Phenolphthalein: Phthalic Anhydride and Phenol Heated with Sulphuric Acid (Cohen, 1920)

The titration indicator, made as Baeyer made it: phthalic anhydride and phenol heated with concentrated sulphuric acid, then washed, dissolved in alkali, thrown down with acid and cleaned in alcohol with animal charcoal. 10 g of anhydride gives about 5 g. Phenolphthalein is a white, granular powder, melting at 250-253 °C, hardly soluble in water, readily in hot alcohol, and crimson in alkali. Not given: the strength and amounts of the caustic soda, acetic acid and hydrochloric acid. Source: J. B. Cohen, Practical Organic Chemistry (1920), Preparation 81, after Baeyer (1876, 1880). Picture: TimJW12, Wikimedia Commons, CC BY-SA 4.0.