Question

Aniline reacts with which of the following to form a Schiff's base (a) benzaldehyde (b) acetone (c) acetic acid (d) both (a) and (b)

Short answer

The correct answer is (d) both (a) and (b).

Step-by-step solution

Understand the Reaction

Aniline is an aromatic amine that can participate in nucleophilic addition reactions with carbonyl compounds to form Schiff's bases. Schiff's bases are formed when an amine reacts with a carbonyl group to create an imine (C=N).

Identify the Carbonyl Compounds

Examine the provided options for possible carbonyl compounds. Benzaldehyde (option a) and acetone (option b) both contain carbonyl groups. Benzaldehyde is an aromatic aldehyde, and acetone is a ketone.

Reaction with Benzaldehyde

When aniline reacts with benzaldehyde, the nitrogen from the aniline forms a bond with the carbon of the carbonyl group in benzaldehyde, releasing water, and forming a Schiff's base (an imine).

Reaction with Acetone

Similarly, aniline reacts with acetone by forming a bond between the nitrogen of aniline and the carbon atom of the carbonyl group in acetone, also forming a Schiff's base.

Confirm the Answer

Since both benzaldehyde and acetone can react with aniline to form Schiff's bases, the correct answer is option (d), both (a) and (b).

Key concepts

Nucleophilic Addition Reaction

Nucleophilic addition reactions are a type of chemical reaction where a nucleophile forms a bond with an electrophilic carbon atom. This often occurs in molecules containing a carbonyl group, which consists of a carbon atom double-bonded to an oxygen atom.

The oxygen, being more electronegative, pulls electron density away from the carbon, making it positively charged and susceptible to attack by nucleophiles. In the case of Schiff's base formation, the nitrogen atom of an amine acts as the nucleophile.

• Nucleophiles are electron-rich species that donate an electron pair to form a new chemical bond.
• The carbon in a carbonyl group is typically electrophilic, making it a good target for nucleophilic attack.
• This reaction is essential for forming imines, key intermediates in many chemical syntheses.

Carbonyl Compound

Carbonyl compounds are a major class of organic molecules characterized by a carbon atom double-bonded to an oxygen atom, forming the functional group \(\mathrm{C=O}\). This group is highly versatile, acting as a site for various chemical reactions.

Carbonyl compounds are classified depending on the groups attached to the carbon atom.

• Aldehydes: Have at least one hydrogen atom attached to the carbonyl carbon. Benzaldehyde is an example that can react to form a Schiff's base.
• Ketones: Have two alkyl (or aryl) groups attached to the carbonyl carbon, like in acetone, another compound capable of Schiff's base formation.
• The carbonyl group typically makes these molecules polar and reactive towards nucleophiles.

Imine Formation

Imine formation is an important process in organic chemistry for creating compounds that contain a carbon-nitrogen double bond, denoted as \(\mathrm{C=N}\). Imines are typically formed from the reaction between primary amines and carbonyl compounds, like aldehydes or ketones.

During this reaction, the nucleophilic nitrogen of the amine attacks the electrophilic carbon in the carbonyl group, eventually releasing a molecule of water and forming a stable imine.

• The process often involves dehydration, where water is a by-product.
• Imine formation is reversible under certain conditions, allowing the possibility of dynamic covalent chemistry.
• This reaction is utilized in synthesizing various chemical products, including pharmaceuticals and polymers.

Aniline Reactions

Aniline is a simple aromatic amine with the chemical formula \(\mathrm{C_6H_5NH_2}\), known for its reactivity due to the lone pair of electrons on the nitrogen atom.

Aniline readily participates in reactions with carbonyl compounds to form Schiff's bases, showcasing its ability as a nucleophile.

• In the context of Schiff's base formation, aniline's nitrogen lone pair attacks the electrophilic carbonyl carbon.
• This reaction involves aromatic stabilization, where the benzene ring stabilizes the lone pair, enhancing nucleophilicity.
• Aniline's reactions are not limited to carbonyl chemistry but include acylation, sulfonation, and more.

Understanding these reactions is critical for applications in dyes, polymers, and pharmaceutical chemistry.