- Structure
- Nomenclature
- Physical properties
- Physical state
- Molecular weight
- Melting point
- Boiling point
- Flashpoint
- Density
- Solubility
- Dissociation constant
- Chemical properties
- Location in nature
- Effect of the ingestion of stearic acid with food on human health
- Obtaining
- Applications
- In various applications
- To catch disease-carrying mosquitoes
- References
The stearic acid is a solid organic compound with the chemical formula CH 3 (CH 2) 16 COOH. It is a carboxylic acid that belongs to the group of long chain saturated fatty acids. It is yellowish white in color and has an odor similar to that of tallow or animal fat.
It is called a fatty acid because it is present in many animal and vegetable fats and oils. It is part of the metabolism of most living things and is generally found in the form of the glycerin ester.
Solid stearic acid. Adam Rędzikowski. Source: Wikimedia Commons.
Cocoa has it in a high proportion, as well as the tallow of bovine animals, pork fat and butter. It is also present in vegetable oils such as corn. To obtain it, tristearin is hydrolyzed, that is, it is treated with water and alkali.
The ingestion of stearic acid with food and its effect on health currently poses doubts for researchers. It seems that it has more harmful than beneficial effects.
It is useful in the preparation of drugs, water-insulating packaging, paraffin candles, lubricating greases, materials for molding figures, cosmetics, ointments, creams, among many other applications.
Structure
The stearic acid molecule has a linear chain of 18 carbon atoms in which the last carbon atom is part of a carboxylic group –COOH. The carbon chain has only single CC bonds as it is a saturated fatty acid.
Its expanded formula is:
CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -COOH
Stearic acid molecule structure. You can see its long saturated chain and the -COOH group at the end. Wolfgang Schaefer. Source: Wikimedia Commons.
Nomenclature
-Stearic acid
-Octadecanoic acid
-Stearophanic acid
Physical properties
Physical state
White to slightly yellow, crystalline solid with a mild sebum-like odor.
Molecular weight
284.5 g / mol
Melting point
69.3 ºC
Boiling point
383 ºC
Flashpoint
196 ºC (closed cup method).
Density
0.9408 g / cm 3 at 20 ° C
Solubility
Insoluble in water and floats on it. Slightly soluble in alcohol. Soluble in ether, acetone and chloroform.
Dissociation constant
pK a = 4.75
Chemical properties
Stearic acid reacts with sodium hydroxide (NaOH) to form sodium stearate which is a soap. Most soaps contain sodium stearate.
Stearic acid and sodium stearate are generally considered safe and non-toxic compounds.
Location in nature
Stearic acid is one of the constituents of many oils and fats of vegetable and animal origin. It is generally in the form of its glycerin ester.
Lard. One of its components is stearic acid. Rasbak. Source: Wikimedia Commons.
It is present in many solid fats such as tallow and to a lesser extent in semi-solid fats such as lard, butter and in vegetable oils such as corn and cotton.
Butter, food that contains stearic acid. Author: Congerdesign. Source: Pixabay.
It is an important component of cocoa butter (38%) and shea (African tree that produces a type of nuts) (38.1%).
Cocoa nibs. Cocoa butter is very rich in stearic acid. Author: Dghchocolatier. Source: Pixabay.
It is part of the metabolism of many living things, such as plants, mammals, humans, crustaceans and algae. This means that, for example, humans can synthesize it in their body.
Effect of the ingestion of stearic acid with food on human health
Stearic acid, although it occurs naturally in the human body, is also ingested with foods that contain it both from its source and added to its composition.
It should be noted that among industrially processed foods, trans fats have been discontinued because they are very harmful to human health. These fats were replaced by saturated fatty acids, including stearic acid.
The effects of this substitution are still under study. In general, long-chain saturated fatty acids increase low-density cholesterol levels, which is related to mortality from coronary and heart disease.
However, some studies indicate that stearic acid lowers low-density cholesterol, which suggests that it has antiatherogenic properties, that is, it does not cause the formation of plaques in the arteries, but rather favors the health of the blood vessels.
On the other hand, other research indicates that it has the highest prothrombotic potential of long chain saturated fatty acids, this means that it can promote blood vessel plugging events.
In addition, high levels of stearic acid in the blood have been found to be toxic to certain cells of the pancreas, which can aggravate the symptoms of type 2 diabetes. This disease is common in people who are very overweight.
Overweight person. It is not advisable to eat foods with stearic acid as it could cause or increase type 2 diabetes disease. Author: Sedatgunduz. Source: Pixabay.
It is for these reasons that its effects are still being investigated since it has not been possible to clarify whether its action is favorable or not to the health of the human organism.
Obtaining
It can be obtained by hydrolysis of C 3 H 5 glycerin or tristearin stearate (COOC 17 H 35) 3, according to the following chemical reaction:
Triestearin + Sodium hydroxide → Sodium stearate + Glycerin
To produce it commercially, the hydrogenation of 18-carbon unsaturated fatty acids is carried out, such as those contained in cotton seeds and other vegetables.
In other words, hydrogen is added to the C = C double bonds of unsaturated fatty acids, remaining as CC single bonds, as follows:
–CH = CH– + H 2 → –CH 2 –CH 2 -
Applications
In various applications
Stearic acid is an important commercial chemical compound.
It is used in the pharmaceutical industry for the manufacture of various medicines, such as suppositories, coated pills for intestinal ailments or to coat bitter remedies, among others. It is also an ingredient in ointments or ointments.
Because it is insoluble in water, it is used in the food industry for insulating packaging and in the preparation of various types of waterproof materials.
It is also used as an ingredient in jellies, puddings, candies and non-alcoholic beverages because it gives them a certain viscosity.
It is used in the manufacture of stearin candles and is added to paraffin wax in small quantities. Due to its texture, it is also used in moldable materials that are used to make three-dimensional models.
It also works in coatings against static electricity.
Its sodium salt is a soap and is also used to harden soaps. Because it is a harmless compound for humans, it is used to make cosmetics, as an emollient or a fatliquor in creams. It also serves to soften plastics.
Soaps generally contain sodium stearate which is a derivative of stearic acid. Author: Theresaharris10. Source: Pixabay.
Cosmetic creams often contain stearic acid. Author: Photosforyou. Source: Pixabay.
Stearic acid is used to prepare other chemical compounds such as certain metallic stearates, for example aluminum, which is used to make lubricating greases by thickening the oils that make them up.
In addition, it is an ingredient in some pesticides, is used in varnish dryers and as a vulcanization activator for synthetic rubber.
To catch disease-carrying mosquitoes
Stearic acid has been used successfully in ultraviolet (UV) light traps to attract dengue-transmitting mosquitoes.
Its characteristic smell is similar to that of lactic acid, which is the one found on the skin of human beings, so when it is placed in the traps, it attracts mosquitoes, which are trapped in the device and die.
References
- Tvrzicka, E. et al. (2011). Fatty acids as biocompounds: Their role in human metabolism, health and disease - A review. Part 1: Classification, dietary sources and biological functions. Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub. 2011 Jun; 155 (2): 117-130. Recovered from biomed.upol.cz.
- Tseng, W.-H. et al. (2019). Secondary Freedom Lens Device Design with Stearic Acid for A Low-Glare Mosquito-Trapping System with Ultraviolet Light-Emitting Diodes. Electronics 2019, 8, 624. Recovered from mdpi.com.
- Van Nostrand's Encyclopedia of Chemistry (2005). Stearic Acid and Stearates. Recovered from onlinelibrary.wiley.com.
- US National Library of Medicine. (2019). Stearic acid. Recovered from: pubchem.ncbi.nlm.nih.gov.
- Lu, H. et al. (2016). Elevated circulating stearic acid leads to a major lipotoxic effect on mouse pancreatic beta cells in hyperlipidaemia via a miR-34a-5p-mediated PERK / p53-dependent pathway. Diabetologia 2016, 59 (6): 1247-57. Recovered from ncbi.nlm.nih.gov.