Acetic acid formation via the hydration of gas-phase ketene under ambient conditions

We have monitored changes in the infrared spectrum of gas-phase ketene in the presence of water vapor at 295 K. The products observed from ketene hydration are acetic acid, acetic acid dimer, and acetic anhydride. The time-dependence of product formation supports a reaction mechanism in which ketene hydrates to form acetic acid, which then combines with another acetic acid monomer to form a dimer, or with ketene to form acetic anhydride. These results show that ketene can undergo hydration under atmospherically-relevant temperatures and relative humidities. This reaction could be a source of atmospheric carboxylic acids, especially in biomass burning plumes.