Solvents

Solvents are extensively used:

• In the chemical laboratory as a medium for organic reactions and analytical separations
• Industrially, in the production of a variety of goods ranging from cosmetics, pharmaceuticals, and personal care items to textiles, paints, and pesticides

Solvents are generally classified as polar and nonpolar. A parameter known as the dielectric constant is a rough measure of solvent polarity or its ability to stabilize charges. The higher the dielectric constant, the more polar the solvent (or any substance for that matter). By this measure, water (which dissolves ionic or charged compounds such as inorganic salts) is a most polar solvent, having a dielectric constant of 78 at 25ºC. In general, solvents with dielectric constants greater than 15 are considered polar. These solvents include, among others, acetone, acetonitrile, dimethylformamide (DMF), dimelthylsulfoxide (DMSO), ethanol, isopropanol, and methanol. Expectedly, the least polar (or the most nonpolar) solvents are the alkanes pentane, hexane, heptane (dielectric constant less than two), and the aromatics benzene, toluene, and xylene (dielectric constants less than three). Other common nonpolar solvents (with dielectric constants less than 15) include acetic acid, chloroform, diethyl ether, ethyl acetate, methylene chloride, and pyridine. “Like dissolves like” is a good rule of thumb, i.e., polar solvents dissolve polar compounds.

Hazardous properties of solvents — such as toxicity, flammability, and volatility — vary extensively.