Ring-cleavage Reactions of Aromatic Hydrocarbons Studied by FT–IR Spectroscopy. II. Photooxidation of o -, m -, and p -Xylenes in the NO x –Air System

Abstract

α-Dicarbonyl compounds produced in the photooxidation of o-, m-, and p-xylenes were analyzed quantitatively using long-path FT–IR spectroscopy. Glyoxal, methylglyoxal, and biacetyl were observed in the case of o-xylene, and glyoxal and methylglyoxal were observed in cases of m- and p-xylenes. Yields of glyoxal, methylglyoxal, and biacetyl were 8, 23, and 10% (mole/mole) of o-xylene consumed, respectively. Yields of glyoxal and methylglyoxal were 13 and 42% in the case of m-xylene, and 24 and 12% in the case of p-xylene. These yields could be explained by the ring cleavage of 6,7-dioxabicyclo[3.2.1]octane compounds of OH–aromatics-O2 adduct. Formations of maleic anhydride was observed in the case of o-xylene and it is suggested that maleic anhydride is produced from cis-2-butenedial. Formation of 3-hexene-2,5-dione (unsaturated γ-dicarbonyl) was observed from p-xylene. The ring-cleavage process accounts for 41, 55, and 36% of the total reaction in o-, m-, and p-xylenes, respectively.