Chemical Bonding and Molecular Structure

Sucrose

+Sucrose is common sugar. It is a disaccharide, a molecule composed of two monosaccharides are glucose and fructose. In plants, sucrose is naturally produced, from which table sugar is refined.

Sucrose

                                                                                                     Sucrose

What is Sucrose?

Sucrose has the molecular formula \(C_{12}H_{22}O_{11}\). As per human consumption, sucrose is extracted and refined from either sugarcane or sugar beet. Sugar mills are typically located in tropical regions near where sugarcane is grown – crush the cane. Basically, it produces raw sugar that is shipped to other factories for refining into pure sucrose.

Sugar beet factories are located in temperate climates. It is a place where the beet is grown and processed and then the beets directly into refined sugar. The refining process of sugar involves washing the raw sugar crystals before dissolving them into a sugar syrup. This sugar syrup is filtered and then passed over carbon to remove any residual colour.

The sugar syrup is later concentrated by boiling syrup under a vacuum. It is then crystallized as the final purification process to produce crystals of pure sucrose. These crystals are clear, odourless, and sweet. Sugar is usually added ingredient in food production and food recipes. About 185 million and more tonnes of sugar are produced worldwide.

Etymology of Sucrose

The word sucrose was given in 1857. It was given by English chemist William Miller from the French sucre (“sugar”). The generic chemical suffix for sugars is -ose. The abbreviated term that is ‘Suc’ is in use for sucrose in the scientific literature. The name saccharose was given in 1860 by the French chemist Marcellin Berthelot. Saccharose is an obsolete name for sugars. It is especially for sucrose.

Sources of Sucrose

In nature, sucrose is mainly present in many of the plants, and in particular their roots, fruits and nectars. It serves as a way to store energy, primarily from photosynthesis. Many mammals, birds, insects and bacteria accumulate and feed on the sucrose in plants and also for some it is their main food source. Seen from a human consumption perspective, honeybees are important because they accumulate sucrose and produce honey. It is an important foodstuff all over the world. The carbohydrates in honey itself consist of fructose and glucose with trace amounts of sucrose only.

As fruits ripen, their sucrose content usually rises sharply, but there are some fruits that contain almost no sucrose. These fruits are grapes, cherries, blueberries, blackberries, figs, pomegranates, tomatoes, avocados, lemons and limes. Though, with the emergence of industrialization, it has been increasingly refined and consumed in all types of processed foods.

Structure of Sucrose

The glycosidic linkage in sucrose connects the two carbohydrate groups. There are no anomeric hydroxyl groups in a sucrose molecule. Therefore, sucrose can is classified as a non-reducing sugar as it does not act as a reducing agent.

Properties of Sucrose

The Molar Mass or Molecular Weight of sucrose is 342.30 g/mol. The density of sucrose is \(1.587 g/cm^3\). The physical appearance of sucrose is white and crystalline solid. The melting point of sucrose is 459 K.

Physical Properties of Sucrose

  1. Sucrose has a monoclinic crystal structure.
  2. Sucrose when subjected to high temperatures is over \(186^oC\). This compound decomposes and yields caramel.
  3. The solubility of sucrose in water is at a temperature of \(20^oC\) is 203.9g/100mL
  4. The standard enthalpy of combustion corresponding to sucrose is \(5647 kJ.mol^{-1}\).

Chemical Properties of Sucrose

Thermal Degradation of Sucrose:

When sucrose is heated to temperatures above 186 degrees Celsius, sucrose undergoes a decomposition reaction to give rise to caramel. Similar to other carbohydrates, sucrose undergoes combustion in the presence of oxygen to yield water \(H_2O\) and carbon dioxide \(CO_2\) as the products. Sucrose reacts with potassium nitrate that is a powerful oxidizing agent with the chemical formula KNO3 to yield a special type of fuel called rocket candy. The chemical equation for the reaction between sucrose and potassium nitrate is

\(C_{12}H_{22}O_{11} + 6KNO_3 \rightarrow  3K_2CO_3 + 3N_2 + 9CO + 11H_2O\)

Also, sucrose undergoes a combustion reaction with chloric acid to yield hydrochloric acid, water, and carbon dioxide. This reaction can be represented by the following chemical equation:

\(C_{12}H_{22}O_{11} + 8HClO_3 \rightarrow  8HCl + 11H_2O + 12CO_2\)

Dehydration of Sucrose with Sulfuric Acid

Sucrose is subjected to the process of dehydration in the presence of sulfuric acid to get a black solid that is rich in carbon. The idealized chemical equation for this process.

\(C_{12}H_{22}O_{11} + H_2SO_4 → 11H2_O + 12C\) (carbon-rich solid) + heat

It should be noted that a small amount of \(SO_3\) can be produced in this process.

Hydrolysis

Hydrolysis of sucrose breaks the glycosidic bond in sucrose converting it into glucose and fructose. It is so slow that solutions of sucrose can sit for years with negligible change. If the enzyme sucrase is added to the reaction, the reaction will proceed rapidly. The process of hydrolysis is accelerated with the help of acids, such as cream of tartar or lemon juice, both weak acids. Also, gastric acidity converts sucrose into glucose and fructose during digestion. The bond between them is an acetal bond which can be broken by an acid.

Synthesis and Biosynthesis of Sucrose

The biosynthesis of sucrose proceeds through the precursors UDP-glucose and fructose 6-phosphate. It is catalysed by the enzyme sucrose-6-phosphate synthase. The energy for the reaction completion is gained by the cleavage of uridine diphosphate (UDP). Sucrose is produced by plants, algae and cyanobacteria but not by other organisms. Sucrose is the product of photosynthesis. It is found in many food plants along with the monosaccharide fructose. In many fruits like pineapple and apricot, sucrose is the actual and main sugar.

Uses of Sucrose

Some uses of sucrose are as follows

  1. It is one of the most important components of soft drinks and other beverages.
  2. This compound is in use in many pharmaceutical products.
  3. It serves as a chemical intermediate for many emulsifying agents and detergents.
  4. It serves as a food thickening agent and also as a food stabilizer.
  5. The shelf lives of many food products, such as jams and jellies, are extended with the help of this compound.
  6. The use of sucrose in baking results in the brown colour of the baked products.
  7. This compound also serves as an antioxidant as the compound inhibits oxidation.
  8. Sucrose is broadly in use as a food preservative.

FAQs on Sucrose

Question 1: Is sucrose soluble in ethanol?
Answer: Sugar or sucrose is slightly soluble in ethanol. In addition to it, if the alcohol is cold it will dissolve even less of the sucrose. The sugar that is not dissolved within the ethanol settles at the bottom of the bottle. The salt is also very water-soluble.

Question 2: What is the function of sucrose in plants?
Answer: Sucrose is the most common type of carbohydrate in use for the carriage of carbon in a plant. Sucrose can be dissolved in water, thus retaining a stable structure of itself. Sucrose is then be transported into the phloem by plant cells, the special vascular tissue intended for sugar transport.

Question 3: What foods contain sucrose?
Answer: Sucrose is found in fruits and vegetables. It is also processed for use in cooking and food processing from sugar cane and sugar beets. The sucrose is found naturally in sugar cane, sugar beets, bananas, grapes, carrots, and other fruits and vegetables.

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