Selective chlorination of chlorotrifluoroethylene telomers

Abstract

A process is disclosed for purifying and stabilizing a mixture of regular chlorotrifluoroethyelne telomers of formula RCXCl(CF.sub.2 CFCl).sub.n Br from bromine-containing irregular telomer impurities of similar molecular weight. The telomer mixture is produced by reacting chlorotrifluoroethylene with a telogen of formula RCXClBr, where R is CF.sub.2 Br, or Cl, and X is Cl or F. The telomer mixture is then chlorinated using either elevated temperature alone (100.degree. C.-350.degree. C.), or a combination of elevated temperatures (100.degree. C.-200.degree. C.) and light energy primarily of the wavelength region greater than about 3000.degree.A. Under these conditions, CFClBr telomer end group of the regular or normal telomer is chlorinated to form --CFCl.sub.2 end groups, while the bromine-containing irregular telomer impurities (whose bromine-containing end groups are substantially only --CF.sub.2 Br) are substantially not chlorinated. The desired regular telomers can then be readily separated from the higher boiling impurities by distillation. Any --CF.sub.2 Br groups present in the isolated regular telomer are then further stabilized by prolonged chlorination under the above conditions or at elevated temperatures (100.degree. C.-350.degree. C.) with irradiation by a UV lamp.