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Synlett 2011(15): 2265-2269  
DOI: 10.1055/s-0030-1261180
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Aerobic Oxybromination of Phenols Catalyzed by Sodium Nitrite under Mild Conditions

Li Xua, Yong Wangb, Xin Wenb, Chengrong Dingb, Guofu Zhang*b,c, Xinmiao Liangc
a Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. of China
b College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014, P. R. of China
Fax: +86(571)88320147; e-Mail: gfzhang@zjut.edu.cn;
c Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P. R. of China
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Publikationsverlauf

Received 2 June 2011
Publikationsdatum:
12. August 2011 (online)

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Abstract

An efficient catalytic system for oxybromination of phenols under mild conditions has been developed, which utilizes sodium nitrite as the catalyst, dioxygen or air as the terminal oxidant, aqueous hydrobromic acid or molecular bromine as the bromine resource. From both the atom-economic and environmental points of view, the developed protocol is expected to provide a valuable synthetic method for practical applications in laboratory or industry.

Key words

oxybromination - phenols - atom economy - oxygen - ­sodium nitrite

17

Representative Procedure
In a 250 mL Schlenk flask equipped with magnetic stirrer, filled with dioxygen beforehand, was placed phenol (0.4706 g, 5.00 mmol) dissolved in MeCN (10.0 mL) under O2. Then a 42% aq solution of HBr (1.0125 g, 5.25 mmol) was added to the solution. Next, the NaNO2 (0.0103 g, 0.15 mmol) was added in one portion, and the system was immediately sealed. The reaction mixture was stirred at 25 ˚C. After the reaction, the solvent was removed under vacuum, and the residue was washed with sat. NaHCO3 solution and extracted with Et2O. The organic extract was dried over with anhyd Na2SO4. After removing the solvent under vacuum, the residue was purified by column chromatography to afford the desired products, 2- and 4-bromophenol. The yield was 0.7962 g (92%).
4-Bromophenol
¹H NMR (400 MHz, CDCl3): δ = 6.70-6.72 (m, 2 H, ArH), 7.31-7.33 (m, 2 H, ArH) ppm. ¹³C NMR (100 MHz, CDCl3): δ = 113.0, 117.1, 132.5, 154.2 ppm.
2-Bromophenol
¹H NMR (400 MHz, CDCl3): δ = 5.51 (s, 1 H, OH), 6.78-6.83 (m, 1 H, ArH), 7.00-7.04 (m, 1 H, ArH), 7.19-7.25 (m, 1 H, ArH), 7.44-7.47 (m, 1 H, ArH) ppm. ¹³C NMR (100 MHz, CDCl3): δ = 110.1, 116.1, 121.7, 129.0, 132.0, 152.0 ppm.