Potassium 2,5-dihydroxybenzenesulfonate

Place hydroquinone (25 g, 0.2270 mol) and n-heptane (75 mL) in a round-bottom flask. Cool the flask to approximately 10-15°C, then simultaneously add sulfuric acid (36 N, 22.2 g) dropwise. Continue stirring for approximately 10-15 minutes. Slowly raise the temperature to 50-55°C and continue stirring for 3 hours. Then cool the reaction mixture to 25-35°C and add ethyl acetate (250 mL) to dissolve the formed solid. Slowly add a solution of potassium 2-ethylhexanoate (41.3 g, 0.2265 mol) in ethyl acetate (250 mL). Stir the reaction mixture further for one hour. Filter the precipitated crude solid and wash with ethyl acetate.