A solvent is a liquid substance that lets other substances to get dissolved in it. The water is a universal solvent and is least expensive and also widely. But there are other solvents preferred based on the need like ethanol, oils, petroleum products, etc.
They find many applications in the formulation of food, drugs, cosmetics (lipsticks) and also in research.
Common Examples of Solvents include
- Carbon disulfide
- Carbon tetrachloride
- Formic acid
- Acetic Acid
- Trifluoroacetic acid
- Dimethyl sulfoxide
- Dibutyl phthalate
- Petroleum ether
Solvents are chemical compounds that are physically liquids at room temperature. Besides these, even gases can act as solvents when required.
Whereas in the industry, these solvents are used fundamentally for the extraction, purification and also molding of substances into different shapes.
There are different types of solvents that are routinely used
Different types of solvents
Solvents can be briefly classified based on their chemical nature and behavior.
A. Based upon Polarity:
In general, most solvents have polarity in their internal chemistry.
This polarity is due to the concentration of opposite charges on one of the atoms or elements inside a solvent molecule.
It imparts changes on the solute molecule structure such that they get dissolved by forming ions.
When a solute is mixed in a solvent, the solvent molecules dissolve the solute by separating apart the solute molecules using forces like hydrogen bonding, Vanderwal forces, etc.
Examples: Sodium chloride has a NaCl molecule, which breaks into Na+ and Cl- ions when dissolved in water.
1. Polar solvents: These are solvents having a dielectric constant of more than 15. They can dissolve salts and other ionizable solutes. Polar solvents examples include water, alcohol. Polar solutes like the salts dissolve in polar solvents.
2. Non-polar solvents. These solvents are nonpolar and have dielectric constants less than 15. They cannot form intermolecular bonds by use of hydrogen bonding, Vanderwal forces, etc. Hence they cannot dissolve polar compounds. Nonpolar solvents examples include Benzene, CCl4.
Fats and oils are soluble in non-polar solvents. Hence to remove lipids from an extract, petroleum ether is used in the industry.
B. Based on Chemical nature:
1. Aprotic solvents: (No protons). These solvents are nonreactive and chemically inert. They neither take protons nor give protons. Ex: benzene (C6H6). Chloroform (CHCl3).
2. Amphiprotic solvents: These solvents can provide and take up protons on reaction. They have a neutral pH. Ex: Water, alcohol.
3. Protogenic solvents (proton+genesis = give): These are the solvents acidic by nature. They can donate a proton and hence called “protogenic.” Ex: HCL, H2SO4, perchloric acid.
4. Protophyllic solvents: These are the solvents that take up protons. They are basic by nature and are mostly alkalies. Ex: NaOH, KOH, etc.
These and protophilic solvents can be again classified as leveling agents and differentiating agents.
A strong acid or base is a leveling agent as it can donate or accept protons to even weak base or acid, respectively.
While weak acids and weak bases cannot do so, they can only give proton to a strong base or take up a proton from a strong acid, respectively. Hence due to this differentiation, they are called differentiating agents.
C) Based on chemistry:
Solvents are also classified based on their center of chemistry due to the presence of some particular elements. These unique elements in solvents bring a total change in their physical and chemical properties.
Inorganic solvents: Solvents without carbon are called inorganic solvents. Ex: water, NaOH, HCl
Organic solvents. Solvents having carbon are called organic solvents. Ex: Alcohols (CH3OH), hydrocarbons solvents like Benzene.
Halogenated solvents: Solvents having halogens are called halogenated solvents. Halogens are elements found in the 17th group of the periodic table.
Deuterated solvents: These solvents have deuterium, a hydrogen isotope, in their molecular structure. They are preferred in experiments where hydrogen has to be avoided. For example, in nuclear magnetic spectroscopy, the solvents with hydrogen can interfere in the analysis. Hence, solvents substituted with deuterium instead of the hydrogen atom are preferred. Their examples include
Deuterated water (D2O), Deuterated methanol (CD3OD), Deuterated acetic acid (CD3COOD), Deuterated trifluoroacetic acid (CF3COOD), etc.
Based on their behavior and properties, solvents are selected for purposes like acid-base titration, complexometry, extraction procedures, solubilization, chromatography, spectrophotometry, etc.
The above nature seems highly specific. Because sugar (C12H22O12) molecules are organic by nature due to the presence of carbon in it. But interestingly, sugar is insoluble in organic solvents like benzene. This is because sugar molecules have polarity and require polar solvents to dissolve. Hence we see sugar dissolves well in plain water, which is inorganic but having polarity.
So among the types of solvents available, to dissolve a solute, one should consider both chemistry and also the polarity.