ISOMERIZATION-REACTIONS OF THE N-C4H9O AND N-OOC4H8OH RADICALS IN OXYGEN

Reactions of n-C4H9O radicals have been investigated in the temperatur e range 343-503 K in mixtures of O-2/N-2 at atmospheric pressure. Flow and static experiments have been performed in quartz and Pyrex vessel s of different diameters, walls passivated or not towards reactions of radicals, and products were analyzed by GC/MS. The main products form ed are butyraldehyde, hydroperoxide C4H8O3 of MW 104, 1-butanol, butyr olactone, and n-propyl hydroperoxide. It is shown that transformation of these RO radicals occurs through two reaction pathways, H shift iso merization (forming C4H8OH radicals) and decomposition. A difference o f activation energies Delta E = (7.7 +/- 0.1 (sigma)) kcal/mol between these reactions and in favor of the H-shift is found, leading to an i somerization rate constant k(isom) (n-C4H9O) = 1.3 x 10(12) exp(-9,700 /RT). Oxidation, producing butyraldehyde, is proposed to occur after i somerization, in parallel with an association reaction of C4H8OH radic als with O-2 producing OOC4H8OH radicals which, after further isomeriz ation lead to an hydroperoxide of molecular weight 104 as a main produ ct. Butyraldehyde is mainly formed from the isomerized radical HOCCCC. + O-2 ... --> O=CCCC + HO2, since (i) the ratio butyraldehyde/(butyra ldehyde + isomerization products) = 0.290 +/- 0.035 (sigma) is indepen dent of oxygen concentration from 448 to 496 K, and (ii) the addition of small quantities of NO has no influence on butyraldehyde formation, but decreases concentration of the hydroperoxides (that of MW 104 and n-propyl hydroperoxide). By measuring the decay of [MW 104] in functi on of [NO] added (0-22.5 ppm) at 487 K, an estimation of the isomeriza tion rate constant OOC4H8OH --> HOOC4H7OH, k(5) approximate to 10(11) exp(-17,600/RT) is made. Implications of these results for atmospheric chemistry and combustion are discussed. (C) 1996 John Wiley & Sons, I nc.