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Stearic acid, also known as octadecanoic acid, is a long-chain saturated fatty acid with the chemical formula C₁₈H₃₆O₂. It is one of the most important fatty acids in organic chemistry and is used in numerous applications in industry and households. In this blog post, we want to take a closer look at the properties, synthesis, and uses of this fascinating compound.

The structure and properties of stearic acid

Stearic acid belongs to the group of aliphatic fatty acids, which are characterized by a long carbon chain. With its 18 carbon atoms, it is classified as a long-chain fatty acid. At the end of the chain is a carboxyl group (-COOH), which gives the acid its acidic character. The remaining carbon atoms carry hydrogen atoms, resulting in a saturated hydrocarbon chain.

The length and saturation of the carbon chain have a decisive influence on the physicochemical properties of stearic acid. For example, it has a relatively high melting point of 69.6 °C because the long carbon chains can interact with each other via van der Waals forces. This high melting point is also the reason why stearic acid is solid at room temperature. Furthermore, stearic acid is soluble in non-polar solvents such as benzene or chloroform, but practically insoluble in polar media such as water.

The synthesis of stearic acid

Stearic acid occurs naturally in various fats and oils, particularly in tallow and palm oil. Industrially, however, it is mostly produced through chemical synthesis. A common method is the hydrolysis of triglycerides, i.e., the splitting of fats under the influence of water. In addition to stearic acid, other fatty acids such as palmitic acid and oleic acid are also produced.

Another possibility is the oxidation of stearyl alcohol, a related compound with 18 carbon atoms. Here, the alcohol is first oxidized to stearaldehyde before further oxidation leads to stearic acid.

In organic synthesis, stearic acid can also be produced from other starting materials, for example by elongating shorter fatty acids or by decarboxylation of fatty acids with more than 18 carbon atoms.

Applications of Stearic Acid

Due to its diverse properties, stearic acid is used in numerous products and industries. Some of the most important application areas are:

Surfactants and Emulsifiers

Stearic acid and its salts (stearates) are used in soaps, shampoos, creams, and other personal care products as surfactants and emulsifiers. They contribute to the cleaning effect and stability of the formulations.

Lubricants and Release Agents

The high melting temperature and good lubricating and sliding properties make stearic acid a valuable component of lubricating greases, lubricants, and release agents.

Candles and Waxes

Stearic acid is used in the production of candles, waxes, and polishes because it has a high melting point and good shape stability.

Plastics and Rubber

In the plastics and rubber industry, stearic acid serves as a plasticizer, lubricant, and stabilizer. It is used in PVC, rubber, paints, and varnishes.

Pharmaceuticals and Cosmetics

Due to its skin compatibility and emulsifying properties, stearic acid is an important component in many pharmaceuticals, creams, ointments, and lotions.

Food Industry

In the food industry, stearic acid is used as a release agent, antifoaming agent, and antioxidant, for example in baked goods, confectionery, or fats.

Further Applications

In addition, stearic acid is used in the textile, paper, and leather industries, as well as in the production of adhesives, paints, and varnishes.

Conclusion

Stearic acid is a fascinating compound with a wide range of applications in industry and household. Its unique physical and chemical properties make it a valuable raw material in organic chemistry and materials technology. Whether as a surfactant, lubricant, plasticizer, or emulsifier – stearic acid is indispensable in many products. Its importance will continue to grow in the future as new applications are constantly being developed.