Electrochemical nitration to synthesize 1,3,4- trinitropyrazole

To explore a sustainable nitration method for energetic materials, thereby mitigating the risks associated with the use of strong acids and oxidants typically employed in conventional synthesis. The electrochemical construction of N-NO₂ is accomplished via a radical mechanism. This process employs inexpensive Fe(NO₃)₃·9H₂O as the nitrating agent, graphite rods as the anode, and platinum sheets as the cathode, with 4-nitropyrazole functioning as the precursor for the synthesis of 1,3,4-trinitropyrazole. The results demonstrate that Fe(NO₃)₃·9H₂O serves as the optimal nitrating agent, effectively balancing economic considerations with environmental benefits. Cyclic voltammetry and radical trapping experiments elucidate the reaction mechanism, in which the deprotonation of hydrogen at position 1 of the pyrazole ring produces nitrogen radicals that react with nitro radicals generated by Fe(NO₃)₃·9H₂O to yield N-NO₂ under appropriate current. Moreover, the amplified reaction signal observed under acidic conditions suggests that the expedited generation of H₂ at the cathode enhances the rate of radical production at the anode, thereby further corroborating the proposed reaction mechanism. 1,4-DNP and 1,3,4-TNP were synthesized via electrochemical nitration using Fe(NO₃)₃·9H₂O instead of mixed acid. The nitrogen radicals generated from the pyrazole ring couple with nitro radicals produced by Fe(NO₃)₃·9H₂O under a specified current to form N-NO₂, while H₂ is produced at the cathode. • 1,3,4-TNP was synthesized via electrochemical nitration using Fe(NO₃)₃·9H₂O instead of mixed acids. • The nitrogen radicals generated from the pyrazole ring couple with the nitro radicals produced by Fe(NO₃)₃·9H₂O at 2.6 V (vs. SCE) to form N-NO₂.