Question

Explain Liebermann nitroso reaction for 1, 2, 3 degree amines?

• A. Primary amines react with nitrous acid to form diazonium salts which decompose to alcohols and nitrogen gas. Secondary amines form N-nitrosamines, which are yellow oily liquids. Tertiary amines form soluble nitrosoammonium salts.
• B. Primary amines form stable diazonium salts. Secondary amines form N-nitrosamines. Tertiary amines undergo electrophilic substitution on the ring.
• C. Primary amines form alcohols directly. Secondary amines form nitroso compounds. Tertiary amines react to form salts.
• D. All amines react with nitrous acid to form N-nitrosamines, which are yellow oily liquids.

Answer 1

Answer: (A)

Primary amines react with nitrous acid to form diazonium salts which decompose to alcohols and nitrogen gas. Secondary amines form N-nitrosamines, which are yellow oily liquids. Tertiary amines form soluble nitrosoammonium salts.

Answer 2

The reaction of primary, secondary, and tertiary amines with nitrous acid ($HNO_2$, generated in situ from $NaNO_2$ and dilute acid at 0-5°C) is a key method for their distinction:

1. Primary Amines ($RNH_2$): React to form unstable diazonium salts ($R-N_2^+$). Upon warming, these decompose to yield alcohols and nitrogen gas ($N_2$), observed as effervescence. $RNH_2 + NaNO_2 + 2HCl \xrightarrow{0-5^\circ C} R-N_2^+ Cl^- + NaCl + 2H_2O$ $R-N_2^+ Cl^- \xrightarrow{\Delta} R-OH + N_2 \uparrow + HCl$

2. Secondary Amines ($R_2NH$): React with nitrous acid to form stable N-nitrosamines ($R_2N-N=O$). These are typically yellow, oily liquids insoluble in water. $R_2NH + NaNO_2 + HCl \xrightarrow{0-5^\circ C} R_2N-N=O + NaCl + H_2O$

3. Tertiary Amines ($R_3N$): React with nitrous acid to form soluble nitrosoammonium salts ($[R_3N^+-N=O]Cl^-$). The amine dissolves in the acidic solution, forming a clear, colorless solution. Aliphatic tertiary amines may undergo further reactions upon warming. $R_3N + NaNO_2 + HCl \xrightarrow{0-5^\circ C} [R_3N^+-N=O]Cl^- + H_2O$

The Liebermann nitroso reaction is more commonly associated with phenols, but the reaction of amines with nitrous acid serves as a crucial test for differentiating amine classes.