Pretreatment of secobarbital (I) with hydrochloric acid and hydrogen peroxide was found to make it possible to determine I by the dimethylglyoxime-thiosemicarbazide method used generally for the determination of barbituric acids and, in order to elucidate this reaction mechanism, reaction of I with hydrochloric acid and hydrogen peroxide was examined and a reaction product (IV) was isolated. Treatment of I by the same procedure as for barbital does not result in this reaction but allobarbital and allylisobutylbarbital, having an allyl group, underwent this reaction to give the respective products V and VI. Structural determination of IV, V, and VI was carried out from infrared, nuclear magnetic resonance, and mass spectra, and elemental analyses of IV, V, and VI, and their acetyl derivatives. It was thereby found that IV is 5-(3 -chloro-2-hydroxypropyl)-5- (1-methylbutyl) barbituric acid, V is 5, 5-bis (3-chloro-2-hydroxypropyl) barbituric acid, and VI is 5-(3-chloro-2-hydroxypropyl)-5-isobutylbarbituric acid. These experimental results showed that pretreatment of I with hydrochloric acid and hydrogen peroxide results in the introduction of Cl and OH into the allyl group to form IV which is easily decomposed by sodium hydroxide alkalinity and the product colors with the dimethylglyoxime thiosemicarbazide reagent.
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