Imidazolium Ionic Liquids as Solvents for Cerium(IV)-Mediated Oxidation Reactions

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• 作者：Hasan Mehdi ; Andrea Bodor ; Di&aacute ; na Lantos ; Istv&aacute ; n T. Horv&aacute ; th ; Dirk E. De Vos ; and ; Koen Binnemans
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：January 19, 2007
• 年：2007
• 卷：72
• 期：2
• 页码：517 - 524
• 全文大小：175K
• 年卷期：v.72,no.2(January 19, 2007)
• ISSN：1520-6904

文摘

Use of imidazolium ionic liquids as solvents for organic transformations with tetravalent cerium salts asoxidizing agents was evaluated. Good solubility was found for ammonium hexanitratocerate(IV) (cericammonium nitrate, CAN) and cerium(IV) triflate in 1-alkyl-3-methylimidazolium triflate ionic liquids.Oxidation of benzyl alcohol to benzaldehyde in 1-ethyl-3-methylimidazolium triflate was studied byin-situ FTIR spectroscopy and ¹³C NMR spectroscopy on carbon-13-labeled benzyl alcohol. Careful controlof the reaction conditions is necessary because ammonium hexanitratocerate(IV) dissolved in an ionicliquid can transform benzyl alcohol not only into benzaldehyde but also into benzyl nitrate or benzoicacid. The selectivity of the reaction of cerium(IV) triflate with benzyl alcohol in dry ionic liquids dependson the degree of hydration of cerium(IV) triflate: anhydrous cerium(IV) triflate transforms benzyl alcoholinto dibenzyl ether, whereas hydrated cerium(IV) triflate affords benzaldehyde as the main reaction product.Reactions of ammonium hexanitratocerate(IV) with organic substrates other than benzyl alcohol havebeen explored. 1,4-Hydroquinone is quantitatively transformed into 1,4-quinone. Anisole and naphthaleneare nitrated. For the cerium-mediated oxidation reactions in ionic liquids, high reaction temperatures arean advantage because under these conditions smaller amounts of byproducts are formed.