Osazone

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As osazones one calls the phenylhydrazone of sugars . Unlike normal hydrazones of aldehydes or ketones, however, osazones cannot be called true derivatives of the original sugar, because the structure of the sugar at the atom changes in the course of the reaction through a redox reaction .

history

Emil Fischer discovered in 1874 during work on the diazotization of aniline the phenylhydrazine , later it was used for the characterization of sugars .

presentation

Aldoses with three equivalents of phenylhydrazine form two-fold hydrazones at the - and - atoms, so that one chiral center disappears and the identification of the - epimers becomes possible. The formation of the osazone is shown as follows:

Formation of an osazon by reacting a monosaccharide with three molecules of phenylhydrazine. Please refer to the text for details.

A monosaccharide ( 1 , abbreviated by R ), for example glucose , is combined with phenylhydrazine to form a phenylhydrazone ( 2 ) with elimination of water . If further phenylhydrazine is converted in the reaction, this dehydrates the alcohol group of the sugar which is adjacent to the carbonyl group . This creates aniline and ammonia . An osonhydrazone ( 3 ) is formed as an intermediate product . Finally, a third molecule of phenylhydrazine reacts with the carbonyl group, creating an osazone ( 4a ). This is stabilized by an intramolecular hydrogen bond ( 4b ).

It is not known why an osazone cannot react with another molecule of phenylhydrazine. In the case of glucose, the hydroxyl group on the C3 atom would come into question.

properties

Osazones are yellow, easily crystallizing substances. After the action of strong acids or by boiling in benzaldehyde , an oson can be made from an osazone . Osones are α-ketoaldehydes.

Chemical meaning

Osazone formation is mainly used for the separation and characterization or identification of sugars via the melting point. The - epimers glucose and mannose (both aldoses ) and fructose (a ketose ) give the same osazone in the reaction.

Individual evidence

  1. ^ Wittko Francke and Wolfgang Walter: Textbook of organic chemistry. S. Hirzel Verlag Stuttgart; 24. revised 2004 edition, ISBN 3-7776-1221-9 ; P. 460.
  2. L. Mester, H. El Khadem, D. Horton: Structure of saccharide osazones . In: Journal of the Chemical Society C: Organic . No. 18 , 1970, pp. 2567-2569 , doi : 10.1039 / J39700002567 .