Use of Solvents

Solvents are widely used throughout the chemical industry, for example, in:

• Synthetic Chemistry: as a reaction medium, on both a laboratory and industrial scale, and in work-ups and purifications.
• Analytical Chemistry: for sample extraction and preparation (spectroscopy) and chromatography mobile phase (HPLC, TLC, etc.)
• Crystallography: for recrystallization, to purify compounds, and prepare crystals suitable for analysis.

Solvents are used as a reaction medium for various reasons, including:

• To bring reactants together at suitable concentrations;
• For energy control: 
  • Endothermic reactions require energy – heat can be supplied by heating solution;
  • Exothermic reactions – solvent acts as a heat sink preventing runaway reactions;
• For efficient mixing and stirring;
• To allow the addition of solid reagents as a solution.

Solvent extraction is also a vital part of the purification process. Often more solvent is used in work-up than as reaction medium. Partitioning products between an organic and aqueous phase is an important way of extracting products, although this generates aqueous and organic waste, both of which require disposal.

Solvents have many applications other than synthetic chemistry, for example in paints and adhesives, for cleaning (e.g., dry cleaning), and for extraction (e.g., decaffeination of coffee).

Some common classes of solvents are given below.

Solvent Usage in the Pharmaceutical Industry

In the video below, Denis Prat explains why the pharmaceutical industry uses high quantities of solvents and describes the impact of solvents on the greenness of an active pharmaceutical ingredient (API) synthesis.