Question

We saw in section 17-4 that ketones react with${\mathbf{\text{NaBH}}}_{\mathbf{\text{4}}}$ to yield alcohols. We’ll also see in section 22-3 that ketones react with${\mathbf{\text{Br}}}_{\mathbf{\text{2}}}$ to yield $\mathit{\alpha }$-bromo ketones. Perhaps surprisingly, treatment with${\mathbf{\text{NaBH}}}_{\mathbf{\text{4}}}$ of the$\mathit{\alpha }$ -bromo ketone from acetophenone yields an epoxide rather than a bromo alcohol. Show the structure of the epoxide, and explain its formation.

Acetophenone An $\mathit{\alpha }$-bromo ketone

Short answer

Epoxide

Step-by-step solution

Epoxides

Epoxides are cyclic organic compounds containing one oxygen atom in the carbon ring. Epoxides are formed by the nucleophilic substitution reaction of carbonyl compounds.

Explanation

The mechanism for the formation of epoxide is shown below.

Acetophenone An $\alpha$-bromo ketone Epoxide

The hydride ion from the Sodium boro hydride undergoes a reaction to the carbonyl center to give an oxide ion which then forms epoxide by leaving the Bromide ion from the compound.