A solvent (from the Latin solvere, “loosen”) is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature. Common uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene), as a paint thinner (e.g. toluene, turpentine), as nail polish removers and glue solvents (acetone, methyl acetate, ethyl acetate), in spot removers (e.g. hexane, petrol ether), in detergents (citrus terpenes), in perfumes (ethanol), and in chemical synthesis. The use of inorganic solvents (other than water) is typically limited to research chemistry and some technological processes. In 2005, the worldwide market for solvents had a total volume of around 17.9 million tons, which led to a turnover of about 8 billion Euro.
Properties table of common solvents
The solvents are grouped into non-polar, polar aprotic, and polar protic solvents and ordered by increasing polarity. The polarity is given as the dielectric constant. The properties of solvents that exceed those of water are bolded.
| Solvent | Chemical formula | Boiling point[7] | Dielectric constant[8] | Density | Dipole moment |
|---|---|---|---|---|---|
| Non-polar solvents | |||||
| Pentane | CH3-CH2-CH2-CH2-CH3 | 36 °C | 1.84 | 0.626 g/ml | 0.00 D |
| Cyclopentane | C5H10 | 40 °C | 1.97 | 0.751 g/ml | 0.00 D |
| Hexane | CH3-CH2-CH2-CH2-CH2-CH3 | 69 °C | 1.88 | 0.655 g/ml | 0.00 D |
| Cyclohexane | C6H12 | 81 °C | 2.02 | 0.779 g/ml | 0.00 D |
| Benzene | C6H6 | 80 °C | 2.3 | 0.879 g/ml | 0.00 D |
| Toluene | C6H5-CH3 | 111 °C | 2.38 | 0.867 g/ml | 0.36 D |
| 1,4-Dioxane | /-CH2-CH2-O-CH2-CH2-O-\ | 101 °C | 2.3 | 1.033 g/ml | 0.45 D |
| Chloroform | CHCl3 | 61 °C | 4.81 | 1.498 g/ml | 1.04 D |
| Diethyl ether | CH3CH2-O-CH2-CH3 | 35 °C | 4.3 | 0.713 g/ml | 1.15 D |
| Polar aprotic solvents | |||||
| Dichloromethane(DCM) | CH2Cl2 | 40 °C | 9.1 | 1.3266 g/ml | 1.60 D |
| Tetrahydrofuran(THF) | /-CH2-CH2-O-CH2-CH2-\ | 66 °C | 7.5 | 0.886 g/ml | 1.75 D |
| Ethyl acetate | CH3-C(=O)-O-CH2-CH3 | 77 °C | 6.02 | 0.894 g/ml | 1.78 D |
| Acetone | CH3-C(=O)-CH3 | 56 °C | 21 | 0.786 g/ml | 2.88 D |
| Dimethylformamide(DMF) | H-C(=O)N(CH3)2 | 153 °C | 38 | 0.944 g/ml | 3.82 D |
| Acetonitrile(MeCN) | CH3-C≡N | 82 °C | 37.5 | 0.786 g/ml | 3.92 D |
| Dimethyl sulfoxide(DMSO) | CH3-S(=O)-CH3 | 189 °C | 46.7 | 1.092 g/ml | 3.96 D |
| Polar protic solvents | |||||
| Formic acid | H-C(=O)OH | 101 °C | 58 | 1.21 g/ml | 1.41 D |
| n-Butanol | CH3-CH2-CH2-CH2-OH | 118 °C | 18 | 0.810 g/ml | 1.63 D |
| Isopropanol (IPA) | CH3-CH(-OH)-CH3 | 82 °C | 18 | 0.785 g/ml | 1.66 D |
| n-Propanol | CH3-CH2-CH2-OH | 97 °C | 20 | 0.803 g/ml | 1.68 D |
| Ethanol | CH3-CH2-OH | 79 °C | 24.55 | 0.789 g/ml | 1.69 D |
| Methanol | CH3-OH | 65 °C | 33 | 0.791 g/ml | 1.70 D |
| Acetic acid | CH3-C(=O)OH | 118 °C | 6.2 | 1.049 g/ml | 1.74 D |
| Water | H-O-H | 100 °C | 80 | 1.000 g/ml | 1.85 D |
There’s another powerful way to look at these same solvents. By knowing their Hansen solubility parameter values (HSPiP), which are based on δD=dispersion bonds, δP=polar bonds and δH=hydrogen bonds, you know important things about their inter-molecular interactions with other solvents and also with polymers, pigments, nanoparticles etc. so you can do two things. First, you can create rational formulations knowing, for example, that there is a good HSP match between a solvent and a polymer. Second, you can make rational substitutions for “good” solvents (they dissolve things well) that are “bad” (for the environment, for health, for cost etc.). The following table shows that the intuitions from “non-polar”, “polar aprotic” and “polar protic” are put numerically – the “polar” molecules have higher levels of δP and the protic solvents have higher levels of δH. Because numerical values are used, comparisons can be made rationally by comparing numbers. So acetonitrile is much more polar than acetone but slightly less hydrogen bonding.
| Solvent | Chemical formula | δD Dispersion | δP Polar | δH Hydrogen bonding |
|---|---|---|---|---|
| Non-polar solvents | ||||
| Hexane | CH3-CH2-CH2-CH2-CH2-CH3 | 14.9 | 0.0 | 0.0 |
| Benzene | C6H6 | 18.4 | 0.0 | 2.0 |
| Toluene | C6H5-CH3 | 18.0 | 1.4 | 2.0 |
| Diethyl ether | CH3CH2-O-CH2-CH3 | 14.5 | 2.9 | 4.6 |
| Chloroform | CHCl3 | 17.8 | 3.1 | 5.7 |
| 1,4-Dioxane | /-CH2-CH2-O-CH2-CH2-O-\ | 17.5 | 1.8 | 9.0 |
| Polar aprotic solvents | ||||
| Ethyl acetate | CH3-C(=O)-O-CH2-CH3 | 15.8 | 5.3 | 7.2 |
| Tetrahydrofuran(THF) | /-CH2-CH2-O-CH2-CH2-\ | 16.8 | 5.7 | 8.0 |
| Dichloromethane | CH2Cl2 | 17.0 | 7.3 | 7.1 |
| Acetone | CH3-C(=O)-CH3 | 15.5 | 10.4 | 7.0 |
| Acetonitrile (MeCN) | CH3-C≡N | 15.3 | 18.0 | 6.1 |
| Dimethylformamide(DMF) | H-C(=O)N(CH3)2 | 17.4 | 13.7 | 11.3 |
| Dimethyl sulfoxide(DMSO) | CH3-S(=O)-CH3 | 18.4 | 16.4 | 10.2 |
| Polar protic solvents | ||||
| Acetic acid | CH3-C(=O)OH | 14.5 | 8.0 | 13.5 |
| n-Butanol | CH3-CH2-CH2-CH2-OH | 16.0 | 5.7 | 15.8 |
| Isopropanol | CH3-CH(-OH)-CH3 | 15.8 | 6.1 | 16.4 |
| n-Propanol | CH3-CH2-CH2-OH | 16.0 | 6.8 | 17.4 |
| Ethanol | CH3-CH2-OH | 15.8 | 8.8 | 19.4 |
| Methanol | CH3-OH | 14.7 | 12.3 | 22.3 |
| Formic acid | H-C(=O)OH | 14.6 | 10.0 | 14.0 |
| Water | H-O-H | 15.5 | 16.0 | 42.3 |
Consider a simple example of rational substitution. Suppose for environmental reasons we needed to replace the chlorinated solvent, chloroform, with a solvent (blend) of equal solvency using a mixture of two non-chlorinated solvents from this table. Via trial-and-error, a spreadsheet or some software such as HSPiP[9][10] we find that a 50:50 mix of toluene and 1,4 dioxane is a close match. The δD of the mixture is the average of 18.0 and 17.5 = 17.8. The δP of the mixture is the average of 1.4 and 1.8 = 1.6 and the δH of the mixture is the average of 2.0 and 9.0 = 5.5. So the mixture is 17.8, 1.6, 5.5 compared to Chloroform at 17.8, 3.1, 5.7. Because Toluene itself has many health issues, other mixtures of solvents can be found using a fullHansen solubility parameter dataset.