Metal and H₂O₂ Free Aerobic Oxidative Aromatic Halogenation with [RNH₃⁺] [NO₃^–]/HX and [BMIM(SO₃H)][NO₃)_x(X)_y] (X = Br, Cl) as Multifunctional Ionic Liquids

Abstract

Novel multifunctional ionic liquids (ILs) are generated by addition of HBr or HCl to alkylammonium nitrates ([RNH3(+)] [NO3(-)]) and to 3-methyl-1-(butyl-4-sulfonyl)imidazolium nitrate ([BMIM(SO3H)][NO3]). The resulting [RNH3(+)] [NO3(-)]/HX and mono (3-methyl-1-(butyl-4-sulfonyl)imidazolium) monohalogenide mononitrate ([BMIM(SO3H)][NO3)x(X)y] (X = Br, Cl)) systems act as solvent and promoter for aerobic oxidative halogenation of arenes under mild conditions in high yields that can be repeated over several cycles.

A Metal-Free and Ionic Liquid-Catalyzed Aerobic Oxidative Bromination in Water

“…[12][13][14] Thus, following these previous accounts (reaction was carried out in an open system where air is an available source of oxygen), several organic nitrate ILs were scanned using anisole as a model substrate to determine the best catalyst (Table 1). These ILs can be easily synthesized by adding nitric acid to an ethanol solution of amines.…”

“…According to previous reports, [12][13][14] a possible mechanism for this oxidative bromination is presented in Scheme 4, which can be described as a sequential cascade of double-cycle oxidationreduction reactions. Therefore, the entire reaction uses oxygen as oxidant and is catalyzed by nitrate (Eqn 1).…”

“…Therefore, the entire reaction uses oxygen as oxidant and is catalyzed by nitrate (Eqn 1). [12] 6ArH…”

“…Recently, the aerobic oxidative halogenation of aromatic compounds has been examined in ionic liquids (ILs) to overcome these problems. [12] Only a few papers refer to the investigation of this field so far. All of them have lower bromine atom economy because of the excessive amounts of HBr employed (up to 200 mol-%).…”

“…[12a,12d] Another problem is the use of more than stoichiometric amount ILs as a promoter and a cosolvent. According to the proposed mechanism therein, [12][13][14] the nitrate ionic liquids can be recovered by O 2 or air in these systems. Thus, it motivates us to find an efficient catalyst to catalyze the oxidative bromination with high bromine atom economy.…”