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Direct carbonylation of aromatic semi-carbazones and azines Millward, Stewart

Abstract

Benzophenone semicarbazone reacted with carbon monoxide at about 300 atmospheres and at 235-245° in the presence of preformed dicobalt octacarbonyl as catalyst to yield 3-phenylphthalimidine (XXXVII), 3-phenyl-2-(N-benzhydrylcarboxamido)phthalimidine (XXXIV), N,N’-dibenzhydrylurea (XXXV), and N-benzhydrylurea (XXXVI). At 200-220° benzophenone semicarbazone gave N-benzhydrylurea (XXXVI), benzophenone azine (XXXVIIl), and benzophenone 4benzhydrylsemicarbazone (XXXJX). When the reaction temperature was further reduced to 175-180°, benzophenone semicarbazone did not produce the carbonylation product obtained in the second experiment but only the degradation and reduction products, XXXVIIl and XXXIX respectively. Carbonylation of benzophenone azine (XXXVIIl) at 235-245° produced 3-phenylphthalimidine (XXXVIl), whereas carbonylation of benzophenone 4-benzhydrylsemicarbazone at the same temperature yielded 3-phenylphthalimidine and 3-phenyl-2-(N-benzhydryl-carboxaraido)phthalimidine (XXXIV). An independent synthesis of the latter compound and of benzophenone 4-benzhydrylsemicarbazone, both in good yield, has been carried out. When benzaldehyde semicarbazone was carbonylated at 200-220° only the degradation product, benzaldehyde azine (XLIl) was formed. Increasing the temperature to 235-245° did not alter the course of the reaction. Carbonylation of benzaldehyde azine at 235-245° yielded 2-benzylphthalimidine (XLVIIl), phthalimidine (L), and 2-(N-benzyl-carboxamido)phthalimidine (XLVI). The significance of the presence of phthalimidine and 2-(N-benzylcarboxaraido)phthalimidine in the carbonylation products of benzaldehyde azine is discussed in regard to the mechanism of the cyclization reaction. A mechanism is proposed for the cyclization reaction and evidence is presented in support of the proposal. The ureido group (-NHCONH₂) or its degradation products has been shown to have an inhibitory effect on the catalytic activity of dicobalt octacarbonyl. An independent synthesis of 2-(N-benzyIcarboxamido)phthalimidine is also reported.

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