Synthesis of fluorinated telomers Part 7. Telomerization of 1,1-difluoro-2-chloroethylene and 1,2-difluoro-1,2 dichloroethylene with methanol

Abstract

Radical telomerizations of 1,1-difluoro-2-chloroethylene and 1,2-difluoro-1,2-dichloroethylene with methanol, leading to chlorofluoroalcohols, are presented. The optimization of the synthesis conditions led to 3-chloro-2,2-difluoropropanol and 2,3-dichloro-2,3-difluoropropanol in 80% and 89% conversion, respectively, much higher than those reported in the literature. The best conditions were achieved when 2,5-bis(tert-butylperoxy)-2,5–dimethylhexane (DHBP) was used as the initiator at 407 K with an initial ([MeOH]₀/[alkene]₀) molar ratio, R₀, of 40. The unsymmetrical alkene led to one isomer only, in contrast to the formation of two isomers from chlorotrifluoroethylene. Furthermore, this study has shown the influence of the fluorine and chlorine atoms of the olefin in directing the radical reaction. Hence, by its polar and steric effects, the chlorine atom in these alkenes does not favor the radical addition of HOCH₂˙. In contrast, the inductive effects of the fluorine atom increase the reactivity of the hydroxymethyl radical. A decreasing reactivity series of different chlorofluoroolefins with respect to the radical addition of methanol is proposed with the optimal conditions for each telomerization: F₂CCCl₂ > F₂CCFCl > ClCFCFCl > F₂CCHCl and an overall reactivity series of different fluoroalkenes with methanol is also suggested.