Question

Each of the following reaction types occurs during the Gabriel synthesis EXCEPT: a. decarboxylation. b. nucleophilic substitution. c. dehydration. d. hydrolysis.

Short answer

c. dehydration.

Step-by-step solution

Identify the Gabriel Synthesis process

Gabriel synthesis is a method used to synthesize primary amines. It involves the reaction of potassium phthalimide with an alkyl halide, followed by hydrolysis and decarboxylation.

Analyze the given reaction types

The reaction types provided are decarboxylation, nucleophilic substitution, dehydration, and hydrolysis. Identify if each of these reactions is part of the Gabriel synthesis process.

Check each reaction type

Gabriel synthesis involves: 1. Nucleophilic substitution: Potassium phthalimide attacks the alkyl halide. 2. Hydrolysis: The phthalimide ring is hydrolyzed to phthalic acid and the primary amine. 3. Decarboxylation: Removal of a carboxyl group as CO2 occurs during hydrolysis.

Identify the exception

Focus on verifying the involvement of dehydration. Dehydration does not occur in the Gabriel synthesis steps. Therefore, it is the exception.

Key concepts

primary amines synthesis

The Gabriel synthesis is a popular method used to synthesize primary amines.
Primary amines are compounds that contain an -NH2 group, connected to an alkyl or aryl group. Gabriel synthesis takes a special approach to avoid over-alkylation, which is common in simpler methods.
To create these amines, the process starts with potassium phthalimide reacting with an alkyl halide. This initial step forms an N-alkyl phthalimide intermediate.
Thereafter, this intermediate undergoes hydrolysis and decarboxylation to finally yield a primary amine.

nucleophilic substitution

One of the most vital steps in Gabriel synthesis is nucleophilic substitution.
Nucleophilic substitution is a reaction where a nucleophile, which is a chemical species that donates an electron pair, replaces a leaving group in a molecule.
In the Gabriel synthesis, potassium phthalimide serves as the nucleophile.
The target for this nucleophile is the alkyl halide.
When potassium phthalimide attacks the alkyl halide, it results in the formation of the N-alkyl phthalimide intermediate.
This step is crucial for introducing the alkyl group to the nitrogen atom.

hydrolysis

Hydrolysis is another integral step in the Gabriel synthesis.
Hydrolysis is a chemical process where water is used to break down compounds.
For the Gabriel synthesis, hydrolysis happens in two parts: breaking the phthalimide ring and converting the intermediate to the final amine product.
The hydrolytic conditions break the bond between the nitrogen and the carbon atoms in the ring, forming phthalic acid and releasing the primary amine.
This step ensures that the amine is free from the phthalimide group, completing the synthesis.

decarboxylation

Decarboxylation is the removal of a carboxyl group from a molecule, releasing carbon dioxide (CO2).
In Gabriel synthesis, decarboxylation occurs during the hydrolysis step.
When N-alkyl phthalimide undergoes hydrolysis, it breaks down into phthalic acid and a primary amine.
During this step, the removal of the carboxyl group as CO2 happens, leading to the simplification of the intermediate into the desired primary amine.
This step is necessary to obtain a pure primary amine at the end of the synthesis.