Synthesis and hydrolysis of substituted tetrahydropyrimidinium salts. Behaviour of the degradation products on varyingpH

Autor: Liliana Orelli, Mónica Dalmaso, Beatriz M. Fernández, Ana M. Reverdito, I. A. Perillo
Rok vydání: 1991
Předmět:
Zdroj: Journal of Heterocyclic Chemistry. 28:273-281
ISSN: 1943-5193
0022-152X
Popis: Reaction of 1,2-diaryl-3-methyl-1,4,5,6-tetrahydropyrimidinium iodides 1a-i with alkaline solutions afforded N-aroyl-N-aryl-N'-methyltrimethylenediamines 2a-i. Compounds 2 are stable under acid conditions but in neutral or alkaline media spontaneously rearrange giving N-aroyl-N'-aryl-N-methyltrimethylenediamines 3a-i. Treating compounds 3 with concentrated acids reverse reaction takes place. Kinetic studies were performed on this intramolecular N N' aroyl transfer over the Ho-pH range -0.9 to 2.30. Compounds 3 undergo acyl transfer to give 2 by a mechanism which involves a change in the rate determining step from formation to acid-catalysed decomposition of a six-membered heterocyclic intermediate on going from Ho to pH values. The existence of maxima in the pH rate profile allow to determine apparent pKa values of the hexahydropyrimidine intermediates which gave good correlation with the Swain F substituent constants. Stability of these heterocycles was also predicted by determination of thermodinamic parameters. Comparisons are made with the behaviour of five-membered heterocyclic intermediates (imidazolidine derivatives) which were studied in an earlier paper.
Databáze: OpenAIRE
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