The Interaction of Sulfite Ion with 2,4,6-Trinitrobenzaldehyde: Kinetic, Equilibrium, and Proton Magnetic Resonance Studies
Sulfite ion reacts with 2,4,6-trinitrobenzaldehyde in aqueous solution of ionic strength 0.14 M to yield a 1:1 σ-complex at low sulfite concentrations and a 2:1 σ-complex at high sulfite concentrations. The visible absorption characteristics of these two σ-complexes as well as equilibrium constants and relevant thermodynamic parameters for their formation have been determined. P.m.r. studies demonstrate that two isomeric forms of the 1:1 σ-complex occur in aqueous dimethylsulfoxide solution and two isomeric forms of the 2:1 σ-complex occur in water. In both the 1:1 and the 2:1 complexes isomers are found which contain sulfite ion attached to the C-1 carbon and one of the isomeric 2:1 σ-complexes is postulated to exist in cis and trans forms. Observations are presented concerning the kinetics of the very rapid formation of the 1:1 σ-complex in water.