The technetium-catalysed oxidation of hydrazine by nitric acid

Abstract

Technetium catalyses the oxidation of hydrazine by nitric acid, a reaction which is otherwise very slow except at elevated temperatures and acidities. The reaction displays an induction period followed by a rapid destruction of hydrazine. The induction period covers an initial slow reduction by hydrazine of technetium(VII) to technetium(IV) (the initiation phase) followed by a rapid technetium(IV)-catalysed reduction of technetium(VII) by hydrazine (the induction phase). The fast reaction commences when technetium(VII) has been substantially reduced to technetium(IV). The mechanism of the fast reaction is considered to be the oxidation of technetium(IV) to technetium(VI) by nitrate, followed by reduction of technetium(VI) to technetium(IV) by hydrazine; nitrite produced in the oxidation of technetium(IV) reacts with another molecule of hydrazine to produce hydrazoic acid. On completion of the reaction, technetium is present predominantly as pertechnetate. However, traces of a coloured species are produced during the reaction and this is considered to be an analogue of Eakins Pink Compound ( trans-[(NH 3) 4Tc(NO)(OH 2)] 2+) which is formed by the reaction between hydrazine and technetium(IV). Hydrazoic acid is unstable in the system and is degraded, in part at least, to ammonium nitrate.