Electrophilic Nitration, Halogenation, Acylation, and Alkylation of Alpha, Alpha, Alpha-Trifluoromethoxybenzene

摘要

Electrophilic nitration of alpha, a,a-trifluoromethoxybenzene gave 88-93% para and 12-7% ortho isomer with no meta isomer detected. The relative reactivity of alpha, a,a-trifluoromethoxybenzene compared to benzene (determined in competition experiments) was found to be comparable to that of fluorobenzene. A Hammett-Brown plot of log kX/kH vs. sigma for nitration with nitronium tetrafluoroborate in nitromethane solution gave excellent linear correlation (correlation factor r = 0.999). A sigma value of 0.067 was obtained for the OCF3 group from this plot. FeC13-and I2 catalyzed bromination also showed exclusive para/ortho orientation, whereas in the FeC13-catalyzed chlorination 6% meta isomer was also obtained. FeC13-catalyzed acetylation and benzoylation in nitromethane solution gave predominant (or exclusive) para substitution. The A1C13-catalyzed Friedel-Crafts alklation of alpha, a,a-trifluoromethoxybenzene with tert-butyl and benzyl chlorides gave nearly exclusive para or para/ortho substitution (99.4% para, 0.6% meta, and 85% para, 1% meta, 14% ortho, respectively).