Synthesis and polymerisation of fluorinated monomers bearing a reactive lateral group. Part 5 - Radical addition of iodine monobromide to chlorotrifluoroethylene to form a useful intermediate in the synthesis of 4,5,5-trifluoro-4-ene-pentanol

The synthesis of the new halogenated alcohol BrCF2CFClCH2CHICH2OH as a prec ursor of 4,5,5 trifluoro-4-ene pentanol F2C=CFC3H6OH is based on a two-step process. First, the radical addition of iodine monobromide to chlorotriflu oroethylene (CTFE) led to the expected BrCF2CFClI (I) and ICF2CFClBr (II), but also to BrCF2CFClBr (III) and ICF2CFClI (IV), the amount of which deter mined by F-19 NMR depended on the reaction conditions: by feeding CTFB into IBr continuously or in batches; photochemical or thermal initiations, and with various initial [IBr](0)/[CTFE](0) molar ratios. In most cases, isomer (I) was mainly produced. The second step concerned the addition of such a mixture to allyl alcohol yielding the polyhalogenoalcohol with a quantitati ve conversion of (I). The reactivity of different halogeno end-groups of th ese isomers toward the allyl alcohol was discussed. Reduction of the iodine atom into hydrogen and the halogenated alcohol was accompanied by that of the bromine atom leading to BrCF2CFClC3H6OH and HCF2CFClC3H6OH (V). Dehalog enation of the former alcohol in the presence of zinc led to F2C=CFC3H6OH w hile dehydrochlorination of (V) into trifluorovinyl hydroxy monomers was ac hieved in the presence of potassium hydroxide but in poor yields. Strategie s starting from the radical additions of iodine monochloride and of iodine monobromide were compared showing that the former led to better overall yie lds of trifluorovinyl alcohol than the latter. (C) 1999 Elsevier Science S. A. All rights reserved.