## 1 Introduction
For example, both the [HSO\({}_{3}\)-pmim][OTf] and pyrrolinium 1,1,2,2-tetrafluoro-2-(1,1,2,2-tetrafluoroethoxy)ethanesulfonate ([Pyrro][H(CF\({}_{2}\))\({}_{4}\)O(CF\({}_{2}\))\({}_{2}\)SO\({}_{3}\)]) have been used as BAILs catalysts for the Friedel-Crafts alkylation reaction, and they allow this reaction under solvent-free conditions [29; 30]. [HSO\({}_{3}\)-pmim][OTf] applied for reactions of electron-rich arene with aldehyde can achieve a 93%-97% product yield with five cycles [29]. [Pyrro][H(CF\({}_{2}\))\({}_{4}\)O(CF\({}_{2}\))\({}_{2}\)SO\({}_{3}\)] with a large ionic volume and charge delocalization properties in anion moiety has a low melting point to allow Friedel-Crafts alkylation under low temperature (50 \({}^{\circ}\)C) conditions with as high as a 90% yield after reacting for 12-24 h [30]. Iron-containing magnetic ILs have been firstly published in 2004 [35; 36], and recent studies on iron-catalyzed organic transformations are of great importance because iron is one of the most inexpensive and non-pollutant metals [37; 38]. Unlike AlCl\({}_{3}\)-based catalysts with air- and water-sensitive properties, iron-based catalysts can make reactions both air- and water-stable under mild conditions [39]. Some examples of organic transformations with iron-based ILs as Lewis acidic catalysts or reaction media have been reported [39; 40]. 1-Butyl-3-methylimidazolium tetrachlororferate ([Bmim][FeCl\({}_{4}\)]) has been specifically employed as a catalyst in Friedel-Crafts acylation [41], aryl-Gripard cross-coupling [39], quinazolines synthesis [42], and dimerization reactions [43]. The Lewis acidic ILs are usually used for Friedel-Crafts and coupling reactions because their electron-accepting ability for metals (such as Fe\({}^{3+}\), Al\({}^{3+}\), Zn\({}^{2+}\)) in anion groups can activate the halide from alkyl halide (or acyl halide) [44]. Previous studies have also indicated that the added molar fraction from a metal salt source is an essential factor for Lewis acidic IL activities [18; 45; 46; 47]. For example, when the molar fraction of AlCl\({}_{3}\) in IL BmimCl-AlCl\({}_{3}\) is below 0.5, this IL exhibits its Lewis basicity because the anion of this IL is Cl and AlCl\({}_{4}\). When the molar fraction of AlCl\({}_{3}\) is equal to 0.5, BmimCl-AlCl\({}_{3}\) becomes neutral because only the AlCl\({}_{4}\) anion is in IL. Finally, when the molar fraction is more than 0.5, the BmimCl-AlCl\({}_{3}\) IL shows strong Lewis acidity because in this IL, the major anions are the strong Lewis acidic Al\({}_{2}\)Cl\({}_{7}\)[45; 46]. Similarly, when BmimCl-ZnCl\({}_{2}\) was used as solvent and catalysts for the synthesis of DPM at 80 \({}^{\circ}\)C with a reaction time of 2 h, it was found that when the molar fraction of ZnCl\({}_{2}\) to [Bmim][Cl] is lower than 0.67, this IL without Lewis acidic properties had low catalytic activity, and the obtained DPM yield was only 29.0% and even reached as low as 5.2% (0.6 for 29.0% DPM yield and 0.52 for 5.2%, respectively). However, when the molar fraction of ZnCl\({}_{2}\) to [Bmim][Cl] is more than 0.67, the BmimCl-ZnCl\({}_{2}\) IL with increased Lewis acidic properties can give a 97.8% DPM yield with good catalytic activity even after recycling eight times [47]. Another literature reported that BmimCl-FeCl\({}_{3}\) IL has been used as a catalyst for Friedel-Crafts reactions to obtain benzophenone yields of about 20% and 65% with an FeCl\({}_{3}\) molar fraction of 0.52 and 0.6, respectively. However, a sudden drop in benzophenone yield in the fourth run of the recycling experiment occurred in this IL [48]. This was ascribed to the cumulative FeCl\({}_{3}\) loss during each run, which led to an IL sample with an inferior FeCl\({}_{3}\) molar fraction [48]. Therefore, in order to solve the low benzophenone yield in recycling experiment, the two equivalents of anhydrous FeCl\({}_{3}\) must be repeatedly added in this IL [48].