Sucrose: Definition, Structure, Properties, Uses & Sample Questions

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Sucrose

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Sucrose is a disaccharide, or a molecule made up of two monosaccharides. It is gathered and refined from either sugarcane or sugar beet for human use. Sugar mills crush sugarcane and produce raw sugar, which is sent across to other industries for refining into pure sucrose. They are often found in tropical locations near areas where sugarcane is farmed. 

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Structure of Sucrose

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Though both glucose and fructose are monosaccharides, they combine to form the disaccharide sucrose. This is a crucial technique for energy storage and compression. Plants use this to make it easier for sugar to transfer significant amounts of energy.

The carbonyl group (carbon double linked to an oxygen) is located at the end of the carbon chain in glucose, making it an aldose. The molecule makes a 6-sided ring. On the other side, fructose is a ketose. This indicates that the carbonyl group is located in the molecule's centre. It forces fructose into a five-sided ring structure in this case.

An enzyme supports a plant in making sucrose by smashing these two rings together and extracting a molecule of water. This is known as a condensation reaction, and it results in the formation of a glycosidic link between the two molecules. The reaction might also go the other way, as shown in the figure. A molecule of water can be brought back in to dissolve sucrose into fructose and glucose. This is what sucrose looks like after it's been digested.

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Properties of Sucrose

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Chemical Data

Physical Properties

• Sucrose's crystal structure is monoclinic
• This chemical decomposes at high temperatures (above 186°C), resulting in caramel.
• At 20°C, it dissolves in water with a solubility of 203.9g/100mL.
• The standard enthalpy of combustion for sucrose is 5647 kJ.mol^-1.

Chemical Properties

• Sucrose when combusted goes on to produce carbon dioxide and water as a byproduct.
• This chemical produces hydrochloric acid, carbon dioxide, and water when treated with chloric acid.
• Glucose and fructose is the result when the glycosidic bond connecting the two carbohydrates in a C₁₂H₂₂0₁₁ molecule is broken during hydrolysis.
• Sucrose can be dehydrated with the help of H₂So₄(which works as a catalyst) to produce a black carbon-rich solid.

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Thermal Degradation of Sucrose

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• Sucrose, when subject to temperatures greater than 186° C, degrades to form ‘caramel’. 
• It combusts when exposed to Oxygen to produce water and Carbon dioxide comparable to other carbohydrates. 
• A form of fuel known as, ‘Rocket Candy’ is produced when sucrose reacts with potassium nitrate (KNO₃ – a potent oxidizing agent).

The chemical reaction for Rocket Candy is as follows:

C₁₂H₂₂O₁₁ +6KNO₃+ 3K₂CO₃+3N₂+9CO+11H₂O 

• It's also worth mentioning that sucrose reacts with chloric acid to produce hydrochloric acid, water, and carbon dioxide. The following chemical equation can be used to depict this reaction:

C₁₂H₂₂O₁₁ + 8HClO₃  → 8HCl + 11H₂O + 12CO₂

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Dehydration of Sucrose with Sulfuric Acid

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Sucrose can be dehydrated in the presence of sulfuric acid to produce a black solid with a high carbon content. The idealized chemical equation for the process is as shown below.

C₁₂H₂₂O₁₁ + H₂SO₄ → 11H₂O + 12C (carbon-rich solid) + heat

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Uses of Sucrose

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• One of the most essential ingredients in soft drinks and other liquids is sucrose
• This substance is found in a variety of pharmacological medications
• Many detergents use it as a chemical intermediate.
• It can also be used as a thickening agent and a food stabiliser.
• Sucrose helps to increase the shelf life of numerous food products, such as jams and jellies.
• The brown colour of baked goods is due to the use of sucrose in baking.
• This substance is treated as an antioxidant (a compound that inhibits oxidation).
• Sucrose is frequently used in the food industry as a preservative.

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Things to Remember

• Sucrose is a disaccharide sugar which means it is made up of two monosaccharide sugar units. 
• For sucrose, the two units are glucose and fructose. The word is derived from the French word which means "fruit."
• Sucrose works as a sweetener in foods and soft drinks, as well as in syrup processing, confectionery, preserves and jams, demulcents, and medical items.
• Glucose and fructose is the result when the glycosidic bond connecting the two carbohydrates in a C₁₂H₂₂0₁₁ molecule is broken during hydrolysis.
• In ethanol, sugar (sucrose) is only marginally soluble. Furthermore, when the alcohol is cold, it dissolves much less sugar. The sugar won’t dissolve until the ethanol settles at the bottom of the bottle.

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