Pyridone-5-sulfonic acids

Pyridone IV was converted to its sodium salt by treatment with an equimolar amount of sodium methoxide in methanol (see procedure below under formation of the 3-phenyl-2(lH)pyridone sulfonates). The sodium salt was next treated with the methyl ester of a-bromo-p-toluic acid, obtained by treatment of the acid with BF3 etherate. 

Aminopyridine and l-methyl-2-pyridone are sulfonated under milder conditions (H2S04-S03, 140°C) in the 5-position. 2,6-Di-r-butylpyridine is converted into the 3-sulfonic acid under mild conditions (S02-S03, 0°C) because reaction of S03 at the nitrogen atom is prevented sterically thus, reaction occurs on the free base, under conditions where this is the majority species. 

Hydroxypyridines undergo a variety of other electrophilic substitution reactions. Sulfonation of 2-pyridone with 10% oleum at 180° gave the 5-sulfonic acid.69 110 A-Methyl-2-pyridone is similarly sulfonated with chlorosulfonic acid. The action of fuming sulfuric acid gave a mixture of the 5-sulfonic acid and the 3,5-disulfonie acid. A nitro group at C-5 is said not to hinder the reaction, sulfonation at the... 

The pyridones can be readily halogenated, nitrated and sulfonated. Substitutions in acidic solutions usually proceed via attack on the free pyridone, but in very strong acid, where there is almost complete protonation, 4-pyridone undergoes a slower nitration, via the 0-protonated salt, but with the same regioselectivity. ... 

Metal-acid solutions have been employed in the reduction of nitropyridines to aminopyridines. Zinc dust and acetic acid have been used in the preparation of 3-amino-l-benzyl-4-pyridone or 3-amino-l-benzyl-S-iodo-4-pyridone from the corresponding 3-nitro derivatives. Tin or iron in acids is more popular. For example, 3-amino-2-(o-bromobenzyloxy)-pyridine is obtained by the reduction of 2-(o-bromobenzyloxy)-3-nitropyridine using iron and hydrochloric acid. Various ferrous salts have also been effective reducing agents. Several derivatives of phenyl 5-amino-2-pyridyl sulfide (K-16) (or the sulfone)are... 

Pyridinol or 2-nitro-3-pyridinol and chlorosulfonic acid in chloroform containing dimethylaniline give the 3-pyridyl bisulfate. 2-Pyridone gives the unstable A-sulfonate and 4-pyridone gives both the A-sulfonate and the... 

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