Cosolvent

Their use is most prevalent in chemical and biological research relating to pharmaceuticals and food science, where alcohols are frequently used as cosolvents in water (often less than 5% by volume[1]) to dissolve hydrophobic molecules during extraction, screening, and formulation.

Cosolvents find applications also in environmental chemistry and are known as effective countermeasures against pollutant non-aqueous phase liquids,[2] as well as in the production of functional energy materials[3][4] and synthesis of biodiesel.

Among other results, the study concludes that cosolvent choice is of acute importance in the pharmaceutical industry where percent yield, trace impurities, and processing techniques are chemically, financially, and toxicologically relevant.

They accomplished this yield by utilizing a cosolvent system of hexanes and methylene chloride, and extrapolated the method to include a number of benzyl halide substrates, as well as alcohols, glucose, and ribose derivatives.

[16] Specifically, the group looked at the prune seed meal-catalyzed synthesis of bioactive anti-depressant salidroside, and found that using ethylene glycol diacetate in conjunction with an ionic liquid cosolvent afforded up to a 50% increase in product yield.

Cosolvents have long been reported to be effective tools in environmental chemistry, both as powerful means of pollution remediation and as important additives in syntheses of green technologies, such as solar cells, biofuels, and sorbents.

In some cases, the utilization of cosolvents also allows for satisfaction of a broad goal in the field of green chemistry: reduction in unsustainable solvent use by enhancing substrate solubility or providing greener alternatives.

[19]Complications that arise from using alcohol cosolvents in aqueous remediation include the formation of macroemulsions, desorption of organic contaminants from aquifer solids, and introduction of toxicity, flammability, and explosivity at higher concentrations.

One such application is in the processing of polymer solar cells, where cosolvents have been recognized as being important additives to reduce phase separation of main solvent into droplets, which disrupts continuity in the sample and leads to less favorable morphologies.

For example, in efforts to convert used sunflower oil into biodiesel via transesterification, the utilization of a cosolvent in methanol was found responsible for improving product conversion from 78% to near completion in a short time frame.

Using naphthalene as a representative case of solubilizing hydrophobic organic compounds (HOCs), the authors report that a majority of the most commonly-used parameters fall short of accurately describing solubility, including dielectric constant, partition coefficient, and surface tension.

Cosolvents improve solubility between non-miscible phases, as demonstrated by a solute dissolved in organic solvent but insoluble in water (left). A cosolvent miscible in both phases and able to dissolve the solute is added to form a homogeneous solution of water, organic solvent, and compound (right).
The transesterification reaction by which vegetable oils (red) are reacted with alcohol to yield the associated ester (blue) and glyercol (green). The product esters can be used as biofuel for a variety of purposes.
In the production of polymers, such as those used in solar cell technologies, cosolvents can assist in separation between phases. Beginning with a mixture of polymer and solvent (top), cosolvents encourage the aggregation of polymers (right), simplifying production and improving performance. Without the use of cosolvent, droplets of primary solvent coalesce into distinct domains and polymer is more randomly dispersed (left). Adapted from Janssen et al (2015).