Question

Show the product of Claisen condensation of each ester. (a) Ethyl phenylacetate in the presence of sodium ethoxide (b) Methyl hexanoate in the presence of sodium methoxide

Short answer

Question: Show the product of Claisen condensation for the following esters: (a) Ethyl phenylacetate in the presence of sodium ethoxide (b) Methyl hexanoate in the presence of sodium methoxide Answer: (a) The product of Claisen condensation of ethyl phenylacetate in the presence of sodium ethoxide is an ethyl ester of a β-keto acid with the structure: \[ \ce{CH3CH2O-Ph-CH=C(O^-)OCH2CH3} \] (b) The product of Claisen condensation of methyl hexanoate in the presence of sodium methoxide is a methyl ester of a β-keto acid with the structure: \[ \ce{CH3O(CH2)4CH=C(O^-)OCH3} \]

Step-by-step solution

Ethyl phenylacetate and sodium ethoxide

For ethyl phenylacetate in the presence of sodium ethoxide, begin by identifying nucleophilic and electrophilic sites on the molecules: The oxygen of the ethoxide ion will act as a nucleophile. The carbonyl carbon in ethyl phenylacetate will be electrophilic due to its partial positive charge. 1. Nucleophilic attack: The oxygen of the ethoxide ion attacks the carbonyl carbon in ethyl phenylacetate, forming a new carbon-oxygen bond. 2. Transfer of electrons: The pi electrons of the carbonyl double bond move to the carbonyl oxygen, resulting in the formation of an alkoxide ion. 3. Proton exchange: The alkoxide ion then abstracts a proton from another ethyl phenylacetate molecule, awaiting its turn for nucleophilic attack. This process forms the final β-keto ester product and regenerates the ethoxide ion. The product of Claisen condensation of ethyl phenylacetate in the presence of sodium ethoxide is an ethyl ester of a β-keto acid with the structure: \[ \ce{CH3CH2O-Ph-CH=C(O^-)OCH2CH3} \]

Methyl hexanoate and sodium methoxide

For methyl hexanoate in the presence of sodium methoxide, begin by identifying the nucleophilic and electrophilic sites on the molecules: The oxygen of the methoxide ion will act as a nucleophile. The carbonyl carbon in methyl hexanoate will be electrophilic due to its partial positive charge. 1. Nucleophilic attack: The oxygen of the methoxide ion attacks the carbonyl carbon in methyl hexanoate, forming a new carbon-oxygen bond. 2. Transfer of electrons: The pi electrons of the carbonyl double bond move to the carbonyl oxygen, resulting in the formation of an alkoxide ion. 3. Proton exchange: The alkoxide ion then abstracts a proton from another methyl hexanoate molecule, awaiting its turn for nucleophilic attack. This process forms the final β-keto ester product and regenerates the methoxide ion. The product of Claisen condensation of methyl hexanoate in the presence of sodium methoxide is a methyl ester of a β-keto acid with the structure: \[ \ce{CH3O(CH2)4CH=C(O^-)OCH3} \]