Theoretical studies on the stability of phenylpentazole and its substituted derivatives of –OH, –OCH3, –OC2H5 and –N(CH3)2

Abstract

Phenylpentazole (PhN₅) and its derivatives with 1–3 electron donating substituents (–OH, –OCH₃, –OC₂H₅ and –N(CH₃)₂) were studied using density functional theory. The pyrolysis mechanism and effects of substituents on stabilities were discussed. The activation energies (E_as, 362–402 kJ mol⁻¹) for the cleavage of the C–N bonds linking the aryl and the pentazole are far larger than those (109–117 kJ mol⁻¹) for the breaking of the N–N bonds in the pentazole ring. Decomposition of the pentazole ring should be the initial step of pyrolysis of arylpentazole and its derivatives. The pentazole ring in PhN₅ is stabilized by substituents which increase the electron density and strengthen the delocalization of the N₅ ring. The abilities of these substituents to improve E_a and to decrease the frontier orbital energy gap (E_g) have the same order: –N(CH₃)₂ > –OC₂H₅ > –OCH₃ > –OH.