Study On Synthesis Of 3, 4-ethylenedioxythiophene

Poly-thiophene and its derivatives have specialities such as good electric conductivity, great stability and transmissivity to visible light, so much attention is attracted to the field of polymer conductor materials. Among these materials, the PEDOT (poly(3,4-ethylenedioxythiophene)) is most widely used in industries. Thus, more attention has been paid to the synthesis of EDOT, which is the monomer of PEDOT.The research advances and industrial applications of PEDOT are included in this dissertation, and the synthetic methods of monomer EDOT have been reviewed. The synthetic routes of several important intermediates are improved and optimized based on the classical Five-step method as follows:1. Ethyl chloroacetate and sodium sulfide were used to synthesize the intermediate diethyl thiodiglycolate. Cyclohexane was chosen as the solvent in the first time to avoid the hydrolization of esters in aqueous sodium sulfide, and the yield was increased to 80.6%. The purity of the product was greater than 98% by GC, and the recovery rate of cyclohexane was 81.3%.2. Disodium 2,5-dicarbethoxy-3,4-dioxythiophene was synthesized from diethyl thiodiglycolate and diethyl oxalate via Hinsberg reaction with yield of 93.2%.3. Replace the catalyst potassium carbonate/tetrabutyl ammonium bromide with triethylamine. The intermediate 2,5-dicarbethoxy-3,4-ethylenedioxythiophene was given shorter reaction time and higher selectivity. Furthermore, 1,2-dichloroethane, a cheaper and more available etherifying agent regent, could be used to instead 1,2-dibromoethane. The yield of product was 70.4%, and the recovery rate of the solvent DMF was 84.0%.4. 2,5-Dicarboxy-3,4-ethylenedioxythiophene was got by hydrolyzing its ester in 10% NaOH aqueous solution then acidifying. The yield of product was 80.4%.5. The decarboxylation system of EDOT synthesis was improved. According to the high reaction temperature, molten system of NaCl/AlCl₃ was proposed to replacethe high boiling organic solvents, which is cheaper and cleaner. The product could be distilled out when the reaction finished. The yield of this step was 78.8%, and the purity was greater than 98% by GC. The construction of the product was confirmed by GC/MS, ¹H-NMR, and ¹³C-NMR.The "One-pot" experiment was carried out in this dissertation to predigest the purification of the intermediates, and the product was got by reduced-pressure distillation. The total yield was 24.5%, and the purity was above 98% by GC. After calculation, the cost of the raw materials was ï¿¥357 yuan per kilogram of EDOT, which was much lower than the selling price of ï¿¥8000 yuan/kg, it was shown that the developed technique for EDOT might be highly worthy in industrialization.