Question

Claisen condensation between diethyl phthalate and ethyl acetate followed by saponification, acidification, and decarboxylation forms a diketone, \(\mathrm{C}_{9} \mathrm{H}_{6} \mathrm{O}_{2}\). Propose structural formulas for compounds \(\mathrm{A}\) and \(\mathrm{B}\) and the diketone.

Short answer

Answer: Compound A has a structural formula of \((\mathrm{C}_{6}\mathrm{H}_{4}(\mathrm{CO}_{2}\mathrm{CH}_{2}\mathrm{CH}_{3})(\mathrm{CO}\mathrm{CH}_{2}\mathrm{CO}_{2}\mathrm{CH}_{2}\mathrm{CH}_{3}))\). Compound B has a structural formula of \(( \mathrm{C} _6 \mathrm{H} _4 ( \mathrm{CO} _2 \mathrm{H} ) ( \mathrm{CO} \mathrm{CH} _2 \mathrm{CO} _2 \mathrm{CH} _2 \mathrm{CH} _3 ) )\), and the final diketone has a structural formula of \((\mathrm{C}_{6}\mathrm{H}_{4}( \mathrm{CO} )(\mathrm{CH}_{2}\mathrm{CO} ))\).

Step-by-step solution

Write the structural formulas of diethyl phthalate and ethyl acetate

Diethyl phthalate: \(\mathrm{C}_{12} \mathrm{H}_{14} \mathrm{O}_{4}\) The structural formula is \( ( \mathrm{C} _6 \mathrm{H} _4 ( \mathrm{CO} _2 \mathrm{CH} _2 \mathrm{CH} _3) _2 \) Ethyl acetate: \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}\) The structural formula is \(( \mathrm{CH} _3 \mathrm{CO} _2 \mathrm{CH} _2 \mathrm{CH} _3 )\)

Perform the Claisen condensation

Claisen condensation between diethyl phthalate and ethyl acetate occurs when the alpha hydrogen of ethyl acetate is deprotonated by a strong base (e.g., ethoxide ion). The resulting enolate ion then attacks the carbonyl carbon of diethyl phthalate, resulting in the formation of a tetrahedral intermediate which upon collapsing, undergoes ester group transfer, generating compound A: Compound A: \(\mathrm{C}_{16} \mathrm{H}_{18} \mathrm{O}_{5}\) The structural formula is \((\mathrm{C}_{6}\mathrm{H}_{4}(\mathrm{CO}_{2}\mathrm{CH}_{2}\mathrm{CH}_{3})(\mathrm{CO}\mathrm{CH}_{2}\mathrm{CO}_{2}\mathrm{CH}_{2}\mathrm{CH}_{3}))\)

Perform saponification, acidification, and decarboxylation

Saponification: The process involves the hydrolysis of ester bonds in compound A with a base (e.g., NaOH) to produce carboxylate salts and an alcohol. Acidification: Treating the carboxylate salts with a strong acid (e.g., HCl) to generate a carboxylic acid. Decarboxylation: Heating the carboxylic acid will lead to a loss of carbon dioxide and formation of a new compound. Compound B: \(\mathrm{C}_{14} \mathrm{H}_{12} \mathrm{O}_{4}\) The structural formula for Compound B is \(( \mathrm{C} _6 \mathrm{H} _4 ( \mathrm{CO} _2 \mathrm{H} ) ( \mathrm{CO} \mathrm{CH} _2 \mathrm{CO} _2 \mathrm{CH} _2 \mathrm{CH} _3 ) )\)

Deduce the final diketone structure

The molecular formula for the diketone is \(\mathrm{C}_{9} \mathrm{H}_{6} \mathrm{O}_{2}\). Looking at the structure of Compound B, we can deduce that the final diketone is derived from the decarboxylation of the carboxylic acid part of the molecule: The structural formula for the diketone is \((\mathrm{C}_{6}\mathrm{H}_{4}( \mathrm{CO} )(\mathrm{CH}_{2}\mathrm{CO} ))\).