The chemistry of nitroso-compounds. Part VIII. Denitrosation and deamination of N-n-butyl-N-nitrosoacetamide in aqueous acids

Abstract

Decomposition of N-n-butyl-N-nitrosoacetamide in aqueous acid at 25 °C involves both deamination and denitrosation. Both reactions occur concurrently via different conjugate acid intermediates, with denitrosation becoming predominant at high acidity. Acidity dependences, activation parameters, and solvent deuterium isotope effects [k(H₂SO₄)/k(D₂SO₄)ca. 0·74] show that deamination involves rate-limiting attack by H₂O on an O-conjugate acid, formed in a rapid pre-equilibrium. For denitrosation, proton transfer to the amide nitrogen atom is considered rate limiting because of the substantial solvent deuterium isotope effects [k(H₂SO₄)/k(D₂SO₄)ca. 1·9] and general acid catalysis [k(H₂SO₄) > k(HCIO₄)]: the N-conjugate acid formed breaks down rapidly to products. The unusual slow proton transfer to nitrogen observed is related to the very low basicity of this atom (pK_Aca.–15). These results are discussed in relation to carcinogenesis by N-nitroso-compounds and it is shown further that the nitrosation of amides cannot be catalysed by nucleophilic species (e.g. CI^–) as hitherto supposed.