Nitrous Acid ($HNO_2$)
Reaction with $1^\circ, 2^\circ, 3^\circ$ Amines (Aliphatic vs Aromatic).
Nitrous Acid ($HNO_2$) is an unstable weak acid. It is prepared in situ by reacting Sodium Nitrite ($NaNO_2$) with dilute Hydrochloric Acid ($HCl$) at low temperatures ($0-5^\circ C$). It is primarily used to distinguish between primary, secondary, and tertiary amines.
1. Reaction with Primary ($1^\circ$) Amines
A. Aliphatic Primary Amines
React with $HNO_2$ to form unstable diazonium salts which liberate Nitrogen gas ($N_2$) and form Alcohols.
B. Aromatic Primary Amines (Aniline)
React at low temperature ($0-5^\circ C$) to form stable Benzene Diazonium Chloride. This process is called Diazotization.
2. Reaction with Secondary ($2^\circ$) Amines
Libermann Nitroso Test
Both Aliphatic and Aromatic secondary amines react with $HNO_2$ to form N-Nitrosoamines, which separate as a Yellow Oily Liquid.
Test Confirmation: Upon warming the yellow oil with phenol and conc. $H_2SO_4$, a green solution is obtained, which turns blue on adding alkali (Liebermann's Nitroso Reaction).
3. Reaction with Tertiary ($3^\circ$) Amines
Different Behavior
4. Summary of Identification
| Amine Type | Reaction with $HNO_2$ | Observation |
|---|---|---|
| $1^\circ$ Aliphatic | Forms Alcohol + $N_2$ | Brisk effervescence of $N_2$ gas. |
| $1^\circ$ Aromatic | Forms Diazonium Salt | Clear solution (at $0-5^\circ C$); Dye test positive. |
| $2^\circ$ (Both) | Forms N-Nitrosoamine | Yellow Oily Layer. |
| $3^\circ$ Aliphatic | Forms Nitrite Salt | Clear Solution (Soluble). |
| $3^\circ$ Aromatic | Electrophilic Substitution | Green colored solid/solution. |
Knowledge Check
Test your understanding of HNO2 Reactions
No comments:
Post a Comment