The key difference between stearic acid and oleic acid is that stearic acid is a saturated compound, while oleic acid is an unsaturated compound.
Stearic acid and oleic acid are organic compounds having carbon chains. These are classified as fatty acids according to their chemical structures.
CONTENTS
1. Overview and Key Difference
2. What is Stearic Acid
3. What is Oleic Acid
4. Side by Side Comparison – Stearic Acid vs Oleic Acid in Tabular Form
5. Summary
What is Stearic Acid?
Stearic acid is an organic compound having the chemical formula C17H35CO2H. It is a saturated fatty acid having a carbon chain with 18 carbon atoms. The IUPAC name of this compound is octadecanoic acid. This acid appears as a white waxy substance. The salts and other derivatives of stearic acid are named stearates. This acid has a pungent oily odour.
We can obtain stearic acid through the saponification of fats and oils. There the triglycerides in the fat and oil undergo saponification in the presence of hot water. The resultant compound mixture should be distilled to obtain pure acid. However, the commercially available stearic acid is actually a mixture of stearic acid and palmitic acid.
Figure 01: Chemical Structure of Stearic Acid
When concerning the uses of stearic acid, it is important as a surfactant and as a softening agent due to the presence of a polar head group that can get attached to metal cations. It also has a nonpolar chain which makes it possible to dissolve in organic solvents.
What is Oleic Acid?
Oleic acid is the cis isomer of the fatty acid, having the chemical formula C18H34O2. It is the cis isomer of elaidic acid. This substance occurs as an oily liquid that is colourless and odourless. However, commercially available samples of oleic acid can be yellowish. We can classify oleic acid as a monounsaturated omega-9 fatty acid. The molar mass of this compound is 282.046 g/mol. It has a low melting point (13 Celsius) and a comparatively a high boiling point (360 Celsius). This substance is insoluble in water, and it is soluble in organic solvents such as ethanol.
Figure 02: Chemical Structure of Oleic Acid
The name of this substance comes from the Latin word “oleum”, which means oil or oily. Oleic acid is the most common naturally occurring fatty acid. There are salts and esters of oleic acid named collectively as oleates. Often, we can find oleic acid in its ester form rather than in biological systems. This compound commonly occurs in the form of triglyceride. Common compounds, including phospholipids in cell membranes, cholesterol esters, and wax esters, contain oleic acid components.
Oleic acid forms via biosynthesis, which involves the enzymatic activity of stearoyl-CoA9-desaturase acting on stearoyl-CoA. Here, stearic acid is dehydrogenated to form a monounsaturated derivative, oleic acid.
What is the Difference Between Stearic Acid and Oleic Acid?
The key difference between stearic acid and oleic acid is that stearic acid is a saturated compound, while oleic acid is an unsaturated compound. Moreover, stearic acid has no double or triple bonds between carbon atoms in the carbon chain, whereas oleic acid has a double bond at the middle of its nonpolar carbon chain.
The below infographic tabulates more differences between stearic acid and oleic acid.
Summary – Stearic Acid vs Oleic Acid
In brief, stearic acid and oleic acid are organic acidic compounds. The key difference between stearic acid and oleic acid is that stearic acid is a saturated compound, while oleic acid is an unsaturated compound.
Reference:
1. Elkacmi, Reda, et al. “Extraction of Oleic Acid from Moroccan Olive Mill Wastewater.” BioMed Research International, Hindawi, 10 Jan. 2016, Available here.
Image Courtesy:
1. “Stearic acid” (Public Domain) via Commons Wikimedia
2. “Oleic-acid-skeletal” (Public Domain) via Commons Wikimedia