Which of the following can be used as the halide component of a Friedel craft reaction?

The correct answer is Isopropyl chloride.

Key Points

• The Friedel-Crafts reaction involves the alkylation or acylation of an aromatic ring using a halide and a Lewis acid catalyst such as AlCl₃.
• Isopropyl chloride (a secondary alkyl halide) is suitable for Friedel-Crafts alkylation as it can generate a stable carbocation intermediate.
• Unsaturated halides like chloroethene and halogenated aromatic compounds (e.g., chlorobenzene and bromobenzene) are generally unreactive in this reaction due to resonance stabilization or lack of carbocation formation.
• The reaction requires the halide to form a strong electrophile, which is not feasible with aromatic halides or halides with sp²-hybridized carbons.
• Isopropyl chloride efficiently undergoes the reaction, forming isopropylbenzene (cumene) as the product in the presence of a Lewis acid catalyst.

Additional Information

• Friedel-Crafts Reaction:
  • A type of electrophilic aromatic substitution reaction used to introduce alkyl or acyl groups into an aromatic ring.
  • Requires a Lewis acid catalyst such as AlCl₃, FeCl₃, or BF₃.
  • The reaction occurs via the formation of a carbocation intermediate or an acylium ion, depending on the halide used.
• Unsuitable Halides:
  • Vinyl halides (e.g., chloroethene) and aryl halides (e.g., chlorobenzene) are not suitable for Friedel-Crafts reactions due to resonance stabilization of the halogen-carbon bond.
  • These compounds fail to form a reactive carbocation intermediate essential for the reaction to proceed.
• Carbocation Stability:
  • The success of Friedel-Crafts alkylation depends on the stability of the intermediate carbocation.
  • Isopropyl chloride forms a secondary carbocation, which is sufficiently stable for the reaction to occur.
• Limitations of Friedel-Crafts Alkylation:
  • Polyalkylation can occur, leading to multiple substitutions on the aromatic ring.
  • Deactivating groups on the aromatic ring reduce the reactivity, and such rings may not undergo the reaction.