An organic compound X with the molecular formula C_3H_9N reacts with cold nitrous acid (HN… — JAMB UTME

An organic compound $X$ with the molecular formula $C_3H_9N$ reacts with cold nitrous acid ( $HNO_2$ ) at $0-5^\circ\text{C}$ to produce a yellow, oily liquid without the evolution of nitrogen gas. Which of the following is the IUPAC name of compound $X$ ?

A
Propan-1-amine
$N$ -methylethanamineAnswer
C
Propan-2-amine
D
$N,N$ -dimethylmethanamine

Answer

The correct compound is

N

-methylethanamine because secondary aliphatic amines react with nitrous acid (

HNO_2

) at low temperatures to produce insoluble, yellow oily

N

-nitrosamines without liberating nitrogen gas.

Secondary aliphatic amines such as

N

-methylethanamine react with cold nitrous acid (

HNO_2

) to form

N

-nitrosamines. These compounds are insoluble in water and appear as yellow oily liquids. Because no aliphatic diazonium intermediate breaks down to release gas, no nitrogen gas effervescence is observed.

Step-by-Step Solution

Classify the given structural isomers of

C_3H_9N

by amine degree.

Propan-1-amine and propan-2-amine are primary (

1^\circ

) amines;

N

-methylethanamine is a secondary (

2^\circ

) amine;

N,N

-dimethylmethanamine is a tertiary (

3^\circ

) amine.

Amine classification determines the distinct reaction pathway and observable products with nitrous acid.

Analyze the reaction behavior of each amine class with nitrous acid (

HNO_2

) at

0-5^\circ\text{C}

Primary amines evolve

N_2

gas and form alcohols; secondary amines form yellow oily

N

-nitrosamines without gas evolution; tertiary amines form soluble nitrite salts.

Nitrous acid is used as a qualitative reagent to distinguish between

1^\circ

2^\circ

, and

3^\circ

amines.

Match the observation (yellow oily liquid, no nitrogen gas) to the correct compound.

The observation corresponds uniquely to a secondary amine, which is

N

-methylethanamine.

Only secondary amines undergo nitrosation at the nitrogen atom to form neutral, oily

N

-nitrosamine layers.

Key Concept

Distinction tests for primary, secondary, and tertiary amines using nitrous acid (

HNO_2

)

Question

Answer

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Key Concept

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