2-[(E)-({4-[(4,6-Dimethyl­pyrimidin-2-yl)sulfamo­yl]phen­yl}iminio)meth­yl]-6-hy­droxy­phenolate

The title compound, C₁₉H₁₈N₄O₄S, exists as a zwitterion in the solid state, with nominal proton transfer from a phenol group to the imine N atom. The 2,3-dihy­droxy­benzaldehyde fragment is oriented at a dihedral angle of 35.51 (11)° to the adajacent aniline group and makes a dihedral angle of 76.99 (6)° with the 4,6-dimethyl­pyrimidin-2-amine group. Intra­molecular O—H...O and N—H...O hydrogen bonds close S(5) and S(6) rings, respectively; the same O atom accepts both bonds. In the crystal, polymeric chains along [001] are formed from mol­ecules joined end-to-end by N—H...O and O—H...N hydrogen bonds; these feature R₂³(6) loops. The polymeric chains are linked by C—H...O inter­actions and there are π–π inter­actions between the pyrimidine rings with a centroid–centroid distance of 3.446 (2) Å.