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Target Exam

CUET

Subject

Chemistry

Chapter

Organic: Amines

Question:

Read the passage carefully and answer.

Organic compounds derived from $NH_3$ by replacing one or more H-atoms with alkyl or aryl groups will form primary, secondary and tertiary amines. The common methods which include their preparations are reduction of nitro group, amide group and nitrile group, Gabriel phthalimide synthesis and ammonolysis of alkyl halides. Amines are basic in nature due to the presence of a lone pair of electrons on the nitrogen atom. Important chemical properties of amines include acylation, alkylation and their interaction with nitrous acid. There are various tests which can distinguish different types of amines from each other, for e.g. carbylamine test, Hinsberg's test, coupling reaction etc. Another important class of compounds which can be derived from primary amines is azo compounds. These compounds are intensely colored and widely used as dyes in textile, leather and food industries.

In the following sequence of the conversion, identify the final product (X)

Options:

Correct Answer:

Explanation:

The correct answer is Option (3) →

Based on the reaction sequence provided in the image, the final product (X) is m-bromobenzoic acid (the third option shown).

Here is the step-by-step breakdown of the chemical transformations:

Step-by-Step Reaction Mechanism

  1. Starting Material: 4-nitrotoluene (p-nitrotoluene).

  2. Bromination ($Br_2, Fe$): The methyl group ($-CH_3$) is ortho/para directing, while the nitro group ($-NO_2$) is meta directing. Both groups direct the incoming Bromine to the same position: ortho to the methyl group and meta to the nitro group.

    • Result: 2-bromo-4-nitrotoluene.

  3. Reduction ($Sn/HCl$): This selectively reduces the nitro group ($-NO_2$) to an amino group ($-NH_2$).

    • Result: 2-bromo-4-aminotoluene (also known as 3-bromo-4-methylaniline).

  4. Diazotization ($NaNO_2/HCl, 0\text{--}5°C$): The amino group is converted into a benzene diazonium chloride salt ($-N_2^+Cl^-$).

    • Result: 3-bromo-4-methylbenzene diazonium chloride.

  5. Deamination ($H_3PO_2, H_2O$): Hypophosphorous acid reduces the diazonium group, replacing it with a hydrogen atom and effectively removing it from the ring.

    • Result: Bromotoluene (specifically, 1-bromo-3-methylbenzene or m-bromotoluene).

  6. Oxidation ($KMnO_4, H^+$): Strong oxidation of an alkyl side chain on a benzene ring converts the methyl group ($-CH_3$) into a carboxylic acid group ($-COOH$).

    • Result: m-bromobenzoic acid.

Final Product Structure

The final product is a benzene ring with a carboxylic acid group and a bromine atom in the meta (1,3) position relative to each other.

 

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