Phthalein Reaction and Coupling Reaction

PHTHALEIN REACTION: heating phenol with phthalic anhydride in the presence of concentrated H2SO4 gives phenolphthalein, the familiar acid-base indicator, via double electrophilic attack of two phenol molecules on the anhydride's carbonyl carbons. COUPLING REACTION: phenol couples with benzenediazonium chloride in alkaline solution (273-278 K) at the para position to form p-hydroxyazobenzene, a red-orange azo dye -- an example of the general azo-coupling reaction use …