JEE Mains Chemistry · Amines

Carbylamine and Hinsberg Tests

The carbylamine test picks out primary amines by the smell of an isocyanide, and Hinsberg's reagent sorts primary, secondary and tertiary amines by whether a sulphonamide forms and dissolves in alkali.

All Amines notes JEE Mains Chemistry strategy

Why this matters

Twenty-one PYQs, three numerical, four from 2026. Five test the carbylamine reaction and the isocyanide it gives; eleven test Hinsberg's reagent, often by counting how many amines in a list react or give an alkali-soluble product; five combine several tests to identify an amine from its formula.

Concept 1 of 3: Carbylamine (isocyanide) test for primary amines

Chloroform and alcoholic KOH make dichlorocarbene, which attacks the amine nitrogen. Only a nitrogen with two hydrogens can lose both and end up as R–N≡C, an isocyanide with a very unpleasant smell. Secondary and tertiary amines cannot, so the smell marks a primary amine.

Definition

Heat the amine with $\mathrm{CHCl_3}$ and alcoholic KOH. A foul smell means a primary amine.
Works for primary aliphatic and primary aromatic amines alike. Secondary and tertiary amines give no isocyanide.
The isocyanide can be hydrolysed back by dilute acid: $\mathrm{RNC + 2H_2O \xrightarrow{H^+} RNH_2 + HCOOH}$ .
Isocyanides also form from alkyl halides and AgCN (covalent: nitrogen attacks), while KCN (ionic: carbon attacks) gives nitriles.
The test distinguishes ethylamine from diethylamine; it does not tell aliphatic from aromatic primary amines.

Carbylamine reaction

\mathrm{RNH_2 + CHCl_3 + 3KOH \xrightarrow{\Delta} R{-}N{\equiv}C + 3KCl + 3H_2O}

Worked example

Which of these give the carbylamine test: 4-methylaniline, N-methylaniline, cyclohexylamine and triethylamine?

Practice this conceptself-check · 4 quick reps

The same idea in a real exam question:

JEE Mains · 2021 · Paper 11 · Q37Moderate

Example 1 · Amines · Carbylamine and Hinsberg Tests

Organic compound A with

CHCl_{3}/KOH

gives product

B

which can be decomposed by

H^{+}/H_{2}O

The carbylamine test covers aromatic amines too

Aniline gives phenyl isocyanide just as ethanamine gives ethyl isocyanide. The test separates primary from secondary and tertiary amines, not aliphatic from aromatic.

Isocyanide from a halide needs AgCN

KCN with an alkyl halide gives a nitrile, R–C≡N. AgCN gives the isocyanide, R–N≡C. An aryl halide gives neither under ordinary conditions.

Drill 4 more on carbylamine (isocyanide) test for primary amines

Concept 2 of 3: Hinsberg test: benzenesulphonyl chloride with primary, secondary and tertiary amines

Benzenesulphonyl chloride reacts with any amine that still has an N–H, giving a sulphonamide. What happens next depends on whether an N–H is left. The sulphonyl group makes a remaining N–H acidic, so a primary amine's sulphonamide dissolves in alkali. A secondary amine's sulphonamide has no N–H and stays as a solid. A tertiary amine does not react at all.

Definition

Hinsberg's reagent is benzenesulphonyl chloride, $\mathrm{C_6H_5SO_2Cl}$ ; p-toluenesulphonyl chloride works the same way.
Primary: $\mathrm{RNH_2 \to C_6H_5SO_2NHR}$ , soluble in KOH or NaOH because the N–H is acidic.
Secondary: $\mathrm{R_2NH \to C_6H_5SO_2NR_2}$ , a solid insoluble in alkali.
Tertiary: no reaction; no N–H to replace.
The same rules hold for aryl amines: aniline, N-methylaniline and diphenylamine all react; N,N-dimethylaniline and triphenylamine do not.
The test is used both to tell the three classes apart and to separate a mixture of them.

Amine class	Example	Product with the reagent	Behaviour in alkali
Primary aliphatic	$\mathrm{C_2H_5NH_2}$	$\mathrm{C_6H_5SO_2NHC_2H_5}$	Dissolves: the N–H is acidic
Primary aromatic	$\mathrm{C_6H_5NH_2}$	$\mathrm{C_6H_5SO_2NHC_6H_5}$	Dissolves: the N–H is acidic
Secondary aliphatic	$\mathrm{(C_2H_5)_2NH}$	$\mathrm{C_6H_5SO_2N(C_2H_5)_2}$	Insoluble solid: no N–H left
Secondary aromatic	$\mathrm{C_6H_5NHCH_3}$	$\mathrm{C_6H_5SO_2N(CH_3)C_6H_5}$	Insoluble solid: no N–H left
Tertiary	$\mathrm{(C_2H_5)_3N}$ or $\mathrm{C_6H_5N(CH_3)_2}$	No reaction	The amine is unchanged

Reacts and dissolves: primary. Reacts and stays solid: secondary. No reaction: tertiary.

Practice this conceptself-check · 4 quick reps

The same idea in a real exam question:

JEE Mains · 2022 · 26 June 2022 · Q137Moderate

Example 2 · Amines · Carbylamine and Hinsberg Tests

Which statement is NOT correct for p-toluenesulphonyl chloride?

A secondary amine's product does not dissolve in alkali

The sulphonamide from a secondary amine has no hydrogen on nitrogen, so alkali has nothing to remove. It stays as an insoluble solid. Only a primary amine's product dissolves.

A clear solution means a primary amine

When a primary amine reacts with the reagent in alkali, the sulphonamide dissolves as its salt and the solution stays clear. A precipitate means a secondary amine; an unchanged amine means a tertiary one.

Drill 10 more on hinsberg test: benzenesulphonyl chloride with primary, secondary and tertiary amines

Concept 3 of 3: Identifying an amine from its test results

Most identification questions give a formula and three or four observations. Each observation removes a class: the carbylamine smell means primary, an alkali-soluble Hinsberg product means primary, nitrogen gas with nitrous acid means primary aliphatic, and a coloured dye after diazotisation means primary aromatic. Read every clue against the table before drawing structures.

Definition

Every amine dissolves in dilute mineral acid as its salt; this confirms a base but not its class.
A primary aliphatic amine gives $\mathrm{N_2}$ with nitrous acid in the cold; a primary aromatic amine gives a diazonium salt that couples with β-naphthol to an orange-red dye.
A secondary amine with nitrous acid gives an N-nitrosamine, a yellow oil.
A tertiary aromatic amine such as N,N-dimethylaniline is nitrosated on the ring, para to nitrogen.
Optical activity points to a stereocentre: among $\mathrm{C_4H_{11}N}$ primary amines only butan-2-amine is chiral.

Test	Primary aliphatic	Primary aromatic	Secondary	Tertiary
$\mathrm{CHCl_3}$ + alcoholic KOH, heat	Foul-smelling isocyanide	Foul-smelling isocyanide	No isocyanide	No isocyanide
Hinsberg's reagent, then alkali	Sulphonamide, dissolves	Sulphonamide, dissolves	Sulphonamide, insoluble solid	No reaction
$\mathrm{NaNO_2}$ + HCl, cold	$\mathrm{N_2}$ gas and an alcohol	Diazonium salt, no gas at 273–278 K	N-Nitrosamine, yellow oil	Aliphatic: soluble salt; aromatic: p-nitroso compound
Diazotise, then β-naphthol in NaOH	No dye	Orange-red azo dye	No dye	No dye
Dilute HCl	Dissolves as a salt	Dissolves as a salt	Dissolves as a salt	Dissolves as a salt

The dye test is the one that separates primary aromatic from primary aliphatic amines.

Practice this conceptself-check · 4 quick reps

The same idea in a real exam question:

JEE Mains · 2026 · 23 Jan 2026 Shift 2 · Q45Moderate

Example 3 · Amines · Carbylamine and Hinsberg Tests

A student has been given a compound " x " of molecular formula

C_{6}H_{7}N

. ' x ' is sparingly soluble in water. However, on addition of dilute mineral acid , ' x ' becomes soluble in water. ' x ' when treated with

CHCl_{3}

and KOH (alc.) ' y ' is produced. ' y ' has a specific unpleasant smell. On treatment with benzenesulphonyl chloride, ' x ' gives a compound ' z ' which is soluble in alkali. The number of different "H" atoms present in '

z

' is:-

Dissolving in acid does not identify the class

Primary, secondary and tertiary amines all dissolve in dilute mineral acid as salts. Solubility in acid shows only that the compound is a base.

Benzylamine behaves as an aliphatic amine in the tests

Benzylamine gives the carbylamine test and an alkali-soluble Hinsberg product, but with nitrous acid it gives nitrogen gas and benzyl alcohol, not a stable diazonium salt, so it gives no azo dye.

Drill 4 more on identifying an amine from its test results

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Formulas (1)

Carbylamine (isocyanide) test for primary amines
Carbylamine reaction
$\mathrm{RNH_2 + CHCl_3 + 3KOH \xrightarrow{\Delta} R{-}N{\equiv}C + 3KCl + 3H_2O}$

Reference tables (2)

Hinsberg test: benzenesulphonyl chloride with primary, secondary and tertiary amines5 rows

Amine class	Example	Product with the reagent	Behaviour in alkali
Primary aliphatic	$\mathrm{C_2H_5NH_2}$	$\mathrm{C_6H_5SO_2NHC_2H_5}$	Dissolves: the N–H is acidic
Primary aromatic	$\mathrm{C_6H_5NH_2}$	$\mathrm{C_6H_5SO_2NHC_6H_5}$	Dissolves: the N–H is acidic
Secondary aliphatic	$\mathrm{(C_2H_5)_2NH}$	$\mathrm{C_6H_5SO_2N(C_2H_5)_2}$	Insoluble solid: no N–H left
Secondary aromatic	$\mathrm{C_6H_5NHCH_3}$	$\mathrm{C_6H_5SO_2N(CH_3)C_6H_5}$	Insoluble solid: no N–H left
Tertiary	$\mathrm{(C_2H_5)_3N}$ or $\mathrm{C_6H_5N(CH_3)_2}$	No reaction	The amine is unchanged

Reacts and dissolves: primary. Reacts and stays solid: secondary. No reaction: tertiary.

Identifying an amine from its test results5 rows

Test	Primary aliphatic	Primary aromatic	Secondary	Tertiary
$\mathrm{CHCl_3}$ + alcoholic KOH, heat	Foul-smelling isocyanide	Foul-smelling isocyanide	No isocyanide	No isocyanide
Hinsberg's reagent, then alkali	Sulphonamide, dissolves	Sulphonamide, dissolves	Sulphonamide, insoluble solid	No reaction
$\mathrm{NaNO_2}$ + HCl, cold	$\mathrm{N_2}$ gas and an alcohol	Diazonium salt, no gas at 273–278 K	N-Nitrosamine, yellow oil	Aliphatic: soluble salt; aromatic: p-nitroso compound
Diazotise, then β-naphthol in NaOH	No dye	Orange-red azo dye	No dye	No dye
Dilute HCl	Dissolves as a salt	Dissolves as a salt	Dissolves as a salt	Dissolves as a salt

The dye test is the one that separates primary aromatic from primary aliphatic amines.

Watch out for (6)

The carbylamine test covers aromatic amines too
→ Carbylamine (isocyanide) test for primary amines
Isocyanide from a halide needs AgCN
→ Carbylamine (isocyanide) test for primary amines
A secondary amine's product does not dissolve in alkali
→ Hinsberg test: benzenesulphonyl chloride with primary, secondary and tertiary amines
A clear solution means a primary amine
→ Hinsberg test: benzenesulphonyl chloride with primary, secondary and tertiary amines
Dissolving in acid does not identify the class
→ Identifying an amine from its test results
Benzylamine behaves as an aliphatic amine in the tests
→ Identifying an amine from its test results

Test yourself on Amines

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