Althoughachiral, glycerol isprochiral with respect to reactions of one of the two primary alcohols. Thus, in substituted derivatives, thestereospecific numbering labels the molecule with asn- prefix before the stem name of the molecule.[9][10][11]
Triglycerides can be saponified withsodium hydroxide to give glycerol and fatty sodium salt orsoap.
Typical plant sources includesoybeans orpalm. Animal-derivedtallow is another source. From 2000 to 2004, approximately 950,000 tons per year were produced in the United States and Europe; 350,000 tons of glycerol were produced in the U.S. alone.[12] Since around 2010, there is a large surplus of glycerol as a byproduct ofbiofuel, enforced for example byEU directive 2003/30/EC that required 5.75% of petroleum fuels to be replaced with biofuel sources across allmember states.[7]Crude glycerol produced from triglycerides is of variable quality, with a selling price as low as US$0.02–0.05 per kilogram in 2011.[13] It can be purified in a rather expensive process by treatment withactivated carbon to remove organic impurities, alkali to remove unreacted glycerol esters, andion exchange to remove salts. High purity glycerol (greater than 99.5%) is obtained by multi-step distillation; avacuum chamber is necessary due to its high boiling point (290 °C).[7]
Consequently, glycerol recycling is more of a challenge than its production, for instance by conversion to glycerol carbonate[14] or to synthetic precursors, such asacrolein and epichlorohydrin.[15]
Although more expensive than production from plant or animal triglycerides, glycerol can be synthesized by various routes. DuringWorld War II, synthetic glycerol processes became a national defense priority because it is a precursor tonitroglycerine. Epichlorohydrin is the most important precursor.Chlorination of propylene givesallyl chloride, which is oxidized withhypochlorite todichlorohydrin, which reacts with a strong base to giveepichlorohydrin. Epichlorohydrin can be hydrolyzed to glycerol.Chlorine-free processes from propylene include the synthesis of glycerol fromacrolein andpropylene oxide.[7]
It is also recommended as an additive when polyol sweeteners such aserythritol andxylitol are used, as its heating effect in the mouth will counteract these sweeteners' cooling effect.[17]
A bottle of glycerin purchased at a pharmacyPersonal lubricants commonly contain glycerolGlycerol is an ingredient in products such as hair gelGlycerol suppositories used as laxatives
Taken rectally, glycerol functions as alaxative by irritating the anal mucosa and inducing ahyperosmotic effect,[21] expanding thecolon by drawing water into it to induceperistalsis resulting inevacuation.[22] It may be administered undiluted either as asuppository or as a small-volume (2–10 ml)enema. Alternatively, it may be administered in a dilute solution, such as 5%, as a high-volume enema.[23]
Taken orally (often mixed with fruit juice to reduce its sweet taste), glycerol can cause a rapid, temporary decrease in theinternal pressure of the eye. This can be useful for the initial emergency treatment of severely elevated eye pressure.[24]
In 2017, researchers showed that the probioticLimosilactobacillus reuteri bacteria can be supplemented with glycerol to enhance its production of antimicrobial substances in the human gut. This was confirmed to be as effective as the antibioticvancomycin at inhibitingClostridioides difficile infection without having a significant effect on the overall microbial composition of the gut.[25]
Glycerol has also been incorporated as a component ofbio-ink formulations in the field ofbioprinting.[26] The glycerol content acts to add viscosity to the bio-ink without adding large protein, saccharide, or glycoprotein molecules.
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 or FDA regulatory sense, as glycerol contains three hydroxyl groups.Fluid extract manufacturers often extract herbs in hot water before adding glycerol to makeglycerites.[27][28]
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.[29] That glycerol possesses such high extractive power assumes it is utilized with dynamic (critical) methodologies as opposed to standard passive "tincturing" methodologies that are better suited to alcohol. Glycerol does not denature or render a botanical's constituents inert as alcohols (ethanol,methanol, and so on) 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 orreduction-oxidation of a finished extract's constituents, even over several years.[citation needed] Both glycerol and ethanol are viable preserving agents. Glycerol isbacteriostatic in its action, and ethanol is bactericidal in its action.[30][31][32]
Glycerin, along withpropylene glycol, is a common component ofe-liquid, a solution used with electronic vaporizers (electronic cigarettes). This glycerol is heated with an atomizer (a heating coil often made ofKanthal wire), producing theaerosol that deliversnicotine to the user.[33]
Likeethylene glycol and propylene glycol, glycerol is a non-ionickosmotrope that forms strong hydrogen bonds with water molecules, competing with water-waterhydrogen bonds. This interaction disrupts the formation of ice. The minimum freezing point temperature is about −38 °C (−36 °F) 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.[34][35]
In the laboratory, glycerol is a common component of solvents forenzymaticreagents stored at temperatures below 0 °C (32 °F) due to thedepression of the freezing temperature. It is also used as acryoprotectant where the glycerol is dissolved in water to reduce damage by ice crystals to laboratory organisms that are stored in frozen solutions, such asfungi,bacteria,nematodes, and mammalian embryos. Some organisms like themoor frog produce glycerol to survive freezing temperatures during hibernation.[36]
Glycerol is used as fill forpressure gauges to damp vibration. External vibrations, from compressors, engines, pumps, etc., produceharmonic vibrations withinBourdon gauges that can cause the needle to move excessively, giving inaccurate readings. The excessive swinging of the needle can also damage internal gears or other components, causing premature wear. Glycerol, when poured into a gauge to replace the air space, reduces the harmonic vibrations that are transmitted to the needle, increasing the lifetime and reliability of the gauge.[41]
Glycerol is used by set decorators when filming scenes involving water to prevent an area meant to look wet from drying out too quickly.[42]
Glycerine is also used in the generation oftheatrical smoke and fog as a component of the fluid used infog machines as a replacement forglycol, which has been shown to be an irritant if exposure is prolonged.
Glycerol can be sometimes used as replacement for water inultrasonic testing, as it has favourably higheracoustic impedance (2.42 MRayl versus 1.483 MRayl for water) while being relatively safe, non-toxic, non-corrosive and relatively low cost.[43]
Research continues into potentialvalue-added products of glycerol obtained from biodiesel production.[45] Examples (aside from combustion of waste glycerol):
Glycerol is a precursor for synthesis oftriacylglycerols and ofphospholipids in the liver andadipose tissue. When the body uses stored fat as a source of energy, glycerol andfatty acids are released into the bloodstream.
Glycerol is mainly metabolized in the liver. Glycerol injections can be used as a simple test for liver damage, as its rate of absorption by the liver is considered an accurate measure of liver health. Glycerol metabolism is reduced in both cirrhosis andfatty liver disease.[57][58]
Blood glycerol levels are highly elevated duringdiabetes, and is believed to be the cause of reduced fertility in patients who suffer from diabetes and metabolic syndrome. Blood glycerol levels in diabetic patients average three times higher than healthy controls. Direct glycerol treatment of testes has been found to cause significant long-term reduction in sperm count. Further testing on this subject was abandoned due to the unexpected results, as this was not the goal of the experiment.[59]
Circulating glycerol does notglycate proteins as doglucose or fructose, and does not lead to the formation ofadvanced glycation endproducts (AGEs). In some organisms, the glycerol component can enter theglycolysis pathway directly and, thus, provide energy for cellular metabolism (or, potentially, be converted to glucose throughgluconeogenesis).
Before glycerol can enter the pathway of glycolysis or gluconeogenesis (depending on physiological conditions), it must be converted to their intermediateglyceraldehyde 3-phosphate in the following steps:
Glycerol has very low toxicity when ingested; itsLD50 oral dose for rats is 12600 mg/kg and 8700 mg/kg for mice. It does not appear to cause toxicity when inhaled, although changes in cell maturity occurred in small sections of lung in animals under the highest dose measured. A sub-chronic 90-day nose-only inhalation study in Sprague–Dawley (SD) rats exposed to 0.03, 0.16 and 0.66 mg/L glycerin (Per liter of air) for 6-hour continuous sessions revealed no treatment-related toxicity other than minimalmetaplasia of theepithelium lining at the base of theepiglottis in rats exposed to 0.66 mg/L glycerin.[63][64]
Excessive consumption by children can lead to glycerol intoxication.[65] Symptoms of intoxication includehypoglycemia,nausea and aloss of consciousness. While intoxication as a result of excessive glycerol consumption is rare and its symptoms generally mild, occasional reports of hospitalization have occurred.[66] In the United Kingdom in August 2023, manufacturers of syrup used inslush ice drinks were advised to reduce the amount of glycerol in their formulations by theFood Standards Agency to reduce the risk of intoxication.[67] A 2025 study reported that between 2018 and 2024, at least 21 children aged 2–7 in the UK and Ireland received emergency treatment for symptoms of glycerol intoxication following the consumption of slush ice drinks.[68][69]
Food Standards Scotland advises that slush ice drinks containing glycerol should not be given to children under the age of 4, owing to the risk of intoxication. It also recommends that businesses do not usefree refill offers for the drinks in venues where children under the age of 10 are likely to consume them, and that products should be appropriately labelled to inform consumers of the presence of glycerol.[70]
Historical cases of contamination with diethylene glycol
On 4 May 2007, the FDA advised all U.S. makers of medicines to test all batches of glycerol fordiethylene glycol contamination.[71] This followed an occurrence ofhundreds of fatal poisonings in Panama resulting from a falsified import customs declaration by Panamanian import/export firm Aduanas Javier de Gracia Express, S. A. The cheaper diethylene glycol was relabeled as the more expensive glycerol.[72][73] Between 1990 and 1998, incidents of DEG poisoning reportedly occurred in Argentina, Bangladesh, India, and Nigeria, and resulted in hundreds of deaths. In 1937, more than one hundred people died in the United States after ingesting DEG-contaminated elixir sulfanilamide, a drug used to treat infections.[74]
The origin of thegly- andglu- prefixes forglycols and sugars is fromAncient Greekγλυκύςglukus which means sweet.[75] Nameglycérine was coined ca. 1811 byMichel Eugène Chevreul to denote what was previously called "sweet principle of fat" by its discovererCarl Wilhelm Scheele. It was borrowed into English ca. 1838 and in the 20th c. displaced by 1872 term glycerol featuring an alcohols' suffix -ol.
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