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Molisch Test: Sugar Detection

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Questions and Answers

What is the primary function of the Molisch test?

To analyze the structure of polysaccharides

To detect the presence of sugar alcohols

To indicate the presence of sugars (correct)

To identify the type of sugar present

What happens when aldohexose and ketose sugars are heated with strong, concentrated mineral acids?

They are converted into sugar alcohols

They are converted into polysaccharides

They are dehydrated to form furfural or its derivatives (correct)

They are broken down into disaccharides

What is the first step in the Molisch test when testing disaccharides and polysaccharides?

Dehydration of the sugars

Hydrolysis of the glycosidic bonds (correct)

Formation of furfural derivatives

Condensation with α-Naphtol

What is the role of α-Naphtol in the Molisch test?

It condenses with furfural derivatives to form colored products Signup and view all the answers

Why does the Molisch test take longer with polysaccharides?

Because the glycosidic bonds need to be hydrolysed first Signup and view all the answers

What is not detected by the Molisch test?

Sugar alcohols Signup and view all the answers

Study Notes

Molisch Test

A general non-selective test used to indicate the presence of sugars, including monosaccharides, disaccharides, and polysaccharides.
The test is negative for sugar alcohols, such as sorbitol, mannitol, and 2-deoxy-2-amino acid.

Properties of Sugars

Monosaccharides are stable in dilute mineral acids, even when heated.
When heated with strong, concentrated mineral acids (e.g., H2SO4), aldohexose, aldopentose, and ketose sugars undergo dehydration, forming furfural or furfural derivatives.

Detection Mechanism

Furfural and its derivatives readily condense with α-Naphtol and certain other phenolic compounds to form highly colored products.
In disaccharides (e.g., sucrose) and polysaccharides (e.g., starch, cellulose), concentrated acid first hydrolyzes the glycosidic bonds between the monomer sugars.
This releases the "building block subunits" as monosaccharide sugars, which are then dehydrated by the acid to form furfural or its derivatives.

Limitations

The test is generally slower with polysaccharides.

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Description

The Molisch test is a general test used to detect the presence of sugars, including monosaccharides, disaccharides, and polysaccharides. It is negative for sugar alcohols and 2-deoxy-2-amino acids. Learn about the reaction mechanisms and conditions required for this test.