Aliphatic amines can be distinguished as primary, secondary, or tertiary through various qualitative tests based on their solubility and reactivity.
Below are the key tests used to identify and differentiate between these types of amines:
1. Solubility Test
A. Primary and Secondary Amines:
Generally soluble in water and dilute HCl.
B. Tertiary Amines:
Less soluble in water but dissolve in dilute HCl.
2. Hinsberg Test
A. Primary Amines:
React with Hinsberg's reagent (benzene sulfonyl chloride) to form sulfonamides that are soluble in alkali.
B. Secondary Amines:
Form N,N-dialkylsulfonamides, which are insoluble in alkali.
C. Tertiary Amines:
Do not react with Hinsberg's reagent.
3. Nitrous Acid Test
A. Primary Amines:
React with nitrous acid to form diazonium salts, which decompose to release nitrogen gas and produce an alcohol or aldehyde.
B. Secondary Amines:
React to form yellow-colored N-nitrosoamines.
C. Tertiary Amines:
Do not react in a similar manner.
4. Isocyanide Test (Carbylamine Reaction)
A. Primary Amines:
React with chloroform and alkali to produce foul-smelling isocyanides (carbylamines).
B. Secondary and Tertiary Amines:
Do not react in this test.
Summary Table for Qualitative Tests of Aliphatic Amines
Test | Primary Amines | Secondary Amines | Tertiary Amines |
Solubility Test | Soluble in water and dilute HCl | Soluble in water and dilute HCl (less soluble than primary) | Less soluble in water; soluble in dilute HCl |
Hinsberg Test | Form soluble sulfonamides in alkali | Form insoluble sulfonamides | Do not react |
Nitrous Acid Test | Form diazonium salts, decompose to nitrogen gas and an alcohol or aldehyde | Form yellow-colored N-nitrosoamines | No similar reactivity |
Isocyanide Test (Carbylamine Reaction) | Produce foul-smelling isocyanides | No reaction | No reaction |
This table offers a concise overview of the reactions and outcomes for primary, secondary, and tertiary aliphatic amines when subjected to these tests, helping differentiate between the types of amines based on their chemical behavior.