JEE MainChemistryGeneral Organic Chemistry
Consider the following carboxylic acids: (A) Cyclopent-2,4-diene-1-carboxylic acid (B) Cycloprop-2-ene-1-carboxylic acid (C) Cyclopentanecarboxylic acid (D) But-3-enoic acid The correct increasing order of their rate of decarboxylation on heating with soda lime is:
Options
- A(A) < (D) < (C) < (B)
- B(C) < (D) < (A) < (B)
- C(B) < (C) < (D) < (A)
- D(B) < (D) < (C) < (A)
Correct answer
C. (B) < (C) < (D) < (A)
Step-by-step solution
The decarboxylation of carboxylic acids with soda lime ( NaOH and CaO ) proceeds via the formation of a carbanion intermediate. The rate of the reaction is directly proportional to the stability of the carbanion formed after the removal of CO₂ . The intermediate carbanions formed are: (A) Cyclopent-2,4-diene-1-carboxylic acid forms the cyclopentadienyl anion, which is aromatic ( 6 electrons) and exceptionally stable. (B) Cycloprop-2-ene-1-carboxylic acid forms the cyclopropenyl anion, which is anti-aromatic ( 4 ele