Seliwanoff’s Test

Is a chemical test which distinguishes between aldoses and ketoses sugars.
Ketoses are distinguished from aldoses via their ketone/aldehyde functionality.

If the sugar contains a ketone group, it is a ketose and if it contains an
aldehyde group, it is aldoses.

Seliwanoff’s reagent contain of resorcinol and HCl.

The
test
present
reagent
dehydrates
ketohexoses
to
form
5-
hydroxymethylfurfural further reacts with resorcinol present in the test reagent
to produce a red product within two minutes but aldohexoses react to form the
same product, but do so more slowly.

Glucose and fructose both have the same molecular formula (C6H12O6) but
they differ structurally.
Steps:
1. Put 1 ml of Seliwanoff's reagent in a clean test tube.
2. Add to it about half ml of carbohydrate solution and mix well.
3. Boil the tube in water bath for 2 minute.
4. Formation of red color indicates presence of fructose (ketose sugars).
Test
Observation
Result
Seliwanoff's test
Red color
Ketose sugar ( fructose)
*Note: This test used to differ between fructose and glucose (ketose and aldose
sugars) when the two give the same result with Benedict's test .
*Note: sucrose give a positive result to the test, This is because Sucrose is actually a
disaccharide molecule, consisting of Fructose and Glucose .
*Note: The Seliwanoff’s reagent contains HCl , which is highly corrosive , so it must
be handled carefully.