In the Friedel-Crafts acylation, the attacking species is

Options

A. `AlCl_3`
B. `CH_3COCl`
C. `Cl^+`
D. `CH_3CO^+`

Answer

To solve the question regarding the attacking species in the Friedel-Crafts acylation, let's break down the process step by step.

### Step 1: Understand the Friedel-Crafts Acylation
Friedel-Crafts acylation is an electrophilic aromatic substitution reaction where an acyl group is introduced into an aromatic ring. The reaction typically involves the use of an acyl chloride and a Lewis acid catalyst, such as aluminum chloride (AlCl3).

### Step 2: Identify the Reactants
In this reaction, the main reactants are:
- Acetyl chloride (CH3COCl)
- Aluminum chloride (AlCl3)

### Step 3: Formation of the Electrophile
When acetyl chloride (CH3COCl) reacts with aluminum chloride (AlCl3), the Lewis acid (AlCl3) coordinates with the chlorine atom of the acetyl chloride. This interaction leads to the formation of an acylium ion (CH3C^+=O), which is the active electrophile in this reaction.

**Reaction:**
\[ \text{CH}_3\text{COCl} + \text{AlCl}_3 \rightarrow \text{CH}_3\text{C}^+=\text{O} + \text{AlCl}_4^- \]

### Step 4: Electrophilic Attack on the Benzene Ring
The acylium ion (CH3C^+=O) is now ready to attack the electron-rich benzene ring. The electrophile attacks one of the carbon atoms in the benzene, leading to the formation of a sigma complex (an arenium ion).

### Step 5: Deprotonation
After the electrophilic attack, the sigma complex undergoes deprotonation to restore aromaticity, resulting in the formation of the final product, acetophenone (C6H5COCH3).

### Conclusion
The attacking species in the Friedel-Crafts acylation is the acylium ion, represented as CH3C^+=O.

### Final Answer
The attacking species in the Friedel-Crafts acylation is **CH3CO^+** (the acylium ion).

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