Acetanilide when treated with bromine in acetic acid mainly gives:A. o-BromoacetanilidaB. N-BromoacetanilideC. p-BromoacetanilideD. m-Bromoacetanilide

To determine the product formed when acetanilide is treated with bromine in acetic acid, let's analyze the reaction mechanism and the influence of the functional groups present in acetanilide.

### Structure of Acetanilide

Acetanilide is an amide with the following structure:

\[
\text{C}_6\text{H}_5\text{-NH-CO-CH}_3
\]

In this structure:
- The **acetyl group** (–COCH₃) is electron-withdrawing due to the presence of the carbonyl (C=O) group.
- The **aniline moiety** (C₆H₅NH₂) can undergo electrophilic aromatic substitution because the nitrogen atom has a lone pair of electrons that can donate to the aromatic ring, making it more reactive towards electrophiles.

### Bromination in Acetic Acid

When bromine (Br₂) is added to a solution of acetanilide in acetic acid, bromination occurs primarily at the aromatic ring. The key points to consider are:

1. **Directing Effects of the Amine Group**:
- The amine group (–NH₂) is a **strongly activating group** that directs electrophilic substitution to the ortho (o) and para (p) positions of the aromatic ring due to its ability to donate electron density.
- The carbonyl group (C=O) in the acetanilide is a **deactivating group** that will slightly influence the position of bromination but does not significantly overpower the activation of the ring by the amine group.

2. **Position of Bromination**:
- Because of the electron-donating character of the amine group, bromination will predominantly occur at the **ortho** and **para** positions relative to the amine.
- The ortho position is generally favored due to steric hindrance, as the nitrogen atom is already adjacent to the ring.

### Conclusion

Considering these factors, the main product formed from the bromination of acetanilide in acetic acid is **o-bromoacetanilide**.

Thus, the correct answer is:

**A. o-Bromoacetanilide**