3-[(Z)-(4-Diethyl-amino-6-oxocyclo-hexa-2,4-dien-1-yl-idene)methyl-amino]benzoic acid.

The title compound, C(18)H(20)N(2)O(3), crystallizes as the keto tautomer, unlike the vast majority of similar structures that have been reported that contain the hydr-oxy tautomer. There are two strong hydrogen bonds in the crystal structure, both accepted by the same carbonyl group: one intra-molecular N-H⋯O and one inter-molecular O-H⋯O. As a result, the carbonyl C=O distance is long, at 1.310 (2) Å, which may suggest the mol-ecule has a significant zwitterionic character. The dihedral angle between the benzene ring planes is 15.05 (7)°. As a result of the intramolecular hydrogen bond, the bridging C-C=N-C group is almost coplanar with the benzene ring that has the diethylamino substituent [dihedral angle 2.35 (15)°].