3- Pyridinesulfonic acid

Pyridinesulfonic acid has been prepared by oxidation of 4-pyridinethiol with hydrogen peroxide in barium hydroxide solution, with hydrogen peroxide in glacial acetic acid, with nitric acid-chlorine or nitric acid-chlorine-hydrochloric acid mixtures, and with nitric acid tdone. - The latter reaction gives a mixture of 4-pyridincsulfonic acid and other products, e.g., di-4-pyridyl disulfide dinitrate, and this has led to some confusion in the literature. " - ... 

This is the most convenient preparation of 4-pyridinesulfonic acid, a useful intermediate for the synthesis of various pyridine derivatives. 

When 4-pyridinesulfonic acid is heated with an alkyl amine in the presence of zinc chloride, 4-alkylaminopyridines (IX-48) result. ... 

When 3-aminopyndine is diazotized with hydrochloric acid and sodium nitrite and then treated with acetic acid containing sulfur dioxide and cupric chloride, 3-pyridine ulfonic acid can be isolated. Similarly, 4-aminopyridine-l-oxide gives 4-pyridinesulfonic acid-1 -oxide, but the 2-isomer gives very poor yields of the corresponding sulfonic acid. The preparations and reactions of various 3-pyridinediazonium salts have been reported. 3-Amino-2,6-lutidine... 

Oxidation of a pyridinethione gives the corresponding sulfonic acid, eg, 6-carboxy-2-pyridinesulfonic acid [18616-02-9] from 6-carboxy-2-pyridinethione [14716-87-1] (eq. 14) (41). 

The method described is essentially that of La Forge.2 Nicotinonitrile has also been prepared from nicotinic acid by heating with ammonium acetate and acetic acid,3 from 3-pyridinesulfonic acid by fusion of the sodium salt with sodium cyanide,4 and from 3-bromopyridine and cuprous cyanide.6... 

Pyridinesulfonic acids are strongly acidic, so that the 3-sulfonic acid that forms then protonaies a second molecule of 2.6-fed butylpyridine (/V-protonation is permitted because of the small size of tfie proton). Once protonated. however, further electrophilic attack is strongly disfavoured, and so the overall conversion is limited to 50" ,... 

The sulfonic acids are comparatively weak and exist as zwitterions. They can be esterified with an alcohol and hydrogen chloride for example, but treatment of pyridinesulfonic acids with methyl iodide or dimethyl sulfate and alkali gives Af-methylation. 

Pyridinesulfonic acids exist as zwitterions e.g. 874). As for benzenesulfonic acid, the sulfonic acid group can be replaced by hydroxy or cyano groups under vigorous conditions, e.g. (874) — (873), (875). 

Sulfonation of 2-aminopyridine gives the 5-sulfonic acid exclu-sively.56,109,110 3-Aminopyridine reacts with chlorosulfonic acid to give 3-amino-2-pyridinesulfonic acid (44).103,111 4-Amino-3-pyridine-sulfonic acid is obtained from 4-aminopyridine.112 Arsonation of... 

For 2-benzylaminopyridine the methods of significance in the literature are condensation of 2-pyridinesulfonic acid and benzylamine,4 condensation of the alkali metal salts of 2-amino-pyridine with benzyl chloride,6 reductive alkylation of 2-amino-pyridine in the presence of benzaldehyde and formic acid,2 oxidation of N-benzyl-N-pyridylaminoacetonitrile or N-benzyl-N-pyridylaminoacetaldoxine,6 and the method described here modified by use of an inert solvent.7... 

Most heterocyclic nuclei undergo the sulfonation reaction. Sulfonation of pyridine is difficult. The yield of 3"pyridinesulfonic acid by sulfonation at 390° with oleum is only 13%. The yield is greatly improved by the use of vanadium or mercury salts as catalysts. A critical study of the factors influencing the yield has been made, and a maximum yield of 71% is reported. Fuming sulfuric acid converts quinoline to practically pure 8-quinolinesulfonic acid (54%). The action of concentrated sulfuric acid on dibenzofuran gives 2-dibenzofuransulfonic acid (75%). ... 

Sodium dithionite can also be used as sulfonating agent in special cases, e.g., for iV-heterocyclic nitro compounds whose nitro groups are then simultaneously reduced to amino groups. 5-Amino-4-uracilsulfonic acid was thus prepared from 5-nitrouracil, and 3-amino-4-hydroxy-2-pyridinesulfonic acid from 3-nitro-4-pyridinol.196... 

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