4-Ethoxycarbonyl-5-(pyrazin-2-yl)-1,2-dithiole-3-thione → 4-Carboxy-5-(pyrazin-2-yl)-1,2-dithiole-3-thione

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반응 단계

A solution of 4-ethoxycarbonyl-5-(pyrazin-2-yl)-1,2-dithiole-3-thione (150 g) [prepared as described in Example 31] in acetic acid (6750 cc), concentrated sulphuric acid (515 cc) and water (515 cc) is heated for 2 hours under reflux. After cooling, the product which crystallises is filtered off and washed successively with acetic acid (100 cc) and carbon disulphide (2 × 100 cc). This product is then suspended in water (1350 cc) and stirred for 48 hours at a temperature of about 20° C. The insoluble product is then filtered off and washed with water (2 × 250 cc). After drying, 4-carboxy-5-(pyrazin-2-yl)-1,2-dithiole-3-thione (97.5 g), melting at 225° C, is obtained.

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