Formation and stability of zwitterionic complexes between nitrobenzofuroxans and amines†

Spectroscopic and kinetic investigations on the reactions between 4,6-dinitrobenzofuroxan, 4-nitrobenzofuroxan and tertiary and secondary amines (i.e. 1,4-diazabicyclo[2.2.2]octane, quinuclidine, 1,8-diazabicyclo[5.4.0]undec-7-ene and piperidine) indicate the formation of zwitterionic or anionic complexes. The equilibrium between zwitterionic and anionic complexes is discussed (for reaction with piperidine) on the basis of 1H NMR spectral data, which indicate the presence of anionic complexes arising from the zwitterionic complex by a fast proton departure. The stability and the rate of formation of title complexes are discussed and compared to similar reactions of 1,3,5-trinitrobenzene.