Polyfluorocyclopentadienes. Part VI. Synthesis of 1- and 5-chloropentafluorocyclopentadiene

Abstract

Pyrolysis of pentachloropentafluorocyclopentane over mild steel at ca. 430 °C yields perfluorocyclopentadiene, 1-chloro-2,3,4,5,5-pentafluorocyclopentadiene, 5-chloro-1,2,3,4,5-pentafluorocyclopentadiene, trichloropentafluorocyclopentenes, and perfluoronaphthalene contaminated with traces of chlorofluoronaphthalenes and blue material that might be perfluorofulvalene. Both 1- and 5- chloropentafluorocyclopentadiene readily combine with trifluoronitrosomethane to give Diels–Alder adducts, and 1,4-addition across the dienic system in the 5-chloroisomer also occurs with dimethyl acetylenedicarboxylate. The ¹⁹F n.m.r. spectra of 1- and 5-chloropentafluorocyclopentadiene are discussed and a reassignment of data for hexafluorocyclopentadiene is proposed.