Hydrochloric Acid → 5-Hexyl-2,2'-bithiophene

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Reaction Steps

Preparation of 5,5′″-Bis(4-n-hexyl)-2,2′:5′,2″:5″,2′″-quaterthiophene (6TTTT6) is now discussed. A mixture of 6.2 g of bithiophene, 8.0 g of hexanoic anhydride, and 0.4 g boron trifluoride etherate is heated to about 100° C. and allowed to cool. The resulting mixture is dissolved in toluene, washed with aqueous sodium bicarbonate (allowing for venting of carbon dioxide gas), dried with magnesium sulfate, filtered, concentrated on a rotary evaporator, and chromatographed on 160 grams of silica gel eluting with hexane/methylene chloride mixtures. The product 5′-hexanoylbithiophene is isolated. The 5′-hexanoylbithiophene (3.9 g sample) is added to a stirred mixture of 3.0 g of aluminum chloride and 3.4 g of lithium aluminum hydride suspended in 300 mL of ethyl ether. After 1 hour, 50 mL ethyl acetate and 15 mL of concentrated hydrochloric acid are cautiously added, and the mixture is filtered, concentrated, and eluted through 30 g of silica gel with hexane. The product 5′-hexylbithiophene is isolated. A measured 2.4 g of this compound is dissolved in 150 mL of tetrahydrofuran. A measured 9.6 mmol of butyllithium as a hexane solution is added with stirring and cooling to −78° C. After 20 minutes, 2.6 g of cupric chloride is added. The mixture is allowed to warm to room temperature. After one day, dilute hydrochloric acid is added to dissolve the copper salts, and the mixture is dissolved in toluene, washed with concentrated hydrochloric acid and dilute aqueous ammonia, dried with magnesium sulfate, filtered, concentrated, and triturated with hexane, methanol, and petroleum ether.

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