Problem 90 - A Complete Resource Book in Chemistry for JEE Main

Question

Which reaction product is formed from benzaldehyde and methyl amine? (a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}=\mathrm{NCH}_{3}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{NH}_{2}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CONH}_{2}\)

Step-by-Step Solution

Answer

The reaction product is (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}=\mathrm{NCH}_{3}\).

Step 1: Identify the Reactants

The chemical reaction involves benzaldehyde,  ext{C}_6 ext{H}_5 ext{CHO}, and methyl amine,  ext{CH}_3 ext{NH}_2.

Step 2: Determine the Reaction Type

Benzaldehyde is an aldehyde, and methyl amine is an amine. These two substances typically undergo a condensation reaction to form an imine, also known as a Schiff base.

Step 3: Predict the Product

In a condensation reaction between an aldehyde and a primary amine, the hydrogen atom from the amino group ( ext{NH}_2) and the oxygen from the aldehyde group form water ( ext{H}_2 ext{O}). This results in the formation of a  ext{C}= ext{N} bond, producing an imine compound.

Step 4: Write the Structure of the Imine Product

The structure of the imine product formed is  ext{C}_6 ext{H}_5 ext{CH}= ext{NCH}_3, where the double bond between carbon and nitrogen is characteristic of an imine.

Step 5: Match the Product with the Given Options

From the options provided, (b)  ext{C}_6 ext{H}_5 ext{CH}= ext{NCH}_3 corresponds to the structure of the imine formed from benzaldehyde and methyl amine.

Key Concepts

Benzaldehyde

Benzaldehyde, with the chemical formula \( C_6H_5CHO \), is one of the simplest aromatic aldehydes. It's an organic compound that features a benzene ring, which is a hexagonal arrangement of carbon atoms with alternating double bonds, attached to an aldehyde group \(-CHO\). This compound is commonly used as a flavoring agent due to its characteristic almond-like scent.

• An important feature of benzaldehyde is the carbonyl group \(-CHO\), positioned at the end of the molecule.
• This group is highly reactive, particularly with nucleophiles, making it a crucial player in various chemical reactions, including the formation of Schiff bases and imines.

Benzaldehyde reacts with primary amines, such as methyl amine, to form imines through a process called a condensation reaction.

Methyl amine

Methyl amine is an organic compound and among the simplest amines with the chemical formula \( CH_3NH_2 \). It is a primary amine, signified by the presence of an amino group \(-NH_2\) directly linked to a methyl group \( \mathrm{CH_3} \). This molecule is a colorless gas at room temperature and known for its distinctive smell reminiscent of fish.

• The amino group in methyl amine acts as a nucleophile, actively participating in various reactions due to its lone pair of electrons on the nitrogen atom.
• In reactions with compatible electrophiles like benzaldehyde, it facilitates the formation of bonds with carbon by joining and releasing a small molecule, such as water.

Through such interactions, methyl amine's reactivity is key in synthesizing different organic compounds, including imines.

Imine

Imine compounds are characterized by the presence of a carbon-nitrogen double bond \( \mathrm{C}=\mathrm{N} \). They are sometimes referred to as Schiff bases, notably when the nitrogen atom is bonded to an aryl or alkyl group. The formation of an imine is typically the result of a reaction between an aldehyde (or ketone) and a primary amine, facilitated by a condensation reaction.

• This process usually involves the release of a small molecule, typically water, through the elimination of the hydroxyl group from the aldehyde and a hydrogen atom from the amine.
• The double bond between carbon and nitrogen is crucial to the structure and reactivity of imines, affecting their ability to participate in further transformations.

Imine formation is a central step in the synthesis of many organic compounds, illustrating their role and versatility in organic chemistry.

Condensation Reaction

A condensation reaction is a fundamental type of chemical reaction where two molecules or moieties combine to form a larger molecule, often with the loss of a small molecule such as water or alcohol. In the context of benzaldehyde and methyl amine, a condensation reaction leads to the formation of an imine.

• This reaction is initiated by the nucleophilic attack of the amine's nitrogen on the carbonyl carbon in the aldehyde.
• The condensation leads to the elimination of water, facilitated by the combination of the carbonyl group's oxygen and the hydrogen atoms from the amine's amino group.
• The result is the creation of a double bond between carbon and nitrogen, forming the imine structure.

Condensation reactions are instrumental in synthetic organic chemistry, laying the groundwork for the construction of more complex molecules.