Rate Constants and Mechanisms for the Reaction of OH (OD) Radicals with Acetylene, Propyne, and 2-Butyne in Air at 297 +/-2 K

Article abstract of DOI:10.1021/j100273a039

OH (OD) radical initiated photooxidation of acetylene, propyne, and 2-butyne was studied at atmospheric pressure at 297 +/- 2 K.The rate constants were determined to be (8.8 +/- 2.0)*10^-13, (5.71 +/-0.18)*10^-12, and (3.01 +/- 0.28)*10^-11 cm³ molecule^-1 s^-1 for acetylene, propyne, and 2-butyne, respectively, by the competitive reaction method using cyclohexane as a reference compound (OH+cyclohexane)=(7.57 +/- 0.05)*10^-12 cm³ molecule^-1 s^-1>.The major ultimate products are α-dicarbonyl compounds, i.e., glyoxal from acetylene, methylglyoxal from propyne, and biacetyl from 2-butyne, as well as formic acid from acetylene and propyne and acetic acid from 2-butyne.On the basis of product analyses the reaction of OH with alkynes was deduced to proceed via addition resulting in the formation of hydroxyvinyl radicals, which further react with O2 to give carboxylic acid + RCO or α-dicarbonyl compounds.