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Synlett 2004(12): 2203-2205  
DOI: 10.1055/s-2004-832808
LETTER
© Georg Thieme Verlag Stuttgart · New York

New Selective Metal-Free Oxidations of Primary Alcohols by HNO3 or HNO3 and O2, Catalyzed by Br2

Francesco Minisci*, Ombretta Porta, Francesco Recupero, Carlo Punta, Cristian Gambarotti, Monica Pierini, Laura Galimberti
Dipartimento di Chimica, Materiali e Ingegneria Chimica G. Natta, Politecnico di Milano, via Mancinelli, 7, 20133 Milano, Italy
Fax: +39(02)23993080; e-Mail: francesco.minisci@polimi.it;
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Publication History

Received 10 May 2004
Publication Date:
03 September 2004 (online)

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Abstract

Primary benzylic alcohols are selectively oxidized to the corresponding aromatic aldehydes by molecular oxygen at atmospheric pressure, under Br2-HNO3 catalysis in a biphasic medium (1,2-dichloroethane-water, 5:1) at 60 °C. Under paragonable experimental conditions the aliphatic alcohols are oxidized to esters.

Key words

alcohols - aldehydes - bromine - nitric acid - aerobic oxidation

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Standard Experimental Procedure: A mixture of benzyl alcohol (10 mmol), Br2 (2 mmol), HNO3 (3 mmol) in 20 mL of 1,2 dichloroethane and 4 mL of H2O (biphasic system) was stirred for 24 h under oxygen atmosphere at 60 °C.
The organic phase was separated from the aqueous solution and analyzed by GC with p-chlorobenzaldehyde as internal standard. Conversion of benzyl alcohol was quantitative and benzaldehyde was formed in 96% yield.