C(OC(=O)C)(=O)C.[N+:8]([O-:11])(O)=[O:9].[S:12]1[CH:16]=[CH:15][CH:14]=[C:13]1[C:17]([O:19][CH2:20][CH3:21])=[O:18]>>[N+:8]([C:16]1[S:12][C:13]([C:17]([O:19][CH2:20][CH3:21])=[O:18])=[CH:14][CH:15]=1)([O-:11])=[O:9]To 160 ml. of acetic anhydride cooled to -5° in an ice-salt bath is added 34 ml. of 90% nitric acid dropwise so that the temperature does not rise above 0°. To this mixture is added 62.7 g. of ethyl 2-thiophenecarboxylate dropwise so that the temperature remains below -5°. Reaction is stirred for 1 hour and poured onto ice. The product is filtered, dried, and recrystallized from hexane.
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