Radiation chemistry of aqueous solutions of hydrazine at elevated temperatures. Part 1.—Oxygen-free solutions

Abstract

Rate constants for the reactions of eaq– and ˙OH with N2H4 and N2H5+ in liquid water up to 200 °C have been measured by pulse radiolysis. Linear Arrhenius plots for the reactions of eaq– gave k(20 °C)= 106 and 1.6 × 108 dm3 mol–1 s–1, and Ea= 13.5 and 18.2 kJ mol–1, respectively. H is the product of the reaction with N2H5+. Non-linear Arrhenius behaviour was observed for the reactions of ˙OH with k(20 °C)= 4.5 × 109 and 8.2 × 107 dm3 mol–1 s–1, respectively. The pKa of N2H5+ decreases linearly with temperature from 8.1 at 20 °C to 4.2 at 200 °C. The products of the ˙OH reactions are ˙N2H3 and ˙N2H4+, respectively, and the pKa of ˙N2H4+ also decreases with increasing temperature. The self-reaction of ˙N2H3 shows the same temperature dependence as that of ˙OH with k(20 °C)= 2 × 109 dm3 mol–1 s–1. The product of this reaction is tetrazene. Up to 200 °C the data are consistent with successive eliminations of NH3 to form triazene and then N2. The pH-dependent kinetics of these processes indicate that the decomposition of N3H3 is acid- and base-catalysed over the whole temperature range.