The gas-phase thermal decomposition of cyclobutanol

Abstract

The thermal decomposition of cyclobutanol has been studied in the gas phase in a static system at pressures from 3–6 Torr and temperatures from 250 to 450 °C. The major products observed were ethylene and acetaldehyde, while n-butyraldehyde was a minor product. First-order rate constants based on ethylene formation in a Pyrex vessel conditioned by carbon deposition gave Arrhenius parameters of A = 2.14 (± 0.2) × 1014 s−l and E = 57.3 (± 1) kcal/mol. Under the same conditions, the ratio n-butyraldehyde/ethylene increased with decreasing temperature, corresponding to an activation energy of about 50 kcal/mol for butyraldehyde formation and a frequency factor about 104 times lower than that for ethylene production. In an untreated Pyrex vessel the decomposition showed strong surface catalysis with much lower activation energies for both processes. It is suggested that both ethylene and n-butyraldehyde are formed from a common ĊH2CH2CH2ĊHOH biradical by cleavage and by hydrogen transfer through a 6-membered cyclic transition state respectively. The thermal decomposition is thus the reverse of the Type II and II′ processes observed in the photolysis of n-butyraldehyde.