The preparation of CF 4 by direct fluorination of CaCN 2

Abstract

Graphite-free calcium cyanamide, CaCN 2, reacts stoichiometrically with elemental fluorine according to equ. 1: CaCN 2+3F 2→CaF 2+N 2+CF 4 (1) The presence of trace amounts of CsF suppresses the formation of NF 3, which is formed as a side product up to 5% in the absence of CsF. As CsF catalyses the isomerization of FNCNF to give F 2CN 2 [M.D. Meyers and S. Frank, Inorg. Chem., 5 (1966) 1455], both species are likely to be intermediates in the fluorination pathway of CaCN 2. Whereas the first step (formation of FNCNF or F 2CN 2) is a slow reaction, the fluorination of F 2CN 2 to give CF 4 and N 2 is apparently a fast reaction. (N.B.: difluorodiazirine, F 2CN 2, can be decomposed to difluorocarbene and N 2 either by thermal or by ultraviolet irradiation [R.A. Mitsch, J. Heterocycl. Chem., 1 (1964) 59]). If FNCNF is not converted into F 2CN 2 by CsF catalysis the formation of NF 3 as a side product is in agreement with the NF bonded precursor. After purification by fractional condensation pure CF 4 (yield 89%) is obtained. Vibration (IR, Raman), analytical and mass spectral data of CF 4 are, without exception, in agreement with those reported in the literature [N.N. Greenwood and A. Earnshaw, Chemistry of the Elements, 1st edn., Pergamon Press, Oxford, (1984) p. 322].