Investigation of perfluoroperoxy radicals self-coupling reactions by kinetic EPR spectroscopy

The rate constants and activation parameters for the self-coupling of perfluoroperoxy radicals of structure A and B: C7F15OO. (A) and RFOCF2OO. (B) have been determined in perfluorohexane solution in the temperature range 228-258 K. The magnitude of the rate constants obtained ranks between 6.6 x 10(8) and 2.5 x 10(9) l mol(-1) s(-1) and are therefore, among the largest rate values so far reported in the literature for primary peroxy radicals couplings. The activation energy is positive and lower for the peroxy radicals (A) with respect to the peroxy radicals (B) (10.5 and 23.0 kJ mol(-1), respectively). Analysis by kinetic modeling has shown that the peroxy radicals decay curves are compatible with the participation of peroxy radicals <----> tetroxide equilibria to the reaction mechanism. Upper limit values of k(bs) < 10 and < 20 s(-1) were inferred for the beta-scission reactions of the perfluoroalkylperoxy radicals at 228 and 258 K, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.