Question

Write the reaction of an amino acid with ninhydrin reagent?

Answer 1

When excess of ninhydrin, which is originally yellow in color, reacts with a free $\alpha$-amino acid group, a purple colored dye known as Ruhemann's purple is formed along with an aldehyde and liberation of $C{O}_2$ gas(primary amines does not liberate $C{O}_2$). The presence of Ruhemann's purple imparts purple color to the product which forms the basis of the Ninhydrin test in order to detect amino acids.