Compound (A) `C_(8)H_(9)Br`. Gives a white precipitate when warmed with alcoholic `AgNO_(3)`. Oxidation of (A) gives an acid (B). `C_(8)H_(6)O_(4)`. (B) easily forms anhydride on heating. Identify the compound (A)

Options

A.
B.
C.
D.

Answer

To identify compound (A) with the molecular formula \( C_8H_9Br \), we can follow these steps:

### Step 1: Determine the Degree of Unsaturation
The degree of unsaturation can be calculated using the formula:
\[ \text{Degree of Unsaturation} = C - \frac{H}{2} - \frac{X}{2} + \frac{N}{2} + 1 \]
Where:
- \( C \) = number of carbon atoms
- \( H \) = number of hydrogen atoms
- \( X \) = number of halogens (bromine in this case)
- \( N \) = number of nitrogen atoms

For compound (A):
- \( C = 8 \)
- \( H = 9 \)
- \( Br = 1 \) (which counts as one halogen)

Plugging in the values:
\[ \text{Degree of Unsaturation} = 8 - \frac{9}{2} - \frac{1}{2} + 1 = 8 - 4.5 - 0.5 + 1 = 4 \]
This indicates that compound (A) has a degree of unsaturation of 4, which suggests it contains either one ring and three double bonds, or other combinations of rings and double bonds.

### Step 2: Analyze the Reaction with Alcoholic AgNO3
When warmed with alcoholic \( AgNO_3 \), compound (A) gives a white precipitate of \( AgBr \). This indicates that (A) likely contains a bromine atom that can be replaced by a silver ion, suggesting that (A) is likely a brominated aromatic compound.

### Step 3: Identify the Oxidation Product (B)
The oxidation of compound (A) yields an acid (B) with the formula \( C_8H_6O_4 \). The presence of two additional oxygen atoms compared to (A) suggests that (B) is a carboxylic acid. The fact that (B) can easily form an anhydride upon heating indicates that it is likely phthalic acid.

### Step 4: Determine the Structure of Compound (A)
Given that (B) is likely phthalic acid, we can deduce that compound (A) is likely a brominated derivative of phthalic acid. The structure of phthalic acid is:
\[ \text{Phthalic Acid: } C_6H_4(COOH)_2 \]
If we consider a bromine substituent on the aromatic ring, we can suggest that compound (A) could be 4-bromophthalic acid or a similar structure.

### Conclusion
Based on the analysis, compound (A) is likely **4-bromophthalic acid**.