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

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

References

• 1 Larock RC. Comprehensive Organic Transformations   NCH; New York: 1999.  p.1234 
• 2 Trost BM. Fleming I. Ley SV. Comprehensive Organic Syntheses   Vol. 7:  Pergamon; Oxford: 1991. 
• 3 Amati A. Dosnaldo G. Zhao L. Bravo A. Fontana F. Minisci F. Bjørsvik . Org. Process Res. Dev.  1998,  2:  261 
• 4 Minisci F. Recupero F. Rodinò M. Sala M. Schneider A. Org. Process Res. Dev.  2003,  7:  794 
• 5 Cecchetto A. Fontana F. Minisci F. Recupero F. Tetrahedron Lett.  2001,  42:  6651 
• 6 Minisci F. Recupero F. Peduli GF. Lucarini M. J. Mol. Catal. A  2003,  204:  63 
• Reviews:
• 7a Zhan BZ. Thompson A. Tetrahedron  2004,  60:  2917 
• 7b Sheldon RA. Arends JWCE. Brink GS. Dijksman A. Acc. Chem. Res.  2002,  35:  774 
• Reviews:
• 8a Mallat T. Baiker A. Chem. Rev.  2004,  104:  3037 
• 8b Vinke P. de Wit D. de Goede ATJW. van Bekkum H. Stud. Surf. Sci. Catal.  1992,  72:  1 
• Flash chromatography on silica gel lead to the separation of 8.9 mmol of pure benzaldehyde (91% yield of isolated product). All the reactions of Table 1 were carried out according to this procedure with exception of the examples
• 10a

  under air and

• 10b

  under N₂ atmosphere.

• 11 Deminov ET. Denosava TG. Handbook of Antioxidants   CRC Press; New York: 2000. 
• 12a Atkinsen R. Baulsh DL. Cox RA. Hampson RF. Kerr JA. Rossi MJ. Tral J. J. Phys. Chem. Ref. Data  1999,  111:  4923 
• 12b Luo YR. Handbook of Bond Dissociation Energies in Organic Compounds   CRC Press; New York: 2003.  p.62 

9

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.