Kinetic and experimental study on the reaction of 3,7-dinitro-1,3,5,7-tetraazabicyclo[3.3.1]nonane in nitric acid

Abstract

The nitrolysis of 3,7-dinitro-1,3,5,7-tetraazabicyclo[3.3.1]nonane (DPT) to prepare 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) in fuming HNO₃ between −8 °C to −36 °C was tracked by ¹H-NMR. It is found that DPT converted to 1-nitroso-3,5,7-trinitro-1,3,5,7-tetraazacyclooctane (MNX) immediately at the end of the feeding course; MNX was then gradually nitrolyzed to HMX. The latter reaction followed a pseudo-first order kinetics, and the selectivity of HMX was almost unaffected with the change in reaction temperature based on the kinetics study. The effects of water and N₂O₄ on this reaction were investigated and the results indicated that a small amount of water and N₂O₄ was beneficial to the generation of the intermediate product MNX. On the contrary, the presence of water and N₂O₄ hindered the conversion of MNX to HMX. Nitrosonium in the reaction system has two sources: one is from the nitrogen oxides such as N₂O₄ in fuming nitric acid; the other is from the redox reaction between nitric acid and formaldehyde, which was promoted by the H₂O in fuming nitric acid. Based on the these results, the overall yield of the stepwise method for preparing HMX was up to 82.7% under the optimized reaction conditions.