Electrochemical Studies of the Fries Rearrangement in Ionic Liquids

Abstract

The Fries rearrangement of phenyl benzoate has been studied in the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI BF4). Addition of the proton acid triflic acid was found to shift the reduction potential of phenyl benzoate from -2.0V to -1.1V vs Ag/AgCl, implying protonation of phenyl benzoate by triflic acid. After 1 day, however, the phenyl benzoate reduction potential shifted back to its original value, suggesting that triflic acid slowly reacts with the ionic liquid.

Voltammetric Investigations of the Fries Rearrangement in an Ionic Liquid

“…Figure 1 shows a voltammogram of phenyl benzoate in BMPY TfO, with added 1:1 Hf(TfO) 4 . Addition of the Hf(TfO) 4 did not produce a significant potential shift of the original phenyl benzoate reduction peak, in contrast to behavior observed for fluorenone in this medium (8). After 13 days of heating at 77 0 C, however, the phenyl benzoate reduction process was almost gone, and a broad reduction process at -1.7 V had appeared.…”

“…The effect of various Lewis acids in the Fries rearrangement of phenyl benzoate in ionic liquids has been studied previously in this laboratory ( 1 -5 ). Chloroaluminate (2,3) as well as tetrafluoroborate systems (4) have been found to yield the hydroxybenzophenone rearrangement products commonly found in conventional solvents (6). The present work has extended investigations to 1-butyl-1-methylpyrrolidinium triflate (BMPY TfO).…”

Voltammetric Investigations of the Fries Rearrangement in an Ionic Liquid

“…Previous studies from this laboratory have dealt with the Fries rearrangement (1) of phenyl benzoate in the aluminum chloride : 1-ethyl-3-ethylimidazolium chloride system, in which the rearrangement products 2-hydroxy and 4-hydroxybenzophenone are formed (2,3), and other workers have carried out similar studies (4,5). Subsequent work has involved the investigation of the Fries rearrangement in other single-component ionic liquids such as 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-1methylpyrrolidinium trifluoromethylsulfonate ( triflate ) (6,7). These ionic liquids have very little acidic character, so Lewis acids must be added to them in order to promote the Fries rearrangement.…”