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Synthesis of phenobarbital -2-14C

✍ Scribed by H. A. Dugger; E. Oppenheimer

Publisher: John Wiley and Sons
Year: 1974
Tongue: French
Weight: 108 KB
Volume: 10
Category: Article
ISSN: 0022-2135
DOI: 10.1002/jlcr.2590100120

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✦ Synopsis

The previously reported synthesis of phenobarbital-2-l4C (1) and those of other barbituric acids labeled in the 2-position with carbon-14 (2,3), have employed the base catalysed condensation of the corresponding ester with urea. Although this reaction gives 60-809 yields of various 5,5 dialkyl substituted barbituric acids, attempts in our laboratories to obtain economically satisfactory amounts of phenobarbital-2-14C using this reaction resulted in erratic yields varying from 6-20%. An analysis of the reaction mixture indicated that instead of condensing with urea the diethyl ethylphenylmalonate was undergoing decarboxylation to give sodium carbonate and ethyl a-phenylbutyrate. This side reaction in the preparaion of varicxls substituted barbituric acids was previously noted but was reportedly overcome by using an excess of urea, and avoiding a large excess of base. Since an excess of urea-14C was not practical, an old synthesis first reported by Fischer and Dilthey (5) for 5,5-dialkyl barbituric acids and later reported as a method for phenobarbital (6) was investigated. This synthesis involved heating the ethyl-

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