What is the Schiff Test?
The Schiff test is a chemical test used to check for the presence of aldehydes in a given analyte. This is done by reacting the analyte with a small quantity of a Schiff reagent (which is the product formed in certain dye formulation reactions such as the reaction between sodium bisulfite and fuchsin). The structure of a decolourized Schiff reagent is illustrated below.
In this qualitative test for the aldehyde functional group, the development of a purple or magenta colour upon the addition of a few drops of the analyte to the decolourized Schiff reagent confirms the presence of aldehydes.
Schiff Test Mechanism
The bisulfite and para-rosaniline react together to afford a decolourized adduct whose central carbon is sulfonated. Now, the free & uncharged amine groups belonging to the aromatic ring that react with the aldehyde group to form an aldimine. This aldimine group is an excellent electrophile and, therefore, undergoes further reaction with the bisulfite ion. Finally, a purple or magenta coloured bisulfite adduct is formed.
The general mechanism of the Schiff test is illustrated above. To learn more about the Schiff reagent, the Schiff test, and other related concepts (such as Schiff bases), register with BYJU’S and download the mobile application on your smartphone.