Influence of butadiene-1,3 on ethanal pyrolysis at 495°C

At 495°C and a low extent of reaction, ethanal pyrolysis is slightly inhibited by the addition of small quantities of butadiene-1,3, whereas it is accelerated by more important quantities. The inhibiting effect is interpreted in terms of a free-radical chain mechanism in which the main chain carriers of ethanal pyrolysis (CH₃.free radicals) reversibly add to butadiene-1,3 and yield penten-2-yl (R.) free radicals. These free radicals either react in a metathetical step: or in terminating steps. But butadiene-1,3 also gives rise to new initiation steps: which account for the accelerating effect. Process (i₃) seems to be more important than process (i₂) in the experimental conditions, but its nature could not be identified. The results are consistent with literature data and the following value of k₆: (4.57T in cal/mol).