Thermal Decomposition of 1, 4-Dimethyl-1, 4-bis(methylsubstituted phenyl)-2-tetrazenes

Abstract

1, 4-Dimethyl-1, 4-bis(methyl-substituted pheny1)-2-tetrazenes [1] can be classified into two conformational groups according to spectral data: trans-planar types [1 a, b, c, d] having the methyl groups at 3 or/and 4 positions on phenyl groups, and trans-orthogonal types [1 e, f, g]with the methyl groups at 2 or/and 6 positions on phenyl groups. The rates of thermal decomposition of C have been determined in various protic solvents by means of UV spectroscopy. Rate constants (k) which increase with the polarity of the solvents are in the order [1e]>>[1d]>[1b]> [1c]> [1a]>> [1g]>[1f] in all solvents. A linear relation is found for a plot of ΔH against the solvent polarity parameter (ET). A compensating change is found in ΔH and ΔS for each [1] in various solvents, showing that a single mechanism is operative for the thermal decomposition of [1] in various solvents. On the other hand, the reaction mode differs somewhat between trans-planar and trans-orthogonal types of [1]. The decomposition of [1] appears to proceed via conformational change of trans-planar trans-orthogonal→ cis-orthogonal. Steps a and b are rate-determining step for the decomposition of [1 a, b, c, d] and [1 e, f, g], respectively