65424-60-4Relevant 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 (2007/10/03)
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.
