N-Picrylethylenediamine – methoxide ion interactions: N-deprotonation and σ-complex formation reactions

The interactions of N-picrylethylenediamine as the HCl salt (PED) with methoxide ion in dimethyl sulfoxide – methanol (DMSO/MeOH) media and with 1,4-diazabicyclooctane in dimethyl sulfoxide have been investigated spectrophotometrically at 25.0 °C. Evidence is presented to show that, in solvent mixtures rich in dimethyl sulfoxide (e.g. 95/5, V/V, DMSO/MeOH), deprotonation reactions at the nitrogen centres on the ethylenediamine occur in preference to reactions in which σ-complexes are formed via addition of CH3O− to one or more ring carbon atoms. The initial 1:1 interaction of CH3O− and PED results in the rapid, reversible deprotonation of the NH centre while the 2:1 interaction is associated with rapid, reversible abstraction of H+ from the NH3+ centre. At mole ratios of CH3O− to PED > 3 a σ-complex is formed as a result of the addition of CH3O− ion to a C-3 ring carbon atom of the di-deprotonated PED. The uv–visible absorption properties of these various species are reported and compared to the properties of corresponding species formed in related systems.