Question

Write the reaction of an amino acid with ninhydrin reagent?

Answer 1

Hint: Amino acid are the compounds which consists of amino and the carboxylic group and when they are made to react with the laboratory reagent ninhydrin gives the purple color product (major product) along with the carbon carbon dioxide and aldehyde.

Complete step by step answer:
Amino acids are the organic compounds containing both the amino group and carboxylic group in their molecules. They are represented by the general formula as:
                    

Here, -C- is called alpha carbon because the carbon atom attached next to the carboxylic group is called alpha carbon.
R is the side chain and is different for different amino acids.
-COOH is the carboxylic group.
$-\text{N}{{\text{H}}_{2}}$ is the amino group.

In the amino acid , the acidic properties are due to the $-\text{NH}_{3}^{+}$ group and the basic properties are due to the $\text{-CO}{{\text{O}}^{-}}$.
On the other hand, ninhydrin is an organic compound and is tricycle 1,2,3 -trione and is a very strong oxidizing agent ( that oxidizes the other substance).
When amino acids are made to react with the ninhydrin, they undergo decarboxylation (i.e. there is removal of carbon dioxide) and it produces carbon dioxide , ammonia and an aldehyde and the ninhydrin which had undergone reduction further reacts with the ammonia and produces purple colored complex which is known as the Ruhemann’s purple. The reaction occurs as:

Note: To detect the presence of amino acids , they’re made to react with the ninhydrin reagent which is basically yellow in colour, but when reacted with the amino acids, the resultant product is in purple colour which indicates that amino acid is present in that very compound.