One of the most common in the cosmetic, perfumery, food industries, as well as in the technical field is an organic substance related to alcohols. Its name is propylene glycol. What it is? Consider the properties, structure of the molecule and the field of use of this compound during the article.
Propylene glycol - what is it?
People started using this dihydric alcohol as soon as they found out what useful and important properties it has. Outwardly, it is not much different from ethanol or glycerol, because it is also a clear liquid. True, its viscosity is higher than that of ethanol, but lower than that of glycerol. In terms of toxicity, it is much inferior to its closest homologous neighbor, ethylene glycol.
If ethanediol is the strongest poison, then propylene glycol is not. The use of this substance is based on its physical and chemical properties. If we briefly characterize the main industries in which propylene glycol is present, the application will be expressed by several industries.
- Chemical industry.
- Aviation and automobile construction.
- Oil and gas industry.
- Paint and varnish industry.
- Cosmetic and perfumery industry.
- Food production.
- Technical field of activity.
- The medicine.
It is obvious that the substance under consideration is a valuable chemical raw material and an important object for the normal production and functioning of various structures. That is why the production of this product is calculated in tons annually. Its export and import between countries is also quite active. Almost every area of activity and production affects the possibility of using a substance such as propylene glycol. What it is? What is its chemical structure, formula and properties? We will understand further.
The formula and composition of the molecule
There are several versions of formulas with which you can display not only the qualitative and quantitative composition of the molecule, but also the order of the atoms in it, that is, the structure of the substance.
- Molecular, or empirical. Using this formula, you can judge the composition of the compound. Propylene glycol will look like C 3 H 8 O 2 . But such a record will not make it possible to predict the properties of matter, because the order of atomic bonding is unknown.
- Abbreviated structural formula. In this case, the propylene glycol composition has the same, but the formula can have two types: 1,2 - propanediol CH 2 OH-CHOH-CH 3 and 1,3-propanediol CH 2 OH-CH 2 -CH 2 OH. The position of the functional group affects the chemical activity of the substance. Between themselves, both structures are isomers.
- Full structural formula. It shows every bond in the molecule, including compounds between carbon and hydrogen. In propylene glycol, all bonds are single, sigma-type, so it makes no sense to depict the full structure.
As a simple substance, propylene glycol is a liquid, which is a racemic mixture of two optical isomeric structures. This is due to the asymmetric carbon atom in the chain. Therefore, one rotates the plane of polarization of light to the right, the other to the left. However, the properties of this substance as a whole have practically no effect on it.
Physical properties of the substance
In terms of physical parameters, 100% propylene glycol has the following characteristics.
- Colorless liquid, thick, viscous, has an average density value.
- The taste is sweetish, the smell is specific.
- It is a good solvent for representatives of almost all classes of substances.
- Propylene glycol itself is soluble in water and alcohol, poorly in benzene and ether.
- The boiling point is 45.5 0 C at ordinary pressure. With increasing pressure, the indicator increases.
- It has a high degree of hygroscopicity.
- It exhibits low corrosivity.
Such physical properties determine the main areas of application of this substance. After all, propanediol is able to soften solid media, trap air moisture and bind it, lower the temperature of substances, disperse surrounding compounds. Therefore, it is also used in the food industry.
Chemical properties
From the point of view of chemical activity, 1,3-propylene glycol is a more reactive isomer. In addition, it is he who is able to polymerize. In general, there are several main reactions that this diatomic alcohol can enter.
- Esterification. It interacts with organic and inorganic acids to form esters.
- When reacting with alkalis, it gives glycolates; the same thing happens when interacting with alkali metals.
- It is capable of dehydration with the formation of aldehydes, allyl alcohols, dimethyldioxanes and other products.
- Dehydrogenation reactions lead to the formation of acetols, aldehydes, acids.
- Oxidation is accompanied by the formation of molecules of acetone, propionic aldehyde, lactic acid, formaldehyde and other compounds.
Industrial use of this substance is considered safe for the environment. Indeed, as a result of stepwise decomposition of a molecule, water and carbon dioxide are formed simply. The process goes like this:
- propylene glycol;
- lactic acid;
- PVC (pyruvic acid) ;
- water;
- carbon dioxide.
That is why it is considered possible to use this compound for different purposes: both technical, and food and cosmetic.
Toxicity and effects on the body
Propylene glycol - what is it in terms of the effect on the human body? Numerous studies and experiments have shown that this compound does not have a direct negative effect on living tissues and organs. It does not cause irritation and redness of the skin, does not accumulate in the liver and kidneys, since it decomposes along the way to them.
Experiments on mice that consumed daily propylene glycol proved that it did not affect the health and lives of living things. However, if you use products and preparations containing a large amount of this substance for a long time, the kidneys may suffer, their work and integrity will be impaired. But for this you should use a large amount of almost pure 100% propylene glycol, which, of course, is impossible.
Therefore, the use of this alcohol in the cosmetic, perfumery and food industries is allowed according to all the rules and regulations. The only negative effect it can have on those people who suffer from skin diseases, dermatitis, eczema and complex forms of allergies. In this case, it is not recommended to use creams, ointments, shampoos and other products containing this substance.
Industrial Production
The chemical properties of propylene glycol make it possible to obtain it from propylene oxide under certain temperature conditions (about 200 0 ) and pressure (1.6 MPa). In this case, the products are immediately three substances:
- propylene glycol;
- dipropylene glycol;
- tripropylene glycol.
For further processing and separation, the distillation method is used on a special column. The finished product has a high purity value (99%), so it is immediately ready for use. Food grade propylene glycol undergoes additional processing; its shelf life reaches two years.
Use as antifreeze
First of all, this alcohol is used in industry as a coolant. Propylene glycol can be used in heating plants in the temperature range from -40 0 to +108 0 . Moreover, its low corrosion ability allows you to save equipment. Therefore, propanediol is used for:
- heating systems;
- air conditioning of all types of buildings;
- ventilation;
- food cooling.
Application in cosmetology
The ability of this substance to trap and bind water, disperse, improve consistency, and conduct odor molecules is the basis of its use in cosmetic and perfume industries. In addition, low chemical activity and safety from the point of view of ecology, medicine also determine the choice of this particular component when creating creams, shampoos, pastes, ointments and other products.
There are many organizations that offer to buy propylene glycol. Price depends on product concentration and order volume. It ranges from 150 to 170 rubles per kilogram.
Use in the food industry
In the food industry, propylene glycol is known as E1520. It is part of many products with a pasty, creamy consistency, as well as solid confectionery. Its role is dispersing, softening, cooling, preserving.