The Redox Potential of the Azide/Azidyl Couple

Article abstract of DOI:10.1021/j100292a029

Pulse radiolysis experiments were carried out with neutral aqueous solutions containing azide with iodide, bromide, or thiocyanate to examine possible one-electron transfer rates and equilibria involving the N3 radical/N3(1-) couple.The N3 radical was found to oxidize I(1-) with a rate constant of 4.5E8/M*s.No reaction was observed between I2(1-) radical and N3(1-).With Br(1-), however, the system reached equilibrium, Br2(1-) radical + N3(1-)-><-2Br(1-)+ N3 radical, with k_f = 4.0E8/M*s and k_r = 7.3E3/M²*s.From the equilibrium constant K = 5.5E4 M and the redox potential E(Br2(1-) radical/2Br(1-)) = 1.63 V we calculated E(N3 radical/N3(1-)) = 1.35 +/- 0.02 V vs.NHE.Cyclic voltammetry experiments with N3(1-) showed a single peak on the anodic scan and no peak on the cathodic scan due to the rapid decay of the N3 radicals.From the dependence of peak potential on scan rate we derived E_1/2 for the N3 radical/N3(1-) couple, 1.32 /- 0.03 V vs.NHE.