Experimental and theoretical investigation into the decomposition mechanism of 3,5-dimethyl-4-hydroxyphenylpentazole

3,5-Dimethyl-4-hydroxyphenylpentazole (DHPP) has attracted considerable interest as the most promising precursor for preparing cyclopentazolate (cyclo-N₅^-) anions reported to date. However, there is limited information available regarding its structural properties and thermal stability, which hinders the large-scale preparation of cyclo-N₅^- anions. In this study, optical microscopy and a microgas flowmeter were employed to visualize the rate of gas release during DHPP decomposition, providing insights into its physical properties. Low-temperature ultraviolet-visible (UV-Vis) spectroscopy analysis revealed that the methanol solution of DHPP remains stable at a critical temperature of - 20 °C. Furthermore, the crystal structures of 3,5-dimethyl-4-hydroxyphenylazide (DHPA), 2,6-dimethylbenzoquinone (DBQ), and 4-(4-hydroxy-3,5-dimethylphenyl)imino-2,6-dimethylcyclohexa-2,5-dienone (IDCD) were determined using single-crystal X-ray diffraction, further elucidating the multistep mechanism of DHPP decomposition. The stability of the pentazole ring was assessed using density functional theory (DFT), and the results suggest that the para-hydroxyl or meta-methyl groups may enhance the delocalization of the pentazole ring, thereby improving the stability of DHPP.