POLYHALOGENOALLENES .7. PERFLUORO-(3-METHYLBUTA-1,2-DIENE)

Perfluoro-(3-methylbuta-1,2-diene) can be synthesised by dehydrohalogenation of 2H,2H-hexafluoro-1-iodo-3-trifluoromethylbutane, obtained from thermal reaction of heptafluoro-2-iodopropane with vinylidene fluoride. Controlled dehydrohalogenation of the iodobutane with potassium hydroxide or hot charcoal yields 2H-hexafluoro-3-trifluoromethylbut-1-ene, contaminated with 2H-hexafluoro-3-trifluoromethylbut-2-ene in the case of the latter reagent, which catalyses allylic rearrangement of the but-1-ene. Perfluoro-(3-methylbuta- 1,2-diene) yields a mixture of oligomers and a solid homopolymer when heated under autogenous pressure; it is readily attacked by nucleophiles and gives 3H-pentafluoro-2-methoxy-3-trifluoromethylbut-1-ene, 3H-hexafluoro-3- trifluoromethylbut-1-ene, and perfluoroisoprene when, treated with methanol, caesium fluoride in formamide, or hot anhydrous caesium fluoride, respectively, but it resists attack by anhydrous hydrogen halides.