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Question: Explain the Liebermann nitroso reaction for 1, 2, and 3 degree amines....

Explain the Liebermann nitroso reaction for 1, 2, and 3 degree amines.

A

Primary amines react with nitrous acid to form diazonium salts, which decompose to alcohols and nitrogen gas.

B

Secondary amines react with nitrous acid to form N-nitrosamines, which are yellow oily liquids or solids.

C

Aliphatic tertiary amines react with nitrous acid to form water-soluble alkylnitrosodialkylammonium salts.

D

Aromatic tertiary amines undergo electrophilic substitution on the aromatic ring to form p-nitroso derivatives.

Answer

The Liebermann nitroso reaction describes the distinct reactions of primary, secondary, and tertiary amines with nitrous acid (HNO₂), typically prepared in situ from NaNO₂ and a dilute acid at 0-5 °C, allowing for their differentiation.

Explanation

Solution

  1. Primary Amines (RNH₂): React with nitrous acid to form unstable diazonium salts. These decompose rapidly to produce alcohols and nitrogen gas. The evolution of nitrogen gas is observed as effervescence. RNH2+HNO2→0−5∘C[RN2]+X−→ROH+N2↑\text{RNH}_2 + \text{HNO}_2 \xrightarrow{0-5^\circ C} [\text{RN}_2]^+ \text{X}^- \rightarrow \text{ROH} + \text{N}_2\uparrow

    • Observation: Effervescence due to N₂ gas evolution.

  2. Secondary Amines (R₂NH): React with nitrous acid to form stable N-nitrosamines. These compounds are typically yellow oily liquids or solids and are insoluble in water. R2NH+HNO2→0−5∘CR2N-N=O+H2O\text{R}_2\text{NH} + \text{HNO}_2 \xrightarrow{0-5^\circ C} \text{R}_2\text{N-N=O} + \text{H}_2\text{O}

    • Observation: Formation of a yellow oily liquid or solid.

  3. Tertiary Amines (R₃N): The reaction depends on whether the amine is aliphatic or aromatic.

    • Aliphatic Tertiary Amines: React with nitrous acid to form water-soluble alkylnitrosodialkylammonium salts. The solution remains clear, with no gas evolution or formation of a yellow oil. R3N+HNO2→0−5∘C[R3N+−OH]X−\text{R}_3\text{N} + \text{HNO}_2 \xrightarrow{0-5^\circ C} [\text{R}_3\text{N}^+-\text{OH}] \text{X}^-
      • Observation: Solution remains clear; no gas evolution and no yellow oil.
    • Aromatic Tertiary Amines: Undergo electrophilic substitution on the aromatic ring, usually at the para position, to form p-nitroso derivatives, which are often colored. ArNR2+HNO2→p-O=N-ArNR2+H2O\text{ArNR}_2 + \text{HNO}_2 \rightarrow \text{p-O=N-ArNR}_2 + \text{H}_2\text{O}
      • Observation: Formation of a colored product.