Alkaline hydrolysis of N-nitroso-2-imidazolidone

Abstract

The hydrolysis of N-nitroso-2-imidazolidone has been studied kinetically between pH 8.3 and 12.6. This nitroso compound has an acid–base equilibrium whose constant has been determined spectrophotometrically (pK_a 11.45). Only the acid form is reactive. At pH < 10 hydrolysis is of order less than one with respect to OH^– and is subject to general base catalysis. These results are interpreted in terms of a mechanism involving an initial steady-state hydrate whose decomposition by base leads to the final products. At pH > 10 reaction paths of orders one and two in OH^– appear. The second-order term reflects general base catalysis superimposed on a first-order term in OH^–(the bases dimethylamine, sarcosine, piperidine, and HPO₄^2– have been used). The results are interpreted by an initial OH^– attack on the carbonyl group of the nitroso compound to give an intermediate which in the rate-controlling step reacts with bases, among them water (which explains the first-order term with respect to OH^–). The low value of the Brønsted relation (βca. 0) and the fact that the intermediate possesses no proton yielding a low pK_a value suggest that there is inverse classical general base catalysis.