Stearic acid is the saturated
fatty acidIn chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
with an 18 carbon chain and has the IUPAC name
octadecanoic acid. It is a waxy solid, and its chemical formula is CH
3(CH
2)
16CO
2H. Its name comes from the
GreekGreek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
word στέαρ
"stéatos", which means
tallowTallow is a rendered form of beef or mutton fat, processed from suet. It is solid at room temperature. Unlike suet, tallow can be stored for extended periods without the need for refrigeration to prevent decomposition, provided it is kept in an airtight container to prevent oxidation.In industry,...
. The salts and
esterEsters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s of stearic acid are called
stearates. Stearic acid is noteworthy as the most common saturated fatty acid, another common one being the C16 compound
palmitic acidPalmitic acid, or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated fatty acids found in animals and plants. Its molecular formula is CH314CO2H. As its name indicates, it is a major component of the oil from palm trees . Palmitate is a term for the salts and esters of...
.
Production
It occurs in many animal and vegetable fats and oils, but it is more abundant in animal fat (up to 30%) than vegetable fat (typically <5%). The important exceptions are
cocoa butterCocoa butter, also called theobroma oil, is a pale-yellow, pure edible vegetable fat extracted from the cocoa bean. It is used to make chocolate, biscuits, and baked goods, as well as some pharmaceuticals, ointments, and toiletries...
and
shea butterShea butter is a slightly yellowish or ivory-colored fat extracted from the nut of the African shea tree . It is widely used in cosmetics as a moisturizer, salve or lotion. Shea butter is edible and may be used in food preparation...
where the stearic acid content (as a
triglycerideA triglyceride is an ester derived from glycerol and three fatty acids. There are many triglycerides, depending on the oil source, some are highly unsaturated, some less so....
) is 28–45%.
Stearic acid is prepared by treating these fats and oils with water at a high pressure and temperature (above 200 °C), leading to the
hydrolysisHydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of
triglycerideA triglyceride is an ester derived from glycerol and three fatty acids. There are many triglycerides, depending on the oil source, some are highly unsaturated, some less so....
s. The resulting mixture is then distilled. Commercial stearic acid is often a mixture of stearic and
palmitic acidPalmitic acid, or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated fatty acids found in animals and plants. Its molecular formula is CH314CO2H. As its name indicates, it is a major component of the oil from palm trees . Palmitate is a term for the salts and esters of...
s, although purified stearic acid is available.
In terms of its biosynthesis, stearic acid is produced from carbohydrates via the
fatty acid synthesisFatty acid synthesis is the creation of fatty acids from acetyl-CoA and malonyl-CoA precursors through action of enzymes called fatty acid synthases...
machinery via
acetyl-CoAAcetyl coenzyme A or acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main function is to convey the carbon atoms within the acetyl group to the citric acid cycle to be oxidized for energy production. In chemical structure, acetyl-CoA is the thioester...
.
Uses
Generally applications of stearic acid exploit its bifunctional character, with a polar head group that can be attached to metal cations and a nonpolar chain that confers solubility in organic solvents. The combination leads to uses as a surfactant and softening agent. Stearic acid undergoes the typical reactions of saturated carboxylic acids, notably reduction to
stearyl alcoholStearyl alcohol is a substance prepared from stearic acid by the process of catalytic hydrogenation. It is a fatty alcohol. It takes the form of white solid granules or flakes which are insoluble in water, with a melting point of 60 °C and boiling point of 210 °C...
, and esterification with a range of alcohols.
Soaps, cosmetics, detergents
Stearic acid is mainly used in the production of detergents, soaps, and cosmetics such as
shampooShampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair...
s and
shaving creamShaving cream is a substance that is applied to the face or wherever else hair grows, to provide lubrication and avoid razor burn during shaving. Shaving cream is often bought in a spray can, but can also be purchased in tubs or tubes. Shaving cream in a can is commonly dispensed as a foam or a gel...
products. Soaps are not made directly from stearic acid, but indirectly by
saponificationSaponification is a process that produces soap, usually from fats and lye. In technical terms, saponification involves base hydrolysis of triglycerides, which are esters of fatty acids, to form the sodium salt of a carboxylate. In addition to soap, such traditional saponification processes...
of triglycerides consisting of stearic acid esters.
EsterEsters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s of stearic acid with
ethylene glycolEthylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...
, 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. Detergents are obtained from amides and quaternary alkylammonium derivatives of stearic acid.
Lubricants, softening and release agents
In view of the soft texture of the sodium salt, which is the main component of soap, other salts are also useful for their lubricating properties.
Lithium stearateLithium stearate is a chemical compound with the formula LiO2C16CH3. It is formally classified as a soap . Lithium stearate is a white soft solid, prepared by the reaction of lithium hydroxide and steric acid....
is an important component of
greaseGrease may refer to:* Grease , a type of industrial lubricant* Yellow grease, in rendering, used frying oils, or lower-quality grades of tallow...
. The stearate salts of zinc, calcium, cadmium, and lead are used to soften
PVCPolyvinyl chloride is a plastic.PVC may also refer to:*Param Vir Chakra, India's highest military honor*Peripheral venous catheter, a small, flexible tube placed into a peripheral vein in order to administer medication or fluids...
. 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. Related salts are also commonly used as a
release agentA release agent is a chemical used to get a slip effect. It can provide a solution in processes involving mold release, die-cast release, plastic release, and tire and web release.-Concrete:...
s, e.g. in the production of automobile tires.
Niche uses
Being inexpensively available and chemically benign, stearic acid finds many niche applications. 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 stearateCalcium stearate is carboxylate of calcium that is found in some lubricants and surfactants. It is a white waxy powder.-Production and occurrence:Calcium stearate is produced by heating stearic acid, a fatty acid, and calcium oxide:...
which functions as a release agent. When reacted with
zincZinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
it forms
zinc stearateZinc stearate is a zinc soap that repels water. It is insoluble in polar solvents such as alcohol and ether but soluble in aromatic hydrocarbons when heated. It is the most powerful mold release agent among all metal soaps. It contains no electrolyte and has a hydrophobic effect...
which is used a lubricant for playing cards (fanning powder) to ensure a smooth motion when
fanningFanning can refer to:* Tabuaeran, also known as Fanning Atoll or Fanning Island, one of the Line Islands of the central Pacific Ocean.* Fanning , a revolver shooting technique in which one hand holds the revolver and the other hits the revolver hammer repeatedly for an increased rate of fire.*...
. In
compressed confectionsTableting is a method of confectionery manufacture that shares many similarities with tablet pharmaceutical production.A powder or granule mixture is prepared, a die mold is filled, and then the mixture is compressed and ejected. While drug tablets are constrained to shapes that can be swallowed...
it is used as a lubricant to keep the tablet from sticking to the die.
Fatty acids are classic components of
candleA candle is a solid block or cylinder of wax with an embedded wick, which is lit to provide light, and sometimes heat.Today, most candles are made from paraffin. Candles can also be made from beeswax, soy, other plant waxes, and tallow...
-making. Stearic acid is used along with simple
sugarSugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
or
corn syrupCorn syrup is a food syrup, which is made from the starch of maize and contains varying amounts of maltose and higher oligosaccharides, depending on the grade. Corn syrup is used in foods to soften texture, add volume, prevent crystallization of sugar, and enhance flavor...
as a hardener in candies.
Stearic acid is used to produce
dietary supplementA dietary supplement, also known as food supplement or nutritional supplement, is a preparation intended to supplement the diet and provide nutrients, such as vitamins, minerals, fiber, fatty acids, or amino acids, that may be missing or may not be consumed in sufficient quantities in a person's diet...
s.
In
fireworksFireworks are a class of explosive pyrotechnic devices used for aesthetic and entertainment purposes. The most common use of a firework is as part of a fireworks display. A fireworks event is a display of the effects produced by firework devices...
, stearic acid is often used to coat
metalA metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
powders such as
aluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
and
ironIron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
. This prevents oxidation, allowing compositions to be stored for a longer period of time.
Stearic acid is a common lubricants during
injection moldingInjection molding is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the cavity...
and pressing of
ceramic powdersCeramic forming techniques are ways of forming ceramic shapes. This can be used to make everyday tableware from teapots, to engineering ceramics such as computer parts. Methods for forming powders of ceramic raw materials into complex shapes are desirable in many areas of technology...
. It is also used as a mold release for
foam latexFoam latex is a lightweight, soft form of latex which is used in masks and facial prosthetics to change a person's outward appearance. The Wizard of Oz was one of the first films to make extensive use of foam latex prosthetics in the 1930s...
that is baked in stone molds.
Metabolism
An isotope labeling study in humans concluded that the fraction of dietary stearic acid
oxidativelyRedox reactions describe all chemical reactions in which atoms have their oxidation state changed....
desaturated to
oleic acidOleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable fats. It has the formula CH37CH=CH7COOH. It is an odorless, colourless oil, although commercial samples may be yellowish. The trans isomer of oleic acid is called elaidic acid...
was 2.4 times higher than the fraction of
palmitic acidPalmitic acid, or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated fatty acids found in animals and plants. Its molecular formula is CH314CO2H. As its name indicates, it is a major component of the oil from palm trees . Palmitate is a term for the salts and esters of...
analogously converted to
palmitoleic acidPalmitoleic acid, or -9-hexadecenoic acid, is an omega-7 monounsaturated fatty acid with the formula CH35CH=CH7COOH that is a common constituent of the glycerides of human adipose tissue. It is present in all tissues, but generally found in higher concentrations in the liver...
.
Also, stearic acid was less likely to be incorporated into cholesterol esters.
In epidemiologic and clinical studies stearic acid was associated with lowered LDL
cholesterolCholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...
in comparison with other saturated fatty acids.
These findings may indicate that stearic acid is healthier than other saturated fatty acids.
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