## 2 Direct \(\alpha\)-Halogenation of Aryl Ketones
### Metal Halides (MX)
#### 2.1.6 Ionic Liquids as Halogenation Agent  
IL-based halogenation agents are gaining traction in the literature nowadays, mainly due to their contribution to the good practice ethos in terms of recyclability and reusability. In 2015, \(\alpha\)-bromination and \(\alpha\)-chlorination procedures mediated by, respectively, bis(2-\(N\)-methylimidazoliumethyl)-ether dibromochlorate and dichloroiodate, were reported (Figure 9) [110]. Eight \(\alpha\)-bromoaryl ketones were isolated in excellent yields (88-95%), upon the addition of bis(2-\(N\)-methylimidazoliumethyl)-ether dibromochlorate (0.5 equiv.) to the corresponding ketones under reflux for 8-24 h. Similarly, the reaction with the dichloroiodate analogue generated eight \(\alpha\)-chlorostones in 88-93% isolated yield. This procedure tolerated the presence of electron-withdrawing (i.e., Br, Cl, NO\({}_{2}\)), -donating (i.e., Me, OMe) and acid-sensitive (i.e., OH) groups on the substrates, highlighting its wide applicability. The authors claimed that the ILs can be regenerated and reused; however, no experimental details were provided to support this claim. [PERSON] and [PERSON] illustrated that 1,4-bis(3-methylimidazolium-1-yl)butane dithiormide was an effective bromination agent for arenes and aryl ketones (Figure 10, left) [111]. Upon addition of the IL (0.5 equiv.) in CH\({}_{3}\)CN, \(\alpha\)-bromination of aryl ketones was achieved, yielding three \(\alpha\)-bromoketones (i.e., \(p\)-H, -Me, -OMe) in excellent yields (92-96%). The authors demonstrated that the IL could be regenerated and reused for five successive cycles without a significant loss in activity. The straightforward isolation of the brominated products further highlighted this route's sustainable character (i.e., adding water to the reaction mixture). Another IL-based brominating agent, immobilised on Fe\({}_{2}\)O\({}_{3}\) support, was successfully utilised for the bromination of a variety of alkenes, alkynes,  
Figure 10: Bis(imidazolium)-based (**left**) and Fe\({}_{2}\)O\({}_{3}\)-supported (**right**) dithiormide ILs as effective halogenation agents. Figure 9: Effective IL-based halogenation agents. (Figure 10, right) [112]. The bromination agent was easily separated from the reaction mixture by using an external magnet. When recovered, the authors claimed that the reagent could be reused up to six consecutive runs without any significant loss in activity. Four \(\alpha\)-brominated aromatic ketones were isolated in good to excellent yields (80-90%). The presence of electron-donating substituents decreased the reaction time from eight (for phenylethanolamine) to six hours (for the \(p\)-OMe substituted analogue). Aryl ketones bearing electron-withdrawing groups (i.e., \(p\)-Cl and \(o\)-NO\({}_{2}\)) showed a similar trend. An efficient IL-mediated bromination protocol was also developed by [PERSON] and [PERSON] [113]. [Bmim][Br\({}_{3}\)] mediated the bromination of six aromatic ketones in good to excellent yields (Scheme 43). The procedure tolerated the presence of both electron-donating and -withdrawing substituents on the phenyl ring. The authors stated that the IL could be recycled several times without any loss in bromination efficacy; however, no experimental data were provided in support of this claim. The short reaction times were an important feature of this IL-based halogenation. In 2007, [PERSON] and co-workers designed an acetylmethylimidazolium halide ([Acmim]X) (X = Cl\({}^{-}\), Br\({}^{-}\)) and ceric ammonium nitrate-based \(\alpha\)-chlorination and \(\alpha\)-bromination of ketones (Figure 11, left) [114; 115]. Addition of the IL (1.2 equiv.) and ceric ammonium nitrate (CAN) (2 equiv.) to an aryl ketone, yielded three \(\alpha\)-chloro and three \(\alpha\)-bromoketones (i.e., \(p\)-H, -Me and -OMe substituted) in good yields (80-82% and 80-85%, respectively). The authors mentioned that the selective \(\alpha\)-halogenation of this protocol is linked to its radical nature.