Products from the gas-phase reaction of some unsaturated alcohols with nitrate radicals

Five structurally similar unsaturated alcohols, 2-propene-1-ol (allyl alcoh ol), 3-butene-2-ol, 2-methyl-3-butene-2-ol (MBO232), 2-butene-1-ol (crotyl alcohol) and 3-methyl-2-butene-1-ol (MBO321), were examined to clarify thei r atmospheric degradation pathways via oxidation initiated by NO3 radicals. The reactions were investigated using a 0.153 static glass reactor equippe d with long-path FTIR spectroscopy. The experiments were performed at a pre ssure of 1020 +/- 5 mbar and at a temperature of 297 +/- 2 K in air or nitr ogen as the bath gas. The identified and quantified gas phase products were small carbonyl compounds such as acetone, formaldehyde, acetaldehyde, glyc olaldehyde and 2-nitrooxy acetaldehyde. The specific products and their yie lds varied for the five studied alcohols as follows: formaldehyde 37(+/- 1) % and 2-nitrooxy acetaldehyde 41(+/- 7)% from allyl alcohol; acetaldehyde 2 8(+/- 6)%, formaldehyde 2(+/- 1)% and 2-nitrooxy acetaldehyde 33(+/- 4)% fr om 3-butene-2-ol; acetone 63(+/- 6)% and 2-nitrooxy acetaldehyde 67(+/- 8)% from MBO232; acetaldehyde 12(+/- 2)%, formaldehyde 10(+/- 3)% and glycolal dehyde 7(+/- 2)% from 2-butene-1-ol; acetone 21(+/- 6)%, formaldehyde 11(+/ - 3)% and glycolaldehyde 29(+/- 10)% from MBO321. In addition, yields were estimated for total organic nitrates using an average integrated absorption cross section of unspecified organic nitrates. Tentative reaction schemes were proposed from the yielded products. The distribution between bond brea kage and other processes such as abstraction of a hydrogen atom from the al koxy radical, formed in the degradation process, was estimated. The small c arbonyl compounds were produced by the bond breakage mechanisms. Large mult i-functional organic compounds e.g. 1-hydroxy-3-nitrooxy-3-methyl-2-butanon e from MBO321 were proposed to be formed by hydrogen abstraction. From the product distribution, the contribution of the number of methyl group substi tuents at the alpha and gamma carbon atoms, influencing the bond breakage p attern, is discussed. The observed bond cleavage trends are correlated to a substitution pattern where electron donating methyl substituents increase the stability of the leaving radical groups.