Elimination reactions from trifluoroethanol

Novel chemistry that was initiated by Nakai and co-workers [36, 37] involves elimination of hydrogen fluoride from the tosylate of trifluoroethanol, followed by reaction of the intermediate with appropriate electrophiles (Figure 6.27). A wide range of approaches to the synthesis of difluoromethylene derivatives has ensued. 

An experimental kinetic study has shown that the influence of the a-cyano group on the rate of solvolysis of 2-propyl sulphonates, namely the k(HCMe20Ts)//c(NCCMe20Ts) ratio (extrapolated from 80-170 °C temperature interval to 25 °C) in 100% 2,2,2-trifluoroethanol buffered with 2,6-lutidine, is only 3.5 x 103. This is considerably smaller than the retardation factor expected on the basis of the Taft polar substituent constant. To evaluate the possibility that the investigated methacrylonitrile formation reaction proceed by a rate-limiting concerted E2 elimination, the effect of a-deuterium substitution on the rate of... 

For efficient action of Y as cocatalysts, it is necessary that in reactions with alkyl halides they behave as bases abstracting proton not as nucleophiles entering undesired nucleophilic substitution. From a variety of possible Y-H, only OH acids—alcohols and phenols, and to smaller extent some NH acids—are shown to be proper cocatalysts. In a model studies of base-induced PTC j8-elimination of HBr from cyclohexyl bromide, it was shown that benzyl and benzhydryl alcohols, 2,2,2-trifluoroethanol, trifluoromethylphenyl carbinol, and mesitol are particularly efficient cocatalysts (71) as shown in equation 159. 

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