Investigation of Unexpected Reaction Intermediates in the Alkaline Hydrolysis of Methyl 3,5-Dinitrobenzoate

Abstract

An experimental project aimed at identifying stable reaction intermediates is described. Initially, the studied reaction appears to involve the simple hydrolysis, by aqueous sodium hydroxide, of methyl 3,5-dinitrobenzoate dissolved in dimethyl sulfoxide. On mixing the substrates, however, the reaction mixture unexpectedly turns an intense red in color, a phenomenon that is explained by the generation of stable Meisenheimer complexes following aromatic nucleophilic attack by the hydroxide ion. UV–vis and 1H NMR spectroscopic techniques are employed as analytical tools to follow the reactions and to identify both the intermediates and the final end product. Kinetic and thermodynamic effects associated with the concurrent reactions involving aromatic nucleophilic attack and carbonyl attack (hydrolysis) are invoked to explain the time course of formation of the intermediates and the final product (sodium 3,5-dinitrobenzoate). At the conclusion of the project, students should be able to construct a working hypothesis concerning the mechanism of the reaction sequence.