Reactions of alkylnitrosoureas in aqueous solution

Abstract

The acid- and base-catalyzed decompositions of N-methyl-,N,N'-dimethyl-, and N,N',N'-trimethyl-N-nitrosourea in aqueous solution have been studied. Below pH 2, the N-methyl compound undergoes both denitrosation and hydrolysis to yield methylurea, nitrous acid, methylamine, nitrogen, and carbon dioxide. The acid-catalyzed denitrosation and hydrolysis of the trimethylnitrosourea are somewhat more rapid than the corresponding reactions of N-methyl-N-nitrosourea. The solvent isotope effect, k/sub H/sub 2/O//k/sub D/sub 2/O/ = 1.3, and the absence of chloride ion catalysis suggest that the denitrosation reaction proceeds by a rate-determining proton transfer which is followed by the rapid loss of the nitroso group. The results for the hydrolysis reaction are compatible with a formulation in which a hydrate of the nitrosourea is protonated in a rate-determining step to form a tetrahedral intermediate which subsequently decomposes to yield methyldiazonium hydroxide and a carbamic acid derivative. The base-catalyzed reactions of the mono, di-, and trimethylnitrosoureas are first order in hydroxide ion over a broad pH range. The hydrolysis of N-methyl-N-nitrosourea yields methanol and derivatives of carbamic acid. Salt effects on the reaction rate are negligible except for the influence of lithium ion. The rate constants for the hydrolysis of the mono- and dimethyl compounds depend upon the buffer concentrationat pH 9.5.more » The rate constants for the hydrolysis of the trimethyl compound also depend upon the buffer concentration, but a limiting value is not achieved. The solvent isotope effect for the base-catalyzed reaction, the exchange reaction of water-/sup 18/O with the carbonyl group of the urea, and the fact that N-methyl-N-nitrosourea is hydrolyzed about 2.2 x 10/sup 4/ times more rapidly than N,N',N'-trimethyl-N-nitrosourea suggest that the hydrolysis occurs by a mechanism in which a tetrahedral intermediate is formed.« less