Continuous flow synthesis of dichloroglyoxime

Dichloroglyoxime is an intermediate in the synthesis of the promising energetic material dihydroxylammonium-5,5'-bistetrazole-1,1'-diolate (TKX-50). The classical synthesis by chlorination of glyoxime with elemental chlorine in a batch procedure has numerous disadvantages concerning safety and scalability due to the exothermic and heterogeneous nature of the reaction. Because of to the high reactivity of chloronitroso intermediates and
to prevent an over-chlorination to nitrosyl chlorides, cooling of the dispersion to at least - 20°C is necessary. This requires strong cooling capacity, slow dosing and intense mixing, but still poses the risk of thermal runaway and a large toxic inventory. In order to overcome these drawbacks and still utilize the high atomic economy and the low cost of chlorine as a chlorination reagent, a continuous flow synthesis was developed. The resulting process has
decisive advantages for upscaling the synthesis, such as significantly higher reaction temperature and increased safety. The low volume of the flow reactor provides a lower toxic inventory during the reaction compared to a conventional batch reactor. With a lab bench-scale setup a dichloroglyoxime throughput of 31 g/h was achieved with a yield of 70 %, comparable to the batch reaction. Moreover, the reaction temperature in the flow reactor
could be increased to 20 °C and the chlorine gas is fed into a closed reaction system and fully conversed.