·
Linear Formula HOCH2CH(OH)CH2OH
·
Molecular Weight 92.09
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Beilstein Registry Number 635685
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid
that is sweet-tasting and non-toxic. The glycerol backbone is found in
all lipids known
as triglycerides.
Detailed description
It
is widely used in the food industry as a sweetener and humectant and in pharmaceutical formulations. Glycerol has three hydroxyl groupsthat are
responsible for its solubility in water and its hygroscopic nature.
Applications
Food industry
In food and beverages, glycerol serves as a humectant, solvent, and sweetener, and may help preserve foods. It is also used as
filler in commercially prepared low-fat foods
(e.g., cookies), and as a thickening agent in liqueurs. Glycerol and water
are used to preserve certain types of plant leaves.[12] As a sugar substitute, it has
approximately 27 kilocalories per teaspoon (sugar has 20)
and is 60% as sweet as sucrose. It does not feed the bacteria that form plaques and cause dental cavities[citation needed]. As a food additive, glycerol is
labeled as E number E422. It is added to icing (frosting) to prevent it from
setting too hard.
As used in foods, glycerol is categorized by
the 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. Glycerol has a caloric density
similar to table sugar, but a lower glycemic index and different metabolic pathway within the
body, so some dietary advocates[who?] 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, due to its
heating effect in the mouth, if the cooling effect is not wanted.[13]
Pharmaceutical and personal care applications
Glycerol is used in medical, pharmaceutical and personal care preparations,
mainly as a means of improving smoothness, providing lubrication, and as a humectant. It is found in allergen
immunotherapies, cough syrups, elixirs and expectorants, toothpaste, mouthwashes, skin care products,
shaving cream, hair care products, soaps, and water-based personal lubricants. In solid dosage forms like tablets, glycerol is used as a
tablet holding agent. For human consumption, glycerol is classified by the U.S.
FDA among the sugar alcohols as a caloric macronutrient.
Glycerol is a component of glycerin soap. Essential oils are added
for fragrance. This kind of soap is used by people with sensitive, easily
irritated skin because it prevents skin dryness with
its moisturizing properties. It draws moisture up through skin layers and
slows or prevents excessive drying and evaporation.[citation needed]
Glycerol can be used as a laxative when
introduced into the rectum in suppository or
small-volume (2–10 ml) (enema) form; it irritates the anal mucosa and induces a hyperosmotic effect.[14]
Taken orally (often mixed with fruit juice to reduce
its sweet taste), glycerol can cause a rapid, temporary decrease in the internal pressure of the eye. This can be useful for the initial emergency treatment of
severely elevated eye pressure.[15]
Botanical extracts
When utilized in "tincture" method
extractions, specifically as a 10% solution, glycerol prevents tannins from
precipitating in ethanol extracts of plants (tinctures). It is also used
as an "alcohol-free" alternative to ethanol as a solvent in preparing
herbal extractions. It is less extractive when utilized in a standard tincture
methodology. Alcohol-based tinctures can also have the alcohol removed and
replaced with glycerol for its preserving properties. Such products are not
"alcohol-free" in a scientific sense, as glycerol contains three
hydroxyl groups. Fluid extract manufacturers
often extract herbs in hot water before adding glycerol to make glycerites.[16][17]
When used as a primary "true" alcohol-free
botanical extraction solvent in non-tincture based methodologies, glycerol has
been shown to possess a high degree of extractive versatility for botanicals
including removal of numerous constituents and complex compounds, with an
extractive power that can rival that of alcohol and water–alcohol solutions.[citation needed] That glycerol possesses such high extractive
power assumes it is utilized with dynamic methodologies as opposed to standard
passive "tincturing" methodologies that are better suited to alcohol.
Glycerol possesses the intrinsic property of not denaturing or rendering a
botanical's constituents inert (as alcohols – i.e. ethyl (grain) alcohol,
methyl (wood) alcohol, etc., do). Glycerol is a stable preserving agent for
botanical extracts that, when utilized in proper concentrations in an
extraction solvent base, does not allow inverting or reduction-oxidation of a
finished extract's constituents, even over several years.[citation needed] Both glycerol and ethanol are viable
preserving agents. Glycerol is bacteriostatic in its action, and ethanol is
bactericidal in its action.[18][19][20]
Electronic cigarette liquid
Vegetable glycerin is a common component of e-liquid, a solution used
with electronic vaporizers (electronic cigarettes). This glycerol is heated with an atomizer (a heating coil
often made of Kanthal wire),
producing the aerosol that delivers nicotine to the user. [21]
Antifreeze
Like ethylene glycol and propylene glycol, glycerol is a
non-ionic kosmotrope that
forms strong hydrogen bonds with water molecules, competing with
water-water hydrogen bonds. This disrupts the crystal lattice formation of ice unless the
temperature is significantly lowered. The minimum freezing point temperature is
about −36 °F (−38 °C) corresponding to 70% glycerol in water.
Glycerol was historically used as an anti-freeze for
automotive applications before being replaced by ethylene glycol, which has a lower
freezing point. While the minimum freezing point of a glycerol-water mixture is
higher than an ethylene glycol-water mixture, glycerol is not toxic and is
being re-examined for use in automotive applications.[22][23]
In the laboratory, glycerol is a common component of
solvents for enzymatic reagents stored at temperatures below 0 °C due to
the depression of the
freezing temperature. It is also used as a cryoprotectant where the glycerol is dissolved
in water to reduce damage by ice crystals to laboratory organisms that are
stored in frozen solutions, such as bacteria, nematodes, and mammalian
embryos.
Internal combustion fuel
Glycerol is also used to power diesel generators
supplying electricity for the FIA Formula E series of electric race cars.[24]
Chemical intermediate
Glycerol is used to produce nitroglycerin, which is an
essential ingredient of various explosives such as dynamite, gelignite, and propellants
like cordite. Reliance on
soap-making to supply co-product glycerol made it difficult to increase
production to meet wartime demand. Hence, synthetic glycerol processes were
national defense priorities in the days leading up to World War II.
Nitroglycerin, also known as glyceryl trinitrate (GTN) is commonly used to
relieve angina pectoris, taken in the form of sub-lingual tablets, or as an aerosol
spray.
Allyl iodide, a chemical building block for polymers, preservatives, organometallic catalysts,
and pharmaceuticals, can be synthesized by using elemental phosphorus and iodine on glycerol.[25]
A great deal of research is being conducted to try
to make value-added products from crude glycerol (typically containing 20%
water and residual esterification catalyst)
obtained from biodiesel production.[26] The use of
crude glycerol as an additive to biomass for a renewable energy source when
burned or gasified is also being explored.
·
Conversion to acrolein
Film industry
Glycerol is used by the film industry when filming
scenes involving water to stop areas from drying out too quickly.
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