Hydroxypyridines cations, structure

Fixed derivatives of the two tautomeric forms of 2-hydroxypyridine 1-oxide do not give cations of similar structure which precludes the use of pKa measurements to elucidate its structure (cf. preceding... 

In conclusion, structures containing polyiodide anions, with cationic aromatic ligands as counter parts of formulae [(L)(HL+)] (I ) are known to be synthesized by the treatment of the appropriate amide with HI [26-28], In contrast, the complexes with PYOH, in the present case, were formed by the direct reaction of 2-hydroxypyridine with di-iodine in a molar ratio of 2 1 and 1 2. This is a redox reaction, where 2-hydroxy-pyridine firstly is oxidized to pyridinone-2 radical cation. In the case of 2-hydroxy-pyridine however, peroxide structures are not formed like disulphides in the case of PYSH. Polyiodide anions are simultaneously produced in this case This should be a consequence of redox differences between -SH and OH groups and may be proven a useful pathway for the synthesis of polyiodide materials. 

Hydroxypyridine fV-oxides are also tautomeric the 4-isomer exists in about equal amounts of forms 812 and 813. In 4-hydroxypyrones and -pyridones, the -one (e.g., 814) structure is favored relative to the -one. -Hydroxy-4-pyrones such as kojic acid 815 show phenolic properties. - and -Hydroxy cations (e.g., 816) are the conjugate acids of pyridones and pyrones and are considered in the next section. 

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