The fluorine content of an acyclic saturated compound of the formula C.sub.n F.sub.a X.sub.b having at least one carbon with at least two fluorine substituents (wherein each X is independently selected from Cl and Br, and wherein n is 1 to 4, a is 2 to 10, b is 0 to 8, and a+b equals 2n+2) is reduced by reacting the acyclic saturated compound with HCl in the vapor phase at an elevated temperature in the presence of a catalyst, the mole ratio of HCl to the acyclic saturated compound being at least about 2:1.