Understanding Electrophilic Aromatic Substitution

Electrophilic aromatic substitution is a fundamental type of reaction in organic chemistry where an atom, usually hydrogen, attached to an aromatic system is replaced by an electrophile. This process is key to functionalizing aromatic rings.

Identifying Electrophilic Aromatic Substitution Reactions

Let's examine the given options to determine which one represents an electrophilic aromatic substitution reaction:

• Wurtz reaction: This reaction typically involves coupling two alkyl halides using sodium metal to form a larger alkane. It is not an electrophilic aromatic substitution; it's a free radical or anionic coupling reaction, usually applied to aliphatic systems, although variations exist for aryl halides.
• Friedel craft alkylation: This reaction involves the alkylation of an aromatic ring using an alkyl halide or alkene in the presence of a Lewis acid catalyst (like AlCl₃). The alkyl group acts as an electrophile (often as a carbocation or polarized complex) that attacks the electron-rich aromatic ring. This is a classic example of electrophilic aromatic substitution.
• Kolbe synthesis by electrolysis: This is an electrolytic process where carboxylate salts are decarboxylated and coupled to form alkanes. It involves radical intermediates and is not an electrophilic aromatic substitution reaction.
• Dehydrohalogenation: This is an elimination reaction where a hydrogen atom and a halogen atom are removed from adjacent carbons of an alkyl halide, typically forming an alkene. This is not a substitution reaction, and it doesn't involve electrophilic attack on an aromatic ring.

Based on the analysis, the Friedel craft alkylation is a clear example of an electrophilic aromatic substitution reaction.

How Friedel Craft Alkylation is an Electrophilic Aromatic Substitution

In Friedel craft alkylation, a Lewis acid catalyst helps to generate a strong electrophile (like a carbocation) from an alkyl halide or alcohol. This electrophile then attacks the pi system of the aromatic ring. The aromaticity is temporarily disrupted, and then restored by the removal of a proton, resulting in the substitution of a hydrogen on the ring with an alkyl group. This fits the definition of electrophilic aromatic substitution perfectly.

Therefore, among the given options, the Friedel craft alkylation reaction is the one that represents an electrophilic aromatic substitution.

Summary of Reactions

Understanding different types of organic reactions like electrophilic aromatic substitution and Friedel craft alkylation is crucial in organic chemistry. This example highlights how to classify reactions based on the mechanism and the type of substrate involved.