OBSERVATION OF BIACETYL FROM THE REACTION OF OH-RADICALS WITH ORTHO-XYLENE - EVIDENCE FOR RING CLEAVAGE

Irradiations of NOx/o-xylene/air mixtures have been carried out in a 5800-L evacuable chamber at temperatures ranging from 283 to 323 K in order to obtain information as to the mechanistic pathways occurring in the reactions of OH radicals with aromatic hydrocarbons. Biacetyl was observed to be a product from the reaction of OH radicals with o-xylene which, under the experimental conditions employed, further photooxidized to form significant yields of peroxyacetyl nitrate. From the biacetyl time-concentration profiles and the observed disappearance rates of biacetyl (obtained from separate biacetyl/air and NOx/biacetyl/air irradiations) and o-xylene the fraction of the reaction of OH radicals with o-xylene yielding biacetyl was calculated to be 0.18 ± 0.04, independent of temperature, indicating that ring cleavage in this reaction is a significant process. The observed peroxyacetyl nitrate yields could not be totally accounted for via biacetyl formation, indicating that other ring cleavage reaction pathways, probably involving methylglyoxyl production, are operative. © 1979 American Chemical Society.