27746-48-1Relevant articles and documents
Thermal stability of carbonyl radicals. Part I. Straight-chain and branched C4 and C5 acyl radicals
Jagiella,Libuda,Zabel
, p. 1175 - 1181 (2000)
The competition between thermal decomposition (k(dis)) and O2 addition (k(O2)) of linear and branched C4 and C5 alkanoyl (R-C(.)O, R = alkyl) radicals has been studied in a photochemical reaction chamber made from stainless steel (v = 12 L). RCO radicals were prepared by continuous photolysis of Br2-RC(O)H-O2-NO2-N2 mixtures at wavelengths ≥420 nm. The products CO and RC(O)O2NO2 were analyzed by long-path IR absorption using an FT-IR spectrometer. Rate constant ratios k(dis)/k(O2) were determined at 317 K for n-butyryl, n-pentanoyl, 3-methylbutyryl, 2-methylpropionyl and 2- methylbutyryl and at 6 temperatures between 293 and 317 K for 2,2- dimethylpropionyl (=pivaloyl, t-butyl-CO) radicals. Total pressures were 1 bar (M = N2 + O2). Adopting the literature value of k(O2) for acetyl, unimolecular decomposition rate constants k(dis) were derived from the measured ratios k(dis)/k(O2). k(dis) at 298 K, 1 bar, M = O2 + N2 increases by factors of 35, 54 and 24 for each H atom in CH3CO which is consecutively replaced by a methyl group (corresponding to increasing branching of R). For the unimolecular decomposition of 2,2-dimethylpropionyl radicals, the Arrhenius expression k(dis)(t-butyl-CO) = 6.0 x 1012 exp(- 41.6 kJ mol-1/RT) s-1 (2σ) was derived for the temperature range 293-317 K and a total pressure of 1 bar (M = N2 + O2). The results on k(dis)/k(O2) show that even for the thermally most unstable of the carbonyl radicals studied in this work, i.e. 2,2-dimethylpropionyl, only 1.8% decompose rather than add O2 at 298 K and 1 bar in dry air.
Branching ratios for the reaction of selected carbonyl-containing peroxy radicals with hydroperoxy radicals
Hasson, Alam S.,Tyndall, Geoffrey S.,Orlando, John J.,Singh, Sukhdeep,Hernandez, Samuel Q.,Campbell, Sean,Ibarra, Yesenia
experimental part, p. 6264 - 6281 (2012/08/28)
An important chemical sink for organic peroxy radicals (RO2) in the troposphere is reaction with hydroperoxy radicals (HO2). Although this reaction is typically assumed to form hydroperoxides as the major products (R1a), acetyl peroxy radicals and acetonyl peroxy radicals have been shown to undergo other reactions (R1b) and (R1c) with substantial branching ratios: RO2 + HO2 → ROOH + O2 (R1a), RO 2 + HO2 → ROH + O3 (R1b), RO2 + HO2 → RO + OH + O2 (R1c). Theoretical work suggests that reactions (R1b) and (R1c) may be a general feature of acyl peroxy and α-carbonyl peroxy radicals. In this work, branching ratios for R1a-R1c were derived for six carbonyl-containing peroxy radicals: C2H 5C(O)O2, C3H7C(O)O2, CH3C(O)CH2O2, CH3C(O)CH(O 2)CH3, CH2ClCH(O2)C(O)CH 3, and CH2ClC(CH3)(O2)CHO. Branching ratios for reactions of Cl-atoms with butanal, butanone, methacrolein, and methyl vinyl ketone were also measured as a part of this work. Product yields were determined using a combination of long path Fourier transform infrared spectroscopy, high performance liquid chromatography with fluorescence detection, gas chromatography with flame ionization detection, and gas chromatography-mass spectrometry. The following branching ratios were determined: C2H5C(O)O2, YR1a = 0.35 ± 0.1, YR1b = 0.25 ± 0.1, and YR1c = 0.4 ± 0.1; C3H7C(O)O2, YR1a = 0.24 ± 0.15, YR1b = 0.29 ± 0.1, and YR1c = 0.47 ± 0.15; CH3C(O)CH2O2, Y R1a = 0.75 ± 0.13, YR1b = 0, and YR1c = 0.25 ± 0.13; CH3C(O)CH(O2)CH3, Y R1a = 0.42 ± 0.1, YR1b = 0, and YR1c = 0.58 ± 0.1; CH2ClC(CH3)(O2)CHO, Y R1a = 0.2 ± 0.2, YR1b = 0, and YR1c = 0.8 ± 0.2; and CH2ClCH(O2)C(O)CH3, YR1a = 0.2 ± 0.1, YR1b = 0, and YR1c = 0.8 ± 0.2. The results give insights into possible mechanisms for cycling of OH radicals in the atmosphere.
Formation and Thermal Decomposition of Butyl-Substituted Peroxyacyl Nitrates: n-C4H9C(O)OONO2 and i-C4H9C(O)OONO2
Grosjean, Daniel,Grosjean, Eric,Williams, Edwin L.
, p. 1099 - 1105 (2007/10/03)
The butyl-substituted peroxyacyl nitrates n-C4H9C(O)OONO2 and i-C4H9C(O)OONO2 have been synthesized in the liquid phase, prepared in-situ in the gas phase by sunlight irradiation of aldehyde-NO mixtures, measured by electron capture gas chromatography, and characterized in a number of gas-phase and liquid-phase tests. Gas-phase yields as a fraction of initial NO were 0.39 for the n-butyl isomer and 0.20 for the isobutyl isomer. The corresponding gas-phase aldehyde oxidation mechanisms are outlined. Thermal decomposition in the presence of excess NO yielded n-butanal and isobutanal as the major carbonyl products. Thermal decomposition rates at ambient temperature and atmospheric pressure are comparable to that of PAN , with k298 = 1.8E-4 s-1 for n-C4H9C(O)OONO2 and 2.4E-4 s-1 for i-C4H9C(O)OONO2. Emission data for precursor hydrocarbons indicate C4H9C(O)OONO2/PAN ambient concentration ratios of 0.19 in urban air. Atmospheric implications for the formation and removal of C4H9C(O)OONO2 are briefly discussed.
