Chemistry · Amines · NEET
It gives an N-nitrosamine, a yellow oily liquid with the structure R2N-NO. For example, dimethylamine gives N,N-dimethylnitrosamine, (CH3)2N-NO. The nitrous acid is made in the flask from NaNO2 + HCl (or dil. H2SO4). This is the single fact NEET wants: 2 degree amine + HNO2 gives a yellow oil.
To form a diazonium ion (R-N2+) or to lose N2 gas, the nitrogen must have an H that can be removed after the N-N bond forms. A primary amine (R-NH2) has that extra H. A secondary amine (R2N-H) has only one H, and after the N-NO bond forms the nitrogen is left as R2N-NO with no way to eliminate nitrogen. So the reaction stops at the stable N-nitrosamine and no N2 is evolved.
A primary aliphatic amine (like ethylamine) forms a very unstable aliphatic diazonium salt that instantly loses N2 gas quantitatively and gives an alcohol. A secondary amine forms a stable yellow oily N-nitrosamine and gives no gas. So: bubbles of N2 gas points to primary; a yellow oil that separates points to secondary.
A tertiary amine (R3N) has no N-H at all, so it cannot form an N-nitroso compound the same way. It simply forms a water-soluble salt with the acid (a nitrite salt of the amine). No yellow oil, no gas. This lets HNO2 tell apart all three classes: 1 degree gives gas/alcohol, 2 degree gives yellow oil, 3 degree gives a soluble salt.
Nitrous acid (HNO2) is unstable, so it is generated in the reaction mixture from sodium nitrite and a mineral acid: NaNO2 + HCl gives HNO2 + NaCl. In equations you may see it written as NaNO2/HCl at low temperature. This same reagent diazotises aromatic primary amines, so read the amine class carefully.
N-nitrosamines are known carcinogens (cancer-causing), which is why this reaction is famous. For NEET you only need the chemistry: secondary amine + HNO2 gives R2N-NO, a yellow oily liquid, no N2. Knowing it is carcinogenic is a useful memory tag but not the tested point.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a yellow oily liquid (an N-nitrosamine, R2N-NO) that usually separates out from the aqueous mixture.
(CH3)2NH + HNO2 gives (CH3)2N-NO + H2O. The product is N,N-dimethylnitrosamine, a yellow oil. No N2 gas is released.
No. Nitrogen gas comes only from primary aliphatic amines (via an unstable diazonium salt). Secondary amines stop at the stable nitrosamine.
Primary aliphatic amine gives N2 gas (brisk effervescence) and an alcohol; secondary amine gives a yellow oily nitrosamine; tertiary amine gives only a water-soluble salt. Three different results, one reagent.
By mixing sodium nitrite with a cold mineral acid: NaNO2 + HCl gives HNO2 (nitrous acid) in situ, because free HNO2 is too unstable to store.
