Voltammetric Investigations of the Fries Rearrangement in an Ionic Liquid

Abstract

The electrochemical behavior of phenyl benzoate (PB) in the neutral AlCl3 : 1-ethyl-3-methylimidazolium chloride ionic liquid has been studied. Addition of HfCl4 to phenyl benzoate in this medium produces a positive potential shift for the phenyl benzoate reduction process. Heating the solution to 80oC for 30 hours gives 4-hydroxybenzophenone as the major product. Cyclic voltammetric studies show that HfCl4 reacts with the ionic liquid to produce relatively small amounts of Al2Cl7-, so that HfCl4 is still the principal Lewis acid in this system. Comparison studies using added AlCl3 in place of HfCl4 show similar behavior, with a somewhat different potential shift for the AlCl3 : PB interaction.

Electrochemical Investigation of Ketone Complexation by Lewis Acids in a Chloroaluminate Ionic Liquid

“…There is a possibility that HfCl 4 can abstract a chloride ion from AlCl 4 in the neutral melt to form AlCl 3 , which then quickly forms Al 2 Cl 7 as active Lewis acid. Previous work (9) has shown that this reaction path plays a minor role in this system, which is supported by the voltammetric and spectroscopic findings in the present system.…”

“…A comparison of the effects of HfCl 4 and AlCl 3 additions on the electrochemical behavior of fluorenone in the AlCl 3 : EMIC system has been carried out in order to determine the effects of adding non-AlCl 3 Lewis acids to the system. Such an investigation has already been carried out for the Fries rearrangement of phenyl benzoate in the AlCl 3 : EMIC system (9). The effect of melt acidity on fluorenone electrochemistry in chloroaluminate systems has already been investigated (10), although not in great detail in the neutral region, representing another interesting aspect of this work.…”

Electrochemical Investigation of Fluorenone Complexation by Lewis Acids in Ionic Liquids

“…The observation of only a single reduction process for the complex in Figure 1 is interpreted as the involvement of an ECE (Electron-transfer, Chemical step, Electron-transfer) process for the complex reduction. In other words, an initial reduction step [2] is followed by a complexation step [3], the product of which undergoes reduction (step [4]) at a more positive potential than does the first reduction. This pathway results in a single reduction process, as has been observed for quinone systems.…”

“…Using an appropriate molecular system, electrochemical methods have the ability to provide information about these Lewis acid interactions. [2][3][4][5][6][7][8] In the present work, 9-fluorenone has been chosen as a substrate system due to its stable reduction products and accessible reduction potential in most solvent systems of electrochemical interest. 9 There has been considerable interest in the use of Lewis acids in various ionic liquids, [10][11][12][13][14] although few studies have provided detailed information about Lewis acid behavior.…”

Electrochemical Investigation of Quinone Complexation by Lewis Acids in a Chloroaluminate Ionic Liquid

“…Chloroaluminate ionic liquids provide an extremely broad range of Lewis acidities (1,2) in which to carry out electrochemical studies of various systems (3)(4)(5). Recent work from this laboratory has involved the AlCl 3 : 1-ethyl-3-methylimidazolium chloride ( EMIC ) ionic liquid (6,7). In the neutral ( N = 0.50 ) melt, which is composed of an equimolar mixture of AlCl 3 and EMIC, there is no appreciable amount of the Lewis acid Al 2 Cl 7 - (1,2), and operations in initially neutral melts provide an opportunity to investigate the effects of added Lewis acids.…”