1,2-Dibromoethane → 2,3-Dihydro-thieno(3,4-b)(1,4)dioxin-5,7-dicarboxylic acid

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The salt either 5 or 6 is dissolved in water and acidified with 1 Molar HCl added slowly dropwise with constant stirring until the solution becomes acidic. Immediately following, thick white precipitate falls out. After filtration, the precipitate is washed with water and air-dried to give 2,5-dicarbethoxy-3,4-dihydroxythiophene (7). The salt either (5, 2.5 grams) or 6 can be alkylated directly or the dihydrothiophene derivative (7) can be suspended in the appropriate 1,2-dihaloalkane or substituted 1,2-dihaloalkane and refluxed for 24 hours in the presence of anhydrous K2CO3 in anhydrous DMF. To prepare EDOT, either 1,2-dicholorethane (commercially available from Aldrich) or 1,2-dibromoethane (commercially from Aldrich) is used. To prepare the various substituted EDOT derivatives the appropriate 1,2-dibromoalkane is used, such as 1-dibromodecane, 1,2-dibromohexadecane (prepared from 1-hexadecene and bromine), 1,2-dibromohexane, other reported 1,2-dibromoalkane derivatives, and the like. The resulting 2,5-dicarbethoxy-3,4-ethylenedioxythiophene or 2,5-dicarbethoxy-3,4-alkylenedioxythiophene is refluxed in base, for example 10 percent aqueous sodium hydroxide solution for 1 to 2 hours, and the resulting insoluble material is collected by filtration. This material is acidified with 1 Normal HCl and recrystallized from methanol to produce either 2,5-dicarboxy-3,4-ethylenedioxythiophene or the corresponding 2,5-dicarboxy-3,4-alkylenedioxythiophene. The final step to reduce the carboxylic acid functional groups to hydrogen to produce the desired monomer is given in the references above.

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