6 Questions
What is the primary function of the Molisch test?
To indicate the presence of sugars
What happens when aldohexose and ketose sugars are heated with strong, concentrated mineral acids?
They are dehydrated to form furfural or its derivatives
What is the first step in the Molisch test when testing disaccharides and polysaccharides?
Hydrolysis of the glycosidic bonds
What is the role of α-Naphtol in the Molisch test?
It condenses with furfural derivatives to form colored products
Why does the Molisch test take longer with polysaccharides?
Because the glycosidic bonds need to be hydrolysed first
What is not detected by the Molisch test?
Sugar alcohols
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.
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.
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