Continuous-flow and safe synthesis of 3-amino-4-amidoximinofurazan

Abstract

3-Amino-4-amidoximinofurazan (AAOF) is an important precursor for the synthesis of high energy furazan energetic materials. The traditional batchwise synthesis approach has the shortcomings of low productivity and high possibility of thermal runaway. This article aims to develop a continuous-flow and safe synthesis approach for AAOF. To achieve this goal, the precipitation problems appearing in the oximation and cyclization reaction stages have been first tackled by diluting the hydroxylamine hydrochloride and sodium hydroxide solution with water, which also reduced the thermal risk of AAOF synthesis. The continuous-flow platform for AAOF synthesis has been established, and the continuous-flow operation parameters have been optimized. The optimal temperatures for the nitrosation–rearrangement coupling reaction, neutralization reaction, oximation and cyclization were 15 °C, 15 °C, 25 °C and 115 °C, respectively. The optimal set retention times for these four stages were 15 min, 5 min, 60 min and 10 min, respectively. The continuous-flow synthesis approach offered an optimal yield of AAOF (95%), which is comparable to the result of batch operation. The total flow rate of the whole process is 10.34 mL min⁻¹, and the final productivity is calculated to be about 0.546 mol h⁻¹ of AAOF. The main merits for the continuous-flow synthesis of AAOF include the following: (1) the reaction time is only one-third of that for batch operation and (2) continuous-flow operation is inherently safe due to the lower liquid holdup and stronger temperature control ability. This work is supposed to be beneficial to the continuous and safe synthesis of AAOF.