Kinetics and mechanism of degradation of some 5-allylbarbituric acid derivatives. Part 3: Kinetics of solvolysis of major intermediates of 5.5-diallylbarbituric acid degradation.

Solvolysis of N-diallylacetylurea and 5.5-diallylmalonuric acid was investigated in the pH range ca. 8--12 by means of spectrophotometric and t.l.c. methods. Their log k--pH profiles were constructed from the experimental results obtained by degradation at 70 degrees C. Therefore, specific catalytic rate constants and pKa's were derived. The kinetic mechanism of N-diallylacetylurea solvolysis, resulting among other things from the so-called kinetic salt effect, depends on hydroxyl-ion attack on its undissociated and monoanionic forms. However, the degradation of alpha.alpha-diallylmalonuric acid in the pH range 10--12 is an example of specific base catalysis which can be explained by hydroxyl-ion attack on its monoanionic species. The degradation of alpha.alpha-diallylmalonuric acid below pH=10 does not follow a theoretical equation postulated, because the spectrophotometric method does not allow monitoring the formation of N-diallylacetylurea in the presence of the above acid. Thin-layer chromatography was used to check different pathways of transformations of the intermediate studies.