Radiation chemistry of aqueous solutions of hydrazine at elevated temperatures .2. Solutions containing oxygen

The rate of reaction for (N2H3)-N-. + O-2 --> O-2(.-) + N2H2 + H+ (1) has been measured by pulse radiolysis up to 110 degrees C in aqueous solutions of hydrazine having a pH of 10.3 at room temperature. The values of the kinetic parameters are k(1) = (3.8 +/- 0.1) x 10(8) dm(3) mol(-1) s(-1) at 20 degrees C and E-act = 5.6 +/- 21 kJ mol(-1), This small activation energy is interpreted in terms of the formation of an intermediate adduct (N2H3O2)-N-. which is in a pre-equilibrium with the reactants and whose stability with respect to dissociation back to the reactants decreases with increasing temperature. The rate of the thermal reaction N2H4 + O-2 --> products (12) has also been determined up to 110 degrees C by measuring the decrease in k(1) with increasing age of the oxygenated hydrazine solution in order to monitor the depletion of [O-2]. The kinetic parameters are k(12) = (1.2 +/- 0.8) x 10(-3) dm(3) mol(-1) s(-1) at 20 degrees C and E-act = 70 +/- 5 kJ mol(-1). gamma-Radiolysis studies show that N2H4 is destroyed in a short chain reaction in oxygenated hydrazine solutions with G(-N2H4) proportional to (dose rate)(-05), indicating chain termination by radical-radical reactions. Added EDTA shortens the chain but does not alter the form of the rate law, indicating that metal ions present as impurities accelerate the chain-propagating reactions more than the termination steps. In each case the chain length increases as ca. [N2H4](0.5).