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Gas-phase Reactions (gas-phase + reaction)
Selected AbstractsGas-Phase Reaction of 2-Chlorothiophene with Hydrogen Sulfide in the Presence of Alcohols.CHEMINFORM, Issue 38 2002E. N. Deryagina No abstract is available for this article. [source] Optimization of Enzymatic Gas-Phase Reactions by Increasing the Long-Term Stability of the CatalystBIOTECHNOLOGY PROGRESS, Issue 3 2004Clara Ferloni Enzymatic gas-phase reactions are usually performed in continuous reactors, and thus very stable and active catalysts are required to perform such transformations on cost-effective levels. The present work is concerned with the reduction of gaseous acetophenone to enantiomerically pure ( R)-1-phenylethanol catalyzed by solid alcohol dehydrogenase from Lactobacillus brevis (LBADH), immobilized onto glass beads. Initially, the catalyst preparation displayed a half-life of 1 day under reaction conditions at 40 °C and at a water activity of 0.5. It was shown that the observed decrease in activity is due to a degradation of the enzyme itself (LBADH) and not of the co-immobilized cofactor NADP. By the addition of sucrose to the cell extract before immobilization of the enzyme, the half-life of the catalyst preparation (at 40 °C) was increased 40 times. The stabilized catalyst preparation was employed in a continuous gas-phase reactor at different temperatures (25,60 °C). At 50 °C, a space-time yield of 107 g/L/d was achieved within the first 80 h of continuous reaction. [source] Competitive Hydrogen-Atom Abstraction versus Oxygen-Atom and Electron Transfers in Gas-Phase Reactions of [X4O10].+ (X=P, V) with C2H4CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2010Nicolas Dietl Dipl.-Chem. Why so different? The comparison of the reaction of "bare" [P4O10].+ and [V4O10].+ with ethene by mass-spectrometric and computational studies permits insight into mechanistic aspects of the competition between CH bond activation and oxygen-atom and electron transfers. Whereas [P4O10].+ reacts by homolytic CH bond cleavage and electron transfer, the isostructural [V4O10].+ shows only oxygen-atom transfer (see picture). [source] An Experimental and Theoretical Investigation of Gas-Phase Reactions of Ca2+ with GlycineCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2006Inés Corral Dr. Abstract The gas-phase reactions between Ca2+ and glycine ([Ca(gly)]2+) have been investigated through the use of mass spectrometry techniques and B3-LYP/cc-pWCVTZ density functional theory computations. The major peaks observed in the electrospray MS/MS spectrum of [Ca(gly)]2+ correspond to the formation of the [Ca,C,O2,H]+, NH2CH2+, CaOH+, and NH2CH2CO+ fragment ions, which are produced in Coulomb explosion processes. The computed potential energy surface (PES) shows that not only are these species the most stable product ions from a thermodynamic point of view, but they may be produced with barriers lower than for competing processes. Carbon monoxide is a secondary product, derived from the unimolecular decomposition of some of the primary ions formed in the Coulomb explosions. In contrast to what is found for the reactions of Ca2+ with urea ([Ca(urea)]2+), minimal unimolecular losses of neutral fragments are observed for the gas-phase fragmentation processes of [Ca(gly)]2+, which is readily explained in terms of the topological differences between their respective PESs. [source] Gas-phase reaction of hydroxyl radicals with m -, o - and p -cresolINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2006Cecile Coeur-Tourneur The gas-phase reaction of oxygenated aromatic compounds m -cresol, o -cresol, and p -cresol with hydroxyl radicals has been studied by GC-MS. Experiments have been performed in a large-volume photoreactor (8000 L) at 294 ± 2 K and atmospheric pressure. The relative kinetic method was used to determine the rate constants for these reactions, with 1,3,5-trimethylbenzene as a reference compound. The rate constants obtained are kOH(m -cresol) = (5.88 ± 0.92) × 10,11 cm3 molecule,1 s,1, kOH(o -cresol) = (4.32 ± 0.52) × 10,11 cm3 molecule,1 s,1, and kOH(p -cresol) = (4.96 ± 0.75) × 10,11 cm3 molecule,1 s,1. The degradation products observed and their respective molar yields were methyl-1,4-benzoquinone 12.4 ± 1.2%, 5-methyl-2-nitrophenol 1.5 ± 0.3%, and 3-methyl-2-nitrophenol 1.4 ± 0.3% from m -cresol, methyl-1,4-benzoquinone 5.6 ± 0.9%, and 6-methyl-2-nitrophenol 4.7 ± 0.8% from o -cresol, and 4-methyl-2-nitrophenol 17.2 ± 2.5% from p -cresol. This kinetic and product data are compared with the literature, and the reaction mechanisms are discussed. Our results are in accordance with the previous studies (Atkinson, J Phys Chem Ref Data 1989, Monograph (1), 1,246; Atkinson and Aschmann, Int J Chem Kinet 1990, 22, 59,67; Atkinson et al., Environ Sci Technol 1992, 26, 1397,1403; Atkinson et al., J Phys Chem 1978, 82, 2759,2805; Olariu et al., Atmos Environ 2002, 36, 3685,3697; Semadeni et al., Int J Chem Kinet 1995, 27, 287,304) and confirm the methyl-1,4-benzoquinone yields determined by a different experimental technique (long-path Fourier transform infrared FT-IR (Olariu et al., 2002)). © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 553,562, 2006 [source] Mono and double polar [4 + 2+] Diels,Alder cycloaddition of acylium ions with O -heterodienesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2002Eduardo C. Meurer Abstract Gas-phase reactions of acylium ions with ,,,-unsaturated carbonyl compounds were investigated using pentaquadrupole multiple-stage mass spectrometry. With acrolein and metacrolein, CH3,C+O, CH2CH,C+O, C6H5,C+O, and (CH3)2N,C+O react to variable extents by mono and double polar [4 + 2+] Diels,Alder cycloaddition. With ethyl vinyl ketone, CH3,C+O reacts exclusively by proton transfer and C6H5,C+O forms only the mono cycloadduct whereas CH2CH,C+O and (CH3)2N,C+O reacts to great extents by mono and double cycloaddition. The positively charged acylium ions are activated O -heterodienophiles, and mono cycloaddition occurs readily across their C+O bonds to form resonance-stabilized 1,3-dioxinylium ions which, upon collisional activation, dissociate predominantly by retro-addition. The mono cycloadducts are also dienophiles activated by resonance-stabilized and chemically inert 1,3-dioxonium ion groups, hence they undergo a second cycloaddition across their polarized CC ring double bonds. 18O labeling and characteristic dissociations displayed by the double cycloadducts indicate the site and regioselectivity of double cycloaddition, which are corroborated by Becke3LYP/6,311++G(d,p) calculations. Most double cycloadducts dissociate by the loss of a RCO2COR1 molecule and by a pathway that reforms the acylium ion directly. The double cycloadduct of the thioacylium ion (CH3)2N,C+S with acrolein dissociates to (CH3)2N,C+O in a sulfur-by-oxygen replacement process intermediated by the cyclic monoadduct. The double cycloaddition can be viewed as a charge-remote type of polar [4 + 2+] Diels,Alder cycloaddition reaction. Copyright © 2001 John Wiley & Sons, Ltd. [source] Gas-phase reactions of Cl atoms with hydrochloroethers: relative rate constants and their correlation with substituents' electronegativitiesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2008Pablo R. Dalmasso Abstract Rate constants for the reactions of Cl atoms with CH3OCHCl2 and CH3OCH2CH2Cl were determined at (296,±,2) K and atmospheric pressure using synthetic air as bath gas. Decay rates of these organic compounds were measured relative to the following reference compounds: CH2ClCH2Cl and n -C5H12. Using rate constants of 1.33,×,10,12 and 2.52,×,10,10,cm3,molecule,1,sec,1 for the reaction of Cl atoms with CH2ClCH2Cl and n -C5H12, respectively, the following rate coefficients were derived: k(Cl,+,CH3OCHCl2),=,(1.05,±,0.11),×,10,12 and k(Cl,+,CH3OCH2CH2Cl),=, (1.14,±,0.10),×,10,10, in units of cm3,molecule,1,s,1. The rate constants obtained were compared with previous literature data and a correlation was found between the rate coefficients of some CH3OCHR1R2,+,Cl reactions and ,Electronegativity of CHR1R2. Copyright © 2008 John Wiley & Sons, Ltd. [source] Kinetic and product study of the gas-phase reaction of sabinaketone with OH radicalINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2007Nathalie Carrasco Sabinaketone is one major photooxidation product of sabinene, an important biogenic volatile organic compound. This article provides the first product study and the second rate constant determination of its reaction with OH radicals. Experiments were investigated under controlled conditions for pressure and temperature in the LISA indoor simulation chamber using FTIR spectrometry. Kinetic study was carried out at 295 ± 2 K and atmospheric pressure using the relative rate technique with isoprene as the reference compound. The rate constant was found to be ksabinaketone + OH = (7.1 ± 1.0) × 10,12 molecule,1 cm3 s,1. Acetone and formaldehyde were detected as products of the reaction with the respective yields of Racetone = 0.9 ± 0.2 and RHCHO = 1.2 ± 0.3. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 415,421, 2007 [source] Rate coefficients for the gas-phase reaction of hydroxyl radicals with the dimethylbenzaldehydesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2006Grainne M. Clifford Rate coefficients for the reactions of hydroxyl (OH) radicals with the dimethylbenzaldehydes have been determined at 295 ± 2K and atmospheric pressure using the relative rate technique. Experiments were performed in an atmospheric simulation chamber using gas chromatography for chemical analysis. The rate coefficients (in units of cm3 molecule,1 s,1) are: 2,3-dimethylbenzaldehyde, (25.9 ± 2.8) × 10,12; 2,4-dimethylbenzaldehyde, (27.5 ± 4.4) × 10,12; 2,5-dimethylbenzaldehyde, (27.6 ± 5.1) × 10,12; 2,6-dimethylbenzaldehyde, (30.7 ± 3.0) × 10,12; 3,4-dimethylbenzaldehyde, (24.6 ± 4.0) × 10,12; and 3,5-dimethylbenzaldehyde, (28.2 ± 2.5) × 10,12. The reactivity of the dimethylbenzaldehydes is compared with other aromatic compounds and it is shown that the magnitude of the OH rate coefficients does not depend significantly on the position of the CH3 substituent on the aromatic ring. The rate coefficient data are explained in terms of known mechanistic features of the reactions and the atmospheric implications are also discussed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 563,569, 2006 [source] Kinetics of the gas-phase reaction of CF3OC(O)H with OH radicals at 242,328 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2004L. Chen The rate constants, k1, of the reaction of CF3OC(O)H with OH radicals were measured by using a Fourier transform infrared spectroscopic technique in an 11.5-dm3 reaction chamber at 242,328 K. OH radicals were produced by UV photolysis of an O3,H2O,He mixture at an initial pressure of 200 Torr. Ozone was continuously introduced into the reaction chamber during UV irradiation. With CF3OCH3 as a reference compound, k1 at 298 K was (1.65 ± 0.13) × 10,14 cm3 molecule,1 s,1. The temperature dependence of k1 was determined as (2.33 ± 0.42) × 10,12 exp[,(1480 ± 60)/T] cm3 molecule,1 s,1; possible systematic uncertainty could add an additional 20% to the k1 values. The atmospheric lifetime of CF3OC(O)H with respect to reaction with OH radicals was calculated to be 3.6 years. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 337,344 2004 [source] Rate constants for the gas-phase reaction of CF3CF2CF2CF2CF2CHF2 with OH radicals at 250,430 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2004L. Chen The rate constants k1 for the reaction of CF3CF2CF2CF2CF2CHF2 with OH radicals were determined by using both absolute and relative rate methods. The absolute rate constants were measured at 250,430 K using the flash photolysis,laser-induced fluorescence (FP-LIF) technique and the laser photolysis,laser-induced fluorescence (LP-LIF) technique to monitor the OH radical concentration. The relative rate constants were measured at 253,328 K in an 11.5-dm3 reaction chamber with either CHF2Cl or CH2FCF3 as a reference compound. OH radicals were produced by UV photolysis of an O3,H2O,He mixture at an initial pressure of 200 Torr. Ozone was continuously introduced into the reaction chamber during the UV irradiation. The k1 (298 K) values determined by the absolute method were (1.69 ± 0.07) × 10,15 cm3 molecule,1 s,1 (FP-LIF method) and (1.72 ± 0.07) × 10,15 cm3 molecule,1 s,1 (LP-LIF method), whereas the K1 (298 K) values determined by the relative method were (1.87 ± 0.11) × 10,15 cm3 molecule,1 s,1 (CHF2Cl reference) and (2.12 ± 0.11) × 10,15 cm3 molecule,1 s,1 (CH2FCF3 reference). These data are in agreement with each other within the estimated experimental uncertainties. The Arrhenius rate constant determined from the kinetic data was K1 = (4.71 ± 0.94) × 10,13 exp[,(1630 ± 80)/T] cm3 molecule,1 s,1. Using kinetic data for the reaction of tropospheric CH3CCl3 with OH radicals [k1 (272 K) = 6.0 × 10,15 cm3 molecule,1 s,1, tropospheric lifetime of CH3CCl3 = 6.0 years], we estimated the tropospheric lifetime of CF3CF2CF2CF2CF2CHF2 through reaction with OH radicals to be 31 years. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 26,33, 2004 [source] Kinetic study of the gas-phase reaction of the nitrate radical with methyl-substituted thiophenesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2003B. Cabañas The gas-phase reactions of the NO3 radical with 2-methylthiophene, 3-methylthiophene, and 2,5-dimethylthiophene have been studied, using relative and absolute methods at 298 K. Determination of relative rate was performed using Teflon collapsible bag as the reaction chamber and gas chromatography as the analytical tool. For the absolute method, experiments were carried out using fast-flow-discharge technique with detection of NO3 by laser-induced fluorescence. The temperature dependence was studied by the absolute technique for the reactions of NO3 with 2-methylthiophene and 3-methylthiophene in the range 263,335 K. The proposed Arrhenius expressions for the reaction of the nitrate radical with 2-methylthiophene and 3-methylthiophene are k = (4 ± 2) × 10,16 exp[,(2200 ± 100)/T]] cm3 molecule,1 s,1 and k = (3 ± 2) × 10,15 exp[,(1700 ± 200)/T]] cm3 molecule,1 s,1, respectively. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 286,293, 2003 [source] Kinetics of the gas-phase reaction of n -C6,C10 aldehydes with the nitrate radicalINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2003Jun Noda Rate coefficients for gas-phase reaction between nitrate radicals and the n -C6,C10 aldehydes have been determined by a relative rate technique. All experiments were carried out at 297 ± 2 K, 1020 ± 10 mbar and using synthetic air or nitrogen as the bath gas. The experiments were made with a collapsible sampling bag as reaction chamber, employing solid-phase micro extraction for sampling and gas chromatography/flame ionization detection for analysis of the reaction mixtures. One limited set of experiments was carried out using a glass reactor and long-path FTIR spectroscopy. The results show good agreement between the different techniques and conditions employed as well as with previous studies (where available). With butanal as reference compound, the determined values (in units of 10,14 cm3 molecule,1 s,1) for each of the aldehydes were as follows: hexanal, 1.7 ± 0.1; heptanal, 2.1 ± 0.3; octanal, 1.5 ± 0.2; nonanal, 1.8 ± 0.2; and decanal, 2.2 ± 0.4. With propene as reference compound, the determined rate coefficients were as follows: heptanal, 1.9 ± 0.2; octanal, 2.0 ± 0.3; and nonanal, 2.2 ± 0.3. With 1-butene as reference compound, the rate coefficients for hexanal and heptanal were 1.6 ± 0.2 and 1.8 ± 0.1, respectively. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 120,129, 2003 [source] Mechanism for the gas-phase reaction between OH and 3-methylfuran: A theoretical studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 7 2008Weichao Zhang Abstract The mechanism for the OH + 3-methylfuran reaction has been studied via ab initio calculations to investigate various reaction pathways on the doublet potential energy surface. Optimizations of the reactants, products, intermediates, and transition structures are conducted using the MP2 level of theory with the 6-311G(d,p) basis set. The single-point electronic energy of each optimized geometry is refined with G3MP2 and G3MP2B3 calculations. The theoretical study suggests that the OH + 3-methylfuran reaction is dominated by the formation of HC(O)CHC(CH3)CHOH (P7) and CH(OH)CHC(CH3)C(O)H (P9), formed from two low-lying adducts, IM1 and IM2. The direct hydrogen abstraction pathways and the SN2 reaction may play a minor or negligible role in the overall reaction of OH with 3-methylfuran. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Theoretical study on the gas-phase reaction mechanism between nickel monoxide and methane for syngas productionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2009Hua-Qing Yang Abstract The comprehensive mechanism survey on the gas-phase reaction between nickel monoxide and methane for the formation of syngas, formaldehyde, methanol, water, and methyl radical has been investigated on the triplet and singlet state potential energy surfaces at the B3LYP/6-311++G(3df, 3pd)//B3LYP/6-311+G(2d, 2p) levels. The computation reveals that the singlet intermediate HNiOCH3 is crucial for the syngas formation, whereas two kinds of important reaction intermediates, CH3NiOH and HNiOCH3, locate on the deep well, while CH3NiOH is more energetically favorable than HNiOCH3 on both the triplet and singlet states. The main products shall be syngas once HNiOCH3 is created on the singlet state, whereas the main products shall be methyl radical if CH3NiOH is formed on both singlet and triplet states. For the formation of syngas, the minimal energy reaction pathway (MERP) is more energetically preferable to start on the lowest excited singlet state other than on the ground triplet state. Among the MERP for the formation of syngas, the rate-determining step (RDS) is the reaction step for the singlet intermediate HNiOCH3 formation involving an oxidative addition of NiO molecule into the CH bond of methane, with an energy barrier of 120.3 kJ mol,1. The syngas formation would be more effective under higher temperature and photolysis reaction condition. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Ab initio investigation on the reaction path and rate for the gas-phase reaction of HO + H2O , H2O + OHJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2003Tadafumi Uchimaru Abstract This article describes an ab initio investigation on the potential surfaces for one of the simplest hydrogen atom abstraction reactions, that is, HO + H2O , H2O + OH. In accord with the findings in the previously reported theoretical investigations, two types of the hydrogen-bonding complexes [HOHOH] and [H2OHO] were located on the potential energy surface. The water molecule acts as a hydrogen donor in the [HOHOH] complex, while the OH radical acts as a hydrogen donor in the [H2OHO] complex. The energy evaluations at the MP2(FC) basis set limit, as well as those through the CBS-APNO procedure, have provided estimates for enthalpies of association for these complexes at 298 K as ,2.1 , ,2.3 and ,4.1 , ,4.3 kcal/mol, respectively. The IRC calculations have suggested that the [H2OHO] complex should be located along the reaction coordinate for the hydrogen abstraction. Our best estimate for the classical barrier height for the hydrogen abstraction is 7.8 kcal/mol, which was obtained from the CBS-APNO energy evaluations. After fitting the CBS-APNO potential energy curve to a symmetrical Eckart function, the rate constants were calculated by using the transition state theory including the tunneling correction. Our estimates for the Arrhenius parameters in the temperature region from 300 to 420 K show quite reasonable agreement with the experimentally derived values. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1538,1548, 2003 [source] CH3CH2SCH3,+,OH radicals: temperature-dependent rate coefficient and product identification under atmospheric pressure of air,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2010Gabriela Oksdath-Mansilla Abstract Relative rate coefficients have been determined for the gas-phase reaction of hydroxyl (OH) radicals with ethyl methyl sulfide (EMS) using isobutene as a reference compound. The experiments were performed in a 1080,L quartz glass photoreactor in the temperature range of 286,313,K at a total pressure of 760,±,10,Torr synthetic air using in situ FTIR absorption spectroscopy to monitor the concentration-time behaviors of reactants and products. OH radicals were produced by the 254,nm photolysis of hydrogen peroxide (H2O2). The kinetic data obtained were used to derive the following Arrhenius expression valid in the temperature range of 286,313,K (in units of cm3,molecule,1,s,1): The rate coefficient displays a negative temperature dependence and low pre-exponential factor which supports the existence of an addition mechanism for the reaction involving reversible OH-adduct formation. The results are compared with previous data of other sulfides from the literature and are rationalized in terms of structure,reactivity relationships. Additionally, product identification of the title reaction was performed for the first time by the FTIR technique under atmospheric conditions. Sulfur dioxide, formaldehyde, and formic acid were observed as degradation products in agreement with the two possible reaction channels (addition/abstraction). Copyright © 2010 John Wiley & Sons, Ltd. [source] Gaseous HgH2, CdH2, and ZnH2CHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2005Alireza Shayesteh Abstract Gaseous HgH2, CdH2, and ZnH2 molecules were synthesized by the direct gas-phase reaction of excited mercury, cadmium, and zinc atoms with molecular hydrogen. The molecules were identified by their high-resolution infrared emission spectra, and the metal,hydrogen bond lengths were determined from the rotational analysis of the antisymmetric stretching fundamental bands. [source] Fullerene-like Mo(W)1,xRexS2 NanoparticlesCHEMISTRY - AN ASIAN JOURNAL, Issue 8-9 2008Francis, Leonard Deepak Dr. Abstract Inorganic fullerene-like (IF) Mo1,xRexS2 and W1,xRexS2 nanoparticles have been synthesized by a gas-phase reaction involving the respective metal halides with H2S. The IF-Mo(W)1,xRexS2 nanoparticles, containing up to 5,% Re, were characterized by a variety of experimental techniques. Analyses of the X-ray powder diffraction and different electron microscopy techniques show that the Re is doped in the MoS2 host lattice. Interestingly, Re-doped MoS2 nanotubes are present as well, although in small quantities (,5,%). XPS results confirm the nanoparticles to be more n-type arising from the effect of Re doping. Additionally, density-functional tight-binding (DFTB) calculations support the observed n-type behavior. [source] Rate constants for the gas-phase reactions of nitrate radicals with geraniol, citronellol, and dihydromyrcenol,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2010Joel C. Harrison Terpenes and terpene alcohols are prevalent compounds found in a wide variety of consumer products including soaps, flavorings, perfumes, and air fresheners used in the indoor environment. Knowing the reaction rate of these chemicals with the nitrate radical is an important factor in determining their fate indoors. In this study, the bimolecular rate constants of k (16.6 ± 4.2) × 10,12, k (12.1 ± 3) × 10,12, and k (2.3 ± 0.6) × 10,14 cm3 molecule,1 s,1 were measured using the relative rate technique for the reaction of the nitrate radical (NO3,) with 2,6-dimethyl-2,6-octadien-8-ol (geraniol), 3,7-dimethyl-6-octen-1-ol (citronellol), and 2,6-dimethyl-7-octen-2-ol (dihydromyrcenol) at (297 ± 3) K and 1 atmosphere total pressure. Using the geraniol, citronellol, or dihydromyrcenol + NO3, rate constants reported here, pseudo-first-order rate lifetimes (k,) of 1.5, 1.1, and 0.002 h,1 were determined, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 669,675, 2010 [source] The role of chlorine atoms and hydroxyl radicals in the formation of PCDDs from the oxidative pyrolysis of 2,4,6-trichlorophenolINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2010Lavrent Khachatryan A 132-step gas-phase reaction kinetic model has been combined with a four-step surface model for the formation of 1,3,6,8-tetrachlorodibenzo- p -dioxin (1,3,6,8-TCDD) from the oxidation of 2,4,6-trichlorophenol (2,4,6-TCP) in the presence of hexane. The revised model is based on a simpler model previously published in the literature and modified by adding Cl-releasing and the surface submodels, recalculating polynomial functions for thermodynamic parameters, and updating gas-phase submodels for (i) 1,3,6,8-TCDD formation, (ii) hydrogen oxidation, and (iii) hexane oxidation. The roles of the potential chain carriers, OH and Cl, in the formation of 1,3,6,8-TCDD were specifically addressed. In spite of the reported high reactivity of Cl, it was found that OH:Cl , 1, and OH is the dominant chain carrier from the apparent onset of purely gas-phase reactions at 750 K to 99% conversion of 2,4,6-TCP and hexane at 1075 K. This suggests that oxidation reactions are always dominant in realistic combustion systems, even where there are high concentrations of chlorine and relatively rich burning conditions. The update of the three gas-phase submodels as well as incorporation of Cl-releasing and the surface submodels resulted in improved agreement between calculated and experimental yields of 1,3,6,8-TCDD yields at temperatures as low as 800 K. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 90,97, 2010 [source] Kinetics of the gas-phase reactions of cyclo-CF2CFXCHXCHX , (X = H, F, Cl) with OH radicals at 253,328 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2009L. Chen Rate constants were determined for the reactions of OH radicals with halogenated cyclobutanes cyclo-CF2CF2CHFCH2(k1), trans -cyclo-CF2CF2CHClCHF(k2), cyclo-CF2CFClCH2CH2(k3), trans -cyclo-CF2CFClCHClCH2(k4), and cis -cyclo-CF2CFClCHClCH2(k5) by using a relative rate method. OH radicals were prepared by photolysis of ozone at a UV wavelength (254 nm) in 200 Torr of a sample reference H2OO3O2He gas mixture in an 11.5-dm3 temperature-controlled reaction chamber. Rate constants of k1 = (5.52 ± 1.32) × 10,13 exp[,(1050 ± 70)/T], k2 = (3.37 ± 0.88) × 10,13 exp[,(850 ± 80)/T], k3 = (9.54 ± 4.34) × 10,13 exp[,(1000 ± 140)/T], k4 = (5.47 ± 0.90) × 10,13 exp[,(720 ± 50)/T], and k5 = (5.21 ± 0.88) × 10,13 exp[,(630 ± 50)/T] cm3 molecule,1 s,1 were obtained at 253,328 K. The errors reported are ± 2 standard deviations, and represent precision only. Potential systematic errors associated with uncertainties in the reference rate constants could add an additional 10%,15% uncertainty to the uncertainty of k1,k5. The reactivity trends of these OH radical reactions were analyzed by using a collision theory,based kinetic equation. The rate constants k1,k5 as well as those of related halogenated cyclobutane analogues were found to be strongly correlated with their CH bond dissociation enthalpies. We consider the dominant tropospheric loss process for the halogenated cyclobutanes studied here to be by reaction with the OH radicals, and atmospheric lifetimes of 3.2, 2.5, 1.5, 0.9, and 0.7 years are calculated for cyclo-CF2CF2CHFCH2, trans -cyclo-CF2CF2CHClCHF, cyclo-CF2CFClCH2CH2, trans -cyclo-CF2CFClCHClCH2, and cis -cyclo-CF2CFClCHClCH2, respectively, by scaling from the lifetime of CH3CCl3. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 532,542, 2009 [source] Kinetics of the gas-phase reactions of chlorine atoms with CH2F2, CH3CCl3, and CF3CFH2 over the temperature range 253,553 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2009E. J. K. Nilsson Relative rate techniques were used to study the title reactions in 930,1200 mbar of N2 diluent. The reaction rate coefficients measured in the present work are summarized by the expressions k(Cl + CH2F2) = 1.19 × 10,17T2 exp(,1023/T) cm3 molecule,1 s,1 (253,553 K), k(Cl + CH3CCl3) = 2.41 × 10,12 exp(,1630/T) cm3 molecule,1 s,1 (253,313 K), and k(Cl + CF3CFH2) = 1.27 × 10,12 exp(,2019/T) cm3 molecule,1 s,1 (253,313 K). Results are discussed with respect to the literature data. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 401,406, 2009 [source] Rate coefficients for the gas-phase reactions of OH radicals with methylbutenols at 298 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2004Takashi Imamura 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 [source] Gas-phase radical,radical recombination reactions of nitroxides with substituted phenyl radicalsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2004J. L. Heidbrink Fourier-transform ion cyclotron resonance mass spectrometry has been used to examine gas-phase reactions of four different nitroxide free radicals with eight positively charged pyridyl and phenyl radicals (some containing a Cl, F, or CF3 substituent). All the radicals reacted rapidly (near collision rate) with nitroxides by radical,radical recombination. However, some of the radicals were also able to abstract a hydrogen atom from the nitroxide. The results establish that the efficiency (kreaction/kcollision) of hydrogen atom abstraction varies with the electrophilicity of the radical, and hence is attributable to polar effects (a lowering of the transition-state energy by an increase in its polar character). The efficiency of the recombination reaction is not sensitive to substituents, presumably due to a very low reaction barrier. Even so, after radical,radical recombination has occurred, the nitroxide adduct was found to fragment in different ways depending on the structure of the radical. For example, a cationic fragment was eliminated from the adducts of the more electrophilic radicals via oxygen anion abstraction by the radical (i.e., the nitroxide adduct cleaves heterolytically), whereas adducts of the less electrophilic radicals predominantly fragmented via homolytic cleavage (oxygen atom abstraction). Therefore, differences in the product branching ratios were found to be attributable to polar factors. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 216,229 2004 [source] Kinetics for the gas-phase reactions of OH radicals with the hydrofluoroethers CH2FCF2OCHF2, CHF2CF2OCH2CF3, CF3CHFCF2OCH2CF3, and CF3CHFCF2OCH2CF2CHF2 at 268,308 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2003L. Chen Rate constants were determined for the reactions of OH radicals with the hydrofluoroethers (HFEs) CH2FCF2OCHF2(k1), CHF2CF2OCH2CF3 (k2), CF3CHFCF2OCH2CF3(k3), and CF3CHFCF2OCH2CF2CHF2(k4) by using a relative rate method. OH radicals were prepared by photolysis of ozone at UV wavelengths (>260 nm) in 100 Torr of a HFE,reference,H2O,O3,O2,He gas mixture in a 1-m3 temperature-controlled chamber. By using CH4, CH3CCl3, CHF2Cl, and CF3CF2CF2OCH3 as the reference compounds, reaction rate constants of OH radicals of k1 = (1.68) × 10,12 exp[(,1710 ± 140)/T], k2 = (1.36) × 10,12 exp[(,1470 ± 90)/T], k3 = (1.67) × 10,12 exp[(,1560 ± 140)/T], and k4 = (2.39) × 10,12 exp[(,1560 ± 110)/T] cm3 molecule,1 s,1 were obtained at 268,308 K. The errors reported are ± 2 SD, and represent precision only. We estimate that the potential systematic errors associated with uncertainties in the reference rate constants add a further 10% uncertainty to the values of k1,k4. The results are discussed in relation to the predictions of Atkinson's structure,activity relationship model. The dominant tropospheric loss process for the HFEs studied here is considered to be by the reaction with the OH radicals, with atmospheric lifetimes of 11.5, 5.9, 6.7, and 4.7 years calculated for CH2FCF2OCHF2, CHF2CF2OCH2CF3, CF3CHFCF2OCH2CF3, and CF3CHFCF2OCH2CF2CHF2, respectively, by scaling from the lifetime of CH3CCl3. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 239,245, 2003 [source] Temperature-dependent kinetic study for ozonolysis of selected tropospheric alkenesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2002Elena V. Avzianova Ozonolysis reactions of alkenes are suggested to play major roles in the chemistry of the troposphere. Rate constants for the gas-phase reactions of O3 with a series of alkenes were determined using relative rate technique based on GC/FID measurements of alkene decays. Experiments were carried out in air over the temperature range of 278,353 K at an atmospheric pressure of 760 Torr. An excess of 1,3,5-trimethylbenzene was used as a HO radical scavenger in all experiments. Arrhenius parameters were calculated for ozonolysis of 1-butene, 1-pentene, 1-hexene, 1-heptene, 2-methyl-1-butene, isobutene, trans -2-butene, trans -2-pentene, cis -2-pentene, trans -2-hexene, cis -2-hexene, 3-chloropropene, 1,1-dichloroethene, and isoprene from temperature-dependent studies of the rate constants. The rate constants obtained in this study are compared with previous literature data. A good linear correlation between the logarithms of the rate constants and calculated HOMO energies of selected alkenes is observed. However, no clear correlation could have been drawn for chlorinated substituted alkenes. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 678,684, 2002 [source] The gas-phase oxidation of n -hexadecaneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2001R. Fournet Since n -hexadecane or cetane is a reference fuel for the estimation of cetane numbers in diesel engines, a detailed chemical model of its gas-phase oxidation and combustion will help to enhance diesel performance and reduce the emission of pollutants at their outlet. However, until recently the gas-phase reactions of n -hexadecane had not been experimentally studied, prohibiting a validation of oxidation models which could be written. This paper presents a modeling study of the oxidation of n -hexadecane based on experiments performed in a jet-stirred reactor, at temperatures ranging from 1000 to 1250 K, 1-atm pressure, a constant mean residence time of 0.07 s, and high degree of nitrogen dilution (0.03 mol% of fuel) for equivalence ratios equal to 0.5, 1, and 1.5. A detailed kinetic mechanism was automatically generated by using the computer package (EXGAS) developed in Nancy. The long linear chain of this alkane necessitates the use of a detailed secondary mechanism for the consumption of the alkenes formed as a result of primary parent fuel decomposition. This high-temperature mechanism includes 1787 reactions and 265 species, featuring satisfactory agreement for both the consumption of reactants and the formation of products. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 574,586, 2001 [source] The mechanism of neutral amino acid decomposition in the gas phase.INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2001N -dimethylglycine, N -dimethylglycine ethyl ester, The elimination kinetics of N, ethyl 1-piperidineacetate The gas-phase elimination kinetics of the ethyl ester of two ,-amino acid type of molecules have been determined over the temperature range of 360,430°C and pressure range of 26,86 Torr. The reactions, in a static reaction system, are homogeneous and unimolecular and obey a first-order rate law. The rate coefficients are given by the following equations. For N,N-dimethylglycine ethyl ester: log k1(s,1) = (13.01 ± 3.70) , (202.3 ± 0.3)kJ mol,1 (2.303 RT),1 For ethyl 1-piperidineacetate: log k1(s,1) = (12.91 ± 0.31) , (204.4 ± 0.1)kJ mol,1 (2.303 RT),1 The decompositon of these esters leads to the formation of the corresponding ,-amino acid type of compound and ethylene. However, the amino acid intermediate, under the condition of the experiments, undergoes an extremely rapid decarboxylation process. Attempts to pyrolyze pure N,N-dimethylglycine, which is the intermediate of dimethylglycine ethyl ester pyrolysis, was possible at only two temperatures, 300 and 310°C. The products are trimethylamine and CO2. Assuming log A = 13.0 for a five-centered cyclic transition-state type of mechanism in gas-phase reactions, it gives the following expression: log k1(s,1) = (13.0) , (176.6)kJ mol,1 (2.303 RT),1. The mechanism of these ,-amino acids differs from the decarbonylation elimination of 2-substituted halo, hydroxy, alkoxy, phenoxy, and acetoxy carboxylic acids in the gas phase. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33:465,471, 2001 [source] Kinetics and products of the reactions of selected diols with the OH radicalINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2001Heidi L. Bethel Using a relative rate method, rate constants have been measured at 296 ± 2 K for the gas-phase reactions of OH radicals with 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, and 2-methyl-2,4-pentanediol, with rate constants (in units of 10,12 cm3 molecule,1 s,1) of 27.0 ± 5.6, 23.6 ± 6.3, 33.2 ± 6.8, and 27.7 ± 6.1, respectively, where the error limits include the estimated overall uncertainty of ±20% in the rate constant for the reference compound. Gas chromatographic analyses showed the formation of 1-hydroxy-2-butanone from 1,2-butanediol, 3-hydroxy-2-butanone from 2,3-butanediol, 1-hydroxy-3-butanone from 1,3-butanediol, and 4-hydroxy-4-methyl-2-pentanone from 2-methyl-2,4-pentanediol, with formation yields of 0.66 ± 0.11, 0.89 ± 0.09, 0.50 ± 0.09, and 0.47 ± 0.09, respectively, where the indicated errors are the estimated overall uncertainties. Pathways for the formation of these products are presented, together with a comparison of the measured and estimated rate constants and product yields. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 310,316, 2001 [source] | |||||||||||||||||||||||||