Chapter 19: Problem 437

Propose a likely reaction mechanism and name the end-product (s) for the reaction of a solution containing phenylacetaldehyde and dilute sodium hydroxide.

Short Answer

Expert verified

The reaction between phenylacetaldehyde and dilute sodium hydroxide proceeds through a nucleophilic addition mechanism, leading to the formation of a 2-hydroxy-tetrahydrofuran as the end product. The key steps in this reaction are the nucleophilic attack by the hydroxide ion on the carbonyl carbon, formation of a hydrate intermediate, intramolecular cyclization, and isoconversion to the final product.

Step by step solution

1. Identify phenylacetaldehyde structure

Phenylacetaldehyde (C8H8O) is an aromatic aldehyde with a phenyl group (C6H5) attached to the aldehyde group (CHO). Its structure allows it to undergo nucleophilic addition reactions.

2. Reacting with sodium hydroxide

In the presence of a base like sodium hydroxide (NaOH), the oxygen atom on the aldehyde group becomes more negatively charged and more susceptible to nucleophilic attack. This is due to the lone pair of electrons on the oxygen being able to accept the proton from NaOH, leaving behind an electron pair which can then be utilized for nucleophilic attack.

3. Nucleophilic attack on the carbonyl carbon

The negatively charged oxygen atom on the aldehyde group undergoes nucleophilic attack by the hydroxide ion (OH-) acting as a nucleophile. The carbonyl carbon on the aldehyde group undergoes nucleophilic addition, forming a new C-O bond with the hydroxide ion.

4. Formation of a hydrate intermediate

The nucleophilic addition of a hydroxide ion to the carbonyl carbon results in a hydrate intermediate. This intermediate species has an extra hydroxyl group (OH) attached to the carbonyl carbon, resulting in a geminal diol with the formula C6H5CH(OH)2.

5. Intramolecular cyclization

The hydroxyl group located at the alpha position relative to the carbonyl carbon performs an intramolecular nucleophilic attack on the carbonyl carbon. This cyclization step forms a new C-C bond and generates a cyclic intermediate with a 5-membered ring. The intermediate is known as a hydroxy-tetrahydrofuran, and it also bears a negative charge on the oxygen atom of the remaining hydroxyl group.

6. Isoconversion to key intermediate

In order to complete the reaction, the negatively charged oxygen species donates its electron pair to a nearby proton, forming a molecule of water (H2O) and yielding the key intermediate, which is a 2-hydroxy-tetrahydrofuran.

7. Identify end product

The final end product of the reaction between phenylacetaldehyde and dilute sodium hydroxide is a 2-hydroxy-tetrahydrofuran. The reaction mechanism proceeds in the following manner: 1. Nucleophilic attack by the hydroxide ion on the carbonyl carbon 2. Formation of a hydrate intermediate 3. Intramolecular cyclization to form a hydroxy-tetrahydrofuran intermediate 4. Isoconversion to the key intermediate 5. Formation of the end product, 2-hydroxy-tetrahydrofuran.

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Propose a likely reaction mechanism and name the end-product (s) for the reaction of a solution containing phenylacetaldehyde and dilute sodium hydroxide.

Short Answer

Step by step solution

1. Identify phenylacetaldehyde structure

2. Reacting with sodium hydroxide

3. Nucleophilic attack on the carbonyl carbon

4. Formation of a hydrate intermediate

5. Intramolecular cyclization

6. Isoconversion to key intermediate

7. Identify end product

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