Cl.Cl.[CH3:3][CH:4]1[O:8][C:7]2[CH:9]=[C:10]([NH2:14])[C:11]([NH2:13])=[CH:12][C:6]=2[O:5]1.[OH-].[K+].C(O[C:20]([S-])=[S:21])C.[K+].C(O)(=O)C>C(O)(C)C.O>[CH3:3][CH:4]1[O:5][C:6]2=[CH:12][C:11]3[NH:13][C:20]([SH:21])=[N:14][C:10]=3[CH:9]=[C:7]2[O:8]1
9.9 g of 2-methyl-1,3-benzodioxole-5,6-diamine dihydrochloride were suspended in 125 ml of isopropanol. While stirring there was added dropwise thereto a solution of 4.75 g of potassium hydroxide in 40 ml of water and the mixture was stirred at room temperature for an additional 30 minutes. After adding 7.5 g of purified potassium ethylxanthate, the solution was boiled at reflux overnight, then diluted with 125 ml of water and made neutral with a small amount of glacial acetic acid. The cooled suspension was filtered under suction and the crystals were washed well with water. There were obtained 7.5 g (87.4% of theory) of 2-methyl-5H-1,3-dioxolo(4,5-f)benzimidazole-6-thiol with a melting point above 300° C.
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