Potassium Hydroxide → 4'-Hydroxydiclofenac

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The 2-[(2,6-dichloro-4-methoxyphenyl)amino]phenylacetic acid (0.1 mol) from example 22 was added in portions to a melt of 200 g of pyridine hydrochloride (1.75 mol) at 170° C. The mixture was heated at 180° C. for 3 h and poured onto 2000 ml of ice water while hot. The precipitated product was filtered off, washed with water, and dissolved in 1000 ml of ethyl acetate. The organic phase was washed with 200 ml of 1N HCl in water (2×100 ml) and evaporated to give N-(2,6-dichloro-4-hydroxyphenyl) oxindole. To a solution of 8 g of N-(2,6-dichloro-4-hydroxyphenyl)-oxindole in 200 ml of n-butanol were added 7 g of NaOH and 1 g of KOH, and the reaction mixture was refluxed for 24 h and evaporated in vacuo. The residue was dissolved in 700 ml of water and the aqueous solution was extracted with ether (2×200 ml), cooled to 0° C., and acidified with concentrated HCl. The precipitate was taken up in 300 ml of ether. The organic phase was washed with 30 ml of water, 0.5N NaHCO3 (5×80 ml), and 80 ml of 2N KHCO3 solution. The combined NaHCO3 extracts were cooled to 0° C. and acidified with 2N HCl, and the precipitate was dissolved in 200 ml of ether. The organic layer was washed with 30 ml of water and evaporated to yield 2-[(2,6-dichloro-4-hydroxyphenyl)amino]phenylacetic acid.

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