Benzene-1,2-dicarb-oxy-lic acid-pyridinium-2-olate (1/1).

The asymmetric unit of the title compound, C(5)H(5)NO·C(8)H(6)O(4), contains one o-phthalate acid mol-ecule and one pyridin-2-ol mol-ecule, which exists in a zwitterionic form. In the o-phthalate acid mol-ecule, the carboxyl-ate groups are twisted from the benzene ring by dihedral angles of 13.6 (1)° and 73.1 (1)°; the hy-droxy H atom in the latter group is disordered over two positons in a 1:1 ratio. In the crystal, O-H⋯O and N-H⋯O hydrogen bonds link the mol-ecules into zigzag chains in [-101].