Nitrosation of Meldrum's acid (2,2-dimethyl-1,3-dioxane-4,6-dione) and ethyl acetoacetate

Abstract

At low acidity (below ca. 0.1 mol dm^–3), nitrosation of Meldrum's acid in water takes place via the carbanion (or enolate), both for reactions of H₂NO₂⁺/NO⁺ and XNO species [X = Cl, Br, SCN and ⁺SC(NH₂)₂], whereas at higher acidities another pathway takes over involving reaction via the enol tautomer. These two pathways have been clearly identified kinetically by different dependencies of their rate constants upon the acidity of the solution. In neither case is the ionisation to the carbanion or the enolisation rate-limiting. The carbanion is, as expected, much more reactive than is the enol, and some of its reactions occur at the encounter limit. In contrast, the less acidic ethyl acetoacetate reacts entirely via the enol form, under all conditions. The results from both substrates are compared and discussed, together with other published results in this area.