Azolesulfonic acids

Azolesulfonic acids frequently exist as zwitterions. The usual derivatives are formed, e.g. pyrazole-3-, -4- and -5-sulfonic acids all give sulfonyl chlorides with PCI5. The sulfonic acid group can be replaced by nucleophiles under more or less vigorous conditions, e.g. by hydroxyl in imidazole-4-sulfonic acids at 170 °C, and by hydroxyl or amino in thiazole-2-sulfonic acids. 

Azolesulfonic acids frequently exist as zwitterions. The usual derivatives are formed, e.g., pyrazole-... 

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See also in sourсe #XX -- [ ]

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