Question

Treatment of 1,1-diphenyl-1,2-epoxyethane with aqueous acid yields diphenylacetaldehyde as the major product. Propose a mechanism for the reaction.

Short answer

Mechanism followed as:

Step-by-step solution

Acid-catalyzed ether

Epoxide ring opening occurs on reaction with acid in mild condition due to the ring strain and nucleophilic substitution takes place from the backside followed by $\mathit{S}{\mathit{N}}_{\mathbf{2}}$mechanism and form trans 1,2 diol as a product.

Reaction of given epoxide with H3O+

The $O{H}^{-}$is formed by the $H_3{O}^{+}$ which act as a nucleophile and attack on the epoxide and opening of the ring occur and formation of 1,2 diol occur but 1,2 diol with the phenyl group lead to high un stability due to the presence of high steric hindrance so that 1,2 diol is rearranged to the carbonyl form and the desired product is obtained.

Mechanism

1. Formation of $O{H}^{-}$
2. Attack on the epoxide ring occur
3. 1,2 diol formed’ rearranged to form carbonyl

Reaction of epoxide