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Glycerol - Uses, Structure, Formula, Formation, Chemical and Physical Properties

 

Glycerol, also known as glycerine or propane-1,2,3-triol, is an organic compound that has a wide range of applications in the food, pharmaceutical, medical, and cosmetics industries. 

Glycerin is used as a moisturizer (a hygroscopic substance used to keep things moist), a solvent, and a chemical sweetener in the food and beverage industry. It is also used as a liqueur thickener and in commercially processed low-fat foods. Glycerin is also used in the production of personal care products such as skin care, shaving creams, hair care products, and glycerin soaps. Glycerin is marketed under the brand name 'Glycerin' for general use. It is a mild antibacterial and antiviral wound medicine that has been approved by the FDA. As a result, it is frequently used in the following wound care products: Hydrogel sheets based on glycerin for burns and other wounds. Glycerin is used in the production of various explosives such as smokeless powder, dynamite, gelignite, and nitroglycerin, or glyceryl trinitrate (GTN), which is an essential component of propellants such as cordite.

TABLE OF CONTENTS

Chemical formula of glycerol:

Glycerol is also known as glycerin. Glycerol has 3 carbon atoms, 8 hydrogen atoms, and 3 oxygen atoms and its IUPAC name is 1, 2, 3- Propanetriol or 1, 2, 3- Trihydroxypropane. Glycerol (glycerine) has the following chemical and molecular formula:

Chemical Formula of Glycerol C8H8O3
Expanded Glycerol Molecular Formula CH2OH - CHOH - CH2OH 

Structure of glycerol:

Glycerol is a polyol that contains three hydroxyl ( - OH)groups in its structure.Each of the hydroxyl groups has a covalent bond with the carbon backbone. All  the carbons in the structure are SP3 hybridized.

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Formation of glycerol:

Glycerol is made from triglycerides, which are found in plants and animals. When triglycerides undergo saponification or transesterification, glycerol is produced as a by-product along with fatty acids. The triglycerides are prepared to react with sodium hydroxide to create sodium salts of fatty acids and glycerol during saponification.

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Physical Properties of glycerol:

  • Glycerin has a molecular weight of 92.09 g mol-1 and a density of 1.261 g cm-3.
  • It's a pale yellow liquid with a syrupy texture and a sweet taste.
  • The freezing point of glycerol is 18.070C, and the boiling point is 2900C at a pressure of 760 mm of Hg.
  • It's a pale yellow liquid with a syrupy texture and a sweet taste.
  • Glycerol is hygroscopic, which means it absorbs moisture from the air.
  • Because of the presence of three hydroxyl groups in its structure, it is totally soluble in water and alcohol, but insoluble in chloroform and ether.
  • It is viscous at room temperature, and as the temperature is lowered, the viscosity increases.
  • Glycerol is flammable in nature, although it doesn't burn quickly.

Chemical properties of glycerol:

Reaction of glycerol and potassium permanganate:

This is the rapid oxidation of glycerol by potassium permanganate. Glycerin is a type of alcohol and potassium permanganate is a powerful oxidant. The reaction between these two reactants is almost instantaneous and very dramatic, with a lot of smoke and fire erupting from their mixture.This reaction can be used to show an exothermic reaction as well as the impact of surface area on reaction rate.

When glycerin comes into contact with potassium permanganate, the oxidizing properties of  permanganate ions by glycerin act. Oxidation of  glycerin is very exothermic, and the heat released after a few seconds also ignites glycerin  into a flame and emits smoke. After adding glycerin to the shell, sparks and solid potassium permanganate are expelled from the shell, causing immediate retreat.

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Oxidation of glycerol with different oxidizing agents:

  • Oxidation of glycerol with dilute nitric acid produces glyceric acid and tartronic acid. 
  •  Oxidation of glycerol with Conc Nitric acid  mainly produces glyceric acid. 
  •  Oxidation of glycerol by bismuth nitrate gives mesoxalic acid.
  • . Oxidizing glycerol with Bromine water (or) NaOBr (or) Fenton's reagent (FeSO4 + H2O2) gives a mixture of glyceraldehyde and dihydroxyacetone (glycerose).
  •  Formaldehyde and formic acid are formed during oxidation with Hl10 or lead acetate. 

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Uses of glycerol:

  • The commercial popularity of glycerin is very well-known to us. However, here some more uses of glycerin have been mentioned.
  • Glycerol, when injected into the rectum as an enema, can help reduce the problem of constipation.
  • Some studies have shown that consumption of glycerol along with water keeps hydrated for a longer duration of time. This has been observed by athletes while exercising, on the consumption of the solution, the individuals could practice for a longer duration of time.
  • Glycerol also helps in treating dry, itchy and scaly skin. The application of glycerin soothes the surface of the skin. A combination of glycerin and paraffin is recommended as a treatment option for certain inherited skin conditions.
  • In food industries, glycerol is used as a sweetener, a preservative and a humectant. And in the brewing industry, glycerin is used as a thickening agent in liqueurs. It is also used during the process of fermentation to maintain yeast osmoregulation and as a competitive source of carbon.
  • Nitroglycerin, a derivative of glycerin, is a very powerful explosive and is used as a propellant in rockets and missiles.
  • In the paper and printing industry, glycerin is used as a plasticizer and is used in the softening of paper.
  • Glycerin is used in the making of e-cigarette liquids, in the production of toothpaste and even in some cough syrups.
  • Glycerin is used in filming sets to let the areas remain wet for longer time periods.
  • In the textile industry, glycerin is used in softening and lubricating the yarn.

Glycerol in human body:

Triacylglycerols are the storage form of lipids and serve as an energy stock. In the case when the body is devoid of carbohydrates, these energy stores are broken down into fatty acids and glycerol for the purpose of energy. The glycerol obtained here serves two purposes: it inhibits the process of glycolysis (breakdown of glucose) and itself undergoes the process of gluconeogenesis (production of glucose from non-carbohydrate source) to form glucose. This glucose can later be supplied to the brain for utilization.

Practice problems:

Q1. Glycerol can be formed through digestion of which of the following?

(A) Galactose                                                                         (B) Fats

(C) Glucose                                                                           (D) Sucrose

Answer: (B)

Solution: Heating fats (triglycerides) will lead to the formation of glycerol along with the formation of corresponding acid.

Q2. What is the name of the process of formation of glycerol via formation of allyl chloride?

(A) Epichlorohydrin                                                                 (B) Acrolein

(C) Propylene oxide                                                                  (D) Chloroform process

Answer: (A)

Solution: The epichlorohydrin process is the most important; it involves the chlorination of propylene to give allyl chloride which is oxidized with hypochlorite to dichlorohydrins, which reacts with a strong base to give epichlorohydrin. Glycerol is produced after the hydrolysis of epichlorohydrin

Q3. Glycerol has 

(A) one primary and two secondary  - OH groups

(B) two primary and one secondary - OH groups

(C) Three primary - OH groups

(D) Three secondary - OH groups

Answer: (B)

Solution: By seeing the structure of glycerol we can say that one secondary and two primary - OH groups are present in the glycerol.

Q4. Acidified KMnO4 oxidizes glycerol 

(A) Oxalic acid                                                                   (B) Glyceraldehyde 

(C) Glyceric acid                                                                 (D) Tartronic acid

Answer: (A)

Solution: Oxidation of glycerol with potassium permanganate will give oxalic acid.

Frequently asked question:

Question 1. Why is glycerol soluble in water?

Answer. Glycerin, also known as glycyl alcohol, glycerin or glycerine is water soluble. This property is mainly due to the ability of its polyol group (three - OH groups) to form hydrogen bonds with water molecules. The three  - OH groups of glycerin are polarized, which helps them dissolve easily  in water.

Question 2. What is vegetable glycerin?

Answer. Vegetable glycerin, also known as glycerol, is a clear liquid usually made from soybean, coconut or palm oil. It is odorless and has a moderately sweet taste with a syrup-like consistency.

Question 3. Is glycerine used as a sweetener?.

Answer. Glycerin belongs to a special category of carbohydrates called polyols, which also includes sugar alcohols like sorbitol and erythritol. Glycerin, like sugar alcohols, has a sweet taste, but it is not metabolized as sugar in the body and does not raise blood sugar levels.For that reason, it’s sometimes used as a sweetener in foods marketed to diabetics and low-carb dieters.  Glycerin also has that moisture-attracting property. The same way that adding glycerin to a lotion helps keep your skin stay plump and moist, adding glycerin to foods helps them stay moist. So glycerin is also widely used in food manufacturing as a preservative

Question 4. Is Glycerin Safe?

Answer. Like almost all substances, some people have hypersensitivity or allergies to glycerin. Ingesting sufficient amounts can be toxic. However, glycerin is generally safe because it is usually used to keep foods fresh or as a hypoglycemic sweetener. However, it is not calorie-free. In fact, glycerin contains slightly more calories than sugar and it's only about 60%  sweet, so you may need a little more to get the sweetness you deserve. As with sugar alcohols, high doses of glycerin may have a laxative effect, which may or may not be desirable.

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