Reactivity of fluorocarbon radicals in the low-temperature fluorination of unsaturated perfluorocarbons

Abstract

Calorimetry and ESR spectroscopy were used to study the low-temperature fluorination (77–300 K) of unsaturated perfluorocarbons with fluorine. In the solid phase at 77–100 K (glassy or crystalline state) fluorination does not occur. On transition from glassy systems to the supercooled liquid state formation of molecular complexes in which fluorine is attached to the >CC bond becomes possible. These complexes are stabilized on crystallization of the system; with a further increase in temperature, efficient addition of molecular fluorine takes place in the crystal phase. However, the addition of fluorine by a chain or carbene mechanism must not be ruled out for such systems. Thus, in the case of hexafluoropropene trimer, the addition proceeds as a chain reaction producing long-living free radicals at the initial stage.