Question

Reaction of phenol with acetone in the presence of an acid catalyst gives a compound known as bisphenol A, which is used in the production of epoxy and polycarbonate resins (Section 29.5). Propose a mechanism for the formation of bisphenol A.

Short answer

Question: Propose a mechanism for the reaction of phenol with acetone in the presence of an acid catalyst to form bisphenol A. Answer: The mechanism involves five steps: 1. Acid protonation of the carbonyl oxygen in acetone, forming an oxonium ion. 2. Nucleophilic attack by phenol on the oxonium ion, creating a positively charged intermediate alcohol. 3. Deprotonation of the intermediate alcohol resulting in a neutral alcohol. 4. Reaction of the neutral alcohol with the acid catalyst to create an oxonium ion. 5. Nucleophilic attack by phenol and deprotonation, forming bisphenol A as the final product.

Step-by-step solution

Identify the reactants and products

We have phenol and acetone as reactants, with bisphenol A as the formed product in the presence of an acid catalyst. Phenol: C6H5OH Acetone: CH3COCH3 Bisphenol A: (CH3)2C(C6H4OH)2

Formation of Intermediate Alkyl Oxonium Ion

The acid catalyst protonates the carbonyl oxygen of the acetone, increasing the electrophilicity of the carbonyl carbon. This step generates an oxonium ion as an intermediate. CH3COCH3 + H+ → CH3C(OH+)CH3

Nucleophilic Attack by Phenol

Phenol, acting as a nucleophile, attacks the electrophilic carbonyl carbon of the oxonium ion, creating a new carbon-oxygen bond. This step results in the formation of an alcohol with a positive charge on the oxygen. CH3C(OH+)CH3 + C6H5O- → CH3C(OH)(C6H5O)CH3+

Deprotonation of the Intermediate Alcohol

The intermediate alcohol loses a proton, generating a neutral alcohol and returning the catalyst to the reaction medium. CH3C(OH)(C6H5O)CH3+ → CH3C(O)(C6H5O)CH3 + H+

Repeat Nucleophilic Attack by Phenol and Deprotonation

The alcohol formed in step 4 undergoes the same series of reactions. It reacts with the acid catalyst to form an oxonium ion. CH3C(O)(C6H5O)CH3 + H+ → CH3C(O+)(C6H5O)CH3 Then, Phenol attacks the electrophilic carbon and undergoes deprotonation: CH3C(O+)(C6H5O)CH3 + C6H5O- → (CH3)2C(C6H4OH)2 This forms bisphenol A, completing the reaction mechanism.