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Unformatted text preview: The Wolff-Kischner Reduction: A Special Use of Hydrazones Aldehydes and ketones are reduced to methyl (CH 3 ) and methylene (CH 2 ) groups by the Wolff-Kischner reduction that occurs by way of hydrazones in the presence of concentrated hydroxide solution and high temperature (~200 o C). C CH 2 CH 2 CH 3 O = (i) H 2 NNH 2 (ii) KOH, 200 o C CH 2 CH 2 CH 2 CH 3 The synthetic pathway involves formation of a hydrazone in step (i) that undergoes reductive cleavage in step (ii) in the presence of base at high temperature. C- R O = C- R NNH 2 = ketone or aldehyde hydrazone CH 2- R (i) (ii) A Mechanism for the Wolff-Kischner Reduction Ar-C=O R (i) hydrazone formation + H 2 NNH 2 Ar-C=N-NH 2 R + H 2 O (ii) Ar-C=N-NH 2 R : : reductive cleavage (at high temperature) Ar-C=N-NH R : : :- Ar-C-N=NH R : : :- H 2 O HO- proton transfer Note: This step involves a base-catalyzed isomerization of the hydrazone to an azo compound....
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This note was uploaded on 10/20/2009 for the course CHEM 322BL at USC.
- Organic chemistry