Well-degradation

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The well-reduction (or also known as well-reaction or well-sugar reduction ) is a name reaction of organic chemistry . The reaction was named after the German chemist Alfred Wohl (1863–1939) who discovered it. This is a degradation of an aldose that is shortened by one carbon atom using a reverse Kiliani-Fischer synthesis . In this way, any smaller aldoses can be produced, such as ribose , which is known to be found in RNA ( ribonucleic acid ), ADP ( adenosine diphosphate ) and AMP ( adenosine monophosphate ).

Overview reaction

Probably degradation overview reaction V4.svg

This reaction is about shortening the carbon chain of a sugar. This is achieved by reacting the sugar with acetic anhydride (acetic anhydride), hydroxylamine , sodium acetate , sodium methoxide and hydrochloric acid . Deacylation can then be carried out in order to obtain the sugar.

Reaction mechanism

The following reaction mechanism comes from the book Comprehensive Organic Name Reactions and Reagents and is only one possible reaction mechanism:

Probably degradation reaction mechanism V2a.svg

The aldohexose ( 1 ), shown as a cyclic hemiacetal in Fischer projection , suffers from ring cleavage when hydroxylamine is added . This happens when the hydroxylamine attaches to the carbon atom with the strongest positive charge and a hydroxyl group is formed. By shifting the electrons, an oxime ( 2 ) can be created, for this purpose a proton is split off from the nitrogen and the hydroxyl group from the carbon atom. Subsequently, sodium acetate and acetic anhydride (in this reaction mechanism with "Ac 2 O" hereinafter, where "Ac" an acetyl group ) has been added, whereby an acetylation was performed. When the solution is heated to over 110 ° C, acetic acid is split off and nitrile ( 3 ) is formed. The resulting nitrile ( 3 ) is then reacted with sodium methoxide , in which case sodium cyanide is split off and replaced by methanolate. The hydrochloric acid now ensures that methyl acetate is split off, creating an aldehyde ( 4 ) - a four-fold acetylated aldopentose. Then only the deacetylation has to be carried out, which creates the aldopentose ( 5 ).

Individual evidence

  1. ↑ a b Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , p. 3057.
  2. ↑ a b A. Probably: Degradation of glucose . In: Reports of the German Chemical Society . 26, No. 1, 1893, pp. 730-744. doi : 10.1002 / cber.189302601150 .
  3. ↑ M. Windholz (Ed.): The Merck Index . Ninth Edition. Merck & Co., 1976, pp. ON-95, ISBN 978-0-911910-26-1 .