Seliwanoff's test

Seliwanoff’s test is utilized for the differentiation of aldose and ketose sugars.Reagents consist of resorcinol with Conc. HCl, acid hyrdolysis the polysacchardies and oligosaccharides thus yielding simpler sugars.A ketose is said to be present if the mixture turns red. For a general preview, one way to differentiate ketoses from aldoses is to look for the functional group attached to it. When a ketone is attached to it, it is a ketose; however, if an aldehyde is attached to it, it is an aldose. Ketoses are more rapidly dehydrated than aldoses when heated. 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 the two common sugars which give positive test. Sucrose, a disaccharide consisting of Fructose and Glucose also gives positive test. The reason behind this is the presence of Concentrated HCl which hydrolysis Sucrose into its Components.Thus Fructose being a keto sugar give positive seliwanoff's test.