The Synthesis of EDOT Monomer, and Its Physical and Chemical Properties
EDOT (3,4-ethylenedioxythiophene) chemistry started as early as the 1930s, when the corresponding 2,5-dicarboxylic acid esters were synthesized.1,2 This was the rst description of the special biheterocyclic EDOT system consisting of one 1,4-dioxane ring and one thiophene moiety, annelated over the carbon single ([c]-) bond of the thiophene. One of these early investigations originally was a spinoff from studies in the cantharidin chemistry.2 In a more elaborate study the synthesis of the basic 3,4-dioxy substituted thiophene ring was improved, yielding closely related compounds, for example, 3,4-dimethoxythiophene and several derivatives.3 A detailed synthesis description for 3,4-ethylenedioxythiophene-2,5-dicarboxylic acid (EDOT-2,5dicarboxylic acid) was published by Gogte et al. in 1967.4 The Gogte synthesis started with a Hunsdiecker condensation reaction of oxalic acid diester with thiodiacetic diester to 3,4-dihydroxythiophene-2,5-dicarboxylic acid diester as the rst step. 3,4-Dihydroxythiophene-2,5-dicarboxylic acid diester was alkylated with 1,2-dichloro-or 1,2-dibromoethane and then saponied. Decarboxylation of EDOT-2,5-dicarboxylic acid led to EDOT.5 Since its introduction6 into the chemistry of intrinsically conductive polymers (ICPs), the industrial manufacture is based on the Gogte pathway with minor changes, utilizing copper-catalyzed decarboxylation in the last step (Figure 5.1).5,7,8 Sufcient copper catalysts are basic copper carbonate (CuCO3Cu(OH)2) or copper quinoline complexes.