Rate Constants and Mechanism for Reactions of Ketenes with OH Radicals in Air at 299±2K

Rate constants for reactions of OH radicals with four kinds of simple ketenes (ketene, methylketene: MK, ethylketene: EK, and dimethylketene: DMK) were measured in 1 atm of air at 299±2 K by use of a competitive reaction method. The photolysis of CH3ONO in air was used to generate OH radicals. The rate constants for OH reactions obtained are (1.8±0.2)×10−11, (7.6±1.4)×10−11, (11±3)×10−11 and (10±3)×10−11 cm3 molecule−1 s−1 for ketene, MK, EK, and DMK, respectively. The major product was a carbonyl compound; HCHO from ketene, CH3CHO from MK, and CH3COCH3 from DMK; the yield was ≈80%, 72±17%, and 70±3%, respectively. It is proposed that the reaction proceeded mainly via an OH addition to the olefinic carbons of ketenes and the adduct decomposes to give a carbonyl compound and CO as final products in air.