Preparation And Evaluation Of Ionic Liquid Catalysts For Synthesis Of Bisphenol Compounds

Ionic liquids were widely used in organic synthesis reactions due to their designable structure and adjustable performance.The bisphenol compound was prepared by condensation reaction of carbonyl compound and phenol.The traditional process was realized under the catalysis of proton acid and the promotion of mercapto compound.At present,preliminary studies had been carried out on the use of ionic liquids as a new generation of green catalysts for the catalytic synthesis of bisphenol compounds,but a clear understanding of the structureactivity relationship between the IL structure and the catalytic bisphenol synthesis reaction had not yet been reached.Based on the preliminary work of the research group,1,3-propane sultone was selected to react with 1-methylimidazole,1-methyl-2-mercaptoimidazole,benzothiazole,2-mercaptobenzothiazole and 2,5-dimercapto-1,3,4-thiadiazole,five zwitterions were obtained.The five zwitterions prepared were reacted with sulfuric acid,p-toluenesulfonic acid,and 3-mercaptopropanesulfonic acid to obtain fifteen functionalized ionic liquids.The sulfhydryl units introduced in the structure of these functionalized ionic liquids are different and all have sulfonic acid groups.The structure of the prepared functionalized ionic liquids were characterized by IR,NMR and MS.At the same time,two methods to characterize the catalytic function related to the ability of ionic liquids to affect the synthesis of bisphenol compounds were designed.4-nitroaniline was used as an indicator,combined with Hammett function method to determine the acidity of ionic liquids;5,5’-dithiobis(2-Nitrobenzoic acid)was used as an indicator,combined with the Ellman’s method to determine the effective sulfhydryl content of the ionic liquid.The total acidity of ionic liquids was mainly affected by anions,and the effective sulfhydryl content was mainly related to the structure of the sulfhydryl unit.The fifteen functionalized ionic liquids were used to catalyze the synthesis reaction of bisphenol acid and bisphenol A,and the parameters of the two reactions were optimized by the univariate circulation method.The optimal conditions for the synthesis of disphenolic acid: levulinic acid was 0.005 mol,levulinic acid: phenol: ILs=1:6:0.25,reaction temperature was 60℃,reaction time was 12 h.The optimal conditions for the synthesis of bisphenol A: acetone was 0.02 mol,phenol: acetone:ILs=8:1:0.25,reaction temperature was 45℃,reaction time was 8 h.Under optimal reaction conditions,the catalytic effects of fifteen functionalized ionic liquids on the synthesis of bisphenolic acid and bisphenol A were investigated.The experimental results show that N,N’-bis(3-sulfopropyl)-dimercapto-thiadiazole-3-mercaptopropane sulfonate(IL15)has an excellent effect in the catalytic synthesis of bisphenolic acid.Under normal conditions,the yield of bisphenolic acid reached 92.4%,and the selectivity reached 97.6% after 12 h(about half the time reported in the literature).IL15 catalyzes the synthesis of bisphenol A,the yield of bisphenol A was as high as 97.8%,and the selectivity wss 98.1%The cycling performance of IL15 in the synthesis reaction of bisphenolic acid and bisphenol A was further investigated.The experimental results showed that the IL15 had better catalytic stability,after the ionic liquid was recycled for five times,its catalytic activity basically remains unchanged.