Thermal Gas-Phase Oxidation of Trifluorobromoethene, CF2CFBr, initiated by NO2

V. ARCE; M. DOS SANTOS AFONSO; R. M. ROMANO; J. CZARNOWSKI

Journal of the Argentine Chemical Society

Asociación Química Argentina

Año: 2006 vol. 93 p. 123 - 136

0365-0375

The oxidation of CF2CFBr by molecular O2 initiated by the addition of NO2 to the doublebond of the alkene was studied at 313.4 K, using a conventional static system. The initialpressure of CF2CFBr was varied between 18.8 and 43.9 torr, that of NO2 between 0.9 and4.8 torr and that of O2 between 96.9 and 402.9 torr. The following products were formed:CF2BrC(O)F, as the main product, C(O)F2 and C(O)FBr and small amounts of peroxynitrate,CF2BrCFBrO2NO2, and trifluorobromoethene epoxide.CF2BrC(O)F was characterized by its IR spectrum consistent with both the proposedstructure and the calculations carried out using ab initio and Density Functional Theorymethods. In presence of CF2CFBr the reaction proceeded with a pressure decrease. Afterthe alkene was consumed an increase of the pressure and formation of bromine was observed.The oxidation is a chain reaction of pseudo-zero order with respect to O2 as reactant at thepressure of oxygen used in this work. Its basic steps are: chain initiation by addition of NO2to the double bond leading, through reaction sequence in presence of O2, to generation ofbromine atoms and chain propagation by reaction of Br • with alkene, originatingCF2BrCFBrO2• and CF2BrCFBrO• radicals. The predominant fate of the latter is the bromineatoms extrusion, with C-C bond cleavage playing only a minor role. A full mechanism ispostulated. The value of (2.2 ±1) x 10-5 s-1 was obtained for the room temperature rateconstant for the unimolecular decomposition of CF2BrCFBrO2NO2.