A New Method for the Nitrosation of 1,3-Diketones Applied to 3-Ethyl- and 3-Methyl Pentane-2,4-dione

The nitrosation of 3-ethylpentane-2,4-dione (EPD) and 3-methylpentane-2,4-dione (MPD) has been performed in aqueous acid medium following a new procedure for sample preparation. The two reagents, diketone and sodium nitrite, were mixed together in alkaline medium to give the corresponding enolate (E-) and nitrite ion (NO2-). The enol nitrosation reaction starts after acidifying the reaction medium. Different experimental conditions were tested in order to adapt the reaction time scale to conventional or stopped-flow UV-vis spectrophotometry. The objectives of this study were to demonstrate that the decomposition of nitrous acid is negligible in the time scale of the nitrosation reaction and to corroborate the published reaction mechanism for the nitrosation of some 3-substituted diketones that it was assumed to proceed through a chelate nitrosyl intermediate. The results were compared with that obtained when the last reagent, normally the ketone, was added over an acid mixture of the rest of the reactants, that is, the protocol followed in previously published studies.