Hydrochloric Acid → Methyl 4-amino-2,5-dimethylthiophene-3-carboxylate

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Reaction Steps

A cooled solution of 80 g (0.39 mol) of tetrahydro-4-(hydroxyimino)-2,5-dimethyl-3-thiophenecarboxylic acid, methyl ester (Example D) in 1 L of anhydrous diethyl ether is saturated with dry hydrogen chloride over a period of one hour. The solution is stirred and allowed to reach room temperature over fourteen hours. The resulting precipitate is filtered, dissolved in 200 ml of water, neutralized with concentrated ammonium hydroxide and the aqueous solution is extracted with 200 ml of diethyl ether. The diethyl ether solution is washed with 100 ml of water. The diethyl ether layer is separated, dried over anhydrous Na2SO4 and evaporated to give 34 g of 4-amino-2,5-dimethyl-3-thiophenecarboxylic acid, methyl ester; mp 75°-77° C. after recrystallization from hexane.

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