Safer solvent use in the pharmaceutical industry

Home cleaning products are often a surfactant solution in water, but industrially, oils and greases are regularly removed from surfaces with hydrocarbon solvents or chlorinated solvents. Some domestic cleaning solvents are also based on hydrocarbon solvents when water-based cleaning products are insufficient (e.g. oven cleaners, or white spirit for DIY and maintenance purposes). The cleaning of chemistry glassware or reactors can be conducted with either water or organic solvents depending on the circumstances. The residues in a chemical reactor may be far more diverse in character than the typical stains you would encounter at home, and this will determine the cleaning method.

Formulation solvents are required to dissolve the active ingredients in a product, usually to make a homogeneous solution or dispersion. Additionally, the solvent may impart other useful properties such as viscosity or surface tension. The majority of solvents are used to make paints and other types of coatings. These formulations require that the coating polymer is uniformly mixed with additives such as pigments, and the solvent must be volatile enough to evaporate and create a dry, uniform coating. If the solubility of the active ingredients is low, they will settle out of solution as a precipitate. A low-viscosity or slow-drying solvent may lead to poor coating characteristics, especially on vertical surfaces. These factors need to be considered when formulating a product.

A reaction solvent is usually required to dissolve the other reaction components, but additionally, the solvent influences reaction kinetics, selectivity, and equilibria. A significant body of work has arisen to aid with green solvent selection, particularly for the synthesis of active pharmaceutical ingredients (APIs) (Clark et al., 2016).

Extraction of natural ingredients and the isolation of the reaction products is also solvent dependent, be it through liquid extraction, crystallisation or chromatography. In a multi-step synthesis of a compound, the solvent will usually be different in each reaction (and in each separation process), and cumulatively a lot of solvent is required compared to the amount of products that is made.

Solvent use in Europe by industry: ESIG, 2023.

Renewable solvent selection in medicinal chemistry: Clark, J.H., Hunt, A.J., Moity, L. and Sherwood, J. in Green and Sustainable Medicinal Chemistry : Methods, Tools and Strategies for the 21st Century Pharmaceutical Industry, 2016, RSC, pp. 28-40.