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 H-1 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.