Question

How would you synthesize anethole (Problem 18-54) from phenol?

Short answer

Synthesis of anethole from phenol

Step-by-step solution

Anethole

Anethole is an organic compound containing two functional groups on a benzene ring. One is an ether group, and the other is an unsaturated hydrocarbon side chain. It is methoxy benzene with a prop-1-en-1-yl group in the para position of the ether group.

It is synthesized from phenol and is used as a flavouring agent. It belongs to the class of phenylpropanoid organic compounds. It is a plant metabolite.

Reactivity of phenol

A benzene ring attached to a hydroxyl group is called a phenol. Phenol contains a C-O bond and is formed by replacing the hydrogen on carbon with a hydroxyl group.

The hydroxyl group in the phenol makes the compound ortho-para activating, or it makes the ortho-para positions of the phenol electron-rich. This is due to the resonance in phenol formed due to the lone pair in oxygen.

The O-H bond in phenols is more acidic than in aliphatic alcohols due to resonance stabilization of the phenoxide ion. Therefore, the proton can be replaced with other groups in phenol.

Synthesis of anethole from phenol

The synthesis of anethole from phenol involves two steps: Converting phenol to mehoxy benzene and adding a hydrocarbon functional group.

The phenol first reacts with a strong base like sodium hydride to form sodium phenoxide, which reacts with methyl iodide to form methoxy benzene.

An acyl group is added to the para position of methoxy benzene by electrophilic substitution using acyl chloride. The carbonyl group in the molecule undergoes reduction to form a hydroxyl group. Substitution with phosphorus tribromide followed by beta-elimination in the molecule produces anethole.

Synthesis of anethole from phenol