Photochemistry and free-radical reactions in formamide vapour

Abstract

The photolysis of formamide vapour has been studied at temperatures from 115 to 400°C and pressures from 8 to 50 torr, with 206.2 nm radiation. Products detected were CO, H₂ and NH₃, with quantum yields at 150°C of 0.8, 0.6 and 0.2 respectively. From experiments with added ethylene and with NH₂CDO and ND₂CHO, it was deduced that there were three major primary processes: NH₂CHO +hν→ NH₂+ CO + H (ø= 0.35), → H + NHCHO (ø= 0.22), → NH₃+ CO (ø= 0.45), followed by the reactions, H + NH₂CHO → H₂+ NH₂CO, NH₂+ NH₂CHO → NH₃+ NH₂CO

The reactions of CH₃ with NH₂CHO, ND₂CHO and NH₂CDO were also studied, and approximate Arrhenius parameters were obtained. For the first two compounds, A= 4 × 10⁷(M s)^–1 and E= 7 kcal/mol, and for the last, A=2 × 10⁷ and E= 8. Hydrogen was abstracted almost exclusively from the formyl position, and the deuterium isotope effect was about 6.

Below 200°C, NH₂CO radicals were thermally stable, but at higher temperatures they decomposed, NH₂CO → NH₂+ CO, leading to a chain reaction. Approximate Arrhenius parameters of A= 4 × 10⁹ s^–1 and E= 20 kcal were estimated for this decomposition, which was found to be pressure dependent; limiting high-pressure values of A and E will be considerably higher.