Photooxidation of n-Hexanal in Air

Dilute mixtures of hexanal in synthetic air (up to 100 ppm) were photolyzed with fluorescent UV lamps (275-380 nm) in air at 298 K. The main photooxidation products, identified and quantitatively analyzed by FTIR spectroscopy, were butene, CO, vinylalcohol and ethanal. The photolysis rates and the absolute quantum yield Φ were found to be slightly dependent on the total pressure. At 100 Torr, Φ(100) = 0.43 ± 0.02, whereas at 700 Torr the total quantum yield was Φ(700) = 0.38 ± 0.02. These results may be explained by the collisional deactivations of photoexcited molecules. Two decomposition channels were identified: the radical channel C(5)H(11)CHO → C(5)H(11) + HCO, and the molecular channel C(5)H(11)CHO → C(4)H(8) + CH(2)=CHOH, having the relative yields of 27 and 73 % at 700 Torr. The product CH(2)=CHOH tautomerizes to ethanal.