4. The compound that gives characteristic foul smell upon heating with potassium hydroxide and

chloroform is

The compound that gives a characteristic foul smell upon heating with chloroform and potassium hydroxide is identified through the carbylamine test, specific to primary amines. This test produces isocyanides with a pungent odor. Among the options, histamine (B) is the correct answer as it possesses a primary amine group.​

Test Mechanism

Primary amines (R-NH₂) react with chloroform (CHCl₃) and alcoholic KOH to form dichlorocarbene (:CCl₂), which leads to isocyanide (R-NC) formation, releasing HCl neutralized by KOH. The foul smell confirms the presence of primary aliphatic or aromatic amines. Secondary and tertiary amines do not undergo this reaction.​

Option Analysis

• (A) Isatin: Lacks a primary amine; it is an indoline-2,3-dione with no -NH₂ group, so no reaction occurs.​

• (B) Histamine: Contains a primary amine (-CH₂-CH₂-NH₂) on its side chain attached to imidazole, giving positive carbylamine test.​

• (C) Nicotine: Features a tertiary amine in pyrrolidine and a secondary-like pyridine nitrogen; no primary amine present.​

• (D) Coniine (likely misspelled as Conine): Secondary amine (piperidine ring with propyl substituent), does not give the test.​

• Extra: Methamphetamine: Primary amine (C₆H₅-CH₂-CH(CH₃)-NH₂), would give positive test but not the selected option here.​

Introduction to Carbylamine Test

The carbylamine test foul smell chloroform KOH identifies primary amines in organic chemistry. Heating a primary amine with chloroform and alcoholic KOH produces isocyanide (R-NC), known for its characteristic foul smell. This reaction, also called Hofmann isocyanide test, is crucial for distinguishing primary amines from secondary or tertiary ones in exams like CSIR NET Life Sciences.​

Reaction Mechanism Step-by-Step

• Chloroform with KOH forms dichlorocarbene (:CCl₂).​

• Primary amine attacks carbene, forming intermediate leading to isocyanide after dehydrohalogenation.

• Equation: \ceR−NH2+CHCl3+3KOH−>R−NC+3KCl+3H2O\ceR−NH2+CHCl3+3KOH−>R−NC+3KCl+3H2O.​
  Only compounds with -NH₂ group show foul smell; others fail.​

Applications in Identification

Used to detect primary amines in alkaloids and biomolecules. For instance, histamine’s side-chain primary amine confirms positive result, vital in biochemistry studies.​

Common MCQs and Solutions

• Question: Compound giving foul smell on heating with chloroform and KOH?

• Correct: Primary amine like histamine.

• Incorrect options lack -NH₂: isatin (ketone), nicotine (tertiary), coniine (secondary).​