Fluoro-olefin chemistry. Part 16. Reaction of hexafluoropropene with n-butane and n-pentane

Abstract

Thermal reaction of hexafluoropropene with n-butane at ca. 300 °C gives 1 : 1 and 2 : 1 adducts [major products CF₃CHFCF₂R; R = Buⁿ(11), Bu^s(12), and CHMeCH₂CH₂CF₂CHFCF₃(14)], together with lower alkane adducts H [C₃F₆] R (R = Me, Et, Prⁿ, and Prⁱ) and 1,1,1,2,3,3-hexafluoropropane (4). The 1 : 1 adducts are precursors of the 2 : 1 adducts and the lower alkane adducts, and the structures of the isolated 2 : 1 adducts indicate that C–H bonds α- and β- to the fluoroalkyl group in the 1 : 1 adducts are deactivated towards hydrogen abstraction. It is proposed that the 1 : 1 and 2 : 1 adducts arise by a radical-chain mechanism initiated by hydrogen abstraction from n-butane and the 1 : 1 adducts, respectively, and that the lower alkane adducts are formed via interaction between the 1 : 1 adducts and excited hexafluoro-propene resulting in C–C bond fission. The photochemical and peroxide-initiated reactions give much higher yields of 1 : 1 and 2 : 1 adducts at the expense of the lower alkane adducts. Analogous products are formed in the thermal reaction with n-pentane [major 1 : 1 and 2 : 1 adducts CF₃CHFCF₂R; R = CHMePrⁿ(16), CHEt₂(17), CHMeCH₂CHMeCF₂CHFCF₃(18), and CHMe(CH₂)₃CF₂CHFCF₃(19)], but, surprisingly, 2 : 1 adducts formed via hydrogen abstraction from the γ-C–H bonds (CH₃) of the 1 : 1 adduct (17) are absent.