Cosolvent

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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). Cosolvent.png
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).

In chemistry, cosolvents are substances added to a primary solvent in small amounts to increase the solubility of a poorly-soluble compound. 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. [5] [6]

Contents

The topic of cosolvency has attracted attention from many theorists and practicing researchers who seek to predict the solubility of compounds using cosolvent systems, and it is the subject of considerable research in scientific literature. Studies exist to propose and review methods of modeling cosolvency using calculation, [7] [8] [9] to describe empirical correlations of cosolvents and observed solvation phenomena, [10] [11] and to report the utility of cosolvent systems in various fields. [2] [3] [4] [12]

In pharmaceuticals

Long-standing challenges in pharmaceutical chemistry include overcoming the inherent hydrophobicity/lipophilicity of certain molecules for treatment and finding effective synthesis procedures for complex molecules. Cosolvents are able to aid researchers in both the trials of formulation and synthesis.

Formulation

In pharmaceutical chemistry, numerous methods exist to help solubilize poorly water-soluble drugs for use in treatment. These methods include cosolvency, hydrotropism, complexation, ionization, and using surface active agents. The most pervasive is the application of non-toxic cosolvents with water to produce formulations that can dissolve hydrophobic molecules while maintaining cohesion with biological systems. Common cosolvents for this purpose are ethanol, propylene glycol, glycerine, glycofural, and polyethylene glycols. [7] The effect of cosolvency on drug solubilization can be great, as evidenced by a 2009 study in which researchers from Panjab University showed the solubility of various anti-diabetic drugs increase by more than 500 times by use of a cosolvent. [13]

Synthesis

Cosolvents prove useful in synthetic applications as well as in formulation. Cosolvent systems are commonly specific to the synthetic target being studied, so reviewed here are the generalized findings of several publications that exemplify important points on the subject:

In a 2017 project, researchers at Cornell University studied the effect of cosolvency in oxazolidinone enolizations mediated by lithium hexamethyldisilazide (LiHMDS). This reaction pathway was exemplified by the group in the synthesis of filibuvir, a drug used for the treatment of hepatitis C that is produced on plant-scale by Pfizer. [14] The researchers focus primarily on polymer formation in systems of tetrahydrofuran with hydrocarbon cosolvents, and find that the rate is strongly sensitive to the cosolvent utilized. 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. However, the researchers take care to mention that the mechanisms that bring about these empirical differences in cosolvent systems are not yet well-understood.

A 2016 paper from researchers at Hokkaido University describes a cosolvent-promoted mechanism for benzylating hydroxyl groups in the synthesis of sucrose derivatives. [15] The group reports a method by which the benzylation reaction, empirically low yielding and with significant formation of byproducts due to the generally low reactivity of the target 1’-hydroxyl group in sucrose, was carried out to up to 95% yields with excellent selectivity for the synthetic molecule. 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. This study is one of many where reaction yields in organic synthesis can be optimized by application of polar/non-polar cosolvent systems.

Cosolvents also play a role in the biochemical subdiscipline: a 2012 study from researchers at the South China University of Technology reports how cosolvent parameters can be optimized to obtain higher yields in enzyme-catalyzed reactions. [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. The use of ionic liquids as cosolvents in this study and many similar demonstrates the variability of this methodology, where cosolvent systems can extend beyond standard conventions of polar and non-polar solvents to affect change on a mechanistic level.

In environmental chemistry

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.

Remediation

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. Transesterification Biofuels.png
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 context of aqueous pollutant remediation, cosolvents can be used in a variety of functions, including to enhance the performance of surfactants, to increase solubility of a non-aqueous phase liquid (NAPL), and to physically mobilize NAPLs by decreasing interfacial tension between aqueous and organic phases. [17] Due to toxicological concerns, the main agents used for remediation are aqueous solutions of 1-5% alcohols by volume, which can be flushed through a polluted site and later extracted from the bulk water. This “cosolvent flooding” (called alcohol flooding when using >5% by volume) is often combined with salinity modification, in situ chemical oxidation, and temperature alteration to provide the most effective methods of removing NAPLs from a water source. [18] In situ flushing is a process by which soil is decontaminated in a similar manner as aqueous environments. [19]

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). Polymerformation.png
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).

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. [17]

Green technologies

The versatile and variable nature of cosolvents has allowed them to be used in many applications regarding green technology. 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. [20] In most cases, a cosolvent is used in 1-10% by volume and acts by encouraging polymer aggregation in either the casting or solution evaporation stages. While the use of cosolvents in this context is nearly ubiquitous in organic solar cell research, there remains a lack of understanding on the dynamical processes by which cosolvency achieves this effect. [3] [4] [20]

Cosolvents also play an important role in the production of biofuels from assorted biomass. 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. [21] In another example, a tetrahydrofuran-water mixture was found to be incredibly effective in extracting lignin from biomass to yield fermentable sugars, despite that both THF and water are poor solvents for this purpose. [22] By simplifying the synthesis and processing procedures for these and other developing green technologies, cosolvents are reducing waste from lost yields, poor solubility of substrates, and excess processing. As time moves forward, even better systems are being developed, and directed research into greener cosolvents is being explored. [23]

Approximating cosolvent effects

A variety of models exist to describe and predict the effects of cosolvents. Relying heavily on the application of mathematical models and chemical theory, these models range from simple to relatively complex. The first model and also the simplest is still in use today: the model of Yalkowsky. [7] Yalkowsky’s model utilizes the algebraic mixing rule or log-linear model:

logXm = ƒ1logX1 + ƒ2logX2

Where Xm is the mole fraction solubility of the solute, X1 and X2 denote the mole fraction solubility in neat cosolvent and water.

While this model is only correlative in nature, further analysis allows for the creation of a predictive element. Simplifying the above equation to:

logXm = logX2 + σ • ƒ1

Where σ is the solubilization power of the cosolvent and theoretically is equal to log(X1/X2).

One can incorporate the work of Valvani et al., which shows:

Where M and N are cosolvent constants that are not dependent on the nature of the solute, and have been tabulated for many commonly-used cosolvents. These transformations effectively turn the Yalkowsky log-linear model into a predictive model, where a researcher can predict with fair accuracy the cosolvent concentration for solubilization of a compound using only aqueous solubility data. [7] For a more in-depth discussion of cosolvent modeling systems, the reader is directed to reviews by Jouyban (2008), [7] Smith and Mazo (2008), [8] and for biochemical context, Canchi and Garcia (2013). [9]

A simpler view at choosing cosolvents involves looking at measureable properties of varying cosolvent systems and making a determination from empirical evidence. Researchers from the University of Arizona and the University of Wisconsin-Madison review a selection of parameters in an Environmental Toxicology and Chemistry paper, [24] among them the partition coefficient, surface tension, dielectric constant, interfacial tension, and others. 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. Instead, they find that Hildebrand’s solubility parameter, Et(30), and interfacial tension correlate more favorably with empirical trends. The practicing chemist should take these results into account when developing a cosolvent system for a given target.

Related Research Articles

<span class="mw-page-title-main">Solvation</span> Association of molecules of a solvent with molecules or ions of a solute

Solvation describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the solute, including solubility, reactivity, and color, as well as influencing the properties of the solvent such as its viscosity and density. If the attractive forces between the solvent and solute particles are greater than the attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. The surrounded solute particles then move away from the solid solute and out into the solution. Ions are surrounded by a concentric shell of solvent. Solvation is the process of reorganizing solvent and solute molecules into solvation complexes and involves bond formation, hydrogen bonding, and van der Waals forces. Solvation of a solute by water is called hydration.

<span class="mw-page-title-main">Solubility</span> Capacity of a substance to dissolve in a homogeneous way

In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.

<span class="mw-page-title-main">Surfactant</span> Substance that lowers the surface tension between a liquid and another material

Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word "surfactant" is a blend of surface-active agent, coined c. 1950. As they consist of a water-repellent and a water-attracting part, they enable water and oil to mix; they can form foam and facilitate the detachment of dirt.

<span class="mw-page-title-main">Micelle</span> Group of fatty molecules suspended in liquid by soaps and/or detergents

A micelle or micella is an aggregate of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension. A typical micelle in water forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single-tail regions in the micelle centre.

In the physical sciences, a partition coefficient (P) or distribution coefficient (D) is the ratio of concentrations of a compound in a mixture of two immiscible solvents at equilibrium. This ratio is therefore a comparison of the solubilities of the solute in these two liquids. The partition coefficient generally refers to the concentration ratio of un-ionized species of compound, whereas the distribution coefficient refers to the concentration ratio of all species of the compound.

<span class="mw-page-title-main">Liquid–liquid extraction</span> Method to separate compounds or metal complexes

Liquid–liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds or metal complexes, based on their relative solubilities in two different immiscible liquids, usually water (polar) and an organic solvent (non-polar). There is a net transfer of one or more species from one liquid into another liquid phase, generally from aqueous to organic. The transfer is driven by chemical potential, i.e. once the transfer is complete, the overall system of chemical components that make up the solutes and the solvents are in a more stable configuration. The solvent that is enriched in solute(s) is called extract. The feed solution that is depleted in solute(s) is called the raffinate. Liquid–liquid extraction is a basic technique in chemical laboratories, where it is performed using a variety of apparatus, from separatory funnels to countercurrent distribution equipment called as mixer settlers. This type of process is commonly performed after a chemical reaction as part of the work-up, often including an acidic work-up.

Aqueous biphasic systems (ABS) or aqueous two-phase systems (ATPS) are clean alternatives for traditional organic-water solvent extraction systems.

Deep eutectic solvents or DESs are solutions of Lewis or Brønsted acids and bases which form a eutectic mixture. Deep eutectic solvents are highly tunable through varying the structure or relative ratio of parent components and thus have a wide variety of potential applications including catalytic, separation, and electrochemical processes. The parent components of deep eutectic solvents engage in a complex hydrogen bonding network which results in significant freezing point depression as compared to the parent compounds. The extent of freezing point depression observed in DESs is well illustrated by a mixture of choline chloride and urea in a 1:2 mole ratio. Choline chloride and urea are both solids at room temperature with melting points of 302 °C and 133 °C respectively, yet the combination of the two in a 1:2 molar ratio forms a liquid with a freezing point of 12 °C. DESs share similar properties to ionic liquids such as tunability and lack of flammability yet are distinct in that ionic liquids are neat salts composed exclusively of discrete ions. In contrast to ordinary solvents, such as Volatile Organic Compounds (VOC), DESs are non-flammable, and possess low vapour pressures and toxicity.

In chemistry, a phase-transfer catalyst or PTC is a catalyst that facilitates the transition of a reactant from one phase into another phase where reaction occurs. Phase-transfer catalysis is a special form of catalysis and can act through homogeneous catalysis or heterogeneous catalysis methods depending on the catalyst used. Ionic reactants are often soluble in an aqueous phase but insoluble in an organic phase in the absence of the phase-transfer catalyst. The catalyst functions like a detergent for solubilizing the salts into the organic phase. Phase-transfer catalysis refers to the acceleration of the reaction upon the addition of the phase-transfer catalyst.

Reversed-phase liquid chromatography (RP-LC) is a mode of liquid chromatography in which non-polar stationary phase and polar mobile phases are used for the separation of organic compounds. The vast majority of separations and analyses using high-performance liquid chromatography (HPLC) in recent years are done using the reversed phase mode. In the reversed phase mode, the sample components are retained in the system the more hydrophobic they are.

Micellar liquid chromatography (MLC) is a form of reversed phase liquid chromatography that uses an aqueous micellar solutions as the mobile phase.

Acid–base extraction is a subclass of liquid–liquid extractions and involves the separation of chemical species from other acidic or basic compounds. It is typically performed during the work-up step following a chemical synthesis to purify crude compounds and results in the product being largely free of acidic or basic impurities. A separatory funnel is commonly used to perform an acid-base extraction.

<span class="mw-page-title-main">Chloroauric acid</span> Chemical compound

Chloroauric acid is an inorganic compound with the chemical formula H[AuCl4]. It forms hydrates H[AuCl4]·nH2O. Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar [AuCl4]− anion. Often chloroauric acid is handled as a solution, such as those obtained by dissolution of gold in aqua regia. These solutions can be converted to other gold complexes or reduced to metallic gold or gold nanoparticles.

Paint has four major components: pigments, binders, solvents, and additives. Pigments serve to give paint its color, texture, toughness, as well as determining if a paint is opaque or not. Common white pigments include titanium dioxide and zinc oxide. Binders are the film forming component of a paint as it dries and affects the durability, gloss, and flexibility of the coating. Polyurethanes, polyesters, and acrylics are all examples of common binders. The solvent is the medium in which all other components of the paint are dissolved and evaporates away as the paint dries and cures. The solvent also modifies the curing rate and viscosity of the paint in its liquid state. There are two types of paint: solvent-borne and water-borne paints. Solvent-borne paints use organic solvents as the primary vehicle carrying the solid components in a paint formulation, whereas water-borne paints use water as the continuous medium. The additives that are incorporated into paints are a wide range of things which impart important effects on the properties of the paint and the final coating. Common paint additives are catalysts, thickeners, stabilizers, emulsifiers, texturizers, biocides to fight bacterial growth, etc.

<span class="mw-page-title-main">Non-aqueous phase liquid</span> Liquid solution contaminants that do not dissolve in or easily mix with water

Non-aqueous phase liquids, or NAPLs, are organic liquid contaminants characterized by their relative immiscibility with water. Common examples of NAPLs are petroleum products, coal tars, chlorinated solvents, and pesticides. Strategies employed for their removal from the subsurface environment have expanded since the late-20th century.

The use of ionic liquids in carbon capture is a potential application of ionic liquids as absorbents for use in carbon capture and sequestration. Ionic liquids, which are salts that exist as liquids near room temperature, are polar, nonvolatile materials that have been considered for many applications. The urgency of climate change has spurred research into their use in energy-related applications such as carbon capture and storage.

1,4-butane sultone is a six-membered δ-sultone and the cyclic ester of 4-hydroxybutanesulfonic acid. As a sulfo-alkylating agent, 1,4-butanesultone is used to introduce the sulfobutyl group (–(CH2)4–SO3−) into hydrophobic compounds possessing nucleophilic functional groups, for example hydroxy groups (as in the case of β-cyclodextrin) or amino groups (as in the case of polymethine dyes). In such, the sulfobutyl group is present as neutral sodium salt and considerably increases the water solubility of the derivatives.

<span class="mw-page-title-main">Wetting solution</span> Chemical

Wetting solutions are liquids containing active chemical compounds that minimise the distance between two immiscible phases by lowering the surface tension to induce optimal spreading. The two phases, known as an interface, can be classified into five categories, namely, solid-solid, solid-liquid, solid-gas, liquid-liquid and liquid-gas.

<span class="mw-page-title-main">Cononsolvency</span>

Cononsolvency is a phenomenon where two solvents that can typically readily dissolve a polymer, when mixed, at certain ratios of these two solvents, are no longer able to dissolve the polymer. This phenomenon is in contrast to cosolvency where two solvents that are both poor at dissolving a material, but when the two poor solvents admixed, can form a mixed solvent capable of dissolving the material.

Green solvents are environmentally friendly chemical solvents that are used as a part of green chemistry. They came to prominence in 2015, when the UN defined a new sustainability-focused development plan based on 17 sustainable development goals, recognizing the need for green chemistry and green solvents for a more sustainable future. Green solvents are developed as more environmentally friendly solvents, derived from the processing of agricultural crops or otherwise sustainable methods as alternatives to petrochemical solvents. Some of the expected characteristics of green solvents include ease of recycling, ease of biodegradation, and low toxicity.

References

  1. ↑ Shi, John. Functional Food Ingredients and Nutraceuticals: Processing Technologies, 1st ed. CRC Press: Boca Raton, 2007.
  2. 1 2 Ward, C.H., Oubre, C.L., Lowe, D.F. Surfactants and Cosolvents for NAPL Remediation A Technology Practices Manual, 1st ed. CRC Press: Boca Raton, 1999.
  3. 1 2 3 Halim, Udayabagya; Zheng, Chu Ran; Chen, Yu; Lin, Zhaoyang; Jiang, Shan; Cheng, Rui; Huang, Yu; Duan, Xiangfeng (2013-07-30). "A rational design of cosolvent exfoliation of layered materials by directly probing liquid–solid interaction". Nature Communications. 4: 2213. Bibcode:2013NatCo...4.2213H. doi:10.1038/ncomms3213. PMC   4249658 . PMID   23896793.
  4. 1 2 3 Pascual, Jorge; Kosta, Ivet; Palacios-Lidon, Elisa; Chuvilin, Andrey; Grancini, Giulia; Nazeeruddin, Mohammad Khaja; Grande, Hans J.; Delgado, Juan Luis; Tena-Zaera, Ramón (2018-02-08). "Co-Solvent Effect in the Processing of the Perovskite:Fullerene Blend Films for Electron Transport Layer-Free Solar Cells". The Journal of Physical Chemistry C. 122 (5): 2512–2520. doi:10.1021/acs.jpcc.7b11141. ISSN   1932-7447.
  5. ↑ Chueluecha, Nut; Kaewchada, Amaraporn; Jaree, Attasak (2017). "Enhancement of biodiesel synthesis using co-solvent in a packed-microchannel". Journal of Industrial and Engineering Chemistry. 51: 162–171. doi:10.1016/j.jiec.2017.02.028.
  6. ↑ Littell, M.J. Effect of a co-solvent feedstock on the synthesis of biodiesel via heterogeneous catalysis. Ph.D. Thesis, University of Tennessee. 2015.
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  9. 1 2 Canchi, Deepak R.; García, Angel E. (2013-04-01). "Cosolvent Effects on Protein Stability". Annual Review of Physical Chemistry. 64 (1): 273–293. Bibcode:2013ARPC...64..273C. doi:10.1146/annurev-physchem-040412-110156. ISSN   0066-426X. PMID   23298246.
  10. ↑ Huo, Feng; Liu, Zhiping; Wang, Wenchuan (2013-10-03). "Cosolvent or Antisolvent? A Molecular View of the Interface between Ionic Liquids and Cellulose upon Addition of Another Molecular Solvent". The Journal of Physical Chemistry B. 117 (39): 11780–11792. doi:10.1021/jp407480b. ISSN   1520-6106. PMID   24010550.
  11. ↑ van der Vegt, Nico F. A.; Nayar, Divya (2017-11-02). "The Hydrophobic Effect and the Role of Cosolvents". The Journal of Physical Chemistry B. 121 (43): 9986–9998. doi: 10.1021/acs.jpcb.7b06453 . ISSN   1520-6106. PMID   28921974.
  12. ↑ Breslow, Ronald; Groves, Kevin; Mayer, M. Uljana (1999-07-01). "Antihydrophobic Cosolvent Effects in Organic Displacement Reactions". Organic Letters. 1 (1): 117–120. doi:10.1021/ol990037s. ISSN   1523-7060. PMID   10822546.
  13. ↑ Seedher, N., Kanojia, M. Co-solvent solubilization of some poorly-soluble antidiabetic drugs. Pharm. Dev. Technol.2009, 14(2), 185-192. DOI: 10.1080/10837450802498894.
  14. ↑ Reyes-Rodríguez, Gabriel J.; Algera, Russell F.; Collum, David B. (2017-01-25). "Lithium Hexamethyldisilazide-Mediated Enolization of Acylated Oxazolidinones: Solvent, Cosolvent, and Isotope Effects on Competing Monomer- and Dimer-Based Pathways". Journal of the American Chemical Society. 139 (3): 1233–1244. doi:10.1021/jacs.6b11354. ISSN   0002-7863. PMC   6059651 . PMID   28080036.
  15. ↑ Wang, L., Hashidoko, Y., Hashimoto, M. Cosolvent-promoted o-benzylation with silver(I) oxide: synthesis of 1’-benzylated sucrose derivatives, mechanistic studies, and scope investigation. J. Org. Chem.2016, 81(11), 4464-4474. DOI: 10.1021/acs.joc.6b00144.
  16. ↑ Yang, R.L., Li, N., Zong, M.H. Using ionic liquid cosolvents to improve enzymatic synthesis of arylalkyl ß-D-glucopyranosides. J. Mol. Cat. B.2012, 74, 24-28. DOI: 10.1016/j.molcatb.2011.08.009.
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  18. ↑ Dugan, Pamela J.; Siegrist, Robert L.; Crimi, Michelle L. (2010-06-01). "Coupling surfactants/cosolvents with oxidants for enhanced DNAPL removal: A review". Remediation Journal. 20 (3): 27–49. doi:10.1002/rem.20249. ISSN   1520-6831.
  19. ↑ CLU-IN. In situ flushing. United States Environmental Protection Agency, 2017.
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  21. ↑ Guan, Guoqing; Sakurai, Nozomi; Kusakabe, Katsuki (2009). "Synthesis of biodiesel from sunflower oil at room temperature in the presence of various cosolvents". Chemical Engineering Journal. 146 (2): 302–306. doi:10.1016/j.cej.2008.10.009.
  22. ↑ Smith, Micholas Dean; Mostofian, Barmak; Cheng, Xiaolin; Petridis, Loukas; Cai, Charles M.; Wyman, Charles E.; Smith, Jeremy C. (2016-02-29). "Cosolvent pretreatment in cellulosic biofuel production: effect of tetrahydrofuran-water on lignin structure and dynamics". Green Chemistry. 18 (5): 1268–1277. doi:10.1039/c5gc01952d. ISSN   1463-9270. S2CID   14042376.
  23. ↑ Gale, Ella; Wirawan, Remigius H.; Silveira, Rodrigo L.; Pereira, Caroline S.; Johns, Marcus A.; Skaf, Munir S.; Scott, Janet L. (2016-11-07). "Directed Discovery of Greener Cosolvents: New Cosolvents for Use in Ionic Liquid Based Organic Electrolyte Solutions for Cellulose Dissolution". ACS Sustainable Chemistry & Engineering. 4 (11): 6200–6207. doi:10.1021/acssuschemeng.6b02020. hdl: 1983/a3721e56-521e-48e7-995a-250c0e89d1cb . S2CID   99082596.
  24. ↑ Li, A., Andren, A.W., Yalkowsky, S.H. Choosing a cosolvent: solubilization of naphthalene and cosolvent property. Environ. Toxicol. Chem. 1996, 15, 2233-2239.
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