Seliwanoff’s test is used to differentiate between keto sugar and aldo sugar.
Carbohydrates are converted to furfural derivatives by dilute HCl. Only furfural derivatives of keto-hexoses condense with Resorcinol to form a cherry red complex. This test is positive for sugar (Keto) when it gives cherry red colour complex.
1. Seliwanoff’s Reagent: i. Resorcinol, and ii. Concentrated HCl. 2. Original solution (0.8.) containing a carbohydrate
- Take 3ml of seliwanoff’s reagent in a test tube.
- Add 5ml of original solution.
- Heat the test tube just to boil.
- Avoid prolonged heating otherwise; it gives a false test.
The production of a Red colour indicates a positive reaction.
- No change in colour = Aldo sugar
- If cherry red colour appears = Keto sugar is present.
Avoid prolonged heating. Prolong boiling with aldoses is bound to give a false positive result, as the aldoses also start giving a similar reaction.
- Wash the apparatus before and after the experiment.
- Avoid prolonged heating as it will then gives a false result.