Propylene glycol - what is it? Chemical properties, application

One of the most common in the cosmetic, perfume, food industry, as well as the technical sphere is organic matter, which refers to alcohols. Its name is propylene glycol. What it is? Let's consider properties, a structure of a molecule and area of use of the given connection during article.

Propylene glycol - what is it?

This diatomic spirit people began to use immediately, once they found out what useful and important properties it possesses. Outwardly, it differs little from ethanol or glycerin, because it is also a clear liquid. True, its viscosity is higher than that of ethanol, but lower than that of glycerin. By its toxicity, it is much inferior to the nearest neighbor along the homologous series - ethylene glycol.

If ethanediol is the strongest poison, propylene glycol is not. The use of this substance is based on its physical and chemical properties. If we briefly characterize the main branches in which there is propylene glycol, the application will be expressed by several branches of the economy.

1. Chemical industry.
2. Aviation and automobile construction.
3. Oil and gas industry.
4. Paint and varnish industry.
5. Cosmetic and perfumery industry.
6. Food production.
7. Technical field of activity.
8. Medicine.

It is obvious that 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 calculated in tons annually. Its exports and imports between countries are 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 understand further.

Formula and composition of the molecule

There are several variants of formulas by means of which it is possible to display not only the qualitative and quantitative composition of a molecule, but also the order of the combination of atoms in it, that is, the structure of matter.

1. Molecular, or empirical. According to this formula, one can judge the composition of the compound. Propylene glycol will look like C ₃ H ₈ O ₂ . But such a record will not give an opportunity 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 be of 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. Both structures are isomers.
   
3. Full structural formula. It shows each link in the molecule, including the compounds between carbon and hydrogen. In propylene glycol, all bonds are single, sigma-type, therefore, to represent the complete structure does not make sense.

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, on the properties of this substance as a whole, this practically does not affect in any way.

Physical properties of the substance

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

1. Colorless liquid, thick, viscous, has an average density.
2. The taste is sweet, the smell is specific.
3. It is a good solvent for representatives of virtually all classes of substances.
4. Propylene glycol itself dissolves in water and alcohol, badly in benzene and ether.
5. The boiling point is 45.5 ^° C at normal pressure. With increasing pressure, the indicator increases.
6. Has a high degree of hygroscopicity.
7. Has a low corrosivity.

Such physical properties determine the main areas of application of this substance. After propanediol is able to soften solid media, trap moisture and bind it, lower the temperature of substances, disperse surrounding compounds. Therefore, it is 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 it capable of polymerization. In general, we can identify several basic reactions, in which this diatomic alcohol is able to enter.

1. Esterification. With organic and inorganic acids interacts with the formation of esters.
2. When reacting with alkalis, glycolates are produced, the same thing happens when interacting with alkali metals.
3. It is capable of dehydration with the formation of aldehydes, allylic 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, propionic aldehyde, lactic acid, formaldehyde and other compounds.

The use of this substance in industry is considered safe for the environment. After all, as a result of the stepwise decomposition of the molecule, water and carbon dioxide are simply formed . The process is as follows:

• Propylene glycol;
• lactic acid;
• PVK (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 effect on the body

Propylene glycol - what is this from the point of view of influence on the human body? Numerous studies and experiments have shown that this compound has no 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 used daily propylene glycol, proved that it does not affect the health and life of living beings. However, if the products and preparations containing a large amount of this substance are used for a long time, the kidneys may suffer, their work and integrity will be disrupted. But for this, one should use a large amount of practically pure 100% propylene glycol, which, of course, is impossible.

Therefore, the use of this alcohol in the cosmetic, perfume and food industries is allowed by all rules and norms. The only negative impact it can have on those people who suffer from skin diseases, dermatitis, eczema and complex forms of allergy. In this case, it is not recommended to use creams, ointments, shampoos and other products containing this substance.

Manufacture in industry

The chemical properties of propylene glycol make it possible to obtain it from propylene oxide under certain temperature conditions (about 200 ^° C) and pressure (1.6 MPa). At the same time, the products are just three substances:

• Propylene glycol;
• Dipropylene glycol;
• Tripropylene glycol.

For further processing and separation, a rectification method is used on a special column. The finished product has a high purity (99%), so it is immediately ready for use. Food propylene glycol undergoes additional treatment, 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 heat installations in the temperature range from -40 ⁰ C to +108 ⁰ С. At the same time, its low corrosion ability allows the equipment to be stored. Therefore, propandiol is used for:

• Heating systems;
• Conditioning of all types of buildings;
• Ventilation;
• Cooling of food products.

Application in cosmetology

The ability of this substance to trap and bind water, to disperse, to improve consistency, to carry out the odor molecules lies at the basis of its use in cosmetic and perfumery 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. The price depends on the concentration of the product and on the volume of the order. Ranges from 150 to 170 rubles per kilogram.

Use in food industry

In the food industry, propylene glycol is known as E1520. It is a part of many products with pasty, creamy consistency, as well as hard confectionery products. Its role - dispersing, softening, cooling, canning.