Thymolphthalein is an acid-base indicator that is colorless below pH 9.3 and blue above pH 10.5. The synthesis of thymolphthalein involves the reaction of pthalic anhydride with two equivalents of thymol (2-isopropyl-5-methylphenol) in an acidic medium.
Write a mechanism for the reaction.

• A.
• B.
• C.
• D.

Answer: (C)