Hydrochloric Acid → 7-(4-Propoxyphenyl)-1,1-dioxo-2,3-dihydro-1-benzothiepine-4-carboxylic acid

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Ethyl 7-(4-propoxyphenyl)-1,1-dioxo-2,3-dihydro-1-benzothiepine-4-carboxlate (495 g, 1.24 mol) was dissolved in 4.95 L of tetrahydrofuran and 2.48 L of methanol. Crystals were formed by adding a potassium carbonate (342 g, 2.47 mol) solution in 4.2 L of water and the mixture was heated under reflux for 6.5 hours. Under reflux, 1.85 L of a 3N hydrochloric acid was dropped to form crystals. After cooling, 84 ml of a 6N hydrochloric acid was added at room temperature (pH 2-3) and stirred for 1 hour while cooling in ice. After filtration, the residue was washed with 2.97 L of a mixed solution of tetrahydrofuran/methanol/water=1/1/3 . After vacuum drying (40° C.), 443 g (Yield 96%) of 7-(4-propoxyphenyl)-1,1-dioxo-2,3-dihydro-1-benzothiepine-4-carboxylic acid was obtained as pale yellowish white crystals.

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