Silica-supported Phosphorus Chloride: An Efficient and Recyclable Catalyst for Beckmann Rearrangement of Ketoximes and D
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Silica-supported Phosphorus Chloride: An Efficient and Recyclable Catalyst for Beckmann Rearrangement of Ketoximes and Dehydration of Aldoximes Under Microwave Irradiation Zheng Li Æ Zhong Lu Æ Anguo Zhu Æ Xu Feng Æ Jing Liu Æ Guoqiang Tian
Received: 31 January 2007 / Accepted: 30 August 2007 / Published online: 2 October 2007 Ó Springer Science+Business Media, LLC 2007
Abstract Silica-supported phosphorus chloride has been proved to be an efficient and recyclable catalyst for Beckmann rearrangement of a variety of ketoximes and dehydration of various aldoximes in anhydrous THF under microwave irradiation. This protocol has advantages of high conversion, high selectivity, short reaction time, no environmental pollution, and simple work-up procedure. Keywords Beckmann rearrangement Dehydration Silica-supported phosphorus chloride Oxime Microwave irradiation
1 Introduction The Beckmann rearrangement of ketoximes to the corresponding amides and dehydration of aldoximes to corresponding nitriles are common methods in organic chemistry and are topics of current interest [1]. The conventional Beckmann rearrangement of ketoximes and dehydration of aldoximes usually require the use of strong Bronsted or Lewis acids, i.e. concentrated sulfuric acid [2], trifluoromethanesulfonic acid [3], and polyphosphoric acid [4], which always cause the environmental problems because of the difficulty in separation. Recently, Beckmann rearrangement of ketoximes was reported to utilize many kinds of catalysts, such as BF3Et2O, [5] InCl3, [6] Ga(OTf)3, [7] BPO4, [8] BOP–Cl [9], AlCl3 H2O–KI, [10] cyanuric chloride [11], sulfamic
Z. Li (&) Z. Lu A. Zhu X. Feng J. Liu G. Tian Gansu Key Laboratory of Polymer Materials, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, P.R. China e-mail: [email protected]
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acid [12] and oxalic acid [13]. The dehydration of aldoximes was also reported to conduct by using ClSO3H, [14] Ga(OTf)3, [15] zeolite, [16] ZnO/CH3COCl, [17] KF/ Al2O3, [18] [RuCl2(p-cymene)]2, [19] and Cu(OAc)2 [20] as catalysts. However, some of the catalysts used were corrosive and still difficult to isolate from the systems after the reactions. Very recently, SiO2-supported catalysts such as SiO2supported sulfuric acid [21] and MoO3 [22] have been reported, which could efficiently resolve the separation problem and therefore eliminate the pollution caused by the above catalysts. In addition, Beckmann rearrangement of ketoximes and dehydration of aldoximes were also reported to conduct under microwave irradiation condition, [23] which could significantly accelerate the reaction rate. In continuation of our research on silica-supported catalysts for the important chemical transformation [21a] in this paper, we report silica-supported phosphorus chloride as an efficient and recyclable catalyst for Beckmann rearrangement of ketoximes and dehydration of aldoximes under microwave irradiation.
2 Experimental 1
H NMR spectra were recorded on a Mercury Plus-400 instru
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