Glucose occurs free as well as in combined forms naturally. It is present in sweet fruits and honey. Ripe grapes contain ~ 20% of glucose.
Preparation of Glucose
1. From sucrose: When sucrose is boiled with dil. HCl or H2SO4 in alcoholic solution, glucose, and fructose are obtained in equal amounts.
2. From Starch: Commercially glucose is obtained by hydrolysis of starch by boiling it with dilute H2SO4 at 393 K under pressure.
Properties of Glucose
Glucose has one aldehyde group, one primary, and four secondary hydroxyl groups. The following reactions confirm the presence of a carbonyl group in glucose.
i. Glucose reduces ammoniacal silver nitrate solution (Tollen’s reagent) to metallic silver and also Fehling’s solution to reddish brown cupper (I) oxide and itself gets oxidized to gluconic acid. This confirms the presence of an aldehydic group in glucose.
ii. On oxidation with nitric acid, glucose and also gluconic acid both yield a dicarboxylic acid – saccharic acid. This indicates the presence of a primary alcoholic group in glucose.
Responses