Oxidation of hydrazine by nitric acid

Abstract

Hydrazine is oxidized by hot nitric acid in a first-order reaction to produce N/sub 2/, N/sub 2/O, HN/sub 3/, and NH/sub 4//sup +/. The rate law for the reaction is -d ln (N/sub 2/H/sub 4/)/dt = k(NO/sub 3//sup -/)(H/sup +/)/sup 2/ where k = 5.8 x 10/sup -5/ M/sup -3/ min/sup -1/ at 100/sup 0/C in 5.44 M HNO/sub 3/ and ..mu.. = 6. The data are consistent with a reaction mechanism that involves HN/sub 3/, HNO/sub 2/, and the N/sub 2/H/sub 2/, and the N/sub 2/H/sub 2/ free radical as intermediates and N/sub 2/, N/sub 2/O, and NH/sub 4//sup +/ as products. The Arrhenius equation constants over the temperature range 70-100/sup 0/C were A = 1.2 x 10/sup 11/ M/sup -3/ min/sup -1/ and E = 26 kcal/mol. The reaction is catalyzed by Fe/sup 3 +/, and the rate data are correlated by the semiempirical expression ln((N/sub 2/H/sub 4/)/(N/sub 2/H/sub 4/)/sub 0/) = -(a'(Fe/sup 3 +/) + b'(Fe/sup 2 +/))(H/sup +/)t where a' = 0.114 M/sup -2/ min/sup -1/ and b' = 0.065 M/sup -2/ min/sup 71/. A reaction mechanism is proposed for the ferric-catalyzed reaction whose major reactions involve the reduction of Fe/sup 3 +/ to Fe/sup 2more » +/ by hydrazine and the oxidation of Fe/sup 2 +/ to Fe/sup 3 +/ by nitric acid. 21 references, 12 figures, 6 tables.« less