University:
Harrisburg University of Science and Technology
Course:
HEM 210 | Organic Chemistry I
Academic year:

2022
Views:

45

Pages:

2
Author:

Nesbyenvkk

Lecture notes – The seliwanoffs test and procedure The Seliwanoff’s test definition The Seliwanoff’s test is used to differentiate between sugars that have a ketone group (ketose) and sugars that have an aldehyde group (aldoses). This test is a timed color reaction specific to ketohexoses. There are Objectives of Seliwanoff’s test To detect the presence of ketohexoses in a given sample. To distinguish ketoses from aldoses. The Principle of Seliwanoff’s test The reagent of this test consists of resorcinol and concentrated HCl. The acid hydrolysis of polysaccharides and oligosaccharides yields simpler sugars. Ketoses are more rapidly dehydrated than aldoses. Ketoses undergo dehydration in the presence of concentrated acid to yield 5-hydroxymethyl furfural. The dehydrated ketose reacts with two equivalents of resorcinol in a series of condensation reactions to produce a complex (not a precipitate), termed xanthenoid, with deep cherry red color. The Aldoses may react slightly to produce a faint pink to cherry red color if the test is prolonged. The product and reaction time of the oxidation reaction helps to distinguish between carbohydrates. Other carbohydrates like sucrose and inulin also give a positive result for this test as these are hydrolyzed by acid to give fructose. The Reaction Seliwanoff’s test reaction Figure: Seliwanoff’s test with fructose as an example. Image Source: Yikrazuul. The Requirements Reagent The Seliwanoff’s reagent: add 0.05% resorcinol (m-hydroxybenzene) in 3 N HCl. Dissolve 50 mg resorcinol in 33 ml concentrated HCl and make it 100 ml with water. Test sample Distilled water Materials required The Test tubes Test tube stand Pipettes Equipment Water bath The Procedure of Seliwanoff’s test Take two clean, dry test tubes and add 1 ml of the test sample in one test tube and 1 ml of distilled water in another as blank. Add 2 ml of Seliwanoffs’ reagent to both the test tubes. Keep both the test tubes in a water bath for 1 min. Observe the formation of color and note it down. The Result and Interpretation of Seliwanoff’s test The Seliwanoff’s test The formation of the cherry red-colored complex indicates a positive result which means that the given sample contains ketoses. The absence of such color or the appearance of the color after a prolonged period of time indicates a negative result which means that the test sample doesn’t have ketoses.