Direct fluorination of tetrafluoroethylene at low temperatures

Abstract

Mechanisms for the processes of direct fluorination of tetrafluoroethylene (TFE) in matrices of TFE, hexafluoropropylene (HFP), and dimers and trimers of HFP ((HFP)2 and (HFP)3) from 77 K to 300 K have been developed. Electronic structure calculations at the composite correlated G3(MP2) and G4 molecular orbital theory levels of the energetics of a range of reactions involving TFE and fluorine are presented to aid in the development of these mechanisms. The equilibrium products of the direct fluorination of TFE in the gas phase at varied temperature and initial composition was determined by Gibbs free energy minimization. Spontaneous reactions (explosions) were observed for the fluorination of pure crystalline TFE and HFP. Fluorination of TFE can be performed without explosion in glassy matrixes of (HFP)2 or (HFP)3 at low temperatures. The explosive nature of the reaction decreases in the matrix order TFE > (HFP)2 > (HFP)3. The fluorination of TFE begins at the phase transition temperature of the matrix, i.e., after the transition of devitrified (HFP)2 and (HPF)3 into the supercooled liquid state at 110 K and 150 K, respectively. The experiments show that either the presence of a branched structure (C9F20, the saturated analog of (HFP)3) or the presence of unsaturated bonds (perfluorotoluene) separately cannot provide a medium for the safe fluorination of TFE as the direct fluorination of TFE in these matrices led to an explosion. HFP oligomers provide an effective environment for TFE fluorination because of the presence of double bonds surrounded by the branched perfluorinated groups. The unsaturated bonds of the HFP oligomers are an active participant in the chemical processes involved in the safe, direct fluorination of TFE.