Fluoro-olefins. Part VIII. Preparation and some reactions of perfluoro-2,3-dimethylbut-2-ene and of some tristrifluoromethyl ethylenes
A single-stage preparation of perfluoro-2,3-dimethylbut-2-ene involves the high-temperature reaction of trifluoroiodomethane with perfluorobut-2-yne. Hexafluoro-2-iodo-3-trifluoromethylbut-2-ene, formed at lower temperature from the butyne and trifluoroiodomethane, gives perfluoro-2-methylbut-2-ene by reaction with fluoride ion, and 2H-perfluoro-3-methylbut-2-ene by reduction with zinc and hydrochloric acid. The high reactivity with nucleophiles expected for these olefins from purely electronic considerations is markedly reduced, apparently by steric hindrance; apart from perfluoro-2-methylbut-2-ene, the olefins reacted with methanol only in the presence of base. The iodo-olefin reacts with copper-bronze at high temperatures to give a coupled product formulated as perfluoro-2,3,4,5-tetramethylhexa-2,4-diene.