Hydrazine Oxidation in Aqueous Solutions II: N ₄ H ₄ Decomposition

Abstract The reaction mechanism for the N 2 H 4 homogeneous oxidation in aqueous solutions is more complex than its heterogeneous electrochemical oxidation on the electrode surfaces. Homogenous oxidation of a mixture of non‐labeled ( 14 N 2 H 4 ) and 15 N‐labeled ( 15 N 2 H 4 ) hydrazine in aqueous solutions produces 14 N 15 N, indicating the intermediate existence of N 4 H 6 or N 4 H 4 intermediates with subsequent hydrogen transfers and splitting lateral N─N bonds. To explain the key part of the hydrazine oxidation reaction, the structures, thermodynamics, and electron characteristics of N 4 H 4 in aqueous solution are investigated. Unlike N 4 H 6 , we have not found any spontaneous splitting of the bond between the lateral nitrogens in N 4 H 4 . The most probable products of N 4 H 4 disproportionation are H 2 N─NH 2 and N 2 , which are obtained by splitting the bond between the central nitrogen atoms, and so only 15 N 2 and 14 N 2 molecules are formed. Additionally, the formation of H 3 N─NH and N 2 products is also preferred to structures without N─N fissions. The formation of H 2 N═N and HN═NH is energetically less advantageous. Cyclo‐N 4 H 4 structures are stable, without any N─N fissions, but their energies indicate their vanishing abundance in aqueous solution, so their involvement in hydrazine oxidation is highly improbable. Unlike N 4 H 6 , the oxidation of hydrazine to 14 N 15 N molecules cannot be explained by N 4 H 4 intermediates.