Investigation of the Reaction Mechanism and Theoretical Calculation for the 3,4-Bis(4-nitrofurazan-3-yl)furoxan Synthesis Process: With Insights into Process Optimization

3,4-Bis(4-nitrofurazan-3-yl)furoxan (DNTF) is a high-performance hydrogen-free explosive, its conventional route exhibits that the reaction mechanisms remain ambiguous, high thermal risk and the yield is relatively low. This work clarifies the oxidation/sulfonation mechanism, identifies the cause of oxidant loss, and develops an efficient and safe synthesis. First, the key intermediate 3-(4-aminofurazan-3-yl)-4-(nitrofurazan-3-yl)furoxan (ANTF) and the by-product 3-(4-aminofurazan-3-yl)-4-(amino sulfonic acid furazan-3-yl)furoxan (SNFF) were detected by HPLC-MS technique, it was also discovered and verified that SNFF can catalyze the decomposition of Caro’s acid, causing oxidant collapse by catalytically cleaving the O–O bond of peroxymonosulfuric acid, releasing O2. Besides, density functional theory (DFT) calculation results show that oxidation reaction initiates at the amino group distal to the furoxan oxygen, with the second nitro conversion as the highest-energy step. Furthermore, it is proposed that a sulfonation reaction occurs between 3,4-bis(4-aminofurazan-3-yl)furoxan (DATF) and sulfur trioxide, followed by oxidation to generate SNFF. Notably, reaction calorimetry results showed that the oxidation process still carries a significant risk of a thermal runaway, where both excessively quick and slow feeding rates influence the yield of the oxidation process and enhanced reaction temperature and concentration of Caro’s acid indeed increase the oxidation capacity while suppressing sulfonation side reaction. By considering the balance of thermal risk and optimal process parameters, the DNTF yield could reach 75% with >99% purity.