Chemistry · Amines · NEET
Only PRIMARY amines give the carbylamine test. This includes both aliphatic primary amines (like CH3NH2, methylamine) and aromatic primary amines (like C6H5NH2, aniline). The key is a free -NH2 group. Secondary amines (R2NH) and tertiary amines (R3N) do NOT give this test because they have no -NH2 group. NCERT states this clearly: secondary and tertiary amines do not show this reaction.
The reaction needs a nitrogen with two N-H bonds (an -NH2 group). The dichlorocarbene (:CCl2), formed from CHCl3 and KOH, inserts into these N-H bonds to build the isocyanide (R-N=C). A secondary amine (R2NH) has only one N-H bond and a tertiary amine (R3N) has zero N-H bonds, so neither can form the isocyanide. No isocyanide means no bad smell, so the test is negative.
The reagent is CHCl3 (chloroform, trichloromethane) plus ethanolic KOH, and you heat it. Not CCl4. NCERT gives the exact conditions: heat the primary amine with chloroform and ethanolic potassium hydroxide. A common NEET trap is an option that writes CCl4 or aqueous KOH. Remember: chloroform + alcoholic KOH + heat.
Yes. Aniline (C6H5NH2) is an aromatic PRIMARY amine, so it gives a positive carbylamine test. The reaction is C6H5NH2 + CHCl3 + 3KOH (heat) gives C6H5NC (phenyl isocyanide, foul smell) + 3KCl + 3H2O. But N-methylaniline (secondary) and N,N-dimethylaniline (tertiary) do NOT give the test because they have no -NH2 group.
It is an ISOCYANIDE (also called carbylamine or isonitrile), written R-NC or R-N=C. It is NOT an isocyanate (R-N=C=O). Isocyanate appears in the Hoffmann bromamide reaction, which is a different topic. In the carbylamine test the product is the foul-smelling isocyanide R-NC. Do not confuse the two, this is a classic NEET distractor.
Both find the class of an amine, but they work differently. The carbylamine test detects ONLY primary amines (it gives a bad smell for 1 amines, nothing for 2 and 3). The Hinsberg test uses benzenesulphonyl chloride and can tell all three classes apart. Use carbylamine when you only need to confirm a primary amine; use Hinsberg to separate 1, 2 and 3 amines fully.
Which of the following amines will give the carbylamine test?
Two reactions give the same foul-smelling product Z. Reaction 1: C2H5Cl --[X]--> Z. Reaction 2: C2H5CONH2 --[Br2 + NaOH]--> C2H5NH2 --[CHCl3 / ethanolic KOH, heat]--> Z. X and Z are:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The product is an isocyanide (R-NC), and isocyanides are known for a very strong, unpleasant smell. This bad smell is exactly what makes the test easy to spot in the lab. If you smell nothing, the amine was not primary.
Yes, in a simple way. A primary amine gives a positive test (bad smell). A secondary amine gives a negative test (no smell). So a positive result means primary, and no result means it was secondary or tertiary. To fully separate all three classes, use the Hinsberg test.
No. It is only a detection TEST for primary amines, not a method to make them. A NEET trap (NEET 2017) once listed 'carbylamine reaction' as a way to convert acetamide to methanamine; that is wrong. To make a primary amine from an amide, use Hoffmann bromamide degradation instead.
Yes. NCERT states that both aliphatic and aromatic primary amines give the carbylamine reaction. So methylamine (CH3NH2) and aniline (C6H5NH2) both give a positive test. The only requirement is a free -NH2 group.
Chloroform (CHCl3) and ethanolic (alcoholic) potassium hydroxide, KOH, with heating. Remember all three: CHCl3, alcoholic KOH, and heat. Aqueous KOH or CCl4 in an option is a wrong choice.
