Question

What does sodium phthalate give on reaction with sodalime?

• A. Benzene
• B. Toluene
• C. Phthalic acid
• D. Phenol

Hint:

Sodalime decarboxylation is a common method to convert sodium salts of carboxylic acids into hydrocarbons. For dicarboxylic acids or their salts, if both carboxyl groups are removed, the resulting hydrocarbon will have two fewer carbons than the original acid if it were aliphatic, or result in the base aromatic ring if it was an aromatic dicarboxylic acid like phthalic acid.

Answer 1

The Correct Option is A

Step 1: Carboxylate Reaction with Sodalime
The reaction of a sodium carboxylate with sodalime (NaOH + CaO) is a decarboxylation, removing the -COOH group as carbon dioxide. This typically forms an alkane or aromatic hydrocarbon with one less carbon. Calcium oxide (CaO) keeps the mixture dry and acts as a flux.

Step 2: Sodium Phthalate and Structure
Sodium phthalate is the disodium salt of phthalic acid, an aromatic dicarboxylic acid with two carboxyl groups on adjacent benzene ring carbons.
Its structure is a benzene ring with two -COONa groups on adjacent carbons.

Step 3: Predicting Decarboxylation Product
Decarboxylation of sodium phthalate with sodalime removes both -COONa groups as Na₂CO₃, resulting in a benzene ring. Two CO₂ molecules (as Na₂CO₃) are released.
The reaction: C₆H₄(COONa)₂ + 2(NaOH + CaO) → C₆H₆ + 2Na₂CO₃
Sodium Phthalate → Benzene + Sodium Carbonate

Step 4: Evaluate Options

• Option (1): Benzene: Correct, as the carboxylate groups are removed, leaving benzene.
• Option (2): Toluene: Incorrect. Decarboxylation of sodium phthalate does not add a methyl group.
• Option (3): Phthalic acid: Incorrect. Phthalic acid is the starting material, not the product.
• Option (4): Phenol: Incorrect. Decarboxylation does not add a hydroxyl group.

Step 5: Conclusion
Sodium phthalate reacts with sodalime to produce benzene.

\[ \n\boxed{\text{Benzene}} \n\]\n\n