## 3 Results and Discussion
### Catalytic Application in the Solvent-Free Friedel-Crafts Alkylation Reaction
#### 3.2.6 Catalyst Recycling and Stability  
Further investigation, including evaluating the reusability and stability of catalyst 5c for the Friedel-Crafts alkylation reaction of p-xylene with BnCl, was conducted under the optimum conditions obtained by the above-mentioned test (a temperature of 80 \({}^{\circ}\)C, a reaction time of 30 min, catalyst 5c amount 1.0 mole %, and a molar ratio of p-xylene to BnCl of 6:1). The 5c could be easily separated from the reaction mixture by centrifugation with drying under a vacuum after washing with hexane 2-3 times. Using this process, six consecutive Friedel-Crafts alkylation procedures were conducted, for which the  
Figure 4: The effects of the molar ratio of p-xylene to BnCl on the Friedel–Crafts alkylation reaction (under a 5c catalyst dosage of 1.0 mole %, a reaction time of 0.5 h, and a reaction temperature of 80. Figure 3: The effects of reaction temperature on the Friedel–Crafts alkylation reaction of p-xylene with BnCl (under a 5c catalyst dosage of 1.0 mole %, a reaction time = 0.5 h, and a molar ratio of p-xylene: BnCl = 2:1). results are summarized in Figure 5. The catalytic activity of ILs typically decreases gradually with increases in the catalyst recycle times because the ILs gradually dissolve with the solvent with increases in the number of consecutive reaction times. The striking recycling results shown in Figure 5 show that the product yield was an average of 95.0% with almost no evidence of a decrease in efficiency. Every product yield of the consecutive catalytic run was maintained at a minimum of 90.0% (the first and second run were both 97.0%; the third run was 90.0%, and the fourth run was 92.0%). A 98.0% product yield was even obtained after the sixth reaction run. When compared with some catalysts reported in the literature (shown in Table 2), the 5c had many advantages. Firstly, using 5c can make the reaction solvent-free. Secondly, 5c with air and water stability overcomes the air-sensitive and water-sensitive disadvantages of the AlCl\({}_{3}\)-based systems (AlCl\({}_{3}\), [EMIM]Cl-AlCl\({}_{3}\), and [BMIM]Cl-AlCl\({}_{3}\)). Thirdly, the molar fraction of the FeCl\({}_{3}\) in B-L MILs 5c is only 0.5 (compared with [EMIM]Cl-AlCl\({}_{3}\) (molar fraction \(>\)0.67), [BMIM]Cl-AlCl\({}_{3}\), [BMIM]Cl-FeCl\({}_{3}\), [BMIM]Cl-FeCl\({}_{2}\), and [BMIM]Cl-ZnCl\({}_{2}\) (both the molar fraction of these four IL \(>\)0.67) [15; 47; 48]). Fourthly, 5c is less expensive than the InCl\({}_{3}\) catalyst. Fifthly, 5c lowers the molar ratio of p-xylene to BnCl, shortens the reaction time, and saves the catalyst. Most importantly, 5c with a specific mesomeric effect can overcome the loss of metal chloride salt in each recycling run and keep the molar fraction equal to 0.5 (when compared with [BMIM]Cl-AlCl\({}_{3}\), [BMIM]Cl-FeCl\({}_{3}\), and [BMIM]Cl-FeCl\({}_{3}\)[47; 48]). Therefore, 5c can also improve the non-uniform dispersion, and give excellent reusability more than other reported catalysts (when compared with Bi(OTf)\({}_{3}\)/[EMIM][NTr\({}_{2}\)], Cu(OTf)\({}_{3}\)/[BMIM][BF\({}_{4}\)], Sc(OTf)\({}_{3}\)/[BMIM][SbF\({}_{6}\)], [BMIM][B(HSO\({}_{4}\))\({}_{4}\)], and [Pyro][H(CF2)\({}_{4}\)O(CF\({}_{2}\))\({}_{2}\)SO\({}_{3}\)] [16; 17; 18; 19; 30]) through six consecutive catalytic Friedel-Crafts alkylation runs without a significant loss in product yield (an average of 95.0%). In general, the 5c catalyst with a dual solvent-catalyst function, dual Brensted-Lewis acidity, and excellent catalytic activity is stable enough. Thus, 5c is a promising material for green chemical processes. The reaction scope (including different reaction substrates and other organic reactions with needing acidic catalysts) and limitation will be expanded to investigate in further follow-up and thorough studies. Figure 5: Examination of reusability of B-L MIL 5c (under reaction temperature = 80 \({}^{\circ}\)C, a reaction time = 0.5 h, 5c amount = 1.0 mole %, and a molar ratio (p-xylene:BnCl) = 6:1).