Question

If the Favorskii rearrangement of 2-chlorocyclohexanone is carried out using sodium ethoxide in ethanol, the product is ethyl cyclopentanecarboxylate.

Short answer

Question: Describe the mechanism of Favorskii rearrangement of 2-chlorocyclohexanone using sodium ethoxide in ethanol and the formation of ethyl cyclopentanecarboxylate as the final product.

Step-by-step solution

Deprotonation of 2-chlorocyclohexanone

In the first step, the acidic α-hydrogen in 2-chlorocyclohexanone is deprotonated by sodium ethoxide (NaOEt). This forms a resonance-stabilized enolate ion. The deprotonation occurs specifically at the carbon next to the carbonyl group (C=O) because that location is more acidic due to the stable carbanion being adjacent to the ketone functional group.

Nucleophilic attack on carbonyl carbon

The enolate ion formed in the previous step has a negative charge located on one of the carbons adjacent to the carbonyl group. This negatively charged σ-carbon acts as a nucleophile and attacks the electrophilic carbonyl carbon in 2-chlorocyclohexanone, forming a 5-membered ring intermediate containing an alkoxide ion.

Protonation of alkoxide ion

The alkoxide ion that has been formed in the intermediate is a relatively strong base. Ethanol, which is present in the reaction mixture, can serve as a relatively weak acid to donate a proton to the alkoxide oxygen. This protonation converts the alkoxide into a hydroxyl group and generates ethyl-3-hydroxycyclopentanecarboxylate.

Esterification of the hydroxyl group

In the last step of the rearrangement, the hydroxyl group formed in the previous step undergoes an esterification with ethanol, generating ethyl cyclopentanecarboxylate as the final product. This esterification process involves nucleophilic attack of the alcohol oxygen on the carbonyl carbon, followed by elimination of a water molecule and formation of the ester functional group. In conclusion, the Favorskii rearrangement of 2-chlorocyclohexanone using sodium ethoxide in ethanol provides a step-by-step process of converting the given reactants into ethyl cyclopentanecarboxylate through a series of deprotonation, nucleophilic attack, protonation, and esterification steps.