Polysubstitution is drawback of which reaction

Options

A. friedel craft alkylation
B. friedel craft acylation
C. nitration on aromatic ring
D. chlorination on aromatic ring

Answer

To solve the question regarding polysubstitution being a drawback of a particular reaction, we will analyze the Friedel-Craft alkylation process step by step.

### Step-by-Step Solution:

1. **Understanding Friedel-Craft Alkylation**:
- Friedel-Craft alkylation is a reaction where an alkyl group is introduced into an aromatic ring (like benzene) using an alkyl halide (e.g., ethyl chloride, EtCl) and a catalyst (usually AlCl3).

2. **Formation of the Electrophile**:
- In this reaction, the aluminum chloride (AlCl3) acts as a Lewis acid and reacts with the alkyl halide (EtCl) to form a more reactive electrophile, which is the ethyl cation (CH3CH2+).

3. **Electrophilic Attack**:
- The benzene ring, being rich in π electrons, attacks the ethyl cation, leading to the formation of an ethyl-substituted benzene (alkyl benzene).

4. **Increased Reactivity of the Product**:
- The newly formed alkyl benzene has additional hydrogen atoms on the carbon atom where the ethyl group is attached. This makes the product more reactive than benzene itself due to the electron-donating effect of the alkyl group.

5. **Polysubstitution**:
- Because the alkyl benzene is more reactive, it can undergo further electrophilic substitution reactions. This means that the alkyl benzene can react again with another ethyl cation, leading to polysubstitution (the introduction of more than one alkyl group onto the benzene ring).

6. **Conclusion**:
- The tendency of Friedel-Craft alkylation to lead to polysubstitution is a significant drawback of this reaction. This can result in a mixture of products and reduced selectivity, making it less desirable for synthesizing specific alkylated aromatic compounds.

### Final Answer:
Polysubstitution is a drawback of the Friedel-Craft alkylation reaction.

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