Solvent-Free Basic or KF/Alumina-Assisted Dehydrogenation of Hydrazo Compounds

Abstract

A reduction of organic solvents in the organic chemical industry is of serious importance for sustainable chemistry. With this viewpoint, we successfully established the useful dehydrogenation of hydrazo compounds using basic alumina or KF/alumina ­under solvent-free conditions to afford azo compounds in good to excellent yields.

Key words

solvent-free - alumina - dehydrogenation - hydrazo compounds - azo compounds

References and Notes

• 1a Brennecke JF. Chateauneuf JE. Chem. Rev.  1999,  99:  433 
• 1b Baiker A. Chem. Rev.  1999,  99:  453 
• 1c Jessop PG. Ikariya T. Noyori R. Chem. Rev.  1999,  99:  475 
• 2 Welton T. Chem. Rev.  1999,  99:  2071 
• 3 Solvent-Free Organic Synthesis   Tanaka K. Wiley-VCH; Weinheim: 2003. 
• 4a Preparative Chemistry Using Supported Reagents   Laszlo P. Academic Press; San Diego: 1987. 
• 4b Ono Y. Baba T. Catal. Today  1997,  38:  321 
• 4c Kabalka GW. Pagni RM. Tetrahedron  1997,  53:  7999 
• 4d Minakata S. Mihara M. Sugoh N. Komatsu M. Heterocycles  1998,  47:  133 
• 4e Ono Y. Baba T. Catal.  2000,  15:  1 
• 4f Clark JH. Rhodes CN. Clean Synthesis Using Porous Inorganic Solid Catalysts and Supported Reagents   RSC; Cambridge: 2000. 
• 4g Mihara M. Ishino Y. Minakata S. Komatsu M. Synthesis  2001,  2397 
• 4h Mihara M. Ishino Y. Minakata S. Komatsu M. Synthesis  2003,  2317 
• 4i Mihara M. Ishino Y. Minakata S. Komatsu M. J. Org. Chem.  2005,  70:  5320 
• 4j Mihara M. Ito T. Ishino Y. Oderaotoshi Y. Minakata S. Komatsu M. Tetrahedron Lett.  2005,  46:  8105 
• 5a Shaabani A. Lee DG. Tetrahedron Lett.  2001,  42:  5833 
• 5b Yamaguchi K. Mizuno N. Angew. Chem. Int. Ed.  2002,  41:  4538 
• 5c Bhar S. Chaudhuri SK. Tetrahedron  2003,  59:  3493 
• 6 Kabalka GW. Wang L. Pagni RM. Synlett  2001,  108 
• 7 Mihara M. Ishino Y. Minakata S. Komatsu M. Synlett  2002,  1526 
• 8 Pourjavadi A. Marandi GB. J. Chem. Res., Synop.  2002,  378 
• 9 Bartoli G. Bartolacci M. Giuliani A. Marcantoni E. Massaccesi M. Torregiani E. J. Org. Chem.  2005,  70:  169 
• 10 Zollinger H. Color Chemistry   VCH; Weinheim: 1987. 
• 11 Feigl F. Anger V. Spot Tests in Inorganic Analysis   6th ed.:  Elsevier; Amsterdam: 1972. 
• 12 Shine HJ. J. Am. Chem. Soc.  1956,  78:  4807 
• 13 Dimroth K. Tüncher W. Synthesis  1977,  339 
• 14 Wang C.-L. Wang X.-X. Wang X.-Y. Xiao J.-P. Wang Y.-L. Synth. Commun.  1999,  29:  3435 
• 15 Qiao R.-Z. Zhang Y. Hui X.-P. Xu P.-F. Zhang Z.-Y. Wang X.-Y. Wang Y.-L. Green Chem.  2001,  3:  186 
• 16 Hirano M. Yakabe S. Chikamori H. Clark JH. Morimoto T. J. Chem. Res., Synop.  1998,  770 
• 17 Li X.-C. Wang Y.-L. Wang J.-Y. J. Chem. Res., Synop.  2002,  540 
• 18 Barth M. Shah STA. Rademann J. Tetrahedron  2004,  60:  8703 

19

Basic alumina (lot 20), purchased from ICN, and KF/alumina (batch 16727CO), purchased from Aldrich, were used without further treatment.

20

Azo Compounds - Typical Procedure Hydrazobenzene (1a, 1 mmol) was measured into a 100 mL flask containing KF/alumina (0.5 g). The reaction mixture was stirred at 80 °C for 30 min with blowing air under ambient pressure to obtain a red solid. Then, Et₂O was added to the resulting mixture and filtered on a Büchner funnel to remove the alumina. The alumina was washed with Et₂O and the combined filtrate was concentrated in vacuo. After purification by flash chromatography on silica gel eluting with EtOAc-hexane, azobenzene (2a) was obtained in a yield of 85%.
The reaction was also performed with 1a (10 mmol) and KF/alumina (5 g) following the same procedure except the reaction time. After a heating time of 45 min, 2a was obtained in a yield of 91% by passing through column of silica gel.