Stearic acid

Toxicity

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

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 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.

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.

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.

Synthesis

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 .

brand name

Hystrene 5016 (Witco).

Aroma threshold values

Detection: 20 ppm

Synthesis Reference(s)

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

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

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

Stearic Acid application

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.

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.