Synthesis of fluorinated telomers. Part 6. Telomerisation of chlorotrifluoroethylene with methanol

Abstract

Bulk radical telomerisation of chlorotrifluoroethylene (CTFE) with methanol was investigated for the synthesis of fluorinated alcohols. Improvements in the conversion of CTFE and of the selectivity of the reaction were sought by using different radical initiators (peroxides, percarbonates, peresters) and an excess of methanol. These reactions were compared in terms of CTFE conversion, yield of monoadduct and formation of higher molecular weight telomers. Under these conditions, radical initiated telomerisations systematically led to low molecular weight CTFE telomers. 2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane (DHBP) proved to be the most effective radical initiator. All these experiments revealed the low chain transfer activity of methanol in the presence of CTFE. A thorough structural study of typical CTFE–methanol telomers was performed by ¹⁹F, ¹H and ¹³C NMR spectroscopies. These analytical methods allowed us to prove the highly regioselective formation of HOCH₂CF₂CFClH (produced with a 95% selectivity), showing the regioselectivity of the addition of hydroxymethyl radicals onto the difluoromethylene side of CTFE.