Preparation of chloropentafluoroethane from dichlorotetrafluoroethane - note 1.

Gaseous fluorination with hydrogen fluoride at atmospheric pressure of the two isomers CClF₂CClF₂ and CCl₂FCF₃ was carried out continuously on a chromic oxide based catalyst. The fluorinated derivative, obtained in a yield greater than 90%, was chloropentafluoroethane. Hexafluoroethane and an isomeric mixture of trichlorotrifluoroethane were obtained as by-products. The latter was recycled with unconverted C₂Cl₂F₄ for further fluorination. Both conversion of C₂Cl₂F₄ and selectivity to the formation of C₂ClF₅ were affected by temperature, contact time and molar ratio of the reagents. The catalytic activity of chromic oxide was adversely affected by small amounts of water in the hydrogen fluoride. A difference was also observed in the reactivity of the two isomersCCl₂FCF₃ and CClF₂OClF₂ The formation of C₂Cl₃F₃ as a by-product was due to the disproportionating activity of chromic oxide upon C₂Cl₂F₄.