A simplified two-step synthesis of 3,6-dihydroxypicolinic acid (3-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxylic acid), C6H5NO4 (II), an intermediate in the metabolism of picolinic acid, is described. The crystal structure of II, along with that of a labile intermediate, dipotassium 3-hydroxy-6-(sulfonatooxy)pyridine-2-carboxylate monohydrate, 2K+·C6H3NO7S2−·H2O (I), is also described. Compound I comprises a pyridine ring with carboxylate, hydroxyl (connected by an intramolecular O—H⋯O hydrogen bond), and sulfate groups at the 2-, 3-, and 6-positions, respectively, along with two potassium cations for charge balance and one water molecule of crystallization. These components are connected into a three-dimensional network by O—H⋯O hydrogen bonds arising from the water molecule, C—H⋯O interactions and π–π stacking of pyridine rings. In II, the ring nitrogen atom is protonated, with charge balance provided by the carboxylate group (i.e., a zwitterion). The intramolecular O—H⋯O hydrogen bond observed in I is preserved in II. Crystals of II have unusual space-group symmetry of type Abm2 in which extended planar networks of O—H⋯O and N—H⋯O hydrogen-bonded molecules form sheets lying parallel to the ac plane, constrained to b = 0.25 (and 0.75). The structure was refined as a 50:50 inversion twin. A minor disorder component was modeled by reflection of the major component across a mirror plane perpendicular to c.
Digital Object Identifier (DOI)
Funding for this research was provided by: The OSU Emeritus Academy.
Analytical data were provided by Robertson Microlit Laboratories.Supplementary crystallographic information: 3D view
Behrman, Edward J. and Parkin, Sean R., "Synthesis and Crystal Structures of 3,6-Dihydroxypicolinic Acid and Its Labile Intermediate Dipotassium 3-Hydroxy-6-(Sulfonatooxy)Pyridine-2-Carboxylate Monohydrate" (2021). Chemistry Faculty Publications. 180.
Crystal structure: contains datablocks I, II, global. DOI: https://doi.org//10.1107/S2056989021004904/hb7975sup1.cif
hb7975Isup2.hkl (200 kB)
Structure factors: contains datablock I. DOI: https://doi.org//10.1107/S2056989021004904/hb7975Isup2.hkl
hb7975IIsup3.hkl (58 kB)
Structure factors: contains datablock II. DOI: https://doi.org//10.1107/S2056989021004904/hb7975IIsup3.hkl
hb7975Isup4.cml (3 kB)
Supporting information file. DOI: https://doi.org//10.1107/S2056989021004904/hb7975Isup4.cml
hb7975IIsup5.cml (2 kB)
Supporting information file. DOI: https://doi.org//10.1107/S2056989021004904/hb7975IIsup5.cml
hb7975.pptx (494 kB)