Question

Would N-acylated amino acids give a color reaction with ninhydrin? EXPLAIN YOUR ANSWER.

Answer 1

No, N-acylated amino acids would not give the color (especially blue color) with the ninhydrin.

Ninhydrin reacts with the free amine group (NH₂) to give a blue colored solution. Only primary amines can give this blue colored solution not the secondary or tertiary amines or amines attached to a quaternary carbon.

Ninhydrin reaction is most widely used in the solid phase peptide synthesis to monitor the progress of the coupling reaction. This test is known as Kaiser test.

If the coupling is successful, there won¨t be any color or yellow colored solution in Kaiser test (since there is no free amine group)

If coupling is unsuccessful, there will be free amine group and the color of the solution is blue in Kaiser test