Stearic acid

Toxicity

Acute oral toxicity (LD50): 4640 mg/kg [Rat]. Acute dermal toxicity (LD50): >5000 mg/kg Rabbit.

Description

Stearic acid (STAIR-ik or STEER-ik) is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH₃(CH₂)₁₆CO₂H. Its name comes from the Greek word στ?αρ "stéar", which means tallow. The salts and esters of stearic acid are called stearates. Stearic acid is one of the most common saturated fatty acids found in nature following palmitic acid.

Description

Stearic acid is a long-chain saturated fatty acid. It is a major component of cocoa butter and has also been found in beef fat and vegetable oils. Unlike many long-chain saturated fatty acids, dietary stearic acid does not induce hypercholesterolemia or raise LDL-cholesterol.

Chemical properties

Stearic acid, CH3(CH2)16COOH, is a white or colorless, waxlike solid with a melting point of 70°C (158 OF), and a boiling point of 232°C (450 OF) at 2 kPa. It is soluble in alcohol, ether, and chloroform,and is insolublein water. Stearic acid, nature's most common fatty acid, is derived from natural animal and vegetable fats. Also known as n-octadecanoic acid, stearic acid is used in the preparation of metallic stearates, as a lubricant, and in pharmaceuticals, cosmetics, candles, and food packaging.

Chemical properties

Stearic acid is a hard, white or faintly yellow-colored, somewhat glossy, crystalline solid or a white or yellowish white powder. It has a slight odor (with an odor threshold of 20 ppm) and taste suggesting tallow.

Chemical properties

Stearic acid has a characteristic odor and taste resembling tallow. It is a mixture of solid organic acids obtained from fats consisting chiefly of stearic acid (C18H36O2) and palmitic acid (C16H32O2).

Occurrence

Stearic acid is naturally present in the glycerides of animal fats and most vegetable oils. Reported found in fresh apple, banana, Vitis vinifera L., melon, tomato, ginger, blue cheeses, cheddar cheese, Swiss cheese, feta cheese, buttermilk, raw fatty fish, raw lean fish, raw shrimp, grapefruit juice, guava, papaya, cucumber, saffron, pork and lamb liver, pork fat, hop oil, beer, cognac, rum, whiskies, sherry, tea, peanut oil, soybean, roast coconut, coconut milk, avocado, passion fruit, rose apple, mushroom, starfruit, fenugreek, mango, cardamom, cooked rice, prickly pear, dill seed, buckwheat, malt, wort, cassava, loquat, shrimp, crab, cape gooseberry and Chinese quince.

The Uses of Stearic acid

Stearic Acid is an anti-inflammatory agent that induces ICAM-1 expression. It is the main ingredient used in making bar soaps and lubricants. It occurs naturally in butter acids, tallow, cascarilla bark, and in other animal fats and oils. Stearic acid may cause allergic reactions in people with sensitive skin and is considered somewhat comedogenic.

The Uses of Stearic acid

Pharmaceutic aid (emulsion adjunct); pharmaceutic aid (tablet and/or capsule lubricant).

The Uses of Stearic acid

Stearic Acid is a fatty acid that is a mixture of solid organic acids obtained principally from stearic acid and palmitic acid. it is practi- cally insoluble in water. it functions as a lubricant, binder, and defoamer. it is used as a softener in chewing gum base.

The Uses of Stearic acid

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 alcohol, 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 shampoos and shaving cream products. Soaps are not made directly from stearic acid, but indirectly by saponification of triglycerides consisting of stearic acid esters. 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. 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 stearate is an important component of grease. The stearate salts of zinc, calcium, cadmium, and lead are used to soften PVC. 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 release agents, 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 mixed in water and the suspension 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. When reacted with zinc it forms zinc stearate which is used a lubricant for playing cards (fanning powder) to ensure a smooth motion when fanning. In compressed confections, it is used as a lubricant to keep the tablet from sticking to the die.
Fatty acids are classic components of candle - making. Stearic acid is used along with simple sugar or corn syrup as a hardener in candies.
Stearic acid is used to produce dietary supplements.
In fire works, 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. Stearic acid is a common lubricant during injection molding and pressing of ceramic powders. It is also used as a mold release for foam latex that is baked in stone molds. .

Background

Stearic acid (IUPAC systematic name: octadecanoic acid) is one of the useful types of saturated fatty acids that comes from many animal and vegetable fats and oils. It is a waxy solid.

Definition

ChEBI: A C18 straight-chain saturated fatty acid component of many animal and vegetable lipids. As well as in the diet, it is used in hardening soaps, softening plastics and in making cosmetics, candles and plastics.

Production Methods

Stearic acid is manufactured by hydrolysis of fat by continuous exposure to a countercurrent stream of high-temperature water and fat in a high-pressure chamber. The resultant mixture is purified by vacuum steam distillation and the distillates are then separated using selective solvents.
Stearic acid may also be manufactured by the hydrogenation of cottonseed and other vegetable oils; by the hydrogenation and subsequent saponification of olein followed by recrystallization from alcohol; and from edible fats and oils by boiling with sodium hydroxide, separating any glycerin, and decomposing the resulting soap with sulfuric or hydrochloric acid. The stearic acid is then subsequently separated from any oleic acid by cold expression.
Stearic acid is derived from edible fat sources unless it is intended for external use, in which case nonedible fat sources may be used. The USP32–NF27 states that stearic acid labeled solely for external use is exempt from the requirement that it be prepared from edible sources. Stearic acid may contain a suitable antioxidant such as 0.005% w/w butylated hydroxytoluene.

Definition

A solid carboxylic acid present in fats and oils as the glyceride.

Production Methods

Stearic Acid 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 butter and shea butter where the stearic acid content (as a triglyceride) 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 hydrolysis of triglycerides. The resulting mixture is then distilled. Commercial stearic acid is often a mixture of stearic and palmitic acids, although purified stearic acid is available.
In terms of its biosynthesis, stearic acid is produced from carbohydrates via the fatty acid synthesis machinery via acetyl-CoA .

Preparation

Commercially it is produced by the hydrogenation of the unsaturated 18-carbon fatty acids of soybean, cottonseed or other vegetable oils. When obtained from animal fats by hydrolysis and fractional crystallization, commercial stearic acid is a mixture of solid organic acids, chiefly palmitic and stearic acids. Commercial products containing about 90% stearic acid are produced by hydrolysis and crystallization of a completely hydrogenated vegetable oil or by fractional distillation of fatty acid mixtures obtained from tallow

brand name

Hystrene 5016 (Witco).

Aroma threshold values

Detection: 20 ppm

Synthesis Reference(s)

Synthetic Communications, 15, p. 759, 1985 DOI: 10.1080/00397918508063869

General Description

White solid with a mild odor. Floats on water.

Air & Water Reactions

Slightly soluble in water.

Reactivity Profile

Stearic acid is incompatible with strong oxidizers and strong bases. Stearic acid is also incompatible with reducing agents.

Health Hazard

Compound is generally considered nontoxic. Inhalation of dust irritates nose and throat. Dust causes mild irritation of eyes.

Fire Hazard

Stearic acid is combustible. Stearic acid can heat spontaneously.

Pharmaceutical Applications

Stearic acid is widely used in oral and topical pharmaceutical formulations. It is mainly used in oral formulations as a tablet and capsule lubricant, although it may also be used as a binder or in combination with shellac as a tablet coating. It has also been suggested that stearic acid may be used in enteric tablet coatings and as a sustained-release drug carrier.
In topical formulations, stearic acid is used as an emulsifying and solubilizing agent. When partially neutralized with alkalis or triethanolamine, stearic acid is used in the preparation of creams. The partially neutralized stearic acid forms a creamy base when mixed with 5–15 times its own weight of aqueous liquid, the appearance and plasticity of the cream being determined by the proportion of alkali used.
Stearic acid is used as the hardening agent in glycerin suppositories.
Stearic acid is also widely used in cosmetics and food products.

Biochem/physiol Actions

β-Oxidation of stearic acid yields eight FADH2 (flavin adenine dinucleotide) and NADH2 (nicotinamide adenine dinucleotide) molecules and nine acetyl-CoA molecules.

Safety Profile

Poison by intravenous route. A human sktn irritant. Questionable carcinogen with experimental tumorigenic data by implantation route. Combustible when exposed to heat or flame. Heats spontaneously. To fight fire, use CO2, dry chemical. When heated to decomposition it emits acrid smoke and irritating fumes.

Safety

Stearic acid is widely used in oral and topical pharmaceutical formulations; it is also used in cosmetics and food products. Stearic acid is generally regarded as a nontoxic and nonirritant material. However, consumption of excessive amounts may be harmful.
LD50 (mouse, IV): 23 mg/kg
LD50 (rat, IV): 21.5 mg/kg

Carcinogenicity

Stearic acid was administered subcutaneously to several groups of Swiss–Webster mice at doses of 0.05 or 0.5mg once weekly for 25 weeks (total dose of 1.3–130 mg), 1.0 mg thrice a week for a total of 10 injections or 1.0 mg twice weekly for a total of 82 injections. No neoplasms were reported in these studies . In 3 groups of 10–15 BALB/c mice administered 0.05 mg or 0.5 mg stearic acid (twice weekly for 52 or 57 weeks), one pulmonary neoplasm was detected in each group after 19–21 months.Afewsubcutaneous sarcomas and one adrenal carcinoma were also reported.No injection site sarcomas or other carcinogenic effects were reported by the same authors in a later study of mice injected with 0.05–0.5 mg weekly for 26 weeks. Rats given subcutaneous injections of 0.05 or 0.5 mg stearic acid weekly for 26 weeks did not develop sarcomas at the site of injection. When rat fibroblast cells were transfected with an activated human c-H-ras oncogene and the cells subsequently grown in a medium supplemented with stearic acid (20–80 mM), there was a marked increase in the number of transformed foci. Stearic acid inhibited the colony-forming ability of four out of five rat and two human tumor continuous cell lines in vitro. Using rats pretreated with nitrosomethyl urea as a model for mammary carcinoma, Habib et al. demonstrated that subcutaneous injection of stearic acid at weekly intervals prevented tumor development. Increasing levels of stearate in the diet resulted in decreased mammary tumor incidence and increased time to tumor in mice.

Metabolism

An isotope labeling study in humans 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. These findings may indicate that stearic acid is healthier than other saturated fatty acids.

storage

Stearic acid is a stable material; an antioxidant may also be added to it. The bulk material should be stored in a wellclosed container in a cool, dry place.

Purification Methods

Crystallise stearic acid from acetone, acetonitrile, EtOH (5 times), aqueous MeOH, ethyl methyl ketone or pet ether (b 60-90o), or by fractional precipitation by dissolving in hot 95% EtOH and pouring into distilled water, with stirring. The precipitate, after washing with distilled water, is dried under vacuum over P2O5. It has also been purified by zone melting and partial freezing. [Tamai et al. J Phys Chem 91 541 1987, Beilstein 2 IV 1206.]

Incompatibilities

Stearic acid is incompatible with most metal hydroxides and may be incompatible with bases, reducing agents, and oxidizing agents.
Ointment bases made with stearic acid may show evidence of drying out or lumpiness due to such a reaction when compounded with zinc or calcium salts.
A number of differential scanning calorimetry studies have investigated the compatibility of stearic acid with drugs. Although such laboratory studies have suggested incompatibilities, e.g. with naproxen, they may not necessarily be applicable to formulated products.
Stearic acid has been reported to cause pitting in the film coating of tablets applied using an aqueous film-coating technique; the pitting was found to be a function of the melting point of the stearic acid.

Regulatory Status

GRAS listed. Accepted as a food additive in Europe (fatty acids). Included in the FDA Inactive Ingredients Database (sublingual tablets; oral capsules, solutions, suspensions, and tablets; topical and vaginal preparations). Included in nonparenteral medicines licensed in the UK. Included in the Canadian List of Acceptable Non-medicinal Ingredients.