Question

Which of the following statements are not correct? (a) Hydrolysis of lactose gives D-glucose and D-galactose. (b) In sucrose, glucose is present in the furanose form while fructose is present in the pyranose form. (c) Gun cotton is cellulose triacetate. (d) On heating with dilute \(\mathrm{H}_{2} \mathrm{SO}_{4}\) under pressure, cellulose undergoes hydrolysis to give D-glucose.

Short answer

a) Hydrolysis of lactose gives D-glucose and D-galactose. b) In sucrose, glucose is present in the furanose form while fructose is present in the pyranose form. c) Gun cotton is cellulose triacetate. d) On heating with dilute H2SO4 under pressure, cellulose undergoes hydrolysis to give D-glucose. Answer: Statements (b) and (c) are not correct. In sucrose, both glucose and fructose are present in the pyranose form, not the furanose form. Furthermore, gun cotton is a form of nitrocellulose, not cellulose triacetate.

Step-by-step solution

Statement (a)

Hydrolysis of lactose gives D-glucose and D-galactose. This statement is correct. When lactose undergoes hydrolysis, it is broken down into its constituent monosaccharides, D-glucose and D-galactose.

Statement (b)

In sucrose, glucose is present in the furanose form while fructose is present in the pyranose form. This statement is not correct. Both glucose and fructose are present in the pyranose form in sucrose. In sucrose, the two monosaccharides are linked by an α(1→2) glycosidic bond, with the glucose in its pyranose form and fructose also in its pyranose form.

Statement (c)

Gun cotton is cellulose triacetate. This statement is not correct. Gun cotton is a form of nitrocellulose, not cellulose triacetate. It is produced by treating cellulose with a mixture of nitric acid and sulfuric acid, resulting in the formation of cellulose nitrate. Cellulose triacetate is a different compound used in making photographic films, and it is synthesized using cellulose and acetic anhydride.

Statement (d)

On heating with dilute H2SO4 under pressure, cellulose undergoes hydrolysis to give D-glucose. This statement is correct. During the hydrolysis of cellulose, dilute sulfuric acid (H2SO4) acts as a catalyst to break down the β(1→4) glycosidic bonds between the glucose units, converting the cellulose into its monomer, D-glucose. This process can be carried out under pressure and heat to speed up the reaction.

Key concepts

Lactose Hydrolysis

Lactose is a disaccharide composed of two sugar units: D-glucose and D-galactose. When lactose undergoes hydrolysis, it is split into these two monosaccharides. This reaction is typically catalyzed by the enzyme lactase, which cleaves the glycosidic bond between glucose and galactose.
Lactose hydrolysis is an essential process, especially for lactose-intolerant individuals, as it breaks down lactose for easier digestion. Understanding this process not only aids in grasping basic carbohydrate chemistry but also provides insight into digestive functioning.

• Produces D-glucose and D-galactose.
• Catalyzed by enzyme lactase.
• Important for lactose digestion.

Sucrose Glycosidic Linkage

Sucrose is a common disaccharide found in many dietary items, consisting of glucose and fructose. These two sugar units are linked through an α(1→2) glycosidic bond. While in some carbohydrates, glucose and fructose may appear in different forms, in sucrose, both are present in the pyranose form.
The distinction of the glycosidic linkage in sucrose is vital because it affects the chemical properties of the sugar, including solubility and reactivity. Unlike other sugars, sucrose does not have a free aldehyde or ketone group, making it a non-reducing sugar. Understanding this helps in its identification and role in biochemical pathways.

• Glucose and fructose linked by α(1→2) bond.
• Both are in pyranose form in sucrose.
• Non-reducing sugar due to glycosidic linkage.

Nitrocellulose

Nitrocellulose, often referred to as guncotton, is produced by treating cellulose with a mixture of nitric and sulfuric acids. This process transforms the cellulose by introducing nitro groups, resulting in a product that is highly flammable and explosive.
Nitrocellulose is a derivative of cellulose, which is naturally found in plants. The addition of nitrate groups changes its properties dramatically, making it useful in applications like propellants and lacquers. Its explosive nature lies at the core of its utility in munitions.

• Produced from cellulose and nitric acid.
• Used in explosives and propellants.
• Highly flammable due to nitrate groups.

Cellulose Hydrolysis

Cellulose is a polysaccharide consisting of long chains of glucose units, linked by β(1→4) glycosidic bonds. When cellulose undergoes hydrolysis, these bonds are broken down to release glucose monomers. This reaction is often catalyzed by acids like dilute sulfuric acid and involves heat and pressure to increase the reaction rate.
Understanding cellulose hydrolysis is essential, especially in industries focused on biomass conversion and biofuel production. Breaking down cellulose efficiently is key to converting plant material into glucose, which can then be fermented into ethanol, a biofuel. This process emphasizes the importance of catalytic and environmental conditions for effective hydrolysis.

• Breaks down β(1→4) glycosidic bonds.
• Catalyzed by dilute H2SO4, heat, and pressure.
• Key in biomass conversion processes.