- Kinetics of the C3H7O2 + NO reaction: Temperature dependence of the overall rate constant and the i-C3H7ONO2 branching channel
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The temperature dependence of the overall rate constant for the C3H7O2 + NO reaction and the rate constant for the minor branching-channel resulting in the production of i-C3H7ONO2 have been measured using the turbulent flow technique with high-pressure chemical ionization mass spectrometry for the detection of reactants and products. The temperature dependence of the overall rate constant for the C3H7O2 + NO reaction was investigated between 298 and 213 K at 100 Torr pressure, and the data were fit by the following Arrhenius expression (with 2 standard deviation error limits indicated): 43-0.9+1.0 x 10-12 exp[(268 ± 56)/T] cm3 molecule-1 s-1. This expression agrees well with previous isomer-specific measurements of the n-C3H7ONO2 and i-C3O2 + NO rate constants made at lower pressures. The temperature dependence of the rate constant for the minor reaction channel i-C3H7O2 + NO → i-C3H7ONO2 was investigated between 298 and 213 K at 100 Torr pressure. The following Arrhenius expression was determined for the minor channel: 4.9-2.9+5.3 × 10-16 exp[(1380 ± 230)/T] cm3 molecule-3 s-1. The Arrhenius expressions for the overall rate and the i-C3H7ONO2 producing channel indicate a branching ratio of about 0.006 at 298 K and 0.020 at 213 K at 100 Torr pressure, which is in good agreement with the predictions of a recently revised empirical model for alkyl nitrate branching ratios.
- Chow, Jessica M.,Miller, Angela M.,Elrod, Matthew J.
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- Nitration of alcohols by nitryl fluoride
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A general method for the preparation of nitrates by treatment of alcohols with nitryl fluoride (FNO2) in MeCN in the presence of KF has been developed.
- Fedorov,Eremenko
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- Products and mechanism of the reaction of OH radicals with 2,3,4-trimethylpentane in the presence of NO
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Alkanes are important constituents of gasoline fuel and vehicle exhaust, with branched alkanes comprising a significant fraction of the total alkanes observed in urban areas. Using a relative rate method, a rate constant for the reaction of OH radicals with 2,3,4-trimethylpentane of (6.84 ± 0.12) × 10-12 cm3 molecule-1 s-1 at 298 ± 2 K was measured, where the indicated error is two least-squares standard deviations and does not include the uncertainty in the rate constant for the n-octane reference compound. Products of the gas-phase reaction of OH radicals with 2,3,4-trimethylpentane in the presence of NO at 298 ± 2 K and atmospheric pressure of air have been investigated using gas chromatography with flame ionization detection (GC-FID), combined gas chromatography-mass spectrometry (GC-MS), and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS). Products identified and quantified by GC-FID and GC-MS were (molar yields given in parentheses): acetaldehyde (47 ± 6%), acetone (76 ± 11%), 3-methyl-2-butanone (41 ± 5%), 3-methyl-2-butyl nitrate (1.6 ± 0.2%), and 2-propyl nitrate (6.2 ± 0.8%). These compounds account for 69 ± 6% of the reaction products, as carbon. Additional products observed by API-MS analyses using positive and negative ion modes were C5- and C8-hydroxynitrates and a C 8-hydroxycarbonyl, which, together with the predicted formation of octyl nitrates, account for some or all of the remaining products. The product distribution is compared to those for the linear and branched C 8-alkanes n-octane and 2,2,4-trimethylpentane.
- Aschmann, Sara M.,Arey, Janet,Atkinson, Roger
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- Rates of Reaction between the Nitrate Radical and Some Aliphatic Alcohols
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Rate coefficients for the gas-phase reaction of NO3 with methanol, ethanol and propan-2-ol have been determined.Absolute rates were measured at temperatures between 258 and 367 K using the fast flow-discharge technique.The measured rate coefficients (in units of 1E-15 cm3 molecule-1 s-1) at 295 K are: 0.132+/-0.024, 1.37+/-0.10 and 3.13+/-0.64 for methanol, ethanol and propan-2-ol, respectively.The temperature dependence of the rate coefficients can be expressed as Arrhenius equations: kmethanol = (1.06+/-0.51) E-12exp, kethanol = (6.99+/-1.21)E-13 exp and kpropan-2-ol = (1.54+/-0.75)E-12 exp (in units cm3 molecule-1 s-1).An attempted product study, using N2O5 as the NO3 source, failed since the alcohols react with N2O5, producing alkyl nitrates.The estimated upper limit for rate coefficients for reaction of N2O5 with methanol, ethanol and propan-2-ol at 296 K in the gas phase were (2.0+/-1.0)E-19, (3.9+/-2.0)E-19 and (4.8+/-2.5)E-19 cm3 molecule-1 s-1, respectively.The error limits correspond to the 95percent-confidence interval.
- Langer, Sarka,Ljungstroem, Evert
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- Hydroxyl-radical-initiated oxidation of isobutyl isopropyl ether under laboratory conditions related to the troposphere. Product studies and proposed mechanism
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The products formed by the hydroxyl-radical-initiated oxidation of the model ether, isobutyl isopropyl ether [(CH3)2CHCH2OCH(CH3)2], have been investigated by irradiating synthetic air mixtures containing the substrate, methyl nitrite, and nitric oxide at ppm levels in a Teflon bag reactor at room temperature. The decay of reactant and formation of products were monitored by gas chromatography, mass spectrometry and by HPLC. The molar yields of the major products (mol of product formed/mol of isobutyl isopropyl ether consumed) were as follows: acetone, 0.56 ± 0.04; isopropyl formate, 0.48 ± 0.03; isobutyl acetate, 0.28 ± 0.02; 2-hydroxy-2-methylpropyl acetate [CH3C(O)OCH2C(OH)(CH3)2], 0.25 ± 0.1. The molar yields of the minor products were as follows: isobutyraldehyde, 0.06 ± 0.05; isopropyl nitrate, 0.09 ± 0.06; 1,1,4-trimethyl-3-oxapentyl nitrate [(CH3)2CHOCH2C(CH3) 2(ONO2)], 0.07 ± 0.02; isopropyl isobutyrate [(CH3)2CHC(O)OCH(CH3)2] ca. 0.01; and isobutyl formate, ca. 0.01. The major products are explained by a mechanism involving initial OH attack at the -CH- and -CH2- groups in the alkyl side chains of the ether followed by the subsequent reactions of the resulting carbon-centred, organic peroxy, and organic oxy radicals. The observed products, in conjunction with the proposed reaction pathways, account for a total yield of about 1.15, indicating that all the main routes are accounted for in the degradation of this ether. The major reaction pathways of the three principal organic oxy radicals are summarised as follows (percentage of overall reaction in brackets): (CH3)2C(O)OCH2CH(CH3) 2 → CH3C(O)OCH2CH(CH3)2 + CH3 (28%) (CH3)2CHOCH(O)CH(CH3)2 → (CH3)2CHOC(O)H + CH(CH3)2 (≤48%) (CH3)2CHOCH2C(O)(CH3) 2 → (CH3)2COCH2C(OH)(CH3) 2 (25%) This study supports the finding that organic oxy radicals generated from ethers and containing the structure RCH(O.)OR undergo mainly decomposition by C-C bond cleavage, whereas those oxy radicals with the structure RCH(O.)CH2OR undergo preferential 1,5-H-atom transfer isomerisation reactions. The following rate coefficients (10-12 cm3 molecule-1 s-1) at room temperature for the reactions of OH radicals with the reactant and products have been determined by the relative rate technique: isobutyl isopropyl ether, 19.5 ± 0.4; isobutyl acetate, 6.0 ± 0.5; isobutyraldehyde, 25.8 ± 0.7; isopropyl formate, 2.1 ± 0.1; isopropyl isobutyrate, 6.5 ± 0.4; 1,1,4-trimethyl-3-oxapentyl nitrate, 16.5 ± 0.7; and 2-hydroxy-2-methylpropyl acetate, 9.5 ± 1.6.
- Stemmler, Konrad,Mengon, Wolfgang,Kerr, J. Alistair
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p. 2865 - 2875
(2007/10/03)
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- Peroxyisobutyryl nitrate
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Peroxyisobutyryl nitrate, (CH3)2CHC(O)OONO2(PiBN), has been synthesized in the liquid phase, measured by electron capture gas chromatography (EC- GC), characterized in a number of decomposition tests, and prepared in-situ in the gas phase by sunlight irradiation of isobutyl nitrite, of isobutanal with NO, and of 3-methyl-1-butene with NO in air. The corresponding reaction mechanisms are outlined. In the liquid phase, PiBN decomposes to isopropyl nitrate. In the gas phase, thermal decomposition in the presence of NO yields acetone (91 ± 7%). Isobutanal reacts with OH predominantly (≥98%) by H abstraction from the carbonyl carbon, and 3-methyl-1-butene reacts with OH predominantly (≥98%) by addition on the C=C bond. Reaction with oxygen predominates (≥96%) over unimolecular decomposition for the alkoxy radicals (CH3)2CH(O) and (CH3)2CHCH2(O). Emission inventory data for hydrocarbons that are precursors to PiBN indicate that the PiBN-forming potential relative to that of PAN is ≤0.10. This ratio also represents an upper limit for the positive bias due to PiBN when measuring ambient PAN by EC-GC with packed columns, on which PiBN and PAN co-elute.
- Grosjean,Grosjean,Williams II
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p. 167 - 172
(2007/10/03)
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- Reaction of the Nitrate Radical with Some Potential Automotive Fuel Additives. A Kinetic and Mechanistic Study
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Rate coefficients for the reaction of NO3 with ethyl tert-butyl ether (ETBE), diisopropyl ether (DIPE), and tert-amyl methyl ether (TAME) have been determined.Absolute rates were measured at temperatures between 257 and 367 K using the fast flow-discharge (FFD) technique.Relative rate experiments were also performed at 295 K in a reactor equipped with White optics and using FTIR spectroscopy to follow the reactions.Rate data from FFD experiments can be presented as follows: kETBE=(2.48 +/-0.78)E-12exp, kDIPE=(2.02 +/-0.35)E-12exp, and kTAME=(1.21 +/-0.22)E-12exp (in units of cm3 molecule-1 s-1).The rate coefficients at room temperature from the FFD experiments are in goog agreement with the corresponding rate coefficients from the relative experiments.Products from simulated atmospheric oxidation of the investigated ethers, initiated by the reaction with nitrate radical, were identified using FTIR spectroscopy.The degradation of ETBE results in tert-butyl formate, tert-butyl acetate, formaldehyde, and methyl nitrate, that of DIPE in acetone, isopropyl nitrate, isopropyl acetate, and formaldehyde, and that of TAME in tert-amyl formate, formaldehyde, and tert-amyl nitrate.
- Langer, Sarka,Ljundstroem, Evert
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p. 5906 - 5912
(2007/10/02)
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- Rate Constants of the Reactions of CF3O2, i-C3H7O2 and t-C4H9O2 with NO
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The kinetics of the title reactions have been studied at T = 290 K and p = 2 Torr He using the fast-flow technique combined with molecular-beam sampling mass spectrometry. - In our novel approach, the total rate constant k1 of RO2 + NO -> RO + NO2/RONO2 is determined from the shape of the NO2-growth profile.The validity of the method is demonstrated by the nearly identical results for k1(CF3O2 + NO) obtained from CF3O2-decays: k1 = (1.54 +/- 0.35)*10-11 and from NO2-growths: k1 = (1.51 +/- 0.4)*10-11 cm3 s-1, in excellent agreement also with previous determinations. - Rate coefficient data of alkylperoxy + NO reactions, derived from NO2-profiles, are reported for i-C3H7O2 + NO: k1 = (5.0 +/- 1.2)*10-12 and for t-C4H9O2 + NO: k1 = (4.0 +/- 1.1)*10-12 cm3 s-1.Our results, in combination with literature values for smaller peroxy radicals, indicate a marked decrease of the rate coefficient with increasing CH3-substitution.Including data on haloalkyl- and acetylperoxy reactions, the reactivity of RO2 towards NO is shown to correlate with the electron acceptor/donor properties of substituents on the α-carbon.Atmospheric Chemistry / Chemical Kinetics / Elementary Reactions / Mass Spectrometry / Radicals
- Peeters, J.,Vertommen, J.,Langhans, I.
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p. 431 - 436
(2007/10/02)
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- Formation of Organic Nitro-compounds in Flowing H2O2+NO2+N2+Organic Vapour Systems. Part 3.-Effects of O2 Addition on H2O2+NO2+N2+Alkane Systems
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The effects of oxygen on the product distribution from the surface-initiated reactions in flowing mixtures of H2O2, NO2, N2 and RH, where RH=ethane, propane, n-butane and n-pentane, at 298 K have been studied.In the absence of O2, the principal products are the corresponding nitroalkane, alkyl nitrite and alkyl nitrate.In the presence of sufficiently large concentrations of O2, the predominant product is the alkyl nitrate and the only other products of significance, in some cases, are the corresponding carbonyl compounds.The variation of the product yields with / gives values for the rate-constant ratios k8/(k3+k4) for reaction at both primary and secondary radical sites:.Possible mechanisms by which the products are formed are discussed.
- Baulch, Donald L.,Campbell, Ian M.,Chappel, Jonathan M.
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p. 617 - 628
(2007/10/02)
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- Formation of Organic Nitro-compounds in Flowing H2O2+NO2+N2+Organic Vapour Systems. Part 2.-H2O2+NO2+N2+Alkane System
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The principal products from the surface-initiated reactions in flowing mixtures of H2O2, NO2,N2 and RH, where RH=ethane, propane, n-butane and n-pentane, have been identified as the nitroalkane, alkyl nitrite and alkyl nitrate.The product yields have been measured; in the case of propane the variation of the yields with total gas pressure has also been studied.Values have been obtained for the relative rates of primary and secondary H-atom abstraction from each alkane by OH and for the rate-constant ratios k3/k4 and k5/k6 at 298 K:.The trends in the product yields with the variation of pressure and change of R indicate that RO radicals are produced via reactions (4)-(6) rather than by a single-step reaction of R with NO2.
- Baulch, Donald L.,Campbell, Ian M.,Chappel, Jonathan M.
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p. 609 - 616
(2007/10/02)
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- Alkyl Nitrate Formation from the NOx-Air Photooxidations of C2-C8 n-Alkanes
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The yields of alkyl nitrates formed in the NOx-air photooxidations of the homologous series of n-alkanes from ethane through n-octane have been determined at 299 +/- 2 K and 735 torr total pressure for two different chemical systems.Alkyl peroxy radicals were generated by reaction of the n-alkanes with OH radicals (generated from the photolysis of methyl nitrite in air) or Cl atoms (from photolysis of Cl2 in air).The alkyl nitrate yields obtained from the two systems, corrected for secondary reactions, were in agreement within the experimental errors and increased monotonically with the carbon number of the n-alkane, from x-air photooxidations of the large n-alkanes.
- Atkinson, Roger,Aschmann, Sara M.,Carter, William P. L.,Winer, Arthur M.,Pitts, James N.
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p. 4563 - 4569
(2007/10/02)
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- Direct vs. Indirect Mechanisms in Organic Electrochemistry. Estimates of Activation Energies for Hydrogen Atom Transfer Processes of Relevance in Indirect Mechanisms Using the Bond Energy-Bond Order (BEBO) and Equibonding Methods
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Activation energies for a number of hydrogen abstraction reactions of interest in mechanistic organic electrochemistry have been calculated using the bond energy-bond-order (BEBO) and equibonding method.The main emphasis has been put on processes with bearing on the problem of deciding between direct and indirect mechanisms in anodic oxidation, viz. acyloxylation, hydroxylation, methoxylation, nitrooxylation, cyanation, carbomethoxylation and azidation.The results indicate that indirect mechanisms might play a more important role than presently assumed.
- Eberson, Lennart
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p. 481 - 492
(2007/10/02)
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