A process is disclosed for producing 1,1,2,2,3,3,4,4-octafluorobutane. The process involves (a) reacting a mixture comprising 2,2,3,3-tetrafluorobutane and chlorine to form a mixture of chloro-compounds wherein compounds of the formula C.sub.4 H.sub.x Cl.sub.6-x F.sub.4 (where x is 0 or 1) comprise at least about 50 mole % of the mixture of chloro-compounds; (b) contacting certain chloro-compounds from (a) and hydrogen fluoride with a fluorination catalyst to form a mixture of fluoro-compounds; and (c) contacting certain fluoro-compounds from (b) and hydrogen with a hydrogenolysis catalyst to produce CHF.sub.2 CF.sub.2 CF.sub.2 CHF.sub.2. Sufficient chloro-compounds formed in (a) and sufficient fluoro-compounds formed in (b) are recycled to provide a selectivity to CHF.sub.2 CF.sub.2 CF.sub.2 CHF.sub.2 of at least about 75% based upon the moles of CH.sub.3 CF.sub.2 CF.sub.2 CH.sub.3 reacted in (a).Also disclosed is a process for the purification of at least one compound selected from the group consisting of CCl.sub.2 F(CF.sub.2).sub.2 CCl.sub.3, CCl.sub.2 F(CF.sub.2).sub.2 CCl.sub.2 F, CCl.sub.2 F(CF.sub.2).sub.2 CClF.sub.2, CClF.sub.2 (CF.sub.2).sub.2 CClF.sub.2, CClF.sub.2 (CF.sub.2).sub.2 CF.sub.3, CHCl.sub.2 (CF.sub.2).sub.2 CCl.sub.2 F, CHClF(CF.sub.2).sub.2 CCl.sub.3, CHCl.sub.2 (CF.sub.2).sub.2 CClF.sub.2, CHClF(CF.sub.2).sub.2 CCl.sub.2 F, CHF.sub.2 (CF.sub.2).sub.2 CCl.sub.3, CHClF(CF.sub.2).sub.2 CClF.sub.2, CHF.sub.2 (CF.sub.2).sub.2 CCl.sub.2 F, CHCl.sub.2 (CF.sub.2).sub.2 CF.sub.3, CHClF(CF.sub.2).sub.2 CF.sub.3, CHF.sub.2 (CF.sub.2).sub.2 CClF.sub.2, CHF.sub.2 CF.sub.2 CF.sub.2 CHF.sub.2, CHF.sub.2 CF.sub.2 CF.sub.2 CH.sub.2 F, CHF.sub.2 CF.sub.2 CF.sub.2 CF.sub.3 and CH.sub.2 FCF.sub.2 CF.sub.2 CF.sub.3 from a mixture of HF and said at least one compound. The purification process involves (a) subjecting the mixture of HF and said compound(s) to a distillation step in which a first distillate is removed; (b) subjecting said first distillate to an additional distillation as described herein; and (c) recovering said compound(s) essentially free of HF as bottoms from either the distillation of (a) or the distillation of (b).New compounds CCl.sub.2 FCF.sub.2 CF.sub.2 CClF.sub.2, CCl.sub.3 CF.sub.2 CF.sub.2 CCl.sub.2 F, CHCl.sub.2 CF.sub.2 CF.sub.2 CCl.sub.3, CHCl.sub.2 CF.sub.2 CF.sub.2 CCl.sub.2 F, CHClFCF.sub.2 CF.sub.2 CCl.sub.3, CHCl.sub.2 CF.sub.2 CF.sub.2 CClF.sub.2, CHClFCF.sub.2 CF.sub.2 CCl.sub.2 F, CHF.sub.2 CF.sub.2 CF.sub.2 CCl.sub.3, CHF.sub.2 CF.sub.2 CF.sub.2 CCl.sub.2 F, CHClFCF.sub.2 CF.sub.2 CF.sub.3, CH.sub.3 CF.sub.2 CF.sub.2 CH.sub.2 Cl and CH.sub.2 ClCF.sub.2 CF.sub.2 CCl.sub.3 are also disclosed, as are compositions which comprise hydrogen fluoride in combination with an effective amount of CHF.sub.2 CF.sub.2 CF.sub.2 CHF.sub.2 to form an azeotrope or azeotrope-like composition with hydrogen fluoride.