Diketones, phytochemical reduction

Preparation and phytochemical reduction of 2,2 -thenoin and 2,2 -thenil have been studied in the authors laboratory (20a). It has been shown that 2,2 -thenoin gives a color reaction similar to that shown by benzoin and other acyloin condensation products in- the presence of alcoholic alkali. The hydroxy ketone may be oxidized by iodine in the presence of sodium methoxide to give the diketone, 2,2 -thenil, in excellent yields. Phytochemical reduction was shown also to be applicable to both compounds. It is significant that thenoin differs from benzoin, since reduction products were not obtained enzymatically from the latter. 

Due to the close relationship between certain a-hydroxy ketones, the acyloins and a-diketones, their behaviors during phytochemical reduction have been treated together (see pp. 86-89). 

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. 

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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