Diacetyl, phytochemical reduction

After phytochemical reduction was noted in the case of aldehydes and ketones, interest arose in the behavior of fermenting cells toward compounds containing several carbonyl groups per molecule, such as diketones and quinones. This class deserves special consideration because the simplest representative, diacetyl, as well as its products of reduction, acetylmethylcarbinol (3-hydroxybutanone) and 2,3-butylene glycol, are connected with the metabolism of numerous cells quinones also are biologically important. 

When a racemic substance is hydrogenated or when the reduction leads to the production of centers of asymmetry, the phytochemical reduction will take at first a completely or partially asymmetric course. Examples of such asymmetric reactions are the conversions of pure racemic valeraldehyde, acetaldol, furoin and furil, diacetyl and acetyl-methylcarbinol to optically active alcohols. Occasionally meso forms also arise, as for example in the case off glycols (p. 84). The reasons for the stereochemical specificity of these reactions have not been clarified. This type of phenomenon has frequently been observed in the related intramolecular dismutation of keto aldehydes, especially if enzyme materials of differing origins are used. 

The phytochemical reducibility of quinones was first demonstrated in the case of p-xyloquinone. This compound is worthy of interest since it is very easily formed from diacetyl by purely chemical means through a type of aldol condensation followed by ring closure. It is reduced to p-xylohydroquinone by fermenting yeast. Benzoquinone, thymoquinone and a-naphthoquinone similarly yield the corresponding hydroquinones. Tetrabromo-o-quinone and anthraquinone proved resistant to attack, while phenanthraquinone could be reduced phyto-chemically to phenanthrahydroquinone in poor yield (9%). Phytochemical reduction can also be accomplished in the dicyclic terpene series. According to unpublished experiments by Neuberg and Peiser, 2,3-dihy-... 

The first experiments made by Neuberg and Nord with the simplest diketone, diacetyl, showed at once that this substance can be hydrogenated phytochemically with comparitive ease. Acetylmethylcarbinol appears as an intermediate (see below), and the end product of reduction is asymmetric and levorotatory. Reduction was effected by the action of fermenting yeast on diacetyl. The 2,3-butanediol that is formed can be isolated by alcohol-ether extraction of the fermentation mixture after concentration in the Faust-Heim apparatus or by steam distillation in an atmosphere of carbon dioxide under ordinary pressure it is then carefully concentrated with the birectifier and obtained in the pure state by final fractionation. 

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