Stearic acid
| Stearic acid[1] | |
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Octadecanoic acid
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Other names
C18:0 (Lipid numbers)
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| Identifiers | |
| CAS number | 57-11-4  |
| PubChem | 5281 |
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SMILES
CCCCCCCCCCCCCCCCCC(=O)O
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| Properties | |
| Molecular formula | C18H36O2 |
| Molar mass | 284.48 g mol−1 |
| Density | 0.847 g/cm3 at 70 °C |
| Melting point |
69.6 °C, 343 K, 157 °F |
| Boiling point |
383 °C, 656 K, 721 °F |
| Refractive index (nD) | 1.4299 |
| (what is this?) (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Stearic acid (first syllable pronounced either steer or stair) or 18:0 is a saturated fatty acid with the formal IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is C18H36O2, or CH3(CH2)16COOH. Its name comes from the Greek word stéar (genitive: stéatos), which means tallow. The salts and esters of stearic acid are called stearates.
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Food sources
It occurs in many animal and vegetable fats and oils, but it is more common in animal fat than vegetable fat. The important exceptions are cocoa butter and shea butter whose fatty acids consist of 28–45% stearic acid.[2]
Production
Stearic acid is prepared by treating animal fat with water at a high pressure and temperature, leading to the hydrolysis of triglycerides. It can also be obtained from the hydrogenation of some unsaturated vegetable oils. Common stearic acid is actually a mix of stearic acid and palmitic acid, although purified stearic acid is available separately.
Uses
Stearic acid is useful as an ingredient in making candles, plastics, dietary supplements, oil pastels and cosmetics, and for softening rubber.[3] It is used to harden soaps, particularly those made with vegetable oil. Stearic acid is used in aerosol shaving cream products.
Stearic acid is also used as a parting compound when making plaster castings from a plaster piece mold or waste mold and when making the mold from a shellacked clay original. In this use, powdered stearic acid is dissolved in water and the solution is brushed onto the surface to be parted after casting. This reacts with the calcium in the plaster to form a thin layer of calcium stearate which functions as a release agent.
Esters of stearic acid with ethylene glycol, glycol stearate and glycol distearate, are used to produce a pearly effect in shampoos, soaps, and other cosmetic products. They are added to the product in molten form and allowed to crystallize under controlled conditions.
In fireworks, stearic acid is often used to coat metal powders such as aluminium and iron. This prevents oxidation, allowing compositions to be stored for a longer period of time.
It is used along with simple sugar or corn syrup as a hardener in candies.
It is used with zinc as zinc stearate as fanning powder for cards to deliver smooth fanning motion.
Stearic acid is one of most commonly used lubricants during injection molding and pressing of ceramic powders.[4]
Stearic acid serves as an epilame (or barrier film) treatment, applied to precision mechanical components to modify the surface properties to reduce the spreading (or creep) of subsequently-applied lubricant films.[5]
Reactions
Stearic acid undergoes the typical reactions of saturated carboxylic acids, notably reduction to stearyl alcohol, and esterification with a range of alcohols.
Stearic acid is used along with castor oil for preparing softeners in textile sizing. They are heated and mixed with caustic potash or caustic soda.
Metabolism
An isotope labeling study in humans[6] concluded that the fraction of dietary stearic acid oxidatively desaturated to oleic acid was 2.4 times higher than the fraction of palmitic acid analogously converted to palmitoleic acid. Also, stearic acid was less likely to be incorporated into cholesterol esters. In epidemiologic and clinical studies stearic acid was associated with lowered LDL cholesterol in comparison with other saturated fatty acids.[7] These findings may indicate that stearic acid is less unhealthy than other saturated fatty acids.
See also
- Magnesium stearate
References
- ↑ Susan Budavari, ed (1989). Merck Index (11th ed.). Rahway, New Jersey: Merck & Co., Inc. p. 8761. ISBN 9780911910285.
- ↑ Beare-Rogers, J.; Dieffenbacher, A.; Holm, J.V. (2001). "Lexicon of lipid nutrition (IUPAC Technical Report)". Pure and Applied Chemistry 73 (4): 685–744. doi:10.1351/pac200173040685. http://iupac.org/publications/pac/73/4/0685/.
- ↑ Wootthikanokkhan, J.; Tunjongnawin, P (2002). "Investigation of the effect of mixing schemes on cross-link distribution and tensile properties of natural–acrylic rubber blends". Polymer Testing 22 (3): 305–312. doi:10.1016/S0142-9418(02)00105-8.
- ↑ Tsenga, Wenjea J.; Mo Liua, Dean; Hsub, Chung-King (1999). "Influence of stearic acid on suspension structure and green microstructure of injection-molded zirconia ceramics". Ceramics International 25 (2): 191–195. doi:10.1016/S0272-8842(98)00024-8.
- ↑ Epilame
- ↑ Emken, Edward A. (1994). "Metabolism of dietary stearic acid relative to other fatty acids in human subjects". American Journal of Clinical Nutrition 60 (6): 1023S–1028S. PMID 7977144.
- ↑ Hunter, J. Edward; Zhang, Jun; Kris-Etherton, Penny M. (January 2010). "Cardiovascular disease risk of dietary stearic acid compared with trans, other saturated, and unsaturated fatty acids: a systematic review". Am. J. Clinical Nutrition (American Society for Nutrition) 91 (1): 46–63. doi:10.3945/ajcn.2009.27661. ISSN 0002-9165. PMID 19939984.
External links
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