THE ELECTRONIC NOSE APPLIED TO FOOD ANALYSIS

The oxidation of CF 2 CFBr by molecular O 2 initiated by the addition of NO 2 to the double bond of the alkene was studied at 313.4 K, using a conventional static system. The initial pressure of CF 2 CFBr was varied between 18.8 and 43.9 torr, that of NO 2 between 0.9 and 4.8 torr and that of O 2 between 96.9 and 402.9 torr. The following products were formed: CF 2 BrC(O)F, as the main product, C(O)F 2 and C(O)FBr and small amounts of peroxynitrate, CF 2 BrCFBrO 2 NO 2 , and trifluorobromoethene epoxide. CF 2 BrC(O)F was characterized by its IR spectrum consistent with both the proposed structure and the calculations carried out using ab initio and Density Functional Theory methods. In presence of CF 2 CFBr the reaction proceeded with a pressure decrease. After the 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 O 2 as reactant at the pressure of oxygen used in this work. Its basic steps are: chain initiation by addition of NO 2 to the double bond leading, through reaction sequence in presence of O 2 , to generation of