The kinetics and mechanism of the acid-catalysed hydrolysis of nitroalkanes

Abstract

The strong acid-catalysed hydrolysis of nitromethane, nitroethane, and 1-nitropropane in aqueous solution to yield hydroxylamine and the corresponding carboxylic acid has been studied. 2-Nitropropane is not appreciably affected under the conditions examined. The effectiveness of the acids in catalysing the reactions was sulphuric > hydrochloric > perchloric acid. The order of reactivity of the nitroalkanes was nitroethane > 1-nitropropane > nitromethane. The slow rate-determining reaction, with an activation energy of about 25 kcal. mole^–1, appears to be the loss of a proton from the cation RCH₂NO₂H⁺ which competes with the rapid reversible reformation of the normal nitroalkane. The production of hydroxylamine from the aci-nitroalkane is most readily explained in terms of a mechanism which involves a nitrile oxide. It is apparent that the related Nef reaction occurs by a ready reaction between the aci-anion and the hydroxonium ion which does not produce the aci-nitroalkane as usually assumed. In the presence of nitric acid oxidation of the hydrolysis products occurs.