Furan Ring Formation in OH-initiated Photooxidation of 1,3-Butadiene and cis-1,3-Pentadiene

Reactions of hydroxyl radicals with 1,3-butadiene and cis-1,3-pentadiene in the presence of oxygen were studied in the gas phase. Two OH radical sources were employed; photolysis of H2O2 at 254 nm and photolysis of methyl nitrite at 360 nm. In the reaction system for 1,3-butadiene, furan was detected besides acrylaldehyde and in the cis-1,3-pentadiene system, 2-methylfuran was detected besides acetaldehyde, acrylaldehyde, and crotonaldehyde by gas chromatographic analysis. Approximate yields of furan and 2-methylfuran were 5.3–6.7% and 6.7–8.4%, respectively, which were sensitive to the conditioning of the surface of reactor but insensitive to hydroxyl radical sources, the surface material of reaction vessel or the surface to volume ratio of reactors. The yields of aldehydes were also measured. Isotopic labeling experiment with 18O2 by use of mass spectrometry indicated that abstraction of vinyl–hydrogen from 1,3-butadiene and cis-1,3-pentadiene occurred about 3% of the time. Photooxidation of 2,5-dihydrofuran initiated with ·OH radicals was also discussed to explain the increase of furan in the dark after the irradiation.