Question

What happens when: Phthalic acid is treated with \( NH_{3} \) followed by heating?

Hint:

Phthalimide is the starting material for synthesizing primary amines without any secondary or tertiary amine contamination.

Answer 1

Concept:

• Carboxylic acids react with ammonia to form ammonium salts.

• Heating the ammonium salt leads to dehydration, forming an amide.

• Strong heating of a dicarboxylic acid derivative like phthalamide leads to further loss of ammonia to form a cyclic imide.
Step 1: Salt formation
Phthalic acid reacts with ammonia to form ammonium phthalate. \[ C_{6}H_{4}(COOH)_{2} + 2NH_{3} \rightarrow C_{6}H_{4}(COONH_{4})_{2} \]

Step 2: Amide formation
Mild heating of ammonium phthalate causes the loss of two water molecules to form phthalamide. \[ C_{6}H_{4}(COONH_{4})_{2} \xrightarrow{\Delta} C_{6}H_{4}(CONH_{2})_{2} \]

Step 3: Imide formation
Strong heating of phthalamide leads to the elimination of one molecule of ammonia, resulting in the formation of a cyclic product. \[ C_{6}H_{4}(CONH_{2})_{2} \xrightarrow{\text{strong } \Delta} \text{Phthalimide} + NH_{3} \]

Step 4: Identify the product
The final product is Phthalimide, a cyclic imide used extensively in the Gabriel Phthalimide Synthesis. The final answer is Phthalimide.