Reaction of ethanol and CH3CH(OH) radicals with atomic and molecular oxygen

Abstract

The reaction of oxygen atoms with ethanol in a fast flow system was studied with a photoionization mass spectrometer. A radical formed from O+C2H5OH was photoionized by the Xe lamp and identified as the alpha-ethanol radical, CH3CH(OH), i.e., CH3CD(OH) (m/e = 46) and CD3CD(OH) (m/e = 49) were observed in reactions of O+CH3CD2OH and C2D5OH, respectively. The major primary product in the subsequent reaction of alpha-ethanol radicals with atomic oxygen was found to be acetaldehyde (79%±8%) and no formation of vinyl alcohol was observed, i.e., CH3CDO (m/e = 45) and CD3CDO (m/e = 48) were observed in reactions of O+CH3CD2OH and C2D5OH, respectively: O(3P)+CH3CH(OH)→CH3CHO+OH (4a). The reaction of 18O(3P)+C2D5OH produced only CD3CDO (m/e = 48). This fact shows that acetaldehyde is produced by the hydrogen abstraction reaction by O(3P) from the O–H in the alpha-ethanol radical. The competition experiment among O(3P) and O2 for the alpha-ethanol radical shows that alpha-ethanol radicals react (0.14±0.04) times more slowly with molecular oxygen than with atomic oxygen. This result suggests that the reaction of alpha-ethanol radicals with molecular oxygen is very rapid, and that the reaction probably proceeds by a two body reaction to form acetaldehyde and HO2.