Synthesis, Characterization And Application Of Br(?)nsted-Lewis Acidic Ionic Liquids

Br(?)nsted-Lewis acidic ionic liquids (B-LAILs) are a novel type of catalysts whichcombine the characters of the dual acidic solid acids and the ionic liquids. Recently, interesthas increased in the use of B-LAILs because they are eco-friendly, have excellent reusabilityand better catalytic performance. But alkyl sultones have to be used as Br(?)nsted acid donor tosynthesize the sulfonic acid type of B-LAILs, which are strong carcinogenicity and greatlylimit the research and application of the B-LAILs. A few other reports rose our interestbecause the hydrochloric acid and sulfuric acid were used as Br nsted acid donor to synthesisN+-H type of B-LAILs, which provides some references because of the green and simplesynthetic routes.N-methylimidazole was used as the cation part of the B-LAILs for its good thermalstability. To establish the green synthetic methods, eco-friendly materials, such as allylchloride, epoxy chloropropane were used to synthesize the sulfonic acid type of B-LAILs.And also, Br nsted acids were introduced by protonating N-methylimidazole withhydrochloric acid and sulfuric acid, which would be used as intermediates to synthesize N+-Htype of B-LAILs. Thought the research of B-LAILs is just catching up, but acidity is theirimportant property. The acidities of the group were characterized and compared to each otherby means of FT-IR in virtue of pyridine and acetonitrile molecular probe, respectively. Thedifferent Lewis acid anions and the same Lewis acid with different mole fractions of the28B-LAILs in3gropes were employed to catalyze rosin dimerization to study their catalyticperformances to evaluate the structure-activity relationship of B-LAILs because of lacking ofquantitative characterization methods of acid. The catalytic performances of the B-LAILswere evaluated based on softening point of the dimeric rosin acid products. The relativeresearch contents are shown as follows.(1) Sulfonic acid groups were introduced by additional reaction of alkenes with allylchloride and sodium bisulfite as the materials and by bisulfite sulfonation method with epoxychloropropane and sodium bisulfite as the materials, and then14sulfonic acid type ofB-LAILs in2groups were synthesized. Green synthetic methods were established by themethods mentioned above without using alkyl sultones compared to the methods known.Furthermore, a simple, convenient and eco-friendly method was established to synthesize the3rdgroup N+-H type of B-LAILs. Detailed, Br nsted acidic ILs were synthesized asintermediates by protonating N-methylimidazole with Br nsted acid donor hydrochloric acidand sulfuric acid. And a group of N+-H type of B-LAILs (1-x)[mim·HCl] x [MClm](MClm=ZnCl2、FeCl3、CuCl, x is the mole fraction of Lewis acid),(1-x)[mim·H2SO4] x [Fe(OH)3](x=0.25) and (1-x)[mim·H2SO4] x [CuO](x=0.33) were synthesized.(2) Different B-LAILs were obtained by varying the Lewis acid and its mole fraction, theacidities of the group were characterized and compared to each other by means of FT-IR invirtue of pyridine and acetonitrile molecular probe, respectively. The characterization resultsindicated that ILs synthesized had both Br nsted and Lewis acid properties when the molefractions of the Lewis is greater than0.5, moreover, the acidity enhanced with the mole fraction of Lewis acid increasing, of course, the N+-H type of B-LAILs (1-x)[mim·H2SO4] x[Fe(OH)3](x=0.25) and (1-x)[mim·H2SO4] x [CuO](x=0.33) had both B and L acidproperties. However, the Lewis acid and its mole fraction did not have a significant impact onB acidity.(3) The dual acidic ionic liquids were employed to catalyze rosin dimerization, theB-LAILs’ catalytic performance and reusability were determined based on the softening pointof the dimeric rosin acid product. The1stgroup sulfonic acid type of B-LAILs weresynthesized by another method with allyl chloride as material, of which (1-x)[mim-PS·HCl] x[ZnCl2](x=0.64) showed better catalytic performance. A dimeric rosin acid with a softeningpoint of110.3oC (circular ball method), which was22.8oC higher than that without usingcatalyst. Besides,(1-x)[mim-HPS·HCl] x [ZnCl2](x=0.6) of the2ndgroup showed goodcatalytic performance, a dimeric rosin acid with the softening point of104.8oC, which was17.3oC higher than that without using catalyst. We believed that the hydroxy introducedaffected the synergetic effect of B and L acid sites, and so caused the difference between2groups of sulfonic acid type of B-LAILs, while the excellent reusability of this group ofB-LAILs also due to the hydroxy introduced increased the viscosity. Among the3rdgroupN+-H type of B-LAILs, a dimeric rosin acid with the softening point of102.4oC was obtainedusing (1-x)[mim·HCl] x [FeCl3](x=0.64) as catalyst, which was14.9oC higher than thatwithout using catalyst. The B-LAILs had good catalytic activity and good reusability, too.TheB-LAILs used were easily separated from the reaction mixture and the catalytic activitybecame weaker after the fifth use, which displayed the potential to replace the traditional acidcatalysts.In a word, green synthetic routes of B-LAILs were established using eco-friendlymaterials, the characterization results indicated that the B-LAILs had both Br nsted andLewis acid properties when x>0.5. B-LAILs showed excellent catalytic performance andreusability based on the softening point and acid value of the dimeric rosin acid product. Thegreen method opens up a new path to synthesize the B-LAILs and gets the research andapplication of B-LAILs out of the dilemma.