Microfluidic continuous flow synthesis of 1,5-ditosyl-1,5-diazocane-3,7-dione using response surface methodology

Abstract 3,3,7,7-tetrakis(difluoroamino) octahydro-1,5-dinitro-1,5-diazocine (HNFX) is a high-density energetic oxidizer with four difluoroamino groups (-NF2). In this study, 1,5-ditosyl-1,5-diazocane-3,7-dione, as an important intermediate for synthesis of HNFX, was successfully synthesized using Swern oxidation in a traditional batch reactor and a continuous flow microreactor, respectively. 1,5-dotosyl-1,5-diazocane-3,7-dione was characterized by HPLC, FTIR, 1H NMR, 13C NMR, Mass spectrometry, and X-ray crystal diffraction. Compared with the traditional batch reactor, the microreactor showed several advantages, including less reaction time, milder reaction temperature, higher yield and selectivity for 1,5-ditosyl-1,5-diazocane-3,7-dione. Moreover, the microreactor could ensure the safer and large-scale industrial production of 1,5-ditosyl-1,5-diazocane-3,7-dione. However, some solids produced in Swern oxidation which might block the channels (diameter of 0.3 mm) in the microreactor. To overcome the challenges, the experimental device was modified to suit for Swern oxidation, contributing to wider application of the microreactor. Besides, response surface methodology (RSM) was introduced and an appropriate mathematical model was built to optimize experimental conditions. The optimum experimental parameters were recommended as 7.8 ℃ for the reaction temperature, 7.7 mL/min for the flow rate, and 6% for the concentration of oxalyl chloride. The actual yield of 1,5-ditosyl-1,5-diazocane-3,7-dione was 89.7%, which was in great agreement with the highest predicted yield (90.1%).