Glycerol

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Glycerol
Glycerol
Ball-and-stick model of glycerol
Space-filling model of glycerol
Sample of glycerine
Names
Preferred IUPAC name
Propane-1,2,3-triol
Other names
Glycerin
Glycerine
Propanetriol
1,2,3-Trihydroxypropane
1,2,3-Propanetriol
Identifiers
56-81-5 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:17522 YesY
ChEMBL ChEMBL692 YesY
ChemSpider 733 YesY
DrugBank DB04077 YesY
ECHA InfoCard 100.000.263
E number E422 (thickeners, ...)
5195
KEGG D00028 YesY
PubChem 753
UNII PDC6A3C0OX YesY
Properties
C3H8O3
Molar mass 92.09 g·mol−1
Appearance colorless liquid
hygroscopic
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)[3]
miscible[1]
Vapor pressure 0.003 mmHg (50°C)[1]
1.4746
Viscosity 1.412 Pa·s[2]
Pharmacology
A06AG04 (WHO) A06AX01 (WHO), QA16QA03 (WHO)
Hazards
Safety data sheet See: data page
JT Baker
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 160 °C (320 °F; 433 K) (closed cup)
176 °C (349 °F; 449 K) (open cup)
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)[1]
REL (Recommended)
None established[1]
IDLH (Immediate danger)
N.D.[1]
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Thermodynamic
data
Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY verify (what is YesYN ?)
Infobox references

Glycerol /ˈɡlɪsərɒl/[4] (also called glycerine or glycerin; see spelling differences) 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. It is widely used in the food industry as a sweetener and humectant and in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature.[5]

Structure[edit]

Although achiral, glycerol is prochiral with respect to reactions of one of the two primary alcohols. Thus, in substituted derivatives, the stereospecific numbering labels each carbon as either sn-1, sn-2, or sn-3.[6][7]

Production[edit]

Glycerol is generally obtained from plant and animal sources where it occurs as triglycerides. Triglycerides are esters of glycerol with long-chain carboxylic acids. The hydrolysis, saponification, or transesterification of these triglycerides produces glycerol as well as the fatty acid derivative:.

SaponificationGeneral.svg

Triglycerides (1) are treated with an alcohol such as ethanol (2) with catalytic base to give ethyl esters of fatty acids (3) and glycerol (4):

Typical plant sources include soybeans or palm. Animal-derived tallow is another source. Approximately 950,000 tons per year are produced in the United States and Europe; 350,000 tons of glycerol were produced per year in the United States alone from 2000 to 2004.[8] Production will increase as the EU directive 2003/30/EC are implemented, which required the replacement of 5.75% of petroleum fuels with biofuel across all member states by 2010, as glycerol is a byproduct in the production of biodiesel. It was projected in 2006 that by the year 2020, production would be six times more than demand.[5][needs update]

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 1–8 U.S. cents per pound in 2011.[9] It can be purified, but the process is expensive. Some glycerol is burned for energy, but its heat value is low.[10]

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 (> 99.5%) is obtained by multi-step distillation; vacuum is helpful due to the high boiling point of glycerol (290 °C).[5]

Synthetic glycerol[edit]

Although usually not cost-effective, glycerol can be produced by various routes from propylene. 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. This epichlorohydrin is then hydrolyzed to give glycerol. Chlorine-free processes from propylene include the synthesis of glycerol from acrolein and propylene oxide.[5]

Synthetic routes to glycerol.png

Because of the large-scale production of biodiesel from fats, where glycerol is a waste product, the market for glycerol is depressed. Thus, synthetic processes are not economical. Owing to oversupply, efforts are being made to convert glycerol to synthetic precursors, such as acrolein and epichlorohydrin.[11] (See the Chemical intermediate section of this article.)

Applications[edit]

Food industry[edit]

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[edit]

Glycerol suppositories used as laxatives

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[edit]

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[edit]

Vegetable glycerin is a common component of e-liquid, a solution used with electronic vaporizers (electronic cigarettes), that is heated with an atomizer to produce a vapor in order to deliver flavors and optionally nicotine.

Antifreeze[edit]

Main article: 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.[21][22]

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[edit]

Used to power diesel generators supplying electricity for the FIA Formula E series of electric race cars.[23]

Chemical intermediate[edit]

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.[24]

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.[25] The use of crude glycerol as an additive to biomass for a renewable energy source when burned or gasified is also being explored.

Film industry[edit]

Glycerol is used by the film industry when filming scenes involving water to stop areas from drying out too quickly.[33]

Ultrasonic couplant[edit]

Glycerol can be sometimes used as replacement for water in ultrasonic testing, as it has favourably higher acoustic impedance (2.42MRayl vs 1.483MRayl for water) while being relatively safe, non-toxic, non-corrosive and relatively low cost.[34]

Metabolism[edit]

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. Circulating glycerol does not glycate proteins as do glucose or fructose, and does not lead to the formation of advanced glycation endproducts (AGEs). In some[which?] 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:

Glycerol Glycerol kinase Glycerol-3-phosphate Glycerol-3-phosphate dehydrogenase Dihydroxyacetone phosphate Triosephosphate isomerase Glyceraldehyde 3-phosphate
Glycerin Skelett.svg ATP ADP Glycerol-3-phosphate.png NAD+ NADH
DHAP struct.svg G3P-2D-skeletal.png
Biochem reaction arrow forward YYNN horiz med.svg Biochem reaction arrow reversible YYYY horiz med.svg Biochem reaction arrow reversible NNNN horiz med.svg
NAD+ NADH

The enzyme glycerol kinase is present mainly in the liver and kidneys, but also in other body tissues, including muscle and brain.[35][36][37] In adipose tissue, glycerol 3-phosphate is obtained from dihydroxyacetone phosphate (DHAP) 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.

Historical cases of contamination with diethylene[edit]

On 4 May 2007, the US Food and Drug Administration advised all US makers of medicines to test all batches of glycerol for the toxic diethylene glycol.[38] 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.[39][40]

Etymology[edit]

The origin of the gly- and glu- prefixes for glycols and sugars is from Greek glukus which means sweet.[41]

Isomers[edit]

1,1,1-Propanetriol, 1,1,2-Propanetriol, 1,1,3-Propanetriol, 1,2,2-Propanetriol.

See also[edit]

References[edit]

  1. ^ a b c d e "NIOSH Pocket Guide to Chemical Hazards #0302". National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ Segur, J. B.; Oberstar, H. E. (1951). "Viscosity of Glycerol and Its Aqueous Solutions". Industrial & Engineering Chemistry. 43 (9): 2117–2120. doi:10.1021/ie50501a040. 
  3. ^ Lide, D. R., ed. (1994). CRC Handbook of Data on Organic Compounds (3rd ed.). Boca Raton, FL: CRC Press. p. 4386. 
  4. ^ Oxford dictionary: definition of glycerol (British & World English)
  5. ^ a b c d Christoph, Ralf; Schmidt, Bernd; Steinberner, Udo; Dilla, Wolfgang; Karinen, Reetta (2006). "Glycerol". Ullmann's Encyclopedia of Industrial Chemistry. Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a12_477.pub2. ISBN 3527306730. 
  6. ^ Hirschmann, H. (1960-10-01). "The Nature of Substrate Asymmetry in Stereoselective Reactions". Journal of Biological Chemistry. 235 (10): 2762–2767. PMID 13714619. 
  7. ^ "IUPAC-IUB Commission on Biochemical Nomenclature (CBN)". European Journal of Biochemistry. 2 (2): 127–131. 1967-09-01. doi:10.1111/j.1432-1033.1967.tb00116.x. 
  8. ^ Nilles, Dave (2005). "A Glycerin Factor". Biodiesel Magazine. 
  9. ^ Pei San Kong, Mohamed Kheireddine Aroua, Wan Mohd Ashri Wan Daud, "Conversion_of_crude_and_pure_glycerol_into_derivatives_A_feasibility_evaluation" Renewable and Sustainable Energy Reviews, 2016, Volume 63, pp. 533-555. doi:10.1016/j.rser.2016.05.054
  10. ^ Sims, Bryan (25 October 2011). "Clearing the way for byproduct quality: why quality for glycerin is just as important for biodiesel". Biodiesel Magazine. 
  11. ^ Yu, Bin (2014). "Glycerol". Synlett. 25 (4): 601–602. doi:10.1055/s-0033-1340636. 
  12. ^ Stevens, Alan. "Preserving flowers and decorative foliages with glycerin and dye" (PDF). 
  13. ^ Nikolov, Ivan. "Functional Food Design Rules". 
  14. ^ "Glycerin Enema". Drugs.com. Retrieved 17 November 2012. 
  15. ^ "Glycerin (Oral Route)". Mayo Foundation for Medical Education and Research. Retrieved 17 November 2012. 
  16. ^ Long, Walter S. (14 January 1916 – 13 January 1917). "The composition of commercial fruit extracts". Transactions of the Kansas Academy of Science. 28: 157–161. doi:10.2307/3624347. JSTOR 3624347. 
  17. ^ Does alcohol belong in herbal tinctures? newhope.com
  18. ^ Lawrie, James W. (1928) Glycerol and the glycols – production, properties and analysis. The Chemical Catalog Company, Inc., New York, NY.
  19. ^ Leffingwell, Georgia and Lesser, Miton (1945) Glycerin – its industrial and commercial applications. Chemical Publishing Co., Brooklyn, NY.
  20. ^ The manufacture of glycerol – Vol. III (1956). The Technical Press, LTD., London, UK.
  21. ^ Hudgens, R. Douglas; Hercamp, Richard D.; Francis, Jaime; Nyman, Dan A.; Bartoli, Yolanda (2007). "An Evaluation of Glycerin (Glycerol) as a Heavy Duty Engine Antifreeze/Coolant Base". SAE Technical Paper Series. SAE Technical Paper Series. 1. doi:10.4271/2007-01-4000. 
  22. ^ Proposed ASTM Engine Coolant Standards Focus on Glycerin. Astmnewsroom.org. Retrieved on 15 August 2012.
  23. ^ Formula E uses pollution-free glycerine to charge cars. fiaformulae.com. 13 September 2014
  24. ^ Datta, Rasek Lal (1914). "The Preparation of Allyl Iodide". Journal of the American Chemical Society. 36 (5): 1005–1007. doi:10.1021/ja02182a023. 
  25. ^ Johnson, Duane T.; Taconi, Katherine A. (2007). "The glycerin glut: Options for the value-added conversion of crude glycerol resulting from biodiesel production". Environmental Progress. 26 (4): 338–348. doi:10.1002/ep.10225. 
  26. ^ Marshall, A. T.; Haverkamp, R. G. (2008). "Production of hydrogen by the electrochemical reforming of glycerol-water solutions in a PEM electrolysis cell". International Journal of Hydrogen Energy. 33 (17): 4649–4654. doi:10.1016/j.ijhydene.2008.05.029. 
  27. ^ Melero, Juan A.; Van Grieken, Rafael; Morales, Gabriel; Paniagua, Marta (2007). "Acidic mesoporous silica for the acetylation of glycerol: Synthesis of bioadditives to petrol fuel". Energy Fuels. 21 (3): 1782–1791. doi:10.1021/ef060647q. 
  28. ^ "Dow achieves another major milestone in its quest for sustainable chemistries" (Press release). Dow Chemical Company. 15 March 2007. 
  29. ^ Ott, L.; Bicker, M.; Vogel, H. (2006). "The catalytic dehydration of glycerol in sub- and supercritical water: a new chemical process for acrolein production". Green Chemistry. 8 (2): 214–220. doi:10.1039/b506285c. 
  30. ^ Watanabe, Masaru; Iida, Toru; Aizawa, Yuichi; Aida, Taku M.; Inomata, Hiroshi (2007). "Acrolein synthesis from glycerol in hot-compressed water". Bioresource Technology. 98 (6): 1285–1290. doi:10.1016/j.biortech.2006.05.007. PMID 16797980. 
  31. ^ Yazdani, S. S.; Gonzalez, R. (2007). "Anaerobic fermentation of glycerol: a path to economic viability for the biofuels industry". Current Opinion in Biotechnology. 18 (3): 213–219. doi:10.1016/j.copbio.2007.05.002. PMID 17532205. Lay summaryScienceDaily (27 June 2007). 
  32. ^ "Dow Epoxy advances glycerine-to-epichlorohydrin and liquid epoxy resins projects by choosing Shanghai site" (Press release). Dow Chemical Company. 26 March 2007. 
  33. ^ Chemicals in Film. reagent.co.uk
  34. ^ Accoustic Properties for Liquids. nde-ed.org
  35. ^ Tildon, J. T.; Stevenson Jr, J. H.; Ozand, P. T. (1976). "Mitochondrial glycerol kinase activity in rat brain". The Biochemical Journal. 157 (2): 513–6. doi:10.1042/bj1570513. PMC 1163884Freely accessible. PMID 183753. 
  36. ^ Newsholme, E. A.; Taylor, K (May 1969). "Glycerol kinase activities in muscles from vertebrates and invertebrates". Biochem. J. 112 (4): 465–74. doi:10.1042/bj1120465. PMC 1187734Freely accessible. PMID 5801671. 
  37. ^ Jenkins, BT, Hajra, AK (1976). "Glycerol Kinase and Dihydroxyacetone Kinase in Rat Brain". Journal of Neurochemistry. 26 (2): 377–385. doi:10.1111/j.1471-4159.1976.tb04491.x. PMID 3631. 
  38. ^ "FDA Advises Manufacturers to Test Glycerin for Possible Contamination". U.S. Food and Drug Administration. 4 May 2007. Retrieved 8 May 2007. 
  39. ^ Walt Bogdanich (6 May 2007). "From China to Panama, a Trail of Poisoned Medicine". New York Times. Retrieved 8 May 2007. 
  40. ^ "10 Biggest Medical Scandals in History". 20 February 2013. 
  41. ^ glyco-, dictionary.com

External links[edit]