What Is Stearic Acid? Structure, Properties & Key Applications
A scientist named Chevreul M.E. initially discovered the Stearic Acid formula (18 carbon atoms) in his fat studies in 1823. Stearic Acid comes after the Grecian term stéar, which means fat (also known as beef fat). It is a long-chain fatty acid (LCFA) with 14 to 18 carbon atoms that is a saturated fatty acid (no C=C double bonds). But, what is Stearic Acid? Stearic Acid is a sticky, whitish substance with a moderate odor that hovers on the surface of liquid naturally. Stearic Acid is found in vegetable and animal fats, with shea butter and cocoa butter being the most common forms. Stearic Acid in cosmetics and plastics, as well as softened plastics and stiffening detergents, are often used. Here you will read about the melting point of Stearic Acid, Stearic Acids in cosmetics, and what is Stearic Acid.
Stearic Acid Formula
As seen in the diagram below, Stearic Acid has an 18-carbon backbone and a straight-chain Stearic Acid structure.
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The above diagram represents the Stearic Acid formula and Stearic Acid structure.
Properties of Stearic Acid Structure
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) |
Production of Stearic Acid
It is made of oils and properties of fatty acids by the saponification of triglycerides with heated liquid at a heat of around 100 degrees Celsius. The resulting solution is distilled. The most commonly available octadecanoic acid is a blend of palmitic and Stearic Acids.
Stereophonic acid has more animal fat than vegetable fat in terms of oils and fats. There are a few outliers, such as shea butter and cocoa butter, which contain roughly 28–45 percent Stearic Acid. It possesses the properties of fatty acids. It's also made biosynthetically from carbs, thanks to the fatty acid machinery. In other words, it is a fatty acid example.
Stearic Acid Use
Since Stearic Acid possesses a bifunctional nature, a polar head unit that may be connected to metallic activities, it offers a wide range of applications. Stearic Acid's apolar branch is also soluble and contains organic substances. As a result of this mixture, Stearic Acid is used as a detergent and relaxing ingredient in a variety of applications.
As well as the usage of Stearic Acid in all of such goods is due to the fact that it is reasonably affordable, inactive, and non-toxic. Furthermore, since Stearic Acid undergoes the normal interactions of saturated carboxylic acids, it is also employed in beverages. Because Stearic Acid resists oxidation, metals may be held for a prolonged period.
Here is a list of commodities that require the use of Stearic Acid:
For the pearly effect,
as a food component in detergents in soaps, cosmetics, and cleaners
As a fantastic softening and releasing agent
Like a negative plate additive in lead-acid battery production
Hardening candies in sugar or corn syrup
Gums for chewing
In order to create vitamins and tablets
Candles are made from fatty acid is Stearic Acid.
As an antioxidant coating for aluminum and iron powder.
The above products are all fatty acid examples.
Stearic Acid Safety
Stearic Acid is a saturated fat that is employed in a variety of diets. And, when contrasted to carbohydrates and other saturated fats. Stearic Acid is far better to consume since it decreases LDL (low-density lipoproteins) cholesterol, also known as nasty cholesterol. Stearic Acid has been shown to be safe in several studies. Animal fats are the predominant dietary source of this acid, with botanical fats providing just a minor contribution (Exceptions: coconut, cocoa butter, palm kernel oil ). Similarly, there is no evidence that Stearic Acid consumption causes heart disease and does not affect a person's blood lipid profile during consumption.
Fun Facts
“Although Stearic Acid is utilized in a variety of foods, it is present in nature in diluted levels. However, if Stearic Acid and magnesium combine, magnesium stearate is created, which is toxic and can cause a variety of negative effects if ingested. This chemical molecule is also flammable and heats up freely, causing irritation to the respiratory organs and skin.”
“The melting point of Stearic Acid is so high because it is a saturated fatty acid”.
FAQs on Stearic Acid: Complete Guide for Students
1. What is stearic acid and what is its chemical formula as per the NCERT syllabus?
Stearic acid is a long-chain saturated fatty acid, which means its hydrocarbon chain contains only single bonds. It is one of the most common fatty acids found in both animal and vegetable fats. According to the IUPAC nomenclature taught in the CBSE syllabus, it is known as octadecanoic acid. Its chemical formula is C₁₈H₃₆O₂, representing an 18-carbon backbone with a carboxylic acid (-COOH) functional group.
2. What are the main physical and chemical properties of stearic acid?
Stearic acid exhibits properties typical of a long-chain carboxylic acid. Key properties include:
- Appearance: It is a waxy, white or yellowish solid at room temperature.
- Solubility: It is largely insoluble in water due to its long, nonpolar hydrocarbon tail, but it is soluble in organic solvents like ethanol and acetone.
- Melting Point: It has a relatively high melting point of around 69.3 °C (156.7 °F).
- Chemical Reactivity: As a carboxylic acid, it can undergo esterification with alcohols and neutralization with bases to form salts called stearates, which are the primary components of many soaps.
3. What are the most common uses of stearic acid in industrial and consumer products?
Stearic acid is widely used across various industries due to its properties as an emulsifier, thickener, and lubricant. Its main applications include the production of soaps and detergents, where it helps create a stable lather and hardens the bar. It is also a key ingredient in cosmetics, such as lotions and creams, to create a smooth texture and act as an emollient. Other important uses are in making candles and crayons to increase their hardness and melting point, and as a softening agent in rubber manufacturing.
4. How does the molecular structure of stearic acid make it effective in soaps?
The effectiveness of stearic acid in soap making is a direct result of its molecular structure. When neutralized with a base (like sodium hydroxide), it forms sodium stearate. This molecule is amphiphilic, meaning it has two distinct parts:
- A long, nonpolar hydrocarbon tail (C₁₇H₃₅–) that is hydrophobic (water-repelling) and readily dissolves in grease and oils.
- A polar carboxylate head (–COO⁻Na⁺) that is hydrophilic (water-attracting) and dissolves in water.
5. Why is stearic acid considered safe for consumption in food products?
Stearic acid is generally recognised as safe (GRAS) for consumption and is found naturally in foods like cocoa butter and animal fats. Unlike some other saturated fats, studies have shown that stearic acid has a neutral or even slightly beneficial effect on blood cholesterol levels. It tends to be rapidly converted into oleic acid (a monounsaturated fat) in the body. This unique metabolic pathway means it doesn't raise LDL ('bad') cholesterol to the same extent as other saturated fatty acids, making it a preferred choice as a food additive.
6. What is the role of stearic acid in cosmetics and skincare products?
In cosmetics and skincare, stearic acid serves multiple functions. It is primarily used as a thickening agent to give lotions and creams a rich, stable consistency. It also acts as an emulsifier, preventing the oil and water components of a formula from separating. Its waxy nature provides an occlusive layer on the skin, helping to lock in moisture and protect the skin's natural barrier from water loss. This makes the skin feel soft and smooth without being overly greasy.
7. Can stearic acid cause skin problems like acne?
While stearic acid is beneficial for its moisturising and cleansing properties, it can be problematic for certain skin types. It has a moderate comedogenic rating, meaning it has the potential to clog pores in individuals with oily or acne-prone skin, potentially leading to breakouts. However, its effect depends on the overall formulation and concentration. For most people with normal or dry skin, it is perfectly safe and effective. If you have sensitive or acne-prone skin, it's advisable to patch-test products containing stearic acid.
8. How is stearic acid different from oleic acid?
Stearic acid and oleic acid are both 18-carbon fatty acids, but they differ in a crucial way that affects their properties:
- Saturation: Stearic acid is a saturated fatty acid, meaning its carbon chain has no double bonds. This makes its structure straight and allows molecules to pack closely, resulting in a solid state at room temperature.
- Unsaturation: Oleic acid is a monounsaturated fatty acid, containing one double bond in its carbon chain. This creates a 'kink' in the molecule, preventing it from packing tightly and making it a liquid (oil) at room temperature.
