Question

Show how the sequence of Michael reaction, hydrolysis, acidification, and thermal decarboxylation can be used to prepare pentanedioic acid (glutaric acid).

Short answer

Answer: The sequence of reactions to prepare pentanedioic acid (glutaric acid) includes Michael reaction, hydrolysis, acidification, and thermal decarboxylation. 1. In the Michael reaction, diethyl malonate attacks ethyl acrylate to form the product: CH2=C(-OEt)(C(=O)OEt)CH2(C(=O)OEt)2. 2. Hydrolysis breaks the ester bonds in the product, resulting in: CH2=CHCOOH + 2HOCH2COOH. 3. Acidification and tautomerization produce: CH3CH2COOH + 2HOCH2COOH. 4. Thermal decarboxylation removes a carboxyl group, yielding pentanedioic acid (glutaric acid): HOOCCH2CH2CH2COOH.

Step-by-step solution

Michael reaction

In the first step, a Michael reaction takes place. The Michael reaction is an addition reaction of a nucleophile and an α,β-unsaturated carbonyl compound. For our example, let's use ethyl acrylate (CH2=CHC(=O)OEt) as the α,β-unsaturated carbonyl compound and diethyl malonate (CH2(C(=O)OEt)2) as the nucleophile. During the Michael reaction, diethyl malonate attacks the α,β-unsaturated carbonyl of ethyl acrylate, and the following product is formed: Product: CH2=C(-OEt)(C(=O)OEt)CH2(C(=O)OEt)2

Hydrolysis

In the second step, the product formed in step 1 undergoes hydrolysis. Hydrolysis is the reaction of breaking the ester bonds by reaction with water. This step breaks the ester bonds: CH2=C(-OEt)(C(=O)OEt)CH2(C(=O)OEt)2 + 5H2O → CH2=CHCOOH + 2HOCH2COOH + 5EtOH The product after hydrolysis: CH2=CHCOOH + 2HOCH2COOH

Acidification

In the third step, the product formed in step 2 is acidified. Acetic acid is added to protonate the alpha carbon and do the tautomerization which will form a β-ketoacid: Product after tautomerization: CH3CH2COOH + 2HOCH2COOH

Thermal decarboxylation

In the final step, the product from step 3 undergoes thermal decarboxylation. Decarboxylation is the process of removing a carboxyl group (COOH) from a molecule, releasing carbon dioxide (CO2). This step converts the β-ketoacid into pentanedioic acid (glutaric acid). The product after decarboxylation: HOOCCH2CH2CH2COOH Now, we have our final product, pentanedioic acid (glutaric acid).