A process is disclosed for reducing the mole ratio of (1) compounds of the formula Y.sup.1Y.sup.2C.dbd.CF.sub.2 wherein Y.sup.1 and Y.sup.2 are each independently H, F, Cl, Br, C.sub.1-C.sub.6 alkyl or C.sub.1-C.sub.6 haloalkyl containing no more than 3 chlorine substituents, 2 bromine substituents and 1 iodo substituent to (2) saturated compounds of the formula C.sub.dH.sub.eF.sub.fCl.sub.gBr.sub.hI.sub.k wherein d is an integer from 1 to 10, and e+f+g+h+k is equal to 2d+2, provided that g is 0, 1, 2 or 3, h is 0, 1 or 2 and k is 0 or 1 and/or unsaturated compounds of the formula Y.sup.3Y.sup.4C.dbd.CY.sup.5Y.sup.6, wherein Y.sup.3, Y.sup.5 and Y.sup.6 are each independently H, F, Cl, Br, C.sub.1-C.sub.6 alkyl or C.sub.1-C.sub.6 haloalkyl containing no more than 3 chlorine substituents, 2 bromine substituents and 1 iodo substituent, provided that Y.sup.5 and Y.sup.6 are not both F, and Y.sup.4 is C.sub.1-C.sub.6 alkyl or C.sub.1-C.sub.6 haloalkyl containing no more than 3 chlorine substituents, 2 bromine substituents and 1 iodo substituent, in a mixture. The process involves contacting the mixture with at least one selective removal agent selected from the group consisting of SO.sub.3 and RSO.sub.3H, wherein R is selected from the group consisting of F, Cl, OH, C.sub.1-C.sub.8 alkyl, C.sub.1-C.sub.8 fluoroalkyl, and C.sub.1-C.sub.8 fluoroalkoxyalkyl containing no more than two ether oxygens to selectively react the formula Y.sup.1Y.sup.2C.dbd.CF.sub.2 compounds.