Addition of free radicals to unsaturated systems. Part VIII. The direction of radical-addition to alkyl- and perfluoroalkyl-acetylenes

Abstract

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).

(E,Z)-1,1,1,4,4,4-Hexafluorobut-2-enes: hydrofluoroolefins halogenation/dehydrohalogenation cascade to reach new fluorinated allene

“…The spectral characteristics of product 6b obtained by us fully correspond to the literature data [19,20]. The 1 H and 19 F NMR spectra of compounds 7a,b also corresponded to the data given in the literature [21,22]. We present here the spectral data for isomer 6a, as well as the missing data of 13 For iodoolefin 7a, we found an alternative route for its synthesis.…”

Stereochemistry of some olefins RfCH=CHI and the preparation of some new cyclopropenes

“…The zinc-hydrochloric acid reduction of 1,1,1,4,4,4-hexafluoro-2-iodobut-2-ene produced a 70% yield of trans-1 , 1 ,l,4,4,4-hexafluorobut-2-ene; and a similar reduction using magnesium gave a 78 % yield of the same butene (3). The trans nature of the iodobutene (implying cis addition) was inferred from these results.…”

“…irradiation to give an equilibrium mixture of 8 to 9 equal to 1.49:l. The ratio present in the product mixture (3) is greater than this, namely, 1.78:l indicating that the trans isomer (8) is formed preferentially by trans addition as it is in the reactions giving 1 and 2. As mentioned in the Introduction cis addition of trifluoroiodomethane to 3,3,3-trifluoropropyne seems to take place (3).…”

“…The product of eq. [3] was found by vapor phase chromatography (v.p.c.) to be a 1 : 1 mixture of isomers (8).…”

Robert Neville Haszeldine. 3 May 1925—13 October 2016

“…They soon established that where the alkene was unsymmetrical, the additions normally proceed via the more stable of the two possible intermediates. They also studied the addition of perfluoroalkyl free-radicals to terminal alkynes (9) and to allene (propadiene) (10).…”