The photochemical reaction of trifluoroiodomethane with the compounds RCiCH yields only CF,*[CH:CRln-CH:CRI, where R = CF,, C,F,, or CH,, and n = 1 or 2. Heptafluoroiodopropane similarly reacts with trifluoromethylacetylene to give C,F,*[CH:C.(CF,)In*CH:CI*CF,. The rate but not the direction of addition of the perfhoroalkyl radical to an acetylene RCiCH is affected by the inductive effect of R. Alternative syntheses for CF,*CH:CH*CF, and CF,*CH:CH*CH,, and ultra-violet and infra-red spectra are reported.
Part V I I PI N attempting to determine how the direction of addition of a radical to an unsaturated system is influenced by the substituents on the unsaturated system, olefins of the type RCHXH, were studied in Part I1 (Haszeldine and Steele, J., 1953, 1199). The present communication describes a similar study with acetylenes, RCICH. The perfluoroalkyl radicals CF, and C,F, were used, prepared by the photolysis of the corresponding fluoroalkyl iodide, and the reasons for the choice of such radicals, and the assumptions made, have been stated earlier (J., 1952, 2504).Trifluoromethylacetylene and trifluoroiodomethane do not react at room temperature in the absence of light. The photochemical reaction proceeds smoothly and with liberation of only small amounts of iodine. The 1 : 1 addition product could be (I) or ( 11), but replacement of its iodine atom by hydrogen by means of zinc and hydrochloric acid gives a high yield of the known trans-hexafluorobut-2-ene (111) which can be derived only from (I).
