Ibuprofen is the active ingredient in pain relieving...

Ibuprofen is the active ingredient in pain relieving compounds. It can be obtained by using following reagents in given sequence on benzene respectively. (I) $\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Cl} /$ Anhydrous $\mathrm{AlCl}_{3}$(III) NBS $(\mathrm{IV}) \mathrm{Zn}-\mathrm{Hg} / \mathrm{HCl}$ (V) $\mathrm{KCN}$ $(\mathrm{VI}) \mathrm{H}_{3} \mathrm{O}^{+}$ What should be the structure of Ibuprofen?

Ibuprofen is the active ingredient in pain relieving compounds. It can be obtained by using following reagents in given sequence on benzene respectively.
(I) $\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Cl} /$ Anhydrous $\mathrm{AlCl}_{3}$(III) NBS
$(\mathrm{IV}) \mathrm{Zn}-\mathrm{Hg} / \mathrm{HCl}$
(V) $\mathrm{KCN}$
$(\mathrm{VI}) \mathrm{H}_{3} \mathrm{O}^{+}$
What should be the structure of Ibuprofen?

Key Concepts

Friedel?Crafts Alkylation

This reaction is a type of electrophilic aromatic substitution in which an alkyl group is introduced onto an aromatic ring. It typically employs an alkyl halide and a Lewis acid catalyst to generate a carbocation, which then reacts with the aromatic system. This method is fundamental in constructing carbon–carbon bonds and expanding aromatic structures in organic synthesis.

Benzylic Halogenation

This process selectively introduces a halogen atom at the benzylic position of an alkyl-substituted aromatic compound. Due to the resonance stabilization of the benzylic radical intermediate, reagents such as N?bromosuccinimide (NBS) are used to achieve a controlled and selective halogenation. It is a key step in modifying the side chain for further functional group transformations.

Reductive Dehalogenation

Reductive dehalogenation involves the removal of a halogen atom from an organic molecule through reduction. Reagents such as Zn–Hg amalgam in acidic conditions are employed for this purpose, converting a halogenated intermediate into a reduced form. This transformation is critical when a halogen must be replaced or removed to allow subsequent functional group modifications.

Nucleophilic Substitution (Cyanation)

In nucleophilic substitution reactions, a nucleophile replaces a leaving group on a substrate. When a cyanide ion is used, it converts a halogenated intermediate into a nitrile, thereby introducing a carbon–nitrogen bond. This reaction is an important method for carbon chain extension and for preparing intermediates that can be thereafter elaborated into other functional groups.

Nitrile Hydrolysis

Nitrile hydrolysis is the conversion of a nitrile functionality into a carboxylic acid group through treatment with acid or base followed by careful work?up. This reaction is crucial in synthetic strategies where a carboxylic acid moiety must be formed from a nitrile intermediate, offering a pathway to introduce functionalities significant in pharmaceuticals and other organic materials.

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