Kinetics and mechanism of the reaction of azide with ozone in aqueous solution

The stoichiometry of the reaction of aqueous ozone with sodium azide was studied at pH 12 (mainly) where a yellow metastable intermediate is observed. We propose that this is hypoazidite (N3O-), analogous to hypobromite, and that it plays a central role in the azide catalyzed decompostion of ozone. The yellow Intermediate is unstable in acid, in which it rapidly decomposes, generating N-2 and NO2-. The rate of reaction was studied at pH 2.0-3.5, with the ionic strength at 0.6 M and temperature at 3-15 degrees C. The intrinsic second-order rate constants were found to be k(HN3) less than or equal to approximate to 400 M(-1)sec(-1) and k(N3)- = (8.7 +/- 0.5) x 10(5) M(-1)sec(-1) (3 degrees C, 0.6 M), both in agreement with the only other previous study. The rate constant at 25 degrees C was estimated using the following experimentally determined parameters: In k(N3)- (M(-1)sec(-1)) = (5.73 +/- 0.36) x 10(3)/T (K) + (28.34 +/- 1.27). The value of k(N3)- estimated in this way is (2.5 +/- 0.1) x 10(6)M(-1)sec(-1) at 25 degrees C and 0.6 M. The enthalpy of reaction (Delta H) is -48 +/- 3 kJ mol(-1).