Phenol is synthesized from cumene via the scheme shown. Suggest the mechanism for each step of the reaction shown. [The oxygens have been screened in blue and orange to assist you.]

Verified step by step guidance

The first step involves the formation of a cumene radical. This is initiated by an initiator, which abstracts a hydrogen atom from the methyl group of cumene, resulting in a radical on the benzylic carbon.

In the second step, the cumene radical reacts with molecular oxygen (O₂) to form a cumene hydroperoxide radical. This occurs through a radical chain mechanism where the radical on the benzylic carbon reacts with O₂ to form a peroxy radical.

The cumene hydroperoxide radical then abstracts a hydrogen atom from another cumene molecule, forming cumene hydroperoxide and regenerating the cumene radical, which can propagate the chain reaction.

In the presence of an acid catalyst (H₃O⁺), the cumene hydroperoxide undergoes acid-catalyzed rearrangement. The oxygen of the hydroperoxide group is protonated, making it a better leaving group, and the bond between the oxygen and the benzylic carbon breaks, forming a carbocation.

The carbocation undergoes a rearrangement to form a more stable phenyl cation, which then reacts with water to form phenol and acetone as the final products. The water molecule attacks the carbocation, leading to the formation of phenol, while the leaving group forms acetone.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

14m

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This process is crucial for understanding how phenol is synthesized from cumene, as it involves the introduction of functional groups onto the aromatic system, enhancing its reactivity and leading to the formation of phenolic compounds.

Radical Mechanisms

Radical mechanisms involve reactions that proceed through the formation of free radicals, which are highly reactive species with unpaired electrons. In the synthesis of phenol from cumene, radical intermediates play a key role, particularly in the oxidation steps where cumene is converted to cumene hydroperoxide, ultimately leading to phenol and acetone.

Hydrolysis of Peroxides

Hydrolysis of peroxides is a reaction where peroxides are converted into alcohols and other products in the presence of water. In the context of phenol synthesis, the hydrolysis of cumene hydroperoxide is a critical step that leads to the formation of phenol and acetone, illustrating the importance of water in facilitating the breakdown of peroxide intermediates.