Staged synthesis of diiodoperfluoro-c3 to c7-alkanes

The process of forming the reaction product comprising the homologue mixture of I(CF2)nI, wherein n is 3 to 7, which contains at least one of the contaminants ICF2I and I(CF2)2I, by the steps comprising

• (a) reacting iodine with hexafluoropropylene oxide at a temperature of 150° C. to 210° C. in a reactor, the amount of said hexafluoropropylene oxide being a portion of the total amount of hexafluoropropylene oxide to be reacted with said iodine, thereby forming a reaction product containing gaseous perfluoroacetyl fluoride as a reaction by-product,
• (b) cooling said reaction product to become liquid except for said gaseous perfluoroacetyl fluoride,
• (c) venting said perfluoroacetyl fluoride from said reactor, and
• (d) repeating said steps (a), (b), and (c) until said total amount of said HFPO is reacted with said iodine,
• and obtaining as a result thereof said reaction product comprising said homologue mixture.