A substance that allows the dispersion of another substance in its medium is called a solvent, solvent or dispersant. In other words, it is that substance that dissolves or dilutes the solute. Normally the solvent establishes the physical state of the solution. Therefore, the solvent is said to be the component of a solution that is in the same physical state as the solution. In a solution of water and table salt, water is the solvent because it disperses the salt in its medium.
Water is a polar, inorganic solvent, often called ” universal solvent ” because it is used to dissolve many substances.
Characteristics
The rule of polarity of molecules is respected, where the polar solvent dissolves the polar molecule, and the nonpolar solvent dissolves the nonpolar molecule. When a certain substance (organic for example) has two different groups that differ in polarity characteristics, it is observed which one prevails, and the solvent will be similar to it.
But the interaction between the solvent and the solute is related to the difference (or absence) of the dispute between the polar and nonpolar parts.
Many solvents used in industry are highly volatile substances, that is, they evaporate easily, so they can be inhaled (introduced into the body through aspiration, through the nose or mouth). Another characteristic is that they are flammable, that is, they burn easily.
Physical properties
Solvents can be classified into two categories: polar and non-polar.
Generally, the dielectric constant of the solvent provides an approximate measure of a solvent’s polarity. The strong polarity of water is indicated by it, at 20 ° C, with a dielectric constant of 80.10.
Solvents with a dielectric constant less than 15 are generally considered nonpolar. Technically, the dielectric constant measurements of a solvent are the ability that they have to reduce the intensity of the electric field existing around a charged particle that is immersed in it.
This reduction is compared to the field intensity of the charged particle in a vacuum. In other words, the dielectric constant of the solvent can be thought of as its ability to reduce the internal rate of solute.
The dielectric constants and dipole moment represent the polarity of the solvent and the polarization of an isolated molecule, respectively. As solvents are used by chemists to carry out chemical reactions or observe chemical and biological phenomena, more specific measurements of polarity are mandatory.
The Grunwald Winstein equation measures polarity in terms of the influence of the solvent on the accumulation of positive charge of a solute during a chemical reaction.
- Kosower scale measures polarity in terms of the influence of the solvent on the maximum ultraviolet absorption peaks of a salt, usually pyridium iodide.
Donors, number of donors, and acceptors are scales of polarity measured in terms of how a solvent interacts with specific substances, such as a strong Lewis acid or a strong Lewis base .
The polarity, polarizability (dipole moment) and hydrogen bonding of a solvent determines what type of compounds it is capable of dissolving and with what other solvents or liquid compounds it is miscible (can mix).
As a general rule, polar solvents dissolve polar compounds better and nonpolar solvents dissolve nonpolar compounds better: ” like dissolves like .”
Polar compounds such as sugars (sucrose, for example) or ionic compounds , such as inorganic salts (for example, table salt) only dissolve in very polar solvents, such as water while strongly non-polar compounds, such as oils or waxes They only dissolve in non-polar organic solvents, such as hexane.
Similarly, water and hexane (or vinegar and vegetable oil) are not miscible with each other and quickly separate into two layers, even after being shaken.
Classification of polar solvents
Polar solvents with a static relative permittivity greater than 15 can be classified as protic and aprotic:
Protic polar solvents
In solution they form hydrogen bonds and can donate hydrogen, that is, they give up protons . Water is a polar protic solvent.
Aprotic polar solvents
They cannot form hydrogen bonds, they cannot give up protons, such as acetone and dichloromethane. In chemical reactions, the use of favorable polar solvents favors the SN1 reaction mechanism, while polar aprotic solvents favor the SN2 reaction mechanism.
Solvents are grouped into non-polar, protic polar and aprotic polar and are ordered by increasing polarity.
Examples of solvents
Polar Protic Solvents
- Water
- Acetic acid
- Isopropyl alcohol
- Ethyl alcohol
- methyl alcohol
Polar Aprotic Solvents
- Acetone
- Ethyl acetate
- Acetonitrile
- Dimethyl sulfoxide
- Dimethylformamide
- 1,2-dimethoxyethane
Nonpolar Solvents
- Dichloromethane
- Chloroform
- Pentane
- Hexane
- Cyclohexane
- Benzene
Solvent recycling
There are companies that operate in the recycling of solvents, however they must have an environmental permit or license to be able to recycle, transport or store industrial waste.
In order to carry out the recovery and refining activities of solvents, mineral, vegetable and animal oils, the chemical industries are subject to an environmental license. The conversion of waste into raw materials can bring countless business and job opportunities to the industry.