Seliwanoff's test

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Positive Seliwanoff’s test

Seliwanoff’s test is a chemical test which distinguishes between aldose and ketose 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 an aldose. This test is based on the fact that, when heated, ketoses are more rapidly dehydrated than aldoses. It is named after Theodor Seliwanoff, the chemist that first devised the test.

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Seliwanoff-Reaction

The reagents consist of resorcinol and concentrated hydrochloric acid:

• The acid hydrolysis of polysaccharides and oligosaccharides yields simpler sugars followed by furfural.

• The dehydrated ketose then reacts with the resorcinol to produce a deep cherry red color. Aldoses may react slightly to produce a faint pink color.

Fructose and sucrose are two common sugars which give a positive test. Sucrose gives a positive test as it is a disaccharide consisting of fructose and glucose.