Chemistry of Glucose: Preparation, Properties, Test and Uses of Glucose

Glucose is commonly called Grape sugar or Dextrose. The name Dextrose is from "Dextrorotatory", a term used to describe the ability of natural glucose solution, in stereo-isomerism, to rotate plane polarised light to the right. This is why it is simply called D-Glucose. The other type of glucose call the L-Glucose (laevorotatory glucose) rotates polarised light to the left and is uncommon in nature.

Glucose undergoes an array of chemical reactions in both living systems and the laboratory. Glycolysis is the most frequent reaction of glucose in biological systems. Here, the reaction can occur in both unicellular organisms like in the formation of ATP in E.coli, and complex multicellular system where it forms ATP and serve as a precursor to the citric acid cycle and the electron transport chain.

Although glucose is prepared from higher carbohydrates (polysaccharides) by various biological traditional methods, controlled chemical laboratory methods can also be used to prepare and standardise Glucose.

The most common method of preparation involves the hydrolysis of starch with dilute acid. Here, the polysaccharides complex starch molecule is hydrolysed with water to form large amount of glucose molecules.

(C₆H₁₀O₅)_n + nH₂O → nC₆H₁₂O₆

The procedure involves heating starch with two times its mass of dilute tetraoxosulphate(VI) acid for two hours to form glucose solution. Then the solution is neutralised of the acid by the addition of solid sodium trioxocarbonate(IV). The solution is then filtered with a filter paper and pieces of charcoal is added and shaken vigorously to decolorise the solution. The charcoal is filtered off, and the solution is concentrated and cooled to crystallize the glucose into colourless solid.

Glucose like other carbohydrates could readily undergo dehydration in the presence of concentrated acid to form black residue of carbon. Here, concentrated tetraoxosulphate(VI) acid is heated with glucose to liberate water leaving behind solid mass or residue of carbon.

C₆H₁₂O₆ → 6C + 6H₂O

Another very important property of glucose is in how it is fermented to ethanol. Here, glucose solution can can be fermented in the presence of the yeast enzyme zymase to form ethanol (C₂H₅OH) and carbon(IV) oxide gas (CO₂)

C₆H₁₂O₆ (aq) → 2C₂H₂OH(aq) + 2CO₂(g)

Glucose fermentation is what happens in the array of fermentation in diverse culture and traditions from around the world.

Another important property of glucose lies in the presence of the alkanal group (-CHO). This group is responsible for the change in the colour of Fehling's solution to red. That is glucose reduces Cu²⁺ to Cu¹⁺ where the Fehling solution is turned into red precipitate of copper(I) oxide.

The property of glucose as a reducing agent is essential for the test for glucose. Here, a few drops of Fehling solution is added to 5cm³ of glucose solution in a test-tube. The solution is boiled until a brick-red precipitate is formed.

Glucose is an essential part of carbohydrates formed from an array of carbohydrate diets during digestion within the alimentary canal of humans and other animals. Since it is the end product of digestion that is directly absorbed by diffusion into the body, pre-prepared glucose is now used as immediate source of energy for sick people and people who are engaged in strenuous exercises like in sporting activities. Glucose has also found commercial importance in food processing where it is essential in the manufacture of Sweet, Candy, Jam, Chocolate, e.t.c.