Question

Do all amino acids give a positive xanthoproteic test?

Answer 1

Xanthoproteic test:

1. Xanthoproteic test is used to detect the presence of aryl amino acids.
2. Amino acids are organic functional groups in which a nitrogen atom is bonded to two hydrogen atoms and one carbon atom of the alkyl or aryl group.
3. In the xanthoproteic test, we add hot nitric acid $\left({\mathrm{HNO}}_3\right)$ in a solution of protein which forms yellow-coloured nitro derivatives in the solution.
4. All aryl amino acids give xanthoproteic test except phenylalanine, this is so because the benzene group present in phenylalanine is very stable and it does not react with nitric acid in normal conditions.
5. Therefore, all amino acids do not give a positive xanthoproteic test