counter anion displacementreactions of unstable pyridine-F2 compounds, fluorination of salts of pyridines with protonic acids or silyl esters with F2, and/ or fluorination of Lewis acid complexes of pyridines. The scope of each method was examined in detail. Each of the N-fluoropyridinium salts was assigned as the first stable 1 : 1 salt structure of the pyridine nucleus and halogenatom on the basis
A 2-halopyridine-6-sulfonic acid and its salt represented by the formula: ##STR1## wherein X is a halogen atom, and M is a hydrogen atom or a metal atom. The compounds are useful as intermediates for producing fluorinating agents (reagents for introducing fluorine atoms).