RADIATION-CHEMISTRY OF AQUEOUS-SOLUTIONS OF HYDRAZINE AT ELEVATED-TEMPERATURES .1. OXYGEN-FREE SOLUTIONS

Rate constants for the reactions of e(aq)(-) and (OH)-O-. with N2H4 an d N2H5+ in liquid water up to 200 degrees C have been measured by puls e radiolysis. Linear Arrhenius plots for the reactions of e(aq)(-) gav e k(20 degrees C) = 10(6) and 1.6 x 10(8) dm(3) mol(-1) s(-1), and E(a ) = 13.5 and 18.2 kJ mol(-1), respectively. H is the product of the re action with N2H5+. Non-linear Arrhenius behaviour was observed for the reactions of (OH)-O-. with k(20 degrees C) = 4.5 x 10(9) and 8.2 x 10 (7) dm(3) mol(-1) s(-1), respectively. The pK(a) of N2H5+ decreases li nearly with temperature from 8.1 at 20 degrees C to 4.2 at 200 degrees C. The products of the (OH)-O-. reactions are (N2H3)-N-. and (N2H4+)- N-., respectively, and the pK(a) of (N2H4+)-N-. also decreases with in creasing temperature. The self-reaction of (N2H3)-N-. shows the same t emperature dependence as that of (OH)-O-. with k(20 degrees C) = 2 x 1 0(9) dm(3) mol(-1) s(-1). The product of this reaction is tetrazene. U p to 200 degrees C the data are consistent with successive elimination s of NH3 to form triazene and then N-2. The pH-dependent kinetics of t hese processes indicate that the decomposition of N3H3 is acid- and ba se-catalysed over the whole temperature range.