Exploration Of Polymer Supported Yb(NTf₂)₃ And Bi(OTf)₃ Catalyzed Acylation Of Isobutylbenzene

As a kind of outstanding weakly coordinating anions, bis[(perfluoroalkyl)sulfonyl]imide anions have been receiving continuous interests and have been extensively studied in recent years. Metal bis[(perfluoroalkyl)sulfonyl]imides complexes were found to play an active role in the development of highly efficient Lewis acid catalyst. Yb(NTf2)3 was thought to be the best catalyst in the system of catalysts as La(NTf2)3,Sm(NTf2)3 and Yb(NTf2)3. Nevertheless, the tedious workup to recover the catalyst after reactions make it economically unusable and retrain it for laboratory use only.In this paper, we used polystyrene as the supported polymer, on which Yb(NTf2)3 was immobilized through a series of organic reaction. According to the theory of micellar catalysis, a new kind of polymer-supported catalyst was prepared and related research was reported.In order to evaluate the catalytic properties of this supported catalyst, we then used it in several fundamental and important Lewis acid-catalyzed reactions such as acylation, esterification and nitration. It is found that its reactivity was very satisfying, almost the same as the monomeric Lewis acid. The catalyst can be recovered by simple filtration and could be reused. But the activity of the recovered catalyst decreased gradually after each recycle. In general, there was nearly a twenty percent declination after four times of uses, which indicated that Yb(NTf2)3 lost partly in the process of reaction due to dissolvent and other reasons. This disadvantage is indeed the ubiquitous problem challenging the research of polymer-supported catalyst. Out work had a positive exploration on the polymer supported Lewis acid catalyst and paved a way to the continuous research aiming to improve its stability. In addition, as Friedel-Crafts acylation is concerned, the reaction is generally performed using stoichiometric aluminium trichloride as a Lewis acid catalyst, which brought out serious effluent problems. The present widely studied transition metal perfluorosulfonate only work with highly electron-donative aromatics because of its low Lewis acidity. For example, while the acylation proceeded with anisole, acylation of benzene and toluene did not occur. We now applied catalytic Bi(OTf)3 to the acylation of isobutylbenzene, synthesized an importand mediate of Ibuprofen 4-isobutylacetophenone. LiClO4 was found to have a remarkable acceleration to the acylation. By using 4 M LiClO4-CH3NO2 as the medium, Bi(OTf)3 demonstrated much higher catalytic activity and yielded better results. Furthermore, the effect of reaction time, reaction temperature, catalyst dosage, acylation reagent and solvent were systematically studied, based on which the optimum condition was set up.