4-Sulfophthalic acid → 4-Hydroxyphthalic acid

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Reaction Steps

In a stainless steel beaker with a steel stirrer a mixture of 300 g KOH (5.36 mole), 150 g NaOH (3.75 mole), 120 g of a 50% aqueous solution of 4-sulfophthalic acid (~0.25 mol) was heated for 4 hr on an oil bath. It was then cooled such that it remained molten and poured into 600 ml ice + water. With cooling it was neutralized to pH 9.0 without noting any precipitate of m-hydroxybenzoic acid by-product. It was then acidified, evaporated to dryness in a rotary evaporator and extracted in a Soxhlet to separate the soluble product from the insoluble inorganics. Crude yield 26 g (59%, M.P. 175°-180° C. Recrystallized from ~2 vol boiling water. Yield 19.5 g (44%), M.P. 201°-3° C.

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