionation in acidic and slightly basic solutions strongly supports the importance of a dimeric intermediate 2HOI ⇌ I2O·H2O in the mechanism © 2004 Wiley Periodicals, Inc Int J Chem Kinet 36:480–493, 2004

Measurements of the kinetics of the OH-initiated oxidation of methyl vinyl ketone and methacrolein

Abstract: The mechanisms of the OH-initiated oxidation of methyl vinyl ketone and methacrolein have been studied at 300 K and 100 Torr total pressure, using a turbulent flow technique coupled with laser-induced fluorescence detection of the OH radical. The rate constants for the OH + methyl vinyl ketone and OH + methacrolein reactions were measured to be (1.78 ± 0.08) × 10−11 and (3.22 ± 0.10) × 10−11 cm3 molecule−1 s−1, respectively, and were found to be in excellent agreement with previous studies. In the presence of O2 and NO, the OH radical propagation and the loss of OH through radical termination resulting from the production of methyl vinyl ketone- and methacrolein-based alkyl nitrates were measured at 100 Torr total pressure and compared to the simulations of the kinetics of these reaction systems. The results of these experiments are consistent with an overall rate constant of (2.0 ± 1.3) × 10−11 cm3 molecule−1 s−1 for both the methyl vinyl ketone-based peroxy radical + NO and methacrolein-based peroxy radical + NO reactions, each with branching ratios of 0.90 ± 0.10 for the bimolecular channel (oxidation of NO to NO2) and 0.10 ± 0.10 for the termolecular channel (production of methyl vinyl ketone- and methacrolein-based alkyl nitrates). © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 12–25, 2003

Energy transfer effects during the multichannel decomposition of ethanol

Abstract: Rate constants and expressions for the initial processes in the decomposition of ethanol have been derived on the basis of existing experimental and estimated results Energy transfer effects on the multichannel decomposition processes have been determined through the solution of the master equation and on the basis of exponential-down and step-ladder collisional transition models The predominant (lower threshold) channel is unaffected by the presence of the upper channels and results for the two transition models can be brought into correspondence by using a somewhat higher value for the step-size down parameter in the step-ladder model For the upper channels and with an exponential-down model, the logarithms of the ratio of the rate constants between perturbed and unperturbed systems can be captured by a sigmoidal shaped curve In the case of the step-ladder model, the logarithms of this ratio decreases monotonically Initially, differences between the two models are small (after adjusting the step-size down parameter) The results are compared with the recent simulations of Marinov The order of magnitude differences in rate constants have been traced to the inclusion in the present study of experimental results pertaining to decomposition and the reverse combination processes in addition to the proper treatment of energy transfer effects during multichannel decompositions Some observations regarding the parameterization of this type of pressure dependent data for use in simulations are presented © 2004 Wiley Periodicals, Inc Int J Chem Kinet 36:456–465, 2004

Experimental study of Fuel decomposition and hydrocarbon growth processes for practical Fuel components in nonpremixed flames : Mtbe and related alkyl ethers

Abstract: Fuel decomposition and hydrocarbon growth processes of methyl tert-butyl ether (MTBE) and related alkyl ethers have been studied experimentally in soot-producing nonpremixed flames. Temperature, C1–C12 hydrocarbons, and major species were measured in coflowing methane/air flames whose fuel was separately doped with 5000 ppm of MTBE, n-butyl methyl ether (NBME), sec-butyl methyl ether (SBME), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME; =1,1-dimethylpropyl methyl ether). The consumption rates of the dopants, several simple kinetic calculations, and the dependence of the observed products on fuel composition indicate that the dominant decomposition process was unimolecular dissociation, not H-atom abstraction. The dominant dissociations were four-center elimination of alcohols for the doubly branched ethers (MTBE, ETBE, and TAME) and CO fission for the linear ether (NBME), while four-center elimination and CO fission were comparably important for the singly branched ether (SBME). These dissociations produced alkenes which further reacted to produce alkadienes/alkynes, alkenynes, acetylenic compounds, and aromatics. The dependence of the maximum benzene mole fractions on fuel composition was consistent with benzene formation through reactions of highly-unsaturated C3 and/or C4 hydrocarbons (C3H3, n-C4H3, C4H4, n-C4H5, etc.). © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 345–358, 2004

Thermochemical properties from G3MP2B3 calculations, set-2: Free radicals with special consideration of CH2=CH-C.=CH2, cyclo-.C5H5, .CH2OOH, HO-.CO, and HC(O)O.

Abstract: After a set of 32 free radicals was presented (Int I Chem Kin 34, 550-560, 2002), an additional 60 free radicals (Set-2) were studied and characterized by energy minimum structures, harmonic vibrational wave numbers ω e , moments of inertia I A , i B , and I C , heat capacities C o p (T), standard entropies S o (T), thermal energy contents H o (T)-H o (0), and standard enthalpies of formation Δ f H o (T) at the G3MP2B3 level of theory. Thermodynamic functions at T= 298.15 K are presented and compared with recent experimental values where these are available. The mean absolute deviation between calculated and experimental Δ f H o (298.15) values by the previous set of 32 radicals is 3.91 kJ mol - 1 , For the sake of comparison, only 49 species out of the 60 radicals of Set-2 are characterized by experimental enthalpies of formation. and the corresponding mean absolute deviation between calculated and experimental Δ f H o (298.15) values is 8.96 kl mol - 1 . This situation is cause for demand of more and also more accurate experimental values. In addition to the above properties, parent molecules of a large set of the respective radicals are calculated to obtain bond dissociation energies D o (298.15). Radical stabilization owing to resonance is discussed using the complete sets of total atomic spin densities p as a support. In particular, a short review about recent developments of the first-order lahn-Teller radical c-C 5 H 5 . is presented In addition, radicals with negative bond energies are described, such as . CH 2 OOH where the reaction path to CH 2 O + HO' has been calculated, as well as radicals which have two different parent molecules, for example C=N-O . . For the reaction HO' + CO → H . + CO 2 , two reaction paths are characterized by a total of 14 stationary points where the intermediate radicals HO- . CO and HC(O)O . are involved.

Oxidation of lactic acid by water soluble (colloidal) manganese dioxide

Abstract: Spectrophotometric method has been used to characterize water-soluble colloidal manganese dioxide obtained by the redox reaction between sodium thiosulphate and potassium permanganate in neutral aqueous medium which showsa single peak in the visible region with λ m a x = 425 nm. The kinetics of the oxidation of lactic acid by colloidal manganese dioxide (oxidant) has been investigated spectrophotometrically under pseudo-first-order conditions of excess lactic acid. The rate of the noncatalytic reaction pathway was slow which increased with increasing lactic acid concentration. The reaction was first-order with respect to ‖oxidant] as well as ‖actic acid‖. In presence of manganase(II) and fluoride ions, the noncatalytic path disappeared completely while the oxidation rate of autocatalytic path increased and decreased, respectively with increasing [Mn(II)] and [F - 1 ]. A mechanistic scheme in conformity with the observed kinetics has been proposed with the rate-law: v= -d[MnO 2 ]/dt k 1 k 2 [MnO 2 ][H + ][lactic acid] T /([H + ‖+K a )(k - 1 +k 2 ).

Kinetics and mechanism of the pyridinolysis of aryl dithiobenzoates in acetonitrile

Abstract: The kinetics and mechanism of the aminolysis of aryl dithiobenzoates (RC(S)SC6H4Z; R = Ph) with pyridines (XC5H4N) in acetonitrile at 60.0°C have been studied. A biphasic Bronsted plot is obtained with a change in slope from a large value (βX ≅ 0.7–0.8) to a small value (βX ≅ 0.2) at pKa° = 5.2, which is interpreted to indicate a change of the rate-determining step from breakdown to formation of the zwitterionic tetrahedral intermediate, T±, at pKa = 5.2 as the pyridine basicity is increased. Rates are compared with those corresponding values for aryl dithioacetates (R = Me). The faster rates for R = Me than for R = Ph, for the rate-limiting formation of T±, can be attributed to the hyperconjugative charge transfer effect of the Me group, pseudo-πMe π*C=S. Clear-cut change in the cross-interaction constants, ρXZ, from +1.47 to −0.20 supports the proposed mechanistic change. The breakpoint at pKa° = 5.2 for R = Ph in the present work is in agreement with those for the pyridinolysis of R = Me and 2-furyl, and attests to the insignificant effect of acyl group, R, on the breakpoint. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 434–440, 2004

Rate coefficients for the gas-phase reactions of OH radicals with methylbutenols at 298 K

Abstract: The relative-rate method has been used to determine the rate coefficients for the reactions of OH radicals with three C5 biogenic alcohols, 2-methyl-3-buten-2-ol (k1), 3-methyl-3-buten-1-ol (k2), and 3-methyl-2-buten-1-ol (k3), in the gas phase. OH radicals were produced by the photolysis of CH3ONO in the presence of NO. Di-n-butyl ether and propene were used as the reference compounds. The absolute rate coefficients obtained with the two reference compounds agreed well with each other. The O3 and O-atom reactions with the target alcohols were confirmed to have a negligible contribution to their total losses by using two kinds of light sources with different relative rates of CH3ONO and NO2 photolysis. The absolute rate coefficients were obtained as the weighted mean values for the two reference compound systems and were k1 = (6.6 ± 0.5) × 10−11, k2 = (9.7 ± 0.7) × 10−11, and k3 = (1.5 ± 0.1) × 10−10 cm3 molecule−1 s−1 at 298 ± 2 K and 760 torr of air. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 379–385 2004

Absolute rate constants for the gas-phase ozonolysis of isoprene and methylbutenol

Abstract: The reactions of the biogenic organic compounds isoprene and 2-methyl-3- buten-2-ol (MBO) with ozone have been investigated under controlled conditions for pres- sure (atmospheric pressure) and temperature (293 ± 2 K), using FTIR spectrometry. CO was added to scavenge hydroxyl radical formation during the ozonolysis experiments. Reaction rate constants were determined by absolute rate technique, by measuring both ozone and the organic compound concentrations. The measured values were k1 = (1.19 ± 0.09) × 10 −17 cm 3 molecule −1 s −1 for the reaction between ozone and isoprene and k2 = (8.3 ± 1.0) × 10 −18 cm 3 molecule −1 s −1 for the reaction between ozone and MBO. C

On the evaluation of the nonisothermal kinetic parameters of (GeS2)0.3(Sb2S3)0.7 crystallization using the IKP method

Abstract: The isoconversional method suggested by Friedman and the invariant kinetic parameters method (IKP) were used in order to examine the kinetics of the nonisothermal crystallization of (GeS2)0.3(Sb2S3)0.7. The objective of the paper is to show the usefulness of the IKP method both for determining the activation parameters as well as the model of the investigated process. It was shown that the kinetic triplet [(E, A, f(α), where E is the activation energy, A is the preexponential factor, and f(α) is the differential function of conversion], which results through the application of the IKP method, depends on the set of kinetic models considered. For different sets of kinetic models, proportional values of f(α) are obtained. A criterion for the selection of this set, the use of which lead to the true kinetic triplet corresponding to the analyzed process (E = 163.2 kJ mol−1; A = 2.47 × 1012 min−1 and the Avrami-Erofeev model, Am, for m = 2.5–2.6 was suggested. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 309–315, 2004

Quantum chemical/vRRKM study on the thermal decomposition of cyclopentadiene

Abstract: Thermal decomposition of cyclopentadiene to c-C5H5 (cyclopentadienyl radical) + H (1) and the reverse bimolecular reaction (−1) are studied quantum-chemically at the G2M level of theory. The dissociation pathway has been mapped out following the minimum energy path on the potential energy surface (PES) calculated by the density functional UB3LYP/6-311G(d,p) method. Using isodesmic reaction analysis, the standard enthalpy of formation for c-C5H5 is found to be 62.5 ± 1.3 kcal mol−1, and the c-C5H5H bond dissociation energy is estimated as D°298(c-C5H5H) = 82.5 ± 0.9 kcal mol−1, in excellent agreement with the recent experimental values. Variational rate constants are computed on the basis of a scaled UB3LYP dissociation potential that fits the isodesmic/experimental enthalpy of Reaction (1). At the high pressure limit, k1∞ = 1.55 × 1018T−0.8 exp(−42300/T) s−1 and k−1∞ = 2.67 × 1014 exp(−245/T) cm3 mol−1s−1. The fall-off effects are evaluated by a weak collision master equation/RRKM analysis. Calculated T, P-dependent rate constants are in very good agreement with the most reliable experimental measurements. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 139–151 2004

On the Beckmann rearrangement of ketoximes: A kinetic study in trifluoromethanesulfonic acid

Abstract: The formation and the destruction of an intermediate involved in the Beckmann rearrangement of 2,4,6-trimethylacetophenone oxime have been studied in concentrated trifluoromethanesulfonic acid by kinetic and spectroscopic measurements. Observed (kobs) and thermodynamic rate constants (ko) have been estimated and the values compared with the ones obtained in perchloric, sulfuric, and methanesulfonic acids. In the range 80–100 wt% of sulfuric acid, combined analysis of kobs and ko rates shows a specific catalysis due to [H2SO4] species. In trifluoromethanesulfonic acid, lower rate constants, compared to the values in sulfuric acid, have been observed which differ at 99 wt% by a factor of 103 ca. The catalytic effect of different strong acids, the structure of the intermediate inferred from Raman and NMR spectra, and the role of the ion-pairs involved in the reaction are discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 417–426, 2004

Reduction kinetics of ceria surface by hydrogen

Abstract: Powdered cerium dioxide (ceria, CeO2) as compressed, sintered pellets, of porosity 16.4% and density 5.99 g cm−3, were treated in hydrogen flow at 1 atm and various temperatures to effect reduction. The electrical conductivity was measured in situ during the reduction process. The conductivity increased continuously during the hydrogen treatment because of the creation of anion vacancies and accompanying small polaron electrons. The conductivity–time relationship exhibits three distinct regions indicated as I, II, and III. For each of steps I and II, the conductivity increases exponentially with the reduction. It is suggested from the kinetic analysis of the data that region I is due to desorption of adsorbed oxygen states. Region II appears to be the reduction of surface lattice oxygen. The kinetics of the reactions in both regions I and II obey first-order rate laws with similar activation energies of 86 and 115 kJ mol−1, respectively. Thermogravimetric experiments were used to determine the time needed to remove one monolayer of adsorbed oxygen from the surface. This could be used to estimate the activation energy of the desorption process at 95 kJ mol−1—close to the value measured by conductivity measurements. After completing the surface reduction the electrical conductivity subsequently increased slowly during region III. This step is assigned to a diffusion-controlled process during which the bulk of the pellets are reduced. 1H MASNMR and in situ PXRD experiments confirmed the chemical nature of each of the three steps. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 293–301, 2004

Unusual kinetic role of a water-soluble iron(III) porphyrin catalyst in the oxidation of 2,4,6-trichlorophenol by hydrogen peroxide

Abstract: The oxidation of 2,4,6-trichlorophenol (TCP) to 2,6-dichloro-1,4-benzoquinone (DCQ) by hydrogen peroxide using iron(III) meso-tetra(4-sulfonatophenyl) porphine chloride, Fe(TPPS)Cl, as a catalyst was studied with stopped-flow UV–vis spectrophotometry and potentiometry using a chloride ion selective electrode. The observations are interpreted by a three-step kinetic model: the initial reaction of the catalyst with the oxidant (Fe(TPPS)+ + H2O2 Cat′) produces an active intermediate, which oxidizes the substrate (Cat′ + TCP Fe(TPPS)+ + DCQ + Cl−) in the second step. The third step is the transformation of the catalyst into a much less active form (Cat′ Cat″) and is responsible for the unusual kinetic phenomena observed in the system. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:449–455, 2004.

A computational study of the kinetics and mechanism for the reaction of HCO with HNO

Abstract: The mechanism for the reaction of HCO with HNO has been studied at the G2M level of theory, based on the geometric parameters optimized by the BH&HLYP/6-311G(d, p) method. There are three direct hydrogen abstraction channels producing (1) H2CO + NO, (2) H2NO + CO, and (3) HNOH + CO with barriers of 3.7, 3.9, and 10.4 kcal/mol, respectively. Another important reaction channel, (4), involves an association process forming HN(O)CHO (LM1) with a very small barrier and the subsequent isomerization and decomposition of LM1 producing HNOH + CO as major products. The rate constants of the dominant reaction channels (1), (2), and (4) in the temperature range 200–3000 K have been predicted by the microcanonical RRKM and transition state theory calculations with Eckart tunneling corrections. The theoretical result shows that in the high temperature range ( T > 1500 K), k1 (H2CO + NO) and k2(H2NO + CO) are preponderant, while in the low temperature range, both k4(LM1) and k4(HNOH + CO) appear to be dominant at high and low pressures, respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 205–215, 2004

The comparison of detailed chemical kinetic mechanisms: Application to the combustion of methane

Abstract: Detailed chemical kinetic mechanisms of complex chemical phenomena may be composed of hundreds of species and thousands of individual elementary reactions. It can be an extremely laborious and error-prone procedure to compare two of these mechanisms, particularly if they come from different sources. We have created software tools which help to highlight the differences between mechanisms written in a Chemkin format and demonstrate their applicability to five literature mechanisms describing the high temperature oxidation of methane. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:467–471, 2004

Thermal decomposition of tert‐butyl peroxide in a gas chromatographic reactor: A comparison of kinetic approaches

Abstract: The thermal decomposition of tert-butyl peroxide is investigated utilizing both the column and the injection port of a commercial gas chromatograph (GC) as chemical reactors. Using the injector liner as the reactor, the chromatographic peak areas of the reactant, measured at various injector temperatures, are used in the determination of the activation energy of the decomposition (Ea). With the column serving as the reactor, both the reactant peak areas and the product peak shapes are similarly utilized for this purpose. Values of Ea obtained using different mathematical treatments for each of the three approaches are found to range from 115 to 164 kJ/mol. Of these methods, the column reactor approach utilizing peak area measurements (referred to as PACR, for “peak area, column reactor”) is found to be far superior in terms of its speed, robustness, and its accuracy in determining Ea. The PACR method's effectiveness can be largely attributed to the mathematical treatment that is described in the approach. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 386–393, 2004

Relative reactivity and kinetic pattern of aniline and N‐methylaniline as nucleophiles in aromatic substitution (SNAr) reactions

Abstract: Kinetic results are reported for the reactions of 4-nitrophenyl-2,4,6-trinitrophenyl ether 3 with aniline and N-methylaniline in dimethyl sulphoxide, acetonitrile, methanol, and benzene. The reactions gave the expected 2,4,6-trinitrodiphenylamine and were base catalyzed in all the solvents. Both nucleophiles showed the same kinetic pattern under the same reaction conditions but aniline was found to be considerably more reactive than N-methylaniline. The greater catalytic efficiency of aniline over N-methylaniline is consistent with the proton transfer mechanism of the base-catalyzed step. Dichotomy of amine effects in aromatic substitution (S N Ar) reactions is discussed.

Computational study on the kinetics and mechanisms for the reactions of HCO with HONO and HNOH

Abstract: The kinetics and mechanisms of the HCO reactions with HONO and HNOH have been studied at the G2M level of theory based on the geometric parameters optimized at BH&HLYP/6-311G(d,p). The rate constants in the temperature range 200–3000 K at different pressures have been predicted by microcanonical RRKM and/or variational transition state theory calculations with Eckart tunneling corrections. For the HCO + HONO reaction, hydrogen abstraction from trans-HONO and cis-HONO by HCO produces H2CO + NO2, with the latter being dominant. Two other channels involving cis-HONO by the association/decomposition mechanism via the HC(O)N(O)OH intermediate, which could fragment to give H2O + CO + NO at high temperatures, were also found to be important. For the HCO + HNOH reaction, three reaction channels were identified: one association reaction giving a stable intermediate, HC(O)N(H)OH (LM2), and two hydrogen abstraction channels producing H2CO and H2NOH. The dominant products were predicted to be the formation of LM2 at low temperatures and H2NOH + CO at middle and high temperatures. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 178–187 2004

The hydroxyl radical reaction rate constant and products of 3,5-dimethyl-1-hexyn-3-ol

Abstract: A bimolecular rate constant,kDHO, of (29 ± 9) × 10−12 cm3 molecule−1 s−1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 3,5-dimethyl-1-hexyn-3-ol (DHO, HCCC(OH)(CH3)CH2CH(CH3)2) at (297 ± 3) K and 1 atm total pressure. To more clearly define DHO's indoor environment degradation mechanism, the products of the DHO + OH reaction were also investigated. The positively identified DHO/OH reaction products were acetone ((CH3)2CO), 3-butyne-2-one (3B2O, HCCC(O)(CH3)), 2-methyl-propanal (2MP, H(O)CCH(CH3)2), 4-methyl-2-pentanone (MIBK, CH3C(O)CH2CH(CH3)2), ethanedial (GLY, HC(O)C(O)H), 2-oxopropanal (MGLY, CH3C(O)C(O)H), and 2,3-butanedione (23BD, CH3C(O)C(O)CH3). The yields of 3B2O and MIBK from the DHO/OH reaction were (8.4 ± 0.3) and (26 ± 2)%, respectively. The use of derivatizing agents O-(2,3,4,5,6-pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible DHO/OH reaction mechanisms based on previously published volatile organic compound/OH gas-phase reaction mechanisms. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 534–544, 2004

Kinetics and mechanism of the hydrolytic disproportionation of iodine

Abstract: Kinetics of the hydrolytic disproportionation of I2 was studied by UV–VIS spectrophotometry at 298 K and at the ionic strength 0.2 M (NaClO4) in buffered solutions in the pH range 8.91–10.50 at different initial iodide concentrations. The characterization of this reaction is fundamental for modeling oscillatory and front reactions in the presence of iodine as reactant or intermediate as well as for drinking water treatment. A matrix rank analysis confirmed three absorbing species in the beginning of the reaction, whereas later assumption of two species is enough to describe the experimental data in the visible part of the spectrum. A reaction mechanism was proposed for disproportionation by using fitting/simulation with a multipurpose program package ZiTa, by simultaneous evaluation of 17,906 points in 79 experimental curves. A parameter set was suggested, which was obtained by absolute, relative, and orthogonal fittings of the experimental data. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 596–602, 2004

Kinetics and mechanism of esterification of epoxy resin in presence of triphenylphosphine

Abstract: The kinetics of esterification of bisphenol-A based epoxy resin with acrylic acid in presence of triphenylphosphine has been studied. The reaction exhibits a first-order rate dependence with respect to [Epoxy] and [Catalyst]. A first-order dependence of rate with respect to [Acid] has been observed during a particular kinetic run. However, a retarding effect of [Acid] on the rate has been observed by increasing the initial concentration of acid. A suitable mechanism consistent with the kinetic data is proposed and discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 280–285, 2004

Investigation of the correlation of sensitivity vectors of hydrogen combustion models

Abstract: A well-established method for the analysis of large reaction mechanisms is the calculation and interpretation of the sensitivity of the kinetic model output Yi to parameter changes. Comparison of the sensitivity vectors si ={ ∂Yi /∂p} belonging to different model out- puts is a new tool for kinetic analysis. The relationship of the sensitivity vectors was investi- gated in homogeneous explosions, freely propagating and burner-stabilized laminar flames of hydrogen-air mixtures, using either calculated adiabatic or constrained temperature profiles, for fuel-to-air ratios ϕ = 0.5-4.0. Sensitivity vectors are called locally similar, if the relationship si = λ ij s j is valid, where λ ij is a scalar. In many systems, only approximate local similarity of the sensitivity vectors exists and the extent of it can be quantified by using an appropriate correlation function. In the cases of adiabatic explosions and burner-stabilized flames, accurate local similarity was present in wide ranges of the independent variable (time or distance), and the correlation function indicated that the local similarity was not valid near the concentration extremes of the corresponding species. The regions of poor similarity were studied further by cobweb plots. The correlation relationships found could be interpreted by the various kinetic pro- cesses in the hydrogen combustion systems. The sensitivity vector of the laminar flame velocity is usually considered to be characteristic for the whole combustion process. Our investigations showed that the flame velocity sensitivity vector has good correlation with the H and H2O con- centration sensitivities at the front of the adiabatic flames, but there is poor correlation with the sensitivity vectors of all concentrations in homogeneous explosions. C � 2004 Wiley Periodicals,