General Papers
ARKIVOC 2014 (v) 64-71
A practical approach for regioselective mono-nitration of phenols under mild conditions Ling-Yan Chen, Tao Liu, Xiaokun Zhou, and Zhihua Sun* College of Chemistry and Chemical Engineering, Shanghai University of Engineering Science, 333 Longteng Road, Shanghai, 201 620, China E-mail:
[email protected] DOI: http://dx.doi.org/10.3998/ark.5550190.p008.587 Abstract Cu(NO3)2.3H2O was demonstrated to be an efficient, regioselective and inexpensive nitrating reagent for the synthesis of mono-nitro substituted phenolic compounds. 12 examples of different phenols were examined. Good yields (67-90%) have been achieved. Keywords: Nitration, regioselective, metal nitrates, phenolic compounds
Introduction Nitration of aromatic compounds is one of the most important reactions in organic synthesis, since the nitro compounds are very useful in many industrial processes.1-5 They often are critical materials for pharmaceuticals, perfumes, plastics and so on.6-8 Usually, nitration reactions suffer from low regioselectivity and over nitration.9-12 The typical process usually requires using mixture of concentrated or fuming nitric acid and concentrated sulfuric acid. The disposal of strong acid waste and generation of nitrogen oxide are environmental concerns. Therefore, traditional nitration method seems uneconomical and hazardous. Nitrophenols, among these useful nitro compounds, present similar problems during synthesis. And as phenols are highly reactive, the nitration of phenols using strong acids is always unselective and leads to side products such as dinitro compounds, oxidized products, and so on. In the last decade, much effort has been made on nitration of phenols.13-20 A variety of acidic nitrating agents, including concentrated nitric acid, nitrogen oxides, anhydrides or triflates, and solid acids have been employed. Also many methods have been reported using metal nitrates as source of nitronium ion.21-30 However, these metal nitrates often need extra co-reagents such as phase transfer catalysts or expensive ionic liquids achieve desirable outcomes. Therefore, it is worthwhile to seek for alternative methods that could overcome these problems.
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