A process is disclosed for making RR1R2CCR1R2F wherein R is selected from the group consisting of CH3, CH2F, C2H4F, and F(CF2)nCH2CH2 where n is an integer from 1 to 10, each R1 is independently selected from the group consisting of H, Cl, F and CF3, and each R2 is independently selected from the group consisting of H, F and CF3. The process involves reacting RF with R1R2C═CR1R2 in the presence of SbF5 to produce a product mixture comprising RR1R2CCR1R2F, wherein the reaction temperature is from about −60° C. to about −10° C., provided that total number of carbon atoms in R1R2C═CR1R2 is 5 or less.