Stearic Acid

Stearic acid is an 18 carbon chain, saturated fatty acid. The IUPAC name of stearic acid is Octadecanoic acid, and it is even called as Stereophonic acid.It is usually found in several plants and animal fats too. It is a significant component found in shea butter and cocoa butter. It has a waxy texture. The chemical formula is C18H36O2. Stearates and esters are its salts. The appearance of this acid is whitish. It is a bit solid and has a pungent and oily odor. It floats on water, and is soluble in alkyl acetate, alcohol, and phenyl.  The primary function of stearic acid is to act as a plant metabolite, an algal metabolite, a Daphnia Magna metabolite, and a human metabolite. 


Stearic Acid Structure And Properties


Properties:

Chemical Formula of Stearic acid

C18H36O2

Molar Mass of Stearic acid

284.484 g·mol-1

The density of Stearic acid

0.9408 g/cm3, at 20°C

0.847 g/cm3, at 70 °C

The melting point of Stearic acid

69.3 °C in 156.7 °F; 342.4 K

The boiling point of Stearic acid

Decomposes at 361 °C in 682 °F; 634 K

232 °C 

In 450 °F; 505 K

at 15 mmHg

Thermal Conductivity

0.173 W/m·K (70 °C)

Refractive index (nD)

1.4299 (80 °C)


Structure

Stearic acid has a crystal-like structure, and the physical appearance of this acid looks like the below-given picture: 


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and it can be represented chemically as: 


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Stearic Acid Uses

There are many uses of stearic acid because it has a bifunctional character, a polar head group that can be linked with metal actions. Also, the nonpolar chain in stearic acid is soluble and has organic solvents. Hence because of this combination, there are various uses of stearic acid as a surfactant and softening agent. 


And the significant reason behind the use of stearic acid in all these products is, it's very inexpensive, relatively inert and non-toxic too.  Moreover, Stearic acid goes through the typical reactions of saturated carboxylic acids because of which it is used with drinks also.  Metals can be stored for a long time, as stearic acid prevents oxidation.


Here is a list of materials, in which stearic acid is used:

  • As a food additive

  • In making cleansers

  • In soaps, cosmetics, and detergents for the pearly effect

  • As a great releasing and softening agent

  • As a negative plate additive for manufacturing lead-acid batteries

  • In sugar or corn syrup for hardening candies

  • In chewing gums

  • To make supplements and tablets

  • The fatty acid in the stearic acid is used for candle making

  • As a coat for aluminium and iron powder, for preventing oxidation.


How is Stearic Acid Produced?

Stearic acid is produced by the fats and oils through the saponification of the triglycerides. Hot water at about the temperature rate of 100°C is used for production. The resultant mixture is then distilled.


The commercial stearic acid is always a mixture of stearic and palmitic acids, although one can choose purified stearic acid if it's available.


The Fats and oils of purified stearic acid are more productive in animal fat that is up to 30%, but in vegetable fat, it is typically less than 5%. Although, there are some exceptions like the cocoa butter and shea butter.  The stearic acid content used in this is a triglyceride (derived from three molecules), and it is up to 28 – 45%.


While in terms of its biosynthesis, stearic acid is manufactured from carbohydrates with the help of the fatty acid synthesis machinery. Wherein acetyl-CoA contributes to two-carbon building blocks.


Side - Effects of Stearic Acid

Although stearic acid is used in various food items, it is found in diluted forms in nature. But when stearic acid is accumulated with magnesium, magnesium stearate is formed, which is harmful and can have different side effects if consumed. Also, this chemical compound is combustible and gets heated spontaneously, which can irritate the respiratory system and the skin too.

FAQ (Frequently Asked Questions)

1. Is Stearic Acid Safe for Consumption?

Stearic acid is a type of saturated fat used in different diets. And as compared with carbs and other saturated fats, stearic acid is much healthier for consumption, as it lowers the LDL (low-density lipoproteins) cholesterol, which is usually referred to as bad cholesterol. Many research has proved the safety of stearic acid. The primary dietary source of this acid is through animal fats, and less in plant fats (Exceptions: coconut, cocoa butter, palm kernel oil ). Similarly, there is no heart-related risk seen by the consumption of stearic acid, and it provides neutral effects to a person's blood lipid profile during intake.

2. What Does Stearic Acid do to the Skin?

As stearic acid is used in soaps and face cleansers, it helps to remove the dirt and bacteria from the surface of the skin. The creamy yet waxy texture of stearic acid is very gentle, and hence it's used in the body care product. It not only locks the moisture and dryness of skin but also it protects the skin surface by loss of water through the waxy protective barrier. It does not even clog pores, and it is also safer for sensitive skin, although if there is any irritation faced, it's better to do a sensitivity test before application. Hence, stearic acid is quite safe for skin too.

3. Is Stearic Acid Soluble in Water?

Stearic acid is soluble in many organic solvents. For example, it is moderately soluble in alcohols, phenyls, and alkyl acetates. The compound is soluble in carbon tetrachloride, carbon disulfide, and methyl formate (even known as methyl methanoate). Stearic acid's solubility in dichloromethane under ambient temperatures approximates to 3.58 grams per 100 grams of dichloromethane.


Stearic acid is not relatively soluble in water, only a fraction of a milligram of stearic acid can be liquefied in as much as a hundred grams of water. While in chloroform,  the solubility of stearic acid is 15.54 grams per hundred grams.