3,4-Dihydroxythiophene-2,5-dicarboxylic Acid Diethyl Ester is an intermediate used to prepare alkylenedioxythiophene monomers to obtain electrochromic conducting polymers.
GENERAL METHODS: Example B1 10.3 g of diethyl thiodiacetate (product of Example A6) was mixed with 10.96 g of diethyl oxalate (Acros, Belgium) and cooled in a water bath at 0-10 °C. An ethanol solution containing sodium ethanolate (Acros, Belgium) was slowly added dropwise to the mixture with sufficient stirring. Subsequently, the reaction mixture was transferred to a microwave reactor and microwave heated at 100 W power, 2.45 GHz frequency for 60 min, keeping the reaction temperature at 68 °C. Upon completion of the reaction, the pH of the reaction solution was adjusted to 7.0-7.5 with HCl (Scharlau, Australia) to terminate the reaction, followed by removal of ethanol by evaporation. The pH was adjusted to 2.5-3.0 by adding HCl to the dried residue and the product was precipitated by adding 400 mL of deionized water. The precipitate was collected by filtration and dried in an oven to give 8.58 g of diethyl 3,4-dihydroxythiophene-2,5-dicarboxylate in 65.3% yield.
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