FULL PAPER * E-mail: arashghch58@yahoo.com or a.ghorbani@mail.ilam.ac.ir; Tel./Fax: 0098-0841-2227022 Received August 9, 2010; revised October 19, 2010; accepted December 21, 2010. Chin. J. Chem. 2011, 29, 731—734 © 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 731 A Mild Procedure for the Preparation of o-Nitrophenols by Nitro Urea or Ammonium Nitrate in the Presence of Silica Sulfuric Acid (SiO 2 -OSO 3 H) Ghorbani-Choghamarani, Arash* Nikoorazm, Mohsen Goudarziafshar, Hamid Naserifar, Zahra Zamani, Parisa Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516 Ilam, Iran A mixture of ammonium nitrate or nitro urea and silica sulfuric acid was found to be efficient and environmen- tally friendly nitrating media for the preparation of orto-nitro phenols in dichloromethane at room temperature. Keywords nitration, phenol, nitro urea, ammonium nitrate, silica sulfuric acid Introduction Nitration of aromatic compounds is one of the most fundamental and useful reactions for introducing the nitrogen atom directly into aromatic rings. 1 Nitration of aromatic compounds is an industrially important reac- tion as the nitrated products are intermediates for fine chemicals and pharmaceuticals. 2 The nitration of phe- nols is a fundamental unit process of great industrial importance generating commercially valuable interme- diates and there is a great need for regio-selective pollu- tion free processes. 3 Usually, nitrations of phenols are not region-selective and are the cause of environmental concerns regarding the disposal of large excesses of con- centrated nitric acid and non-environmentally friendly metallic catalysts or reagents [such as WO 3 HNO 3 , 4 TiO 2 - [Ti 4 H 11 (PO 4 ) 9 ]•nH 2 O/HNO 3 , 5 Yb-Mo-HKSF-HNO 3 , 6 ZnCl 2 /HNO 3 , 7 TBAB/HNO 3 , 8 Bi 5 O(OH) 9 (NO 3 ) 4 /SOCl 2 , 9 (NH 4 ) 2 SO 4 •NiSO 4 •6H 2 O/HNO 3 , 10 ([bmim][HSO 4 ])/ NaNO 3 , 11 montmorillonite KSF/HNO 3 , 12 silica sulfuric acid/NaNO 3 13 and Hf or Zr oxychloride com- plex-KSF/HNO 3 14 ] in these processes. Therefore, de- signing systems, which reduce the mentioned problems, is of great interest. Results and discussion Recently we have examined a variety of heteroge- neous systems, generating nitronioum ion 2 (NO ) + which was used for different organic reactions. 15-21 In this light, we decided to disclose a new procedure for the nitration of substituted phenols by a mixture con- taining ammonium nitrate or nitro urea and silica sulfu- ric acid. Ammonium nitrate is a cost, effective, nontoxic and environmentally friendly chemical, which is used in fertilizer industry and as an explosive in mining opera- tions. Ammonium nitrate has been also applied as re- agent in different chemical reactions. 22-25 Nitro urea was prepared via our newly reported procedure. 26 Consequently, herein we decided to report a metal- free, green and heterogeneous procedure for the nitra- tion of substituted phenolic compounds by ammonium nitrate and/or nitro urea and silica sulfuric acid under mild and heterogeneous conditions (Scheme 1). Scheme 1 (a) X = Y = H; (b) X = Cl, Y = H; (c) X = F, Y = H; (d) X = OMe, Y = H; (e) X = Br, Y = H; (f) X = OCH2Ph, Y = H; (g) X = Y = Cl; (h) X = CH3, Y = Ome; (i) X = CH3, Y = H; (j) X = Ph, Y = H; (k) X = (CH3)3C, Y = H; (l) X = (CH3)2CH, Y = H; (m) X = OPh, Y = H; (n) X = Me, Y = (CH3)3C Result of the nitration reactions including molar ratio of reagents, time and yields of nitarated phenols are summarized in Table 1. All of the o-nitrophenos were easily obtained via mixing the corresponding phenols with ammonium ni- trate (NH 4 NO 3 ) or nitro urea (NH 2 CONHNO 2 ) and silica sulfuric acid (SiO 2 -OSO 3 H) in dichloromethane and stir- ring the resulting mixture at room temperature. After re- action completion, resulting yellow to orange pasty mix- ture was passed through the column chromatography.