Mechanism of the monomolecular thermal decomposition of 1,5- and 2,5-disubstituted tetrazoles

The kinetic parameters of the thermal decomposition of several pairs of 1(2)-R-5-R′-disubstituted tetrazoles have been determined using the manometric method. The isomers differ only by the position of the substituents linked with the heterocyclic nitrogen atom. The activation entropies are equal to ca. +8 cal mol−1 K−1, the activation energies range from 39 to 48 kcal mol−1. A linear correlation between the logarithms of the rate constants of decomposition of the isomers has been established. The limiting stages of the stepwise mechanism of the monomolecular decomposition, which determines the experimental rates of nitrogen evolution, include the reversible formation followed by decomposition of intermediate azidoazomethines in the case of 1,5-disubstituted tetrazoles and azodiazo compounds for isomeric 2,5-disubstituted tetrazoles. The enthalpies of formation of R(N3)C=NR (R = Me, Ph), C2H3(N3)C=NMe and increments Δf H°[Cd−(C)(N3)], Δf H°[Cd-(Cb)(N3)], and Δf H°[Cd−(Cd)(N3)] have been estimated.