Tetrahydrofuran → 5-Methoxy-3-(1-methylethoxy)benzo[b]thiophene-2-carboxylic acid

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Reaction Steps

To a 12 L 3-necked round-bottomed flask fitted with a mechanical stirrer, a thermometer, an addition funnel and a reflux condenser with a nitrogen inlet are charged 3-chloro-5-methoxybenzo[b]thiophene-2-carbonyl chloride (Example 1) (336 g) and THF (2.3 L). The solution of sodium isopropoxide from above is charged to the THF solution of the acid chloride in four portions causing the temperature of the reaction mixture to rise to 60° C. The flask which contains the sodium isopropoxide is rinsed with THF (275 mL) and the rinse is added to the 12 L reaction flask. The mixture is heated under reflux for 7 hours and then cooled to room temperature and stirred for 12 hours. After cooling to 5° C. to 10° C., concentrated hydrochloric acid (85 mL) is added and the dark mixture stirred for 1 hour to give a final pH of 1.5. The reaction is filtered through filter paper and the filter cake is washed with THF (200 mL). The clear filtrates are charged to a 12 L 3-necked round-bottomed flask fitted with a mechanical stirrer, a thermometer, and a distillation head with reflux condenser and THF is distilled out of the flask under low vacuum to a batch temperature of 50° C. Heptane (3.1 L) is charged to the flask and the slurry is cooled to 5° C. and filtered through filter paper. The filter cake is washed with heptane (300 mL) and the combined filtrates are washed with a sodium bicarbonate solution (3×390 mL) prepared by dissolving sodium bicarbonate (47 g) in deionized water (1170 mL). The heptane solution is charged to a 12 L 3-necked round-bottomed flask fitted with a mechanical stirrer, a thermometer, and a distillation head with reflux condenser and heptane is distilled out of the flask under low vacuum to a batch temperature of 70° C. Upon cooling, IPA (815 mL) and a solution of potassium hydroxide (392 g) in deionized water (1570 mL) are charged to the 12 L flask. The distillation head is replaced with a reflux condenser and the dark solution is heated to reflux and stirred for 4 hours and then cooled to room temperature and stirred for 16 hours. The reflux condenser is again replaced with a distillation head and IPA is distilled out at atmospheric pressure to a batch temperature of 95° C. Deionized water (1570 mL) is added to the solution which is then cooled to 5° C. to 10° C. and adjusted to pH 8 using concentrated hydrochloric acid (480 mL). The aqueous solution is extracted with methyl isobutyl ketone (MIBK) (2×500 mL) and the combined MIBK extracts are extracted with deionized water (300 mL). The aqueous solutions are combined and stirred with PWA carbon (50 g) at room temperature for 16 hours. The solution is filtered through filter paper coated with supercel and the filter cake is washed with deionized water (2×300 mL). The pale yellow filtrates are transferred to a 12 L 3-necked round-bottomed flask fitted with a mechanical stirrer and a thermometer. With agitation, the solution is cooled to 5° C. to 10° C. and concentrated hydrochloric acid (70 mL) is added to give a final pH of 2. The slurry is stirred for 2 hours at 5° C. to 10° C. and the crude product is collected on filter paper and washed with deionized water (3×400 mL). The off-white product is dried in a vacuum oven at 50° C. to afford 215.1 g of the title compound;

Provenance & Evidence