One Pot Synthesis of Imines from Aromatic Nitro Compounds with a Novel Ni/SiO 2 Magnetic Catalyst
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One Pot Synthesis of Imines from Aromatic Nitro Compounds with a Novel Ni/SiO2 Magnetic Catalyst Yunfeng Zheng Æ Kun Ma Æ Hui Li Æ Jing Li Æ Jianguo He Æ Xun Sun Æ Rong Li Æ Jiantai Ma
Received: 20 September 2008 / Accepted: 9 November 2008 / Published online: 26 November 2008 Ó Springer Science+Business Media, LLC 2008
Abstract We have successfully prepared a novel Ni/SiO2 magnetic catalyst, and put it into the process of one pot synthesis of imines directly from aromatic nitro compounds and aldehydes for the first time. The catalyst has been characterized by XRD, IR, TEM, SEM, TPR, H2-TPD and XPS. The prominent merits of the Ni/SiO2 magnetic catalyst passivated with a gas mixture are that it can be stored safely in air below 423 K and needs no activation before use. In the catalytic test, most conversion and selectivity is almost up to 100%, and it is found that the catalyst is highly efficient, stable, and reusable for the synthesis of imines. Keywords One pot synthesis Imines Novel Ni/SiO2 magnetic catalyst Nitroaromatic compounds Surface passivated
1 Introduction Imines and their derivatives are versatile intermediates in organic synthesis [1], in particular for the preparation of heterocycles [2], anti-inflammatory agents [3], non-natural aminoacids [4], liquid crystalline materials [5], and anticancer agents [6]. Since the first preparation of imines was reported by Schiff more than a century ago [7], a variety of methods/ systems for the synthesis of imines have been described, such as ZnCl2 [8], TiCl4 [9], MgSO4–PPTS [10], alumina [11], Ti(OR)4 [12], Er(OTf)3 [13], MgSO4 [14], MgClO4
Y. Zheng K. Ma H. Li J. Li J. He X. Sun R. Li J. Ma (&) College of Chemistry and Chemical Engineering, Lanzhou University, 730000 Lanzhou, People’s Republic of China e-mail: [email protected]
[15], P2O5/Al2O3 [16], CuSO4 [17], and NaHCO3 [18], in which metal species act as Lewis acids to activate the carbonyl group as well as facilitating the removal of water. In the past few years, with the development of experimental techniques, some innovations were reported, including solid-state synthesis [19], solvent-free/clay/microwave irradiation [20], water suspension medium [21], solvent/ reflux [22], infrared irradiation/no solvent [23], K-10/ microwave [24], silica/ultrasound irradiation [25], NaHSO4SiO2/microwave/solvent-free [26], dirhodium Caprolactamate [27], [bmim]BF4/molecular sieves [28] and et al. The methods/systems aforementioned showed some disadvantages such as the requirements of high reaction temperatures, prolonged reaction periods, moisture sensitive catalysts, large quantities of aromatic solvents, costly dehydrating reagents/catalysts and special instruments [25]. As an alternative, one pot system for imine synthesis has been under investigations, such as Rh6(CO)16 [29], PdCl2 (PPh3)2/SnCl2/CO [30], Pd/C/H2 [31], and Ru3(CO)12/CO [32]. However, these protocols required transition-metal catalysts, elevated pressures, high temperatures, which made them far from ideal for laboratory-scal
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