Benzene Oxidation in the Troposphere. Theoretical Investigation on the Possible Competition of Three Postulated Reaction Channels

Ghigo, Giovanni; Tonachini, Glauco

doi:10.1021/ja973956r

Cited by 53 publications

(77 citation statements)

References 16 publications

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“…The reversibility, also indicated in Figure 1, was predicted theoretically 9,17,18 and was known from liquid phase, 19 but the peroxy radical was found to be unexpectedly short-lived (2.5 ms in synthetic air) on account of competing loss processes of the adduct:…”

Section: Introductionsupporting

confidence: 54%

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Formation of Peroxy Radicals from OH−Toluene Adducts and O₂

Bohn

2001

J. Phys. Chem. A

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The gas-phase reaction of OH radicals with toluene and toluene-d 8 and reactions of the resulting OH adducts with O 2 were studied in N 2 /O 2 mixtures at atmospheric pressure and room temperature. OH production was performed by pulsed 248 nm photolysis of H 2 O 2 . Cw UV-laser long-path absorption at 308 nm was used for time-resolved detection of OH and OH-toluene adducts. The reaction OH + toluene was studied in N 2 and O 2 and similar rate constants of (5.70 ( 0.19) × 10 -12 cm 3 s -1 (N 2 ) and (5.60 ( 0.14) × 10 -12 cm 3 s -1 (O 2 ) were obtained at 100 kPa. For toluene-d 8 the corresponding rate constants are (5.34 ( 0.34) × 10 -12 cm 3 s -1 (N 2 ) and (5.47 ( 0.14) × 10 -12 cm 3 s -1 (O 2 ). Absorption cross-sections of (1.1 ( 0.2) × 10 -17 cm 2 were determined for both the OH-toluene and OH-toluene-d 8 adduct at 308 nm. Rate constants of (4.7 ( 1.4) × 10 -11 cm 3 s -1 and (1.8 ( 0.5) × 10 -10 cm 3 s -1 were determined for the OH-toluene adduct self-reaction and the OH-toluene adduct + HO 2 reaction, respectively. Upper limits e8 × 10 -15 cm 3 s -1 were estimated for any reactions of the OH-toluene adduct with H 2 O 2 or toluene. Adduct kinetics in the presence of O 2 is consistent with reversible formation of peroxy radicals with an estimated rate constant of (3 ( 2) × 10 -15 cm 3 s -1 and an equilibrium constant of (3.25 ( 0.33) × 10 -19 cm 3 (toluene-d 8 : (3.1 ( 1.2) × 10 -19 cm 3 ). The effective adduct loss from the equilibrium can be explained by (i) an additional, irreversible reaction of the adduct with O 2 with a rate constant of (6.0 ( 0.5) × 10 -16 cm 3 s -1 (toluene-d 8 : (4.7 ( 1.2) × 10 -16 cm 3 s -1 ), or (ii) a unimolecular reaction of the peroxy radical, with a rate constant of (1.85 ( 0.15) × 10 3 s -1 (toluene-d 8 : (1.5 ( 0.4) × 10 3 s -1 ). Consequences for the atmospheric degradation of toluene will be discussed.

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Section: Introductionsupporting

confidence: 54%

“…18,37 Recently Molina et al 38 investigated the intermediates of the OH + toluene reaction in the presence of O 2 by chemical ionization mass spectrometry. A mass peak at m/e ) 141 was attributed to the peroxy radical (III) while cyclization forming the bridged species (IV) was assumed to be unimportant due to the short residence time.…”

Section: Discussionmentioning

confidence: 99%

Formation of Peroxy Radicals from OH−Toluene Adducts and O₂

Bohn

2001

J. Phys. Chem. A

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“…More recently, several authors studied the transient absorption of HCHD in the presence of O 2 , Johnson et al (2002), Raoult et al (2004), Grebenkin and Krasnoperov (2004)). provided first evidence of a fast equilibrium (7/-7) in the gas phase, predicted theoretically by Lay et al (1996) and Ghigo and Tonachini (1998) but already observed in water by Pan and Von Sonntag (1990).…”

Section: The Adduct Reaction With Omentioning

confidence: 54%

Consecutive reactions of aromatic-OH adducts with NO, NO<sub>2</sub> and O<sub>2</sub>: benzene, naphthalene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline

et al. 2007

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Abstract. Consecutive reactions of adducts, resulting from OH radicals and aromatics, with the tropospheric scavenger molecules O 2 , NO and NO 2 have been studied for benzene, naphthalene, toluene, m-and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline by observing decays of OH at temperatures where the thermal back-decomposition to OH is faster than 3 s −1 , typically between 300 and 340 K. The experimental technique was resonance fluorescence with flash photolysis of water as source of OH. Biexponential decays were observed in the presence of either O 2 or NO, and triexponential decays were obtained in the presence of NO 2 . The kinetic analysis was performed by fitting the relevant rate constants of the reaction mechanism to whole sets of decays obtained at various concentrations of aromatic and scavenger. In the case of hexamethylbenzene, the biexponential decays suggest the existence of the ipso-adduct, and the slightly higher necessary temperatures show that it is even more stable.In addition, smog chamber experiments at O 2 concentrations from atmospheric composition down to well below 100 ppm have been carried out for benzene, toluene and pxylene. The drop of the effective rate constant of removal by OH occurs at reasonable O 2 levels, given the FP/RF results.Comparison of the adduct reactivities shows for all aromatics of this study that the reaction with O 2 predominates over that with NO 2 under all tropospheric conditions, and that a reaction with NO may only occur after the reaction with O 2 .

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“…It is noted that these products may alternatively be generated from the initial OH adduct by a direct reaction with O 2 (e.g. Lay et al, 1996;Ghigo and Tonachini, 1998). However, the overall chemistry of these representations is indistinguishable, such that the representation employed is consistent with either mechanism.…”

Section: Ro 2 Radicals From H-abstractionmentioning

confidence: 99%

Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part B): tropospheric degradation of aromatic volatile organic compounds

et al. 2003

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Abstract. Kinetic and mechanistic data relevant to the tropospheric degradation of aromatic volatile organic compounds (VOC) have been used to define a mechanism development protocol, which has been used to construct degradation schemes for 18 aromatic VOC as part of version 3 of the Master Chemical Mechanism (MCM v3). This is complementary to the treatment of 107 non-aromatic VOC, presented in a companion paper. The protocol is divided into a series of subsections describing initiation reactions, the degradation chemistry to first generation products via a number of competitive routes, and the further degradation of first and subsequent generation products. Emphasis is placed on describing where the treatment differs from that applied to the non-aromatic VOC. The protocol is based on work available in the open literature up to the beginning of 2001, and some other studies known by the authors which were under review at the time. Photochemical Ozone Creation Potentials (POCP) have been calculated for the 18 aromatic VOC in MCM v3 for idealised conditions appropriate to north-west Europe, using a photochemical trajectory model. The POCP values provide a measure of the relative ozone forming abilities of the VOC. These show distinct differences from POCP values calculated previously for the aromatics, using earlier versions of the MCM, and reasons for these differences are discussed.

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Benzene Oxidation in the Troposphere. Theoretical Investigation on the Possible Competition of Three Postulated Reaction Channels

Cited by 53 publications

References 16 publications

Formation of Peroxy Radicals from OH−Toluene Adducts and O₂

Formation of Peroxy Radicals from OH−Toluene Adducts and O₂

Consecutive reactions of aromatic-OH adducts with NO, NO<sub>2</sub> and O<sub>2</sub>: benzene, naphthalene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline

Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part B): tropospheric degradation of aromatic volatile organic compounds

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Benzene Oxidation in the Troposphere. Theoretical Investigation on the Possible Competition of Three Postulated Reaction Channels

Cited by 53 publications

References 16 publications

Formation of Peroxy Radicals from OH−Toluene Adducts and O2

Formation of Peroxy Radicals from OH−Toluene Adducts and O2

Consecutive reactions of aromatic-OH adducts with NO, NO&lt;sub&gt;2&lt;/sub&gt; and O&lt;sub&gt;2&lt;/sub&gt;: benzene, naphthalene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline

Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part B): tropospheric degradation of aromatic volatile organic compounds

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Formation of Peroxy Radicals from OH−Toluene Adducts and O₂

Formation of Peroxy Radicals from OH−Toluene Adducts and O₂

Consecutive reactions of aromatic-OH adducts with NO, NO<sub>2</sub> and O<sub>2</sub>: benzene, naphthalene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline