In situ generated amine as a Lewis base catalyst in the reaction of 3,7-dinitro-1,3,5,7-tetraazabicyclo[3.3.1]nonane in nitric acid: Experimental and DFT study

摘要

The problem how ammonium nitrate affects the nitrolysis of 3,7-dinitro-1,3,5,7-tetraazabicyclo[3.3.1]nonane (DPT) in nitric acid to prepare 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) has puzzled chemists for decades. In this paper, experimental work and theoretical calculation are described to investigate the long-standing challenge. The experiment results showed that ammonium nitrate or alkylammonium chlorides were in favor of the formation of 1-nitroso-3,5,7-trinitro-1,3,5,7-tetraazacyclooctane (MNX) but hindered the conversion of MNX to HMX. A plausible catalytic mechanism was proposed. In which ammonia or amines, in situ generated from the unfavorable balance with their salts, act as Lewis base catalysts. At the same time, the DFT computation results reveal that rigid bicyclic transition states established with 1 hydroxymethyl -3,5,7-trinitro-1,3,5,7-tetraazacyclooctane, ammonia (or amines) and three water molecules lead to very low activation energies. Then, a novel process for the preparation of MNX with excellent yield up to 78.5% was developed, which is free of the use of NaNO2 or N2O4 as nitroso resources.