Addition of free radicals to unsaturated systems. Part XXI. Reactions of 1H-pentafluoropropene with bromine, hydrogen bromide, and trifluoroiodomethane under free-radical conditions

Abstract

1H-Pentafluoropropene, as a 95 : 5 mixture of cis- and trans-isomers, reacts with bromine in light to give a 75 : 25 mixture of the threo- and erythro-dibromides which on dehydrobromination affords a mixture of cis- and trans-1-bromo-1,2,3,3,3-pentafluoropropene. Photochemical reaction of the olefin with hydrogen bromide gives as the major products a mixture of erythro- and threo-1-bromo-1,2,3,3,3-pentafluoropropane and 2-bromo-1,1,1,2,3-pentafluoropropane in the ratio 70 : 16. The threo-adduct undergoes dehydrobromination to give a mixture of cis- and trans-1H-pentafluoropropene; the two other isomers afford the cis-olefin exclusively. Trifluoroiodomethane reacts with the olefin under photochemical or thermal conditions to give a mixture of erythro- and threo-1,1,1,2,3,4,4,4-octafluoro-2-iodobutane and 1,1,1,2,3-pentafluoro-3-iodo-2-trifluoromethylpropane in the ratios 56 : 40 : 4 and 50 : 43 : 7, respectively; dehydroiodination of the two former adducts separately yields trans-octafluorobut-2-ene and a 95 : 5 mixture of the cis- and trans-olefins, respectively.