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copper; In dimethyl sulfoxide; at 20 - 120℃; for 7.5h;
[0034] 3,4-Dimethoxy-2,5-thiophenedicarboxylic acid (232 g) and copper powder (23 g) were added to DMSO (650 g) at room temperature. The reaction mixture was stirred under oxygen atmosphere for 30 minutes at room temperature and then heated at 120° C. for 7 hours. The reaction mixture was then poured into ice water (500 mL), and the crude product was extracted with ethyl acetate. After drying over anhydrous sodium sulfate, the solvent was removed by evaporation. The residue was vacuum-distilled at 50 mmHg to give 127 g of 3,4-ethylenedioxythiophene in high purity (96percent or higher). The purity was confirmed by gas chromatographic analysis. The chemical structure was confirmed by mass analysis and 1H-NMR.
With copper(I) bromide; In methanol; at 70 - 97℃;Inert atmosphere;
21 g of sodium methoxide and 72 g of methanol were added to a 100 ml four-necked flask (the concentration of sodium methoxide relative to the methanol solvent was 22.6percent by weight based on the total amount of sodium methoxide before the reaction) and dissolved at 70 under an argon atmosphere.After addition of 0.83 g of cuprous bromide, 15 g of 3,4-dibromothiophene was added dropwise, and the reaction solution became colorless transparent to black. After completion of the dropwise addition, 50 g of methanol was distilled off (sodium methoxide to methanol solvent The concentration was 48.8 wtpercent based on the total amount of sodium methoxide before the reaction)The reaction was heated to reflux at 97 .When the reaction was traced by gas chromatography, 3,4-dibromothiophene and 3-bromo-4-methoxythiophene were found to be below the detection limit at the reflux starting time of 5 hours.After water was added to the reaction mixture and the mixture was filtered, the crude product was extracted from toluene, and the toluene layer was washed with water, and then the toluene layer was dried with magnesium sulfate.After the magnesium sulfate was removed by filtration, the toluene layer was concentrated by a rotary evaporator and then subjected to vacuum distillation to obtain 7.28 g (yield: 81.5percent) of 3,4-dimethoxythiophene. The purity of its 3,4-dimethoxythiophene was 98.01percent by gas chromatography.The purity (concentration) by gas chromatography in the present invention was indicated by the area ratio of the peak area obtained by the detection device by FID using Agilent 6890N network GC manufactured by Aglient Technologies.
60%
With copper(l) iodide; In methanol; at 80℃; for 72h;
Step 3: 3,4-dibromothiophene (10 g, 41.2 mmol) is added to 30 g of a methanol-sodium methoxide solution with a mass percent of 30percent and stirred. Then CuI (1.96 g, 10.3 mmol) is added quickly, and refluxed at 80° C. for 72 hrs. The mixture is cooled to room temperature, to which a saturated NaCl solution is added. The mixture is extracted with ethyl acetate several times, and dried over anhydrous sodium sulfate to remove solvents. The crude is passed through a separation column, to give a oily liquid, 3,4-dimethoxythiophene (compound 3), yield 60percent, purity 95percent.
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