Glycerol belongs to the alcohol family of organic compounds and is a clear, colorless, viscous, sweet-tasting liquid with the molecular formula HOCH2CHOHCH2OH. Until 1948, all glycerol was obtained as a byproduct of soap manufacturing from animal and vegetable oils and fats. However, industrial syntheses based on propylene or sugar now account for an increasing share of glycerol production. The term glycerin (or glycerine), introduced by Michel-Eugène Chevreul in 1811, refers to commercial materials that contain more than 95 percent glycerol.
Although Chevreul gave glycerin its name, the substance was first isolated in 1783 by German Swedish chemist Carl Wilhelm Scheele, who described it as the “sweet principle of fat.” Glycerol can be used in a variety of ways. The gum is an essential ingredient in many modern protective coatings, such as automotive enamels and exterior house paints. In the presence of sulfuric acid and nitric acid, glycerin (or nitroglycerine) forms explosive nitroglycerin.
Sugar alcohols include glycerol. Sugar alcohols are white, water-soluble organic compounds with the chemical formula (CHOH)nH2. Sugars are hydrogenated to produce sugar alcohols.
Definition: Is Glycerol An Alcohol?
Glycerol is an odorless, colorless liquid with a sweet taste. It is viscous at room temperature and non-toxic at low concentrations. In 1779, glycerol was discovered. Some literature refers to it as glycyl alcohol, glycerine, or glycerol.
In biological systems, glycogen is seen as an intermediate in carbohydrate and lipid metabolism because surplus carbohydrates can be converted into long-chain fatty acids and esterified with the three hydroxyl groups. Hence, glycerol is considered to be an allergen since it can influence immune reactions in the body through histamine, increased antibody production, and enhanced immune cell activity.
Glycerol increases blood pressure by preferentially attracting water from tissues into the plasma and lymph. The glycerol in glycerol prevents water resorption in nephrons, thereby increasing urine volume.
- IUPAC: Propane-1,2,3-triol
- Chemical formula: C3H8O3
- 1,2,3-trihydroxy-propane or propane-1,2,3-triol
- Derived terms:
- Sn-glycerol-3-phosphorylcholine synthetase
- Glycerol-1-phosphate dehydrogenase
Structure Of Glycerol
Glycerol is a trihydroxy sugar alcohol that has three carbon atoms and three hydroxyl groups. With multiple hydroxyl groups and carbon atoms, it is an organic polyol compound with the IUPAC name 1, 2, 3 – Propanetriol.
There are several ways to represent glycerol’s structure.
The simplest is the image above, which shows three carbon atoms covalently bonded to hydroxyl groups. As shown in the image below, the molecule can also be represented as a Fischer projection, centered on the second carbon atom.
Additionally, the molecule can be represented with a more accurate depiction of bond angles, without explicitly representing hydrogen atoms.
History of Glycerol
An accidental discovery of glycerol was made by a Swedish scientist named K. W. Scheele. A drying plaster named Emplastrum simplex and soap were compared by him. Salve is made from lead salts of fatty acids, while the soap is made from sodium salts of organic acids. He discovered a water-soluble substance with a sweet taste after reacting olive oil with lead monoxide.
Glycerol was the first chemically isolated fat and was originally called the ‘sweet principle’. Scheele analyzed the substance and found it to be different from all other sugars known at the time. The glycerol didn’t crystallize, ferment, and showed greater heat resistance than most other sugars.
Furthermore, he investigated the difference between glycerol and cane sugar, especially the amount of oxygen (or phlogiston, as it was then called) it contained. The oxidation of glycerol by nitric acid takes more nitric acid than cane sugar, as demonstrated by Scheele. When it was reacted with ethanol, it did not produce an alkali. Although it could not be crystallized, it could be distilled. It could also decompose at higher temperatures.
A French scientist named Pelouze elucidated the chemical formula of glycerol in 1836. He proposed the empirical formula C3H8O3. Based on the work of two scientists named Berthelot and Lucea, the structural formula for C3H5(OH)3 was accepted fifty years later.
Due to its use in the manufacture of dynamite, glycerol is a commercially important chemical. Albert Nobel, who later established the Nobel Prizes, developed a safe and reliable method for stabilizing, transporting, and handling trinitroglycerin, which is an explosive compound in dynamite. As a result, glycerol was used for the rapid extraction of mineral ore, as well as many large-scale infrastructure projects that required the blasting of natural structures.
Properties Of Glycerol
- Glycerol has a melting point of 17.8°C. While it has a boiling point of 290°C, it also decomposes at that temperature.
- Due to the presence of three hydroxyl groups, the compound is hygroscopic, with a tendency to absorb moisture from the air.
- This also makes it useful as a humectant in cosmetics and food, retaining water and preventing it from drying out.
- As a result of the polyol groups forming hydrogen bonds with water molecules, glycerol is easily soluble in water. With a specific gravity of 1.26, glycerol is slightly denser than water.
- As a result, when glycerol is poured into a container of water, it sinks to the bottom. However, due to its solubility, glycerol will form an aqueous solution over time and with mild stirring.
- Due to its hygroscopic nature, glycerol can cause mild irritation to the eyes, nose, lungs, and skin. Pure glycerol can dry out the skin and other internal organs when it comes into contact with these moist tissues.
- The same property that makes glycerol a good humectant also allows it to desiccate internal tissues since it can bind to water.
- Furthermore, if a cosmetic preparation with high water content is applied to the skin, especially in an arid environment, the presence of glycerol prevents the lotion, cream, or gel from drying quickly.
- Glycerol’s three hydroxyl groups allow it to form esters with a wide range of organic acids. Triglycerides are formed when all three reactive groups are esterified with long-chain organic fatty acids. In the human body, triglycerides are among the most common lipids.
Uses Of Glycerol
Foods and beverages may be preserved with the addition of glycerol as a humectant, a solvent, and a sweetener. In addition, it is used as a filler in commercially prepared low-fat foods (e.g., cookies) and as a thickener in liqueurs. For example, glycerol and water are used to preserve certain types of leaves. There are approximately 27 kilocalories per teaspoon (compared to 20 in sugar) and it is 60% as sweet as sucrose.
The bacteria that form dental plaque and lead to dental cavities are not fed by it. Food additive glycerol is labeled as E422. Ice (frosting) is treated with it to prevent it from setting too hard.
As used in foods, glycerol is categorized by the U.S. Academy of Nutrition and Dietetics as a carbohydrate. The U.S. Food and Drug Administration (FDA) carbohydrate designation includes all caloric macronutrients excluding protein and fat. The caloric density of glycerol is similar to that of table sugar, but it has a lower glycemic index and a different metabolism, so some dietary advocates accept glycerol as a sweetener compatible with low-carbohydrate diets.
It is also recommended as an additive when using polyol sweeteners such as erythritol and xylitol, which have a cooling effect since it has a heating effect in the mouth if the cooling effect is not desired.
Medical, Pharmaceutical, And Personal Care Applications
Glycerin is an FDA-approved treatment for wounds that is mildly antimicrobial and antiviral. According to the Red Cross, 85% solution of glycerin shows bactericidal and antiviral effects, and wounds treated with glycerin show reduced inflammation after roughly 2 hours. It is therefore widely used in wound care products, such as glycerin-based hydrogel sheets for burns and other wound care.
It is approved for all types of wound care, except third-degree burns, and is used to package donor skin for use in skin grafts. Glycerin is not the only topical treatment not approved for third-degree burns, so this limitation is not specific to it.
Medical, pharmaceutical and personal care preparations use glycerol to improve smoothness, provide lubrication, and act as a humectant.
Topical application of glycerin relieves ichthyosis and xerosis. Allergen immunotherapies, cough syrups, elixirs, expectorants, toothpaste, mouthwashes, skin care products, shaving creams, hair care products, soaps, and water-based personal lubricants contain it. For tablets and other solid dosage forms, glycerol serves as a tablet-holding agent.
For human consumption, glycerol is classified by the U.S. Food and Drug Administration (U.S. FDA) as a caloric macronutrient. Blood banks also use glycol to preserve red blood cells before freezing them.
In glycerin soap, glycerol is a component. Essential oils are added to enhance the fragrance. Because of its moisturizing properties, this type of soap is used by people with sensitive, easily irritated skin. The agent draws moisture up through the skin layers and prevents excessive evaporation and drying.
Upon administration rectally, glycerol functions as a laxative by irritating the anal mucosa and causing a hyperosmotic effect, expanding the colon by drawing water into it, causing peristalsis and constipation. As a suppository or as a small-volume (2–10 ml) enema, it may be administered undiluted. Alternatively, it can be administered in a dilute solution, e.g., 5%, as a high volume enema.
Glycerol can cause a rapid, temporary drop in eye pressure when taken orally (often mixed with fruit juice to reduce its sweet taste). It is useful for treating severely elevated eye pressure in the first instance.
Researchers examined the effects of probiotic Lactobacillus reuteri on Clostridium difficile grown in a lab and found that when the probiotic was supplemented with glycerol, it converted it into the broad-spectrum antimicrobial compound reuterin. The antimicrobic agent reuterin was as effective as vancomycin in inhibiting Clostridium difficile growth.
Additionally, the researchers found that glycerol or L. reuteri alone were not effective against Clostridium difficile, and reuterin did not harm the good bacteria in the gut community.
Glycerol has also been incorporated into bio-ink formulations for bioprinting. It adds viscosity to the bio-ink without adding large protein, carbohydrate, or glycoprotein molecules.
As a 10% solution, glycerol prevents tannins from precipitating in ethanol extracts of plants (tinctures) when used in the “tincture” method extractions. Also, it can be used as a solvent for herbal extractions instead of ethanol because it is “alcohol-free.” It is less extractive than ethanol when used in tincture preparations. Alcohol-based tinctures can also be preserved by replacing alcohol with glycerol.
As glycerol contains three hydroxyl groups, such products cannot be considered alcohol-free, either scientifically or legally. Manufacturers of fluid extracts often extract herbs in hot water before adding glycerol to form glycerites.
As a primary alcohol-free botanical extraction solvent in methodologies other than tinctures, glycerol has been shown to possess a high degree of extraction versatility for botanicals including the removal of numerous constituents and complex compounds, with an extractive power that can rival that of alcohol and water-alcohol solutions.
The high extractive power of glycerol can be attributed to its use with dynamic (i.e. critical) methodologies, as opposed to the standard passive “tincturing” procedures that are more suitable for alcohol. Glycerol has the inherent property of not degrading or energizing botanical constituents like alcohols (e.g. ethyl (grain) alcohol, methyl (wood) alcohol, etc.).
When used in proper concentrations as an extraction solvent base, glycerol prevents the inversion of botanical extracts or mitigates reduction-oxidation of a finished extract’s constituents even after several years. Ethanol and glycerol are both viable preservatives. Bacteriostatic and bactericidal properties of glycerol and ethanol, respectively.
Electronic Cigarette Liquid
Glycerin, along with propylene glycol, is a common component of e-liquid, a solution for electronic vaporizers (electronic cigarettes). Glycerol is heated with an atomizer (a heating coil made of Kanthal wire), producing an aerosol that delivers nicotine to the user.
Glycerol, like ethylene glycol and propylene glycol, forms strong hydrogen bonds with water molecules, competing with water-water hydrogen bonds. This interferes with ice formation. It is about *36 degrees Fahrenheit (*38 degrees Celsius) for 70% of glycerol in water to freeze.
Formerly, glycol was used as an anti-freeze in automotive applications before it was replaced by ethylene glycol, which has a lower freezing point. The minimum freezing point of a glycerol-water mixture is higher than that of an ethylene glycol-water mixture, however, glycerol is not toxic, and its use in automotive applications is being reevaluated.
Due to the depression of the freezing point, glycerol is commonly used as a solvent for enzyme reagents stored at temperatures below 0 °C. Also, it can be used as a cryoprotectant, when the glycerol is dissolved in water to prevent damage by ice crystals to organisms that are stored in frozen solutions, such as fungi, bacteria, nematodes, and mammalian embryos.
Nitroglycerin is derived from glycerol and is an essential component of explosives such as dynamite, gelignite, and propellants such as cordite. Increasing production to meet wartime demand was difficult because soap-making supplied co-product glycerol.
In the days leading up to World War II, synthetic glycerol processes were deemed vital to national defense. Nitroglycerin, also known as glyceryl trinitrate (GTN), is commonly used to relieve angina pectoris and is available as sublingual tablets, patches, or aerosol spray.
Mesoxalic acid is produced by oxidizing glycerol. Hydroxyacetone is obtained by dehydrating glycerol.
To dampen vibrations in pressure gauges, glycerol is used as a fill. Compressors, engines, pumps, etc., produce harmonic vibrations that can cause the needle in Bourdon gauges to move excessively, creating inaccurate readings. Excessive needle swinging can also damage internal gears or other components, resulting in premature wear. By replacing the air space in a gauge with glycerol, harmonic vibrations that are transmitted to the needle are reduced, increasing the gauge’s lifetime and reliability.
Importance Of Glycerol In Biology
Glycerol is essential sugar alcohol for many living things. Among other things, it is a component of lipids, such as glycerides and phospholipids. In addition to fatty acids, glycerol forms glycerides that can be used as an energy source. Triglycerides, for instance, are an important component of animal fats and vegetable oils. Furthermore, glycerol serves as one of the substrates for the synthesis of glycerol-3-phosphate, which is involved in triglyceride biosynthesis, phospholipid biosynthesis, glycolysis, and gluconeogenesis.
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The phospholipids are one of the main structural components of biological membranes. They may also act as second messengers in signal transmission. Various types of phospholipids are involved in different metabolic activities, such as phosphatidic acid, phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, phosphatidylinositol, etc.
Glycerol can be converted into glucose, which is the main metabolite of glycolysis, which is a metabolic pathway through which energy (ATP) is created. The energy created by glycolysis drives a cell’s metabolic activity. Glycerol serves as a glucose precursor when there is not enough glucose available. In contrast to fatty acids, glycerol is more easily absorbed by the brain cells. When glucose is not available, glycerol-turned-glucose can be used for glycolysis by the brain cells.
Glycerol may be synthesized naturally or may be obtained by consuming glycerol-containing foods. As a food sweetener, humectant, thickener, and emulsifier, it is also produced chemically by saponification or the action of superheated steam. Glycerol, one of the sugar alcohols, is classified as a caloric macronutrient by the FDA. Per gram of glycerol, 4.3 kcal is provided.
Conditions Of Use And Important Information
Information on this page should not replace advice from your doctor or healthcare provider and is not intended to cover all possible uses, precautions, interactions, or adverse effects. You may not find this information relevant to your specific health situation. StudyQueries is not a substitute for professional medical advice from your doctor or other qualified health care provider.
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Consult your doctor or health care professional before starting, stopping, or changing any prescribed part of your health care plan or treatment and to determine what course of therapy is right for you. Copyrighted material provided by Natural Medicines Comprehensive Database Consumer Version. All information is evidence-based, objective, and free from commercial bias. The professional medical information on natural medicines can be found in Natural Medicines Comprehensive Database Professional Version.
- Likely Effective for
- When used rectally as a suppository, constipation occurs.
- Possibly Ineffective for
- Helping with weight loss, when taken by mouth.
- Likely Ineffective for
- When taken by mouth, it improves exercise performance. It is used intravenously for treating acute stroke.
- Insufficient Evidence to Rate Effectiveness for
- Helping maintain the body’s water levels (hydration) in athletes and people with intestinal problems.
- Wrinkled skin.
- Other conditions.
To rate glycerol for these uses, more evidence is needed.
Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence using the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, and Insufficient Evidence to Rate (details of each rating).
Glycerol appears to be safe for most adults. Glycerol can cause headaches, dizziness, bloating, nausea, vomiting, thirst, and diarrhea when taken by mouth.
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If injected intravenously (by IV), glycol may not be safe. Red blood cells might be seriously damaged.
Warnings & Special Precautions
Pregnancy and breast-feeding: Not enough is known about the use of glycerol during pregnancy and breastfeeding. Stay on the safe side and avoid use.
Dosing: The following doses have been studied in scientific research:
Rectal: As an adult laxative for constipation: The common dose of glycerol is 2-3 grams in suppository form or a 5-15 mL enema. For children younger than six years old, the dose is 1-1.7 grams as a suppository or a 2-5 mL enema.
- Glycerin Systemic
- Glycerin Ophthalmic
- Glycerin Otic
- Glycerin Topical
- Glycerin/Lidocaine/Petrolatum/Phenylephrine Topical
- Glycerin/Lidocaine/Phenylephrine Topical
- Glycerin/Petrolatum/Phenylephrine/Pramoxine Topical
- Glycerin/Phenol Topical
- Glycerin/Propylene Glycol Ophthalmic
- Glycerin/Witch Hazel Topical
Uses Of Syrup
An acute cough is commonly caused by viral infections of the upper respiratory tract (URTI). Cough is normally a protective reflex to prevent the entry of food and fluid into the respiratory tract, but viral infections then cause inflammation of the upper airways and a sensation of irritation with an urge to cough which results in coughing that is a nuisance rather than a benefit to the subject.
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The sensation of irritation that causes the urge to cough is due to a hypersensitivity of the sensory nerves in the upper airway found mainly in the larynx. Cough can also be initiated by pharyngeal stimulation and this indicates that sensory nerves in the pharynx may also be involved in the generation of cough associated with URTI, as pharyngitis is a common symptom associated with URTI.
Mechanism Of Action Of Glycerol In Soothing Cough
The major effect of cough syrups in soothing cough is due to the properties of the syrup rather than the active ingredients such as dextromethorphan. Up to 85% of the benefit of cough syrups may be due to the physical and chemical effects of the syrup which contribute to its demulcent action.
Glycerol is a component of many cough syrups, especially in honey and lemon syrups where the concentration of glycerol is usually around 0.75 g per 5 mL and where glycerol may be declared as the sole active ingredient of the cough syrup.
The efficacy of glycerol must be related to its physical and chemical properties, as glycerol does not have any known pharmacological actions.
Where to Buy Food Grade Vegetable Glycerin
Vegetable Glycerin (VG) can be found in most pharmacies. There’s a good chance you can find it in your local supermarket or big box store. Oftentimes products are being sold for external use only and have added ingredients. Always make sure that the product you are buying is 100% food-grade vegetable glycerin and is intended for human consumption.
Food Grade Vegetable Glycerin can be purchased online but, as always, make sure you are purchasing a food-grade product if you are using it as an ingredient in a food, beverage, or other product intended for consumption.
What can glycerol be used for?
For constipation, improving hydration and performance in athletes, and for certain skin conditions, glycerol is most commonly used. It is also used for meningitis, stroke, obesity, ear infections, and other conditions, but there is no good scientific evidence supporting these uses.
What is glycerol made from?
Vegetable glycerin, also known as Glycerol or Glycerine, is a clear liquid derived from soybean, coconut, or palm oils. It is odorless and sweet tasting with a syrup-like consistency. Glycerin from vegetables is commonly used in the cosmetic industry but has several other uses as well.
What is an example of glycerol?
Glycerol is essential sugar alcohol for many living things. The first reason is that it is a component of lipids, such as glycerides and phospholipids. Glycerol, together with fatty acids, forms glycerides that can be used as an energy source. For instance, triglycerides are an important component of animal fats and vegetable oils.
Are glycerol and glycerine the same?
The commercial name for glycerol is glycerin, which contains 95% glycerol. Glycerol and glycerin have the same chemical formula, but their nomenclature is different. In the cosmetics industry, glycerin is the most widely used product after fragrances and water.
What products contain glycerol?
It is used in allergy immunotherapies, cough syrups, elixirs and expectorants, toothpaste, mouthwashes, skin care products, shaving cream, hair care products, soaps, and water-based personal lubricants. A tablet-holding agent, glycerol is used in solid dosage forms such as tablets.
Where does glycerol come from in the body?
The liver is thought to be the main site of glycerol uptake and fatty acid reesterification.