Formation mechanisms of 3,4-dinitrofuroxan via nitration reaction of furoxan

Abstract

A systematic investigations on the nitration of furoxan by two typical nitration reagents nitronium tetrafluoroborate (BF4NO2) and dilute nitric acid (HNO3) in chloroform (CHCl3) solvent using density functional theory (DFT) method to reveal the formation mechanism of 3,4-dinitrofuroxan (DNFO) and explore new synthesis routes. The geometry optimizations of the minima and transition states involved in the two nitration reactions are performed at the B3LYP/6-311++G** basis set level. The CCSD single-point energy corrections at the same level are carried out on top of the optimized geometries to obtain the accurate energy. Calculated results demonstrate that the electrophilic substitutions of nitronium ions from the nitration reagents and the abstractions of protons in the complex intermediates are the main formation mechanism of DNFO. BF4− is shown to be a better proton abstracter than HNO3 and H2O due to its no barrier combination with H+. The abstraction of proton by HNO3 is predicted to be more feasible than H2O because it can supply the nitration attacker (NO2+) and release more heat. Chloroform is a feasible solvent and heating properly is necessary for the two reactions due to the relatively high barrier of 37kcal/mol. These conclusions provide some significant indications on the new experimental synthesis of DNFO.