Graduate Thesis Or Dissertation

 

An investigation of the reduction products of 4-amino-2, 6-dichloropyrimidine by catalytic hydrogenation Public Deposited

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  • In recent years nuclear reduction of pyrimidines by catalytic hydrogenation in acid media has been considered a possible synthetic method for the preparation of substituted tetrahydropyrimidines. This technique has the advantage of simplicity over the older condensation methods and is limited only by the preparation of the appropriately substituted pyrimidines. During an investigation of the scope of this nuclear reduction technique, Aft and Christensen found that the tetrahydropyrimidines could not be isolated in pure form as the hydrochloride salts, as shown by deviations between the corresponding actual and theoretical chloride percentages. These surprising results suggested that the nuclear reduction reaction in acid media was not straightforward, contrary to the results of earlier studies, but yield mixtures as shown by paper chromatographic analysis consisting of degradation products along with the desired tetrahydropyrimidine. In order to get a better understanding of the nature of this nuclear reduction reaction, an investigation was undertaken to identify the corresponding degradation products of one of these nuclear reductions. 4-Amino-2, 6-dichloropyrimidine was chosen for the investigation since it was found by Aft and Christensen to undergo considerable degradation during nuclear reduction. 4-Amino-2, 6-dichloropyrimidine upon nuclear reduction would be expected to yield 4-amino-3, 4, 5, 6-tetrahydropyrimidine which upon decomposition could form low molecular weight products such as methylamine, propylamine, ammonia, propanol, etc. which should be easily detected by gas-chromatography. Upon basification of the isolated hydrochloride salts of the reduction products basic material was collected which was found to contain five components by gas chromatography, four of which were identified as ammonia, n-propylamine, propionaldehyde, and n-propanol. Gas chromatographic analysis of the reaction mixture before isolation of the hydrochloride salts showed that carbon dioxide, but not propionaldehyde and n-propanol, was among the reduction products. It was, therefore, concluded that propionaldehyde and n-propanol must have been formed by basic hydrolysis of the tetrahydropyrimidine set free during basification of the hydrochloride salts, and a mechanism was postulated for the formation of ammonia, n-propylamine, and carbon dioxide during nuclear reduction of 4-amino-2, 6-dichloropyrimidine. According to this mechanism, 4-amino-3, 4, 5, 6-tetrahydropyrimidine undergoes hydrolysis in the aqueous acid media yielding the degradation products, accounting for both the low yields and impure nature of this tetrahydropyrimidine obtainable from the nuclear reduction reaction.
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