Photolysis of halogens in presence of trifluoroacetaldehyde. Some reactions of the trifluoroacetyl radical

Abstract

When a halogen X₂ is photolyzed in the presence of CF₃CHO in the vapour phase, the products are CO, CF₃X, CF₃COX and HX, provided that X₂= Br₂ or Cl₂. Quantitative analyses of the products in the range 25–250°C indicate that the overall reactions are [graphic omitted] These are most readily explained by the reactions, X+CF₃CHO →HX+CF₃CO CF₃CO+X₂→CF₃COX+X (6) CF₃CO →CF₃+CO. (7) Assuming that this mechanism is correct, we obtain, k₇/k_6,Br2=(11.4 ± 3.0)× 10^–3 exp [–(8,800 ± 200)/RT], k₇/k_6,Cl2=(6.3 ± 0.8)× 10^–3 exp [–(6,500 ± 100)/RT], mole cm^–3. It is estimated that E₇ 10 kcal mole^–1 and A₇⩽2.6×10¹⁰ sec^–1. Comparisons are made of the reactivities of CF₃CO and CF₃ radicals and of the stabilities of the CF₃CO and CH₃CO radicals. The relevance of the results to the primary act in the photolysis of hexafluoroacetone is discussed. No reaction occurred between CF₃CHO and I₂ under a variety of conditions.