Alkylated aromatic amines are important intermediates in the synthesis of pharmaceuticals, pesticides and ligands. Among the many methods for the synthesis of alkylated aromatic amines, the hydroaromatization of olefins with aromatic amines is a highly efficient and 100% atom-utilizing synthetic method. However, during the reaction of an olefin with an aromatic amine, at least six products are generated, and it is very challenging to precisely regulate the chemistry and regioselectivity of this reaction so as to controllably synthesize a single hydroaromatized product. In addition, the difficulty of recovering and reusing homogeneous catalysts needs to be addressed. Therefore, it is of great significance to develop efficient and highly selective multiphase catalysts for olefin and aromatic amine hydroaromatization reactions.

Shi Feng's group in the State Key Laboratory of Carbonyl Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, is dedicated to the clean synthesis of amines by multiphase catalysis (Nature Commun., Angew. Chem. Int. Ed., Chin. J. Catal., Nature Commun., ACS Catal.). Recently, the group developed the first USY molecular sieve-catalyzed selective hydroaromatization reaction of styrene with aniline derivatives by controllably adjusting the acidity of the molecular sieve (as shown in the figure). The selectivity of a single product for the hydroaromatization of styrene with aniline was up to 85%. Applying this simple catalyst system, a series of hydroaromatized products were synthesized (40 examples in yields up to 95%).

The results of N2 adsorption and desorption experiments showed that a suitable molecular sieve pore size (pore size > 0.5 nm) facilitates the entry of reactants and the escape of products, thus exerting the selective catalytic effect of the molecular sieve.Py-IR characterization demonstrated that Lewis acid promotes the Hofmann-Martius rearrangement of the hydramine product to the hydroaromatization product, which improves the selectivity of the hydrogenaromatization product.NH3-TPD The results indicate that the weak acid sites of the molecular sieves play a key role in the formation of the hydroaromatization products. In addition, the catalyst could be reused at least 10 times while the catalytic activity remained essentially unchanged.

This study lays the foundation for the development of multiphase catalysts for olefin hydroaromatization and provides new ideas. The related research results were published online in Journal of Catalysis. Doctoral student Xinzhi Wang is the first author of the paper, and associate researcher Hongli Wang and researcher Feng Shi are the co-corresponding authors. The research was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China, and the Chinese Academy of Sciences.

USY molecular sieve-catalyzed selective olefin hydrogen aromatization reaction

https://www.cas.cn/syky/202104/t20210408_4784170.shtml