The Preparation of the Stable Tautomers of 4-Mercapto-3-quinolinesulfonic and 1,4-Dihydro-4-thioxo-3-quinolinesulfonic Acids

The reaction of 4-chloro-3-quinolinesulfonic acid (3) with sodium hydrosulfide gives the sodium salt of 1,4-dihydro-4-thioxo-3-quinolinesulfonic acid (4) and 4-mercapto-3-quinolinesulfonic acid (4b).The acidification of aqueous solution of the sodium salt of 4 results in 1,4-dihydro-4-thioxo-3quinolinesulfonic acid (4a).It has been found that in the DMSO solution tautomer (4a) converts into tautomer (4b).The X-Ray analysis of tautomer (4a) indicates that it appeared in a form of betaine (4c).