Propylene glycol - what is it? Chemical properties, application

2024 Author: Howard Calhoun | [email protected]. Last modified: 2024-01-02 13:48

One of the most common in the cosmetic, perfumery, food industry, as well as 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 scope of this compound in the course of 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 glycerin, because it is also a transparent liquid. True, its viscosity is higher than that of ethanol, but lower than that of glycerol. In terms of its toxicity, it is much inferior to its closest neighbor in the homologous series - 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 describe the main industries in which propylene glycol is available, the use will be expressed by several sectors of the economy.

1. Chemical industry.
2. Aircraft and automotive construction.
3. Oil and gas industry.
4. Paint industry.
5. Cosmetics and perfume industry.
6. Food production.
7. Technical field of activity.
8. Medicine.

Obviously, the substance we are considering 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 estimated in tons annually. Its export and import between countries is also quite active. Almost every field 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 investigate further.

Formula and composition of the molecule

There are several variants of formulas that can be used to display not only the qualitative and quantitative composition of a molecule, but also the order of the connection of atoms in it, that is, the structure of a substance.

1. Molecular, or empirical. According to this formula, one can judge the composition of the compound. Propylene glycol will look like C₃H₈O_{2. But such a record will not make it possible to predict the properties of matter, because the order of the connection of atoms is unknown.}

2. Abbreviated structural formula. In this case, the propylene glycol composition is the same, but the formula can have two forms: 1, 2 - propanediol CH₂OH-CHOH-CH₃ and 1, 3-propanediol CH₂OH-CH₂-CH₂OH. The position of the functional group affects the chemical activity of the substance. Between themselves, both structures are isomers.

3. Full structural formula. It shows every bond in a molecule, including the bonds 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 that 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, this practically does not affect the properties of this substance as a whole.

Physical properties of matter

In terms of physical parameters, 100% propylene glycol has the following characteristics.

1. Colorless liquid, thick, viscous, medium density.
2. It tastes sweet, the smell is specific.
3. It is a good solvent for representatives of almost all classes of substances.
4. Propylene glycol itself is soluble in water and alcohol, poorly in benzene and ether.
5. Boiling point - 45.5 0C at normal pressure. With increasing pressure, the indicator increases.
6. Highly hygroscopic.
7. Exhibits low corrosivity.

Similar physical properties and determine the main areas of application of this substance. After all, propanediolIt is able to soften solid media, capture air moisture and bind it, lower the temperature of substances, and disperse surrounding compounds. Therefore, it is also used in the food industry.

Chemical properties

In terms of reactivity, 1, 3-propylene glycol is the more reactive isomer. In addition, it is he who is able to polymerize. In general, there are several main reactions that this dihydric alcohol can enter into.

1. Esterification. It interacts with organic and inorganic acids to form esters.
2. When reacting with alkalis, it gives glycolates, the same thing happens when reacting with alkali metals.
3. Capable of dehydration to form aldehydes, allyl alcohols, dimethyldioxanes and other products.
4. Dehydrogenation reactions lead to the formation of acetols, aldehydes, acids.
5. Oxidation is accompanied by the formation of molecules of acetone, propionaldehyde, lactic acid, formaldehyde and other compounds.

The use of this substance in industry is considered safe for the environment. Indeed, as a result of the stepwise decomposition of the molecule, simply water and carbon dioxide are formed. 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 connection for various purposes: both technical,and food and cosmetic.

Toxicity and effects on the body

Propylene glycol - what is it in terms of its 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. Does not cause irritation and redness of the skin, does not accumulate in the liver and kidneys, as it breaks down on the way to them.

Experiments on mice that consumed propylene glycol daily proved that it does not affect the he alth and life of living beings. 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 in accordance with all 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 0С) and pressure (1, 6MPa). In this case, the products are three substances at once:

• propylene glycol;
• dipropylene glycol;
• tripropylene glycol.

For further processing and separation, the method of rectification on a special column is used. The finished product has a high purity value (99%), so it is immediately ready for use. Food-grade propylene glycol is further processed and has a shelf life of up to two years.

Use as antifreeze

First of all, this alcohol is used in industry as a coolant. Propylene glycol can be used in heating installations in the temperature range from -40 ⁰С to +108 ^{0С. At the same time, its low corrosion ability allows you to save equipment. Therefore, propanediol is used for:}

• heating systems;
• air conditioning of all kinds of buildings;
• ventilation;
• food refrigeration.

Use in cosmetology

The ability of this substance to capture and bind water, disperse, improve consistency, conduct odor molecules underlies its use in cosmetic and perfume industries. In addition, low chemical activity and safety from the point of view of ecology and 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. The price depends on the concentration of the product and on the volume of the order. It ranges from 150 to 170 rubles per kilogram.

Food industry use

In the food industry, propylene glycol is known as E1520. It is part of many products that have a pasty, creamy consistency, as well as hard confectionery. Its role is dispersion, softening, cooling, preservation.