VAPOR-PHASE PHOTOLYSIS OF TRANS-CROTONALDEHYDE

The vapor-phase photolysis of trans-crotonaldehyde (2-buten-1-al) has been investigated at 2654-2537 Å over a wide range of intensities, pressures, and temperatures. At 25° this α,β-unsaturated aldehyde was unusually stable, polymerization being the only significant reaction. Above 100°, reactions leading to the formation of gaseous products became important. The main products in decreasing order of abundance were carbon monoxide, propylene, hydrogen, and methane. Φco was inversely proportional to the initial crotonaldehyde pressure and exceeded unity at 120° and pressures below 10 Torr. At 120°, Φco was directly proportional to the incident light intensity; however, at temperatures greater than 200° the dependence was much less marked. A decomposition mechanism is suggested in which the absorption of radiation initially produced long-lived, thermodynamically unstable isomers, and subsequently a free-radical chain process was initiated by the secondary photolysis and/or thermolysis of one or more of these isomers. © 1969, American Chemical Society. All rights reserved.