Solvents

Solvents are substances, typically liquids, that dissolve solutes to form solutions. They are essential in chemistry, industry, and daily life because they enable reactions, facilitate extraction and purification, and adjust formulation properties. Solvents are broadly characterized by polarity, hydrogen-bonding ability, and volatility. They can be grouped into polar protic solvents (for example water, ethanol, methanol), polar aprotic solvents (such as acetone, dimethyl sulfoxide, acetonitrile, dimethylformamide), and nonpolar solvents (for example hexane, toluene, xylene). Physical properties including boiling point, dielectric constant, and solubility parameters influence solubility and reaction kinetics, and a solvent may dissolve many solutes only if their solubility parameters are similar.

Water is the most common solvent and is often referred to as the universal solvent. Many organic solutes are soluble in polar organic solvents; nonpolar solutes tend to be soluble in nonpolar solvents. Common industrial solvents include acetone, ethanol, ethyl acetate, dichloromethane, toluene, xylene, and hexane, as well as nitriles such as acetonitrile and amides such as DMF or DMSO. Solvents are chosen to maximize solubility while considering reactivity, compatibility with materials, toxicity, flammability, and environmental impact. Some solvents also influence reaction mechanisms or stabilize charged intermediates; others serve primarily as media for dissolution or extraction.

Safety and environmental considerations are central to solvent use. Many solvents are flammable or volatile organic compounds that contribute to air pollution and water contamination if mishandled. Exposure can be hazardous to health, and some solvents pose long-term risks. Disposal and recovery or recycling are important parts of responsible solvent use, and regulations govern labeling, storage, emissions, and waste handling. In green chemistry, preference is often given to safer, readily renewable, or recyclable alternatives, lower-toxicity solvents, and solvent-free or solvent-minimized processes.