In Friedel - Craft acylation the amount of `AlCl_3` that must be taken is

Options

A. in catalytic amount
B. one equivalent
C. more than one equivalent
D. amount does not matter

Answer

### Step-by-Step Solution:

1. **Understanding Friedel-Crafts Acylation**:
Friedel-Crafts acylation is a reaction where an acyl group is introduced into an aromatic ring. The typical reactants include an aromatic compound (like benzene) and an acyl chloride (like acetyl chloride, CH3C(=O)Cl) in the presence of a catalyst.

2. **Role of Aluminum Chloride (AlCl3)**:
In this reaction, AlCl3 acts as a Lewis acid. It coordinates with the acyl chloride to form a more reactive acylium ion (RCO+), which is essential for the electrophilic aromatic substitution mechanism.

3. **Mechanism Overview**:
- The acyl chloride reacts with AlCl3 to form the acylium ion (RCO+).
- The acylium ion then acts as an electrophile and attacks the electron-rich aromatic ring.
- This results in the formation of a resonance-stabilized carbocation intermediate.
- Finally, a proton is abstracted by the AlCl4- ion, regenerating AlCl3 and completing the reaction.

4. **Determining the Amount of AlCl3**:
Since AlCl3 is involved in the formation of the acylium ion and is regenerated at the end of the reaction, it does not get consumed. Therefore, it is used in catalytic amounts.

5. **Conclusion**:
The correct answer to the question regarding the amount of AlCl3 that must be taken in Friedel-Crafts acylation is that it should be used in a catalytic amount.

### Answer:
The amount of AlCl3 that must be taken in Friedel-Crafts acylation is in catalytic amount (Option A).

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