Question

Phenol is heated with phthalic anhydride in presence of conc. $ {H_2}S{O_4} $ . The product gives pink colour with alkali. The product is:
A. phenolphthalein
B. Bakelite
C. salicylic acid
D. fluorescein

Answer 1

Hint: To know the exact answer for the given question, we will check to do the reaction between the phenols is heated with phthalic anhydride in presence of conc. $ {H_2}S{O_4} $ . And then we will also discuss both the reactants separately.

Complete answer:
Phenol is heated with phthalic anhydride in presence of conc. $ {H_2}S{O_4} $ . The product gives a pink colour with alkali. The product is phenolphthalein. In acidic medium phenolphthalein is colourless. It is used as an indicator of acid-base titration.
Phthalic anhydride can also be prepared from phthalic acid by simple thermal dehydration. Uses Phthalate esters plasticizers. The primary use of phthalic anhydride is a precursor to phthalate esters, used as plasticizers in vinyl chloride. Phthalate esters are derived from phthalic anhydride by the alcoholysis reaction.
Whereas, phenol is also a versatile precursor to a large collection of drugs, most notably aspirin but also many herbicides and pharmaceutical drugs. Phenol is a component in liquid–liquid phenol–chloroform extraction technique used in molecular biology for obtaining nucleic acids from tissues or cell culture samples.
Hence, the correct option is (A). phenolphthalein.

Note:
Phthalic acid produces phthalic anhydride in presence of Conc. H 2 SO4 which is a very strong dehydrating agent. Simply on heating also phthalic acid loses a water molecule to produce phthalic anhydride.