REACTIONS OF DISACCHARIDES

 

REACTIONS OF DISACCHARIDES

 

                Disaccharides are obtained by the combination of two mono saccharides by a glycosidic linkage. On treatment with hot acids or with enzymes the disaccharides can be hydrolysed to the constituents monosaccharides, examples of commonly used disaccharides and their constituent monosaccharides are given below.

 

Sucrose :               Sweetening sugar (Cane Sugar) - Glucose + fructose

                                (Aldehydic group of glucose is linked with keto group of fructose.)

 

Lactose :               Milk sugar = Glucose + Galactose

                                (Aldehydic group of galactose is linked with alcoholic group of glucose(4c).

 

Maltose                 :               Malt sugar = Glucose + Glucose. Aldehydic group of glucose is

                                linked with alcoholic group of glucose (4c).

 

Maltose is obtained in hydrolysis of starch and other polysaceharides.

 

Maltose and lactose are reducing sugars, where as sucrose is non redcuing sugar.

 

Perform the following tests with lactose, maltose and sucrose.

 

(1) Molisch test (2) Seliwanoff’s test (3) Barfoed’s test (4) Fehling’s test. (5) Benedict’s test (6) Inversion test, (For sucrose only).

 

Acid Hydrolysis:

                To 5ml of sucrose solution add 5 drops of conc HCl boil for a minute and cool. Neutralize the hydrolysed sample with 40% sodium hydroxide and perform Fehling’s test on it. Write your inference