Radiation Chemical Studies of Azodicarbonamide in Aqueous Solution

Reduction of azocarbonamide by$e{}_{{\rm aq}}{}^{-}$ or by$({\rm CH}_{3})_{2}\dot{{\rm C}}{\rm OH}$ produces a radical anion which undergoes protonation to form a hydrazyl-type radical${\rm H}_{2}{\rm NCONH}\dot{{\rm N}}{\rm CONH}_{2}$. Protonation by H⁺ is diffusion controlled and by H₂ PO₄^- has a rate constant of$1.8\times 10^{8}\ M^{-1}\ {\rm sec}^{-1}$. The reaction of azodicarbonamide with OH takes place with a rate constant of$2.2\times 10^{9}\ M^{-1}\ {\rm sec}^{-1}$. The initial OH adduct$-\dot{{\rm N}}-{\rm N}({\rm OH})-$ rearranges to a$-{\rm NH}-{\rm N}(\dot{{\rm O}})-$ structure and dissociates its proton at pH > 7. Spectral changes due to the rearrangement complicate the absolute measurement of the OH rate constant. Reexamination of the Diamide system showed that the rate constant for the reaction of Diamide with OH is only$4.3\times 10^{9}\ M^{-1}\ {\rm sec}^{-1}$ and that the previously reported higher values are incorrect. ESR experiments were carried out to support the determination of radical structures. Steady-state radiolysis experiments showed that azodicarbonamide is destroyed very efficiently by all the primary radicals and also by the t-butanol radical with G ∼ 6 under most conditions.