Enols derived from malonic acids as intermediates in nitrosation and halogenation

Article abstract of DOI:10.1016/S0040-4020(01)80471-3

Malonic acid, methylmalonic acid, ethylmalonic acid and phenylmalonic acid react with electropholic nitrosating agents and also with bromine and iodine via their corresponding enol or enolate forms. In most cases it is possible to make either the enolisation or reaction of the enol rate-limiting by a suitable choic of reactant concentrations and reactivity. The enolisation rate constants agree resonably well with literature values where they exist. We propose minimum figures of 1.0 x 10^-8 and 1.6 x 10^-8 respectively for K(E) the enolisation equilibrium constant for malonic acid and methylmalonic acid. The kinetic term second order in [malonic acid] or its derivatives (when enolisation is rate limiting) has been shown to arise from a base catalysed component to the reaction brought about by the malonate ion, which dominates at pH values greater than ca. 3.