A method for preparing fluorinated organic compounds comprising contacting hydrogen fluoride with at least one compound of formula I: CX.sub.3CXYCH.sub.3 I where each X is independently Cl, I or Br, and each Y is independently H or F, said contacting step being carried out under conditions effective to produce a compound of formula II CF.sub.3CZCH.sub.2 II where Z is Cl, I, Br, or F.