Glycerol

Source: Wikipedia, the free encyclopedia.
"Glycerine" redirects here. For the song by Bush, see Glycerine (song).
Glycerol
Glycerol
Ball-and-stick model of glycerol
Ball-and-stick model of glycerol
Space-filling model of glycerol
Space-filling model of glycerol
Sample of glycerine
Names
Preferred IUPAC name
Propane-1,2,3-triol[1]
Other names
  • Glycerin
  • Glycerine
  • 1,2,3-Trioxypropane
  • 1,2,3-Trihydroxypropane
  • 1,2,3-Propanetriol
Identifiers
3D model (
JSmol
)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard
 100.000.263 Edit this at Wikidata
E number E422 (thickeners, ...)
IUPHAR/BPS
KEGG
UNII
  • InChI=1S/C3H8O3/c4-1-3(6)2-5/h3-6H,1-2H2 checkY
    Key: PEDCQBHIVMGVHV-UHFFFAOYSA-N checkY
  • InChI=1/C3H8O3/c4-1-3(6)2-5/h3-6H,1-2H2
    Key: PEDCQBHIVMGVHV-UHFFFAOYAF
  • OCC(O)CO
Properties
C3H8O3
Molar mass 92.094 g·mol−1
Appearance Colorless
hygroscopic
liquid
Odor Odorless
Density 1.261 g/cm3
Melting point 17.8 °C (64.0 °F; 290.9 K)
Boiling point 290 °C (554 °F; 563 K)[5]
miscible[2]
log P −2.32[3]
Vapor pressure 0.003 mmHg (0.40 Pa) at 50 °C[2]
−57.06×10−6 cm3/mol
1.4746
Viscosity 1.412 Pa·s (20 °C)[4]
Pharmacology
A06AG04 (WHO) A06AX01 (WHO), QA16QA03 (WHO)
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
1
0
Flash point 160 °C (320 °F; 433 K) (closed cup)
176 °C (349 °F; 449 K) (open cup)
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 15 mg/m3 (total)
TWA 5 mg/m3 (resp)[2]
REL (Recommended)
 None established[2]
IDLH
(Immediate danger)
 N.D.[2]
Safety data sheet (SDS) JT Baker ver. 2008 archive
Supplementary data page
Glycerol (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Glycerol (

miscible with water and is hygroscopic in nature.[7]

Structure

Although achiral, glycerol is prochiral with respect to reactions of one of the two primary alcohols. Thus, in substituted derivatives, the stereospecific numbering labels the molecule with a sn- prefix before the stem name of the molecule.[8][9][10]

Production

Glycerol is generally obtained from plant and animal sources where it occurs in

carboxylic acids. The hydrolysis, saponification, or transesterification
of these triglycerides produces glycerol as well as the fatty acid derivative:

3

NaOH
/ H2O

Rightward reaction arrow

Δ

3 × soap

3 × 

Triglycerides can be saponified with sodium hydroxide to give glycerol and fatty sodium salt or soap.

Typical plant sources include

EU directive 2003/30/EC set a requirement that 5.75% of petroleum fuels were to be replaced with biofuel sources across all member states by 2010. It was projected in 2006 that by 2020, production would be six times more than demand, creating an excess of glycerol as a byproduct of biofuel production.[7]

Glycerol from triglycerides is produced on a large scale, but the crude product is of variable quality, with a low selling price of as low as US$0.02–0.05 per kilogram in 2011.[12] It can be purified, but the process is expensive. Some glycerol is burned for energy, but its heat value is low.[13]

Crude glycerol from the hydrolysis of triglycerides can be purified by treatment with activated carbon to remove organic impurities, alkali to remove unreacted glycerol esters, and ion exchange to remove salts. High purity glycerol (greater than 99.5%) is obtained by multi-step distillation; a vacuum chamber is necessary due to its high boiling point (290 °C).[7]

Synthetic glycerol

Because of the large-scale production of

economical. Owing to oversupply, efforts are being made to convert glycerol to synthetic precursors, such as acrolein and epichlorohydrin.[14]

Although usually not cost-effective because so much is produced from processing of fats, glycerol can be produced by various routes. During

dichlorohydrin, which reacts with a strong base to give epichlorohydrin. Epichlorohydrin can be hydrolyzed to glycerol. Chlorine-free processes from propylene include the synthesis of glycerol from acrolein and propylene oxide.[7]

Applications

Food industry

In food and beverages, glycerol serves as a

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 U.S.

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.

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.[16]

Excessive consumption by children can lead to glycerol intoxication.[17] Symptoms of intoxication include hypoglycemia, nausea and a loss of consciousness (syncope). While intoxication as a result of excessive glycerol consumption is rare and its symptoms generally mild, occasional reports of hospitalization have occurred. In the United Kingdom in August 2023, manufacturers of syrup used in slush ice drinks were advised to reduce the amount of glycerol in their formulations by the Food Standards Agency to reduce the risk of intoxication.[18]

Medical, pharmaceutical and personal care applications

A bottle of glycerin purchased at a pharmacy
Personal lubricants commonly contain glycerol
Glycerol is an ingredient in products such as hair gel
Glycerol suppositories used as laxatives

Glycerol is used in

personal care preparations, often as a means of improving smoothness, providing lubrication, and as a humectant
.

blood banking to preserve red blood cells
prior to freezing.

Glycerol is a component of

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
]

Taken rectally, glycerol functions as a

hyperosmotic effect,[21] expanding the colon by drawing water into it to induce peristalsis resulting in evacuation.[22] It may be administered undiluted either as a suppository 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 the internal 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 probiotic Limosilactobacillus 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 antibiotic vancomycin at inhibiting Clostridioides difficile infection without having a significant effect on the overall microbial composition of the gut.[25]

Glycerol has also been incorporated as a component of bio-ink formulations in the field of bioprinting.[26] The glycerol content acts to add viscosity to the bio-ink without adding large protein, saccharide, or glycoprotein molecules.

Botanical extracts

When utilized in "tincture" method extractions, specifically as a 10% solution, glycerol prevents tannins from precipitating in ethanol extracts of plants (

Fluid extract manufacturers often extract herbs in hot water before adding glycerol to make glycerites.[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.

bacteriostatic in its action, and ethanol is bactericidal in its action.[30][31][32]

Electronic cigarette liquid

electronic cigarettes
to create the vapor

Glycerin, along with

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.[33]

Antifreeze

Main article: Antifreeze

Like

hydrogen 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 for

fungi, bacteria, nematodes, and mammalian embryos. Some organisms like the moor frog produce glycerol to survive freezing temperatures during hibernation.[36]

Chemical intermediate

Glycerol is used to produce a variety of useful derivatives.

angina pectoris, taken in the form of sub-lingual tablets, patches, or as an aerosol
spray.

Trifunctional

polyether polyols are produced from glycerol and propylene oxide
.

Oxidation of glycerol affords mesoxalic acid.[37] Dehydrating glycerol affords hydroxyacetone.

Chlorination of glycerol gives the

1-chloropropane-2,3-diol
:

HOCH(CH2OH)2 + HCl → HOCH(CH2Cl)(CH2OH) + H2O

The same compound can be produced by hydrolysis of epichlorohydrin.[38]

Vibration damping

Glycerol is used as fill for

Bourdon 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.[39]

Niche uses

Entertainment industry

Glycerol is used by set decorators when filming scenes involving water to prevent an area meant to look wet from drying out too quickly.[40]

Glycerine is also used in the generation of theatrical smoke and fog as a component of the fluid used in fog machines as a replacement for glycol, which has been shown to be an irritant if exposure is prolonged.

Ultrasonic couplant

Glycerol can be sometimes used as replacement for water in ultrasonic testing, as it has favourably higher acoustic impedance (2.42 MRayl versus 1.483 MRayl for water) while being relatively safe, non-toxic, non-corrosive and relatively low cost.[41]

Internal combustion fuel

Glycerol is also used to power diesel generators supplying electricity for the

FIA Formula E series of electric race cars.[42]

Research on additional uses

Research continues into potential

value-added products of glycerol obtained from biodiesel production.[43]
Examples (aside from combustion of waste glycerol):

Metabolism

Glycerol is a precursor for synthesis of

triacylglycerols and of phospholipids in the liver and adipose tissue. When the body uses stored fat as a source of energy, glycerol and fatty 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 and fatty liver disease.[55][56]

Blood glycerol levels are highly elevated during diabetes, 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.[57]

Circulating glycerol does not

advanced glycation endproducts (AGEs). In some organisms, the glycerol component can enter the glycolysis pathway directly and, thus, provide energy for cellular metabolism (or, potentially, be converted to glucose through gluconeogenesis
).

Before glycerol can enter the pathway of glycolysis or gluconeogenesis (depending on physiological conditions), it must be converted to their intermediate glyceraldehyde 3-phosphate in the following steps:

ATP
ADP
Rightward reaction arrow with minor substrate(s) from top left and minor product(s) to top right

Glycerol-3-phosphate

The enzyme glycerol kinase is present mainly in the liver and kidneys, but also in other body tissues, including muscle and brain.[58][59][60] In adipose tissue, glycerol 3-phosphate is obtained from dihydroxyacetone phosphate with the enzyme glycerol-3-phosphate dehydrogenase.

Glycerol has very low toxicity when ingested; its

LD50 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 minimal metaplasia of the epithelium lining at the base of the epiglottis in rats exposed to 0.66 mg/L glycerin.[61][62]

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 for diethylene glycol contamination.[63] This followed an occurrence of hundreds 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.[64][65] 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.[66]

Etymology

The origin of the gly- and glu- prefixes for glycols and sugars is from Ancient Greek γλυκύς glukus which means sweet.[67] Name glycérine was coined ca. 1811 by Michel Eugène Chevreul to denote what was previously called "sweet principle of fat" by its discoverer Carl Wilhelm Scheele. It was borrowed into English ca. 1838 and in the 20th c. displaced by 1872 term glycerol featuring an alcohols' suffix -ol.

Properties

Table of thermal and physical properties of saturated liquid glycerin:[68][69]

Temperature (°C) Density (kg/m3) Specific heat (kJ/kg·K)
Kinematic viscosity
(m2/s)
Conductivity
(W/m·K) 		Thermal diffusivity (m2/s) Prandtl number Bulk modulus (K−1)
0 1276.03 2.261 8.31×10−3 0.282 9.83×10−8 84700 4.7×10−4
10 1270.11 2.319 3.00×10−3 0.284 9.65×10−8 31000 4.7×10−4
20 1264.02 2.386 1.18×10−3 0.286 9.47×10−8 12500 4.8×10−4
30 1258.09 2.445 5.00×10−4 0.286 9.29×10−8 5380 4.8×10−4
40 1252.01 2.512 2.20×10−4 0.286 9.14×10−8 2450 4.9×10−4
50 1244.96 2.583 1.50×10−4 0.287 8.93×10−8 1630 5.0×10−4

See also

References

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External links
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