- Rate constants for the decomposition of 2-butoxy radicals and their reaction with NO and O2
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The reactivity of 2-butoxy radicals has been investigated using the laser photolysis/laser induced fluorescence technique. Three reactions have been studied: (i) The rate constants for the reaction with NO have been measured by the same technique at total pressures between 0.03 1 = (4.4 ± 0.6) × 10-12 exp((4.9 ± 0.3) kJ mol -1/RT) cm3 s-1. (ii) The rate constant with O2 has been measured at room temperature and 0.131 bar of helium: k2 = (9 ± 2) × 10-15 cm3 s -1. Significant quenching of 2-butoxy fluorescence by O2 prevented experiments in a larger temperature range: kq,O2 = (4 ± 1) × 10-11 cm3 s-1. (iii) The temperature and pressure dependence of the unimolecular decomposition at total pressures between 0.01 cent have been extracted from a falloff analysis of the experimental results: k3,0,He = 3.2 × 10 -8 exp(-35.9 kJ mol-1/RT) cm3 s-1, k3,∞ = 1.1 × 1014 exp(-53.6 kJ mol -1/RT) s-1, and F3.c = 0.87 - T/870 K. We anticipate an uncertainty of ±30% for these rate constants. These results are in excellent agreement with earlier predictions (C. Fittschen, H. Hippler and B. Viskolcz, Phys. Chem. Chem. Phys., 2000, 2, 1677-1683 (ref. 1); R. Mereau, M.-T. Rayez, F. Caralp and J.-C. Rayez, Phys. Chem. Chem. Phys., 2000, 2, 3765 (ref. 2)).
- Falgayrac,Caralp,Sokolowski-Gomez,Devolder,Fittschen
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Read Online
- Use of perfluorocarboxylic acids to trick cytochrome P450BM3 into initiating the hydroxylation of gaseous alkanes
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It has long been believed that the fatty acid hydroxylase wild-type P450BM3 is unable to oxidize gaseous alkanes. However, the simple addition of a perfluorocarboxylic acid as a dummy substrate to initiate the P450BM3 catalytic cycle enabled the efficient hydroxylation of butane and propane (see picture).
- Kawakami, Norifumi,Shoji, Osami,Watanabe, Yoshihito
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supporting information; experimental part
p. 5315 - 5318
(2011/07/09)
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- Spectrokinetic study of the reaction system of 2NO2?N 2O4 with butanols between 320-358 K in the gas phase
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Spectrokinetic studies of the gas-phase equilibrium between nitrogen tetroxide and butanols in the reaction system 2NO2?N 2O4 (1,2), N2O4+ROH? RONO+HNO3 (3,4) have been undertaken in the temperature range 298-358 K. The products - RONO (n-butyl-ONO, sec-butyl-ONO, iso-butyl-ONO and tert-butyl-ONO) - were identified by their UV spectra and the values of the maxima UV absorption cross sections were determined in the range 320-420 nm at 298 K. The temperature dependences of both the forward and reverse rate constants, k3 and k4, were obtained. The extrapolated values of the forward rate constants are 10-18 k3 av/cm3 molec-1 s-1 3.9±1.0; 1.7±0.3; 4.2±0.8; 5.7±1.1 and the reverse rate constants are 10-20 k4av/cm3 molec -1 s-1 0.3±0.1; 2.3±0.6; 0.4±0.1; 2.3±0.6 at 298 K for the reaction of NO2/N2O 4 with n-butanol, sec-butanol, iso-butanol and tert-butanol, respectively. The activation energy for the forward E3 and for the reverse E4 reaction were derived.
- Wojcik-Pastuszka,Jodkowski
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experimental part
p. 131 - 143
(2009/09/25)
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- Dispersed fluorescence spectroscopy of primary and secondary alkoxy radicals
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Dispersed fluorescence (DF) spectra of 1-propoxy, 1-butoxy, 2-propoxy, and 2-butoxy radicals have been observed under supersonic jet cooling conditions by pumping different vibronic bands of the B-X laser induced fluorescence excitation spectrum. The DF spectra were recorded for both conformers of 1-propoxy, three conformers of the possible five of 1-butoxy, the one possible conformer of 2-propoxy, and two conformers of the possible three of 2-butoxy. Analysis of the spectra yields the energy separations of the vibrationless levels of the ground X and low-lying A electronic state as well as their vibrational frequencies. In all cases, the vibrational structure of the DF spectra is dominated by a CO stretch progression yielding the vco stretching frequency for the X state and in most cases for the A state. In addition to the experimental work, quantum chemical calculations were carried out to aid the assignment of the vibrational levels of the X state and for some conformers the A state as well. Geometry optimizations of the different conformers of the isomers were performed and their energy differences in the ground states were determined. The results of the calculation of the energy separations of the close-lying X and A states of the different conformations are provided for comparison with the experimental observations.
- Jin, Jin,Sioutis, Ilias,Tarczay, Gyoergy,Gopalakrishnan, Sandhya,Bezant, Andrew,Miller, Terry A.
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p. 11780 - 11797
(2008/01/27)
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- Atmospheric fate of alkoxy radicals: Branching ratio of evolution pathways for 1-propoxy, 2-propoxy, 2-butoxy and 3-pentoxy radicals
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As the last step of VOC oxidation in the atmosphere, the evolution of alkoxy radicals determines the nature and the concentration of the secondary compounds formed. Branching ratios between decomposition and reaction with O2 of 1-propoxy, 2-propoxy, 2-butoxy, and 3-pentoxy radicals were measured at room temperature and 1 atm in a simulation chamber using FTIR spectroscopy as an analytical device. The ratio varied depending on the leaving alkyl group and the class of alkoxy. No additional decomposition due to excited radicals was observed. The results could be used directly for tropospheric simulation purposes. Formaldehyde might be a photolytic source of HOx through the production of H and HCO radicals and acetaldehyde is the key precursor of the toxic NOx reservoir, peroxy-acetyl nitrate. In the lower troposphere, 1-propoxy and 2-propoxy radicals react mainly with O2 while decomposition is an important reaction pathway for 2-butoxy and 3-pentoxy. Consequently, C1 and C2 aldehyde production from the two longer chain alkoxys will occur very close to the area of initial VOC oxidation, while for the alkoxys exhibiting a minor decomposition pathway, the formaldehyde or acetaldehyde production will take place after oxidation of all the intermediate secondary compounds, far from the emission area of the primary compound.
- Meunier,Doussin,Chevallier,Durand-Jolibois,Picquet-Varrault,Carlier
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p. 4834 - 4839
(2007/10/03)
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- Relative-rate study of thermal decomposition of the 2-butoxyl radical in the temperature range 280-313 K
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The competition between thermal decomposition (kdis) and reaction with O2 (kO2) has been studied for the 2-butoxyl radical in a newly built 210 L photoreactor constructed of quartz. 2-Butoxyl radicals were generated by continuous 254 nm photolysis of 2-butoxyl iodide in the presence of O2 and NO, using N2 as a buffer gas. Reaction educts and products were analysed by long-path (29 m) IR absorption using an FTIR spectrometer. The ratio kdis/kO2 was derived from the product ratios of acetaldehyde and butanone, corrected for small amounts of side products. At 280, 298, and 313 K and a total pressure of 1 bar (M = O2 + N2), kdis/kO2 was determined at O2 partial pressures between 100 and 1000 mbar. At all temperatures, there was a systematic increase of (kdis/kO2)eff ≡ (Δ[CH3CHO]corr × [O2]) / (2 × Δ[CH3C(O)CH2CH3]) with the partial pressure of O2 which possibly is the result of an additional O2 independent source of acetaldehyde (≈8% of the 2-butoxyl radicals reacting by either of the two competing pathways at 298 K, 1 bar). Pressure-dependence studies between 100 and 1000 mbar support the hypothesis that the additional acetaldehyde originates from the formation of 6-10% chemically activated 2-butoxyl radicals in the temperature range 280-313 K. Correction of (kdis/kO2)eff for the O2 independent yield of acetaldehyde results in kdis/kO2 = (6.8 ± 1.4) × 1017, (2.3 ± 0.5) × 1018, and (5.5 ± 1.1) × 1018 molecule cm-3 at 279.8, 298.2, and 313.5 K, respectively, leading to the Arrhenius expression kdis/kO2 = (2.0 ± 0.5) × 1026exp(-45.4 kJ mol-1/RT) molecule cm-3 at a total pressure of 1 bar. This temperature dependence of kdis/kO2 implies that, depending on temperature, either thermal decomposition or reaction with O2 is the major loss process of 2-butoxyl radicals under the conditions of the lower troposphere. Using literature values for kO2, kdis = 3.9 × 1012exp(-47.1 kJ mol-1/RT) s-1 is derived for a total pressure of 1 bar (M = N2 + O2), which compares very favourably with a recent theoretical estimate (ab initio + RRKM) by Somnitz and Zellner (H. Somnitz and R. Zellner, Phys. Chem. Chem. Phys., 2000, 2, 1907).
- Libuda,Shestakov,Theloke,Zabel
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p. 2579 - 2586
(2007/10/03)
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- Fluorescence excitation spectrum of the 2-butoxyl radical and kinetics of its reactions with NO and NO2
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The (A ← X) fluorescence excitation spectrum of the 2-C4H9O(X) (2-butoxyl) radical in the wavelength range 345-390 nm was obtained using a combined laser photolysis/laser-induced fluorescence (LIF) technique following the generation of the radicals by excimer laser photolysis of 2-butylnitrite at λ = 351 nm. The fluorescence excitation spectrum shows 5 vibronic bands, where the dominant progression corresponds to the CO-stretching vibration in the first electronically excited state with v′CO = (560 ± 10) cm-1. The transition origin was assigned at v00 = (26768 ± 10) cm-1 (λ00 = (373.58 ± 0.15) nm). The kinetics of the reactions of the 2-butoxyl radical with NO and NO2 at temperatures between T = 223-305 K and pressures between p = 6.5-104 mbar have been determined. The rate coefficients for both reactions were found to be independent of total pressure with kNO = (3.9 ± 0.3) × 10-11 cm3 s-1 and kNO2 = (3.6 ± 0.3) times; 10-11 cm3 s-1 at T = 295 K. The Arrhenius expressions have been determined to be kNO = (9.1 ± 2.7) × 10-12 exp((3.4 ± 0.6) kJ mol-1/RT) cm3 s-1 and kNO2 = (8.6 ± 3.3) × 10-12 exp((3.3 ± 0.8) kJ mol-1/RT) cm3 s-1. In addition, the radiative lifetime of the 2-C4H9O(A) radical after excitation at λ = 365.938 nm in the (0,1) band has been determined to be τrad(2-C4H9O(A)) = (440 ± 80) ns. Quenching rate constants of the 2-C4H9O(A) radical were measured to be kq = (4.7 ± 0.3) × 10-10 cm3 s-1 and kq = (5.0 ± 0.4) × 10-12 cm3 s-1 for 2-butylnitrite and nitrogen, respectively.
- Lotz,Zellner
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p. 2607 - 2613
(2007/10/03)
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- Laser-Induced Fluorescence Excitation Spectra of terf-Butoxy and 2-Butoxy Radicals
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Laser-induced fluorescence (LIF) excitation spectra of t-C4H9O (terf-butoxy) and 2-C4H9O (2-butoxy) radicals were investigated in the wavelength range 335-400 nm. The radicals were formed by laser photolysis of the corresponding butyl nitrites at 355 nm. For tert-butoxy, 16 vibronic bands in two progressions were labeled. The dominant progression corresponds to C-O stretching mode with v′c-o = 521 ± 10 cm-1. The transition origin was tentatively assigned at 25 866 cm-1 (386.6 nm). Numerous bands remain unassigned. The LIF excitation spectrum of 2-butoxy, consisting of 15 vibronic bands in four progressions, was observed for the first time. A C-O stretching frequency v′c-o = 567 ± 10 cm-1 was obtained from the dominant progression. The transition origin was tentatively assigned at 26 185 cm-1 (381.9 nm). Three other progressions are evident, which have different vibrational band intervals: 617 ± 10, 590 ± 10, and 552 ± 10 cm-1. Zero-pressure fluorescence lifetimes for numerous vibronic bands of tert-butoxy and 2-butoxy were determined to be about 150 and 85 ns, respectively. These spectra can be used as a convenient spectroscopic tool for kinetic studies of butoxy radicals and should provide a starting point for investigations of their excited states structure and dynamics.
- Wang, Chuji,Shemesh, Liat G.,Deng, Wei,Lilien, Michael D.,Dibble, Theodore S.
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p. 8207 - 8212
(2007/10/03)
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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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- A kinetic study of the influence of alcohols on the nitrosation of morpholine in acid media. Equilibrium constants for the formation of alkyl nitrites
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The effect of the aliphatic alcohols methanol, ethanol, propanol, isopropanol, 2-butanol, isobutanol, and tert-butanol on the rate of nitrosation of morpholine at pH 3 and 25 deg C has been studied.The inhibition observed is attributed to the formation of alkyl nitrites, which are poor nitrosating agents in acid media.The equilibrium constants for the formation of alkyl nitrites from nitrous acid and alcohols have been calculated both spectrophotometrically and from kinetic data for the inhibitory effect, and there is agreement between the two sets of results.The molar absorptivities at 265 nm of the alkyl nitrites have also been determined.When the concentration of alkyl nitrite is very low, a slight catalytic effect considered to be an effect of the medium has been observed.
- Casado, Julio,Lorenzo, Francisco Manuel,Mosquera, Manuel,Prieto, Maria Flor Rodriguez
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p. 136 - 138
(2007/10/02)
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- Gas-phase Reaction of Hydroxyl Radicals with Alkyl Nitrite Vapors in H2O2+NO2+CO Mixtures
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The yields of CO2 from the chain reaction in H2O2+NO2+CO+alkyl nitrite mixtures, in wich OH is the chain carrier and alkyl nitrites induce a chain termination step, have been used to deduce rate constants (ks) for OH attack on alkyl nitrites (RONO) in the vapour phase at ambient temperatures.Values of ks/E9 dm3 mol-1 s-1 as a function of R were determined as follows: 0.71 +/-0.12 (CH3), 1.15+/-0.23 (C2H5), 1.56+/-0.32 (n-C3H7), 3.41+/-1.48 (n-C4H9), 3.89+/-0.58 (sec-C4H9), 3.47+/-0.52 (i-C4H9), 0.91+/-0.15 (t-C4H9), all based on ks=(1.63+/-0.16)E9 dm3 mol-1 s-1 for OH +n-butane.The small increase in ks from R=CH3 to t-4H9 is considered to support a recent postulate that both H-abstraction and NO-abstraction pathways are operative, at least for R=CH3.Under typical, sunlit urban atmosphere conditions it is deduced that OH attack on alkyl nitrites is a minor removal process compared to their photodissociative destruction.
- Audley, Gary J.,Baulch, Donald L.,Campbell, Ian M.,Waters, Des J.,Watling, Gillian
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p. 611 - 618
(2007/10/02)
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