Is acetonitrile and water mutually soluble under any conditions?

Acetonitrile is a common organic solvent. Acetonitrile-water is similar to methanol-water in rP-LIQUID chromatography and is often used as a mobile phase. It is obvious that acetonitrile, like methanol, is a polar solvent. Acetonitrile is generally considered to be miscible with water under any conditions.

Many of the so-called conclusions will be improved with the deepening of scientific research. In this paper, the results of critical learning under this open environment are summarized, and the experimental conditions leading to the phase separation of acetonitrile-aqueous homogeneous solution are listed, as well as the related four extraction methods: acetonitrile salt-out extraction, acetonitrile saccharification extraction, acetonitrile low-temperature extraction and solvent-induced phase change extraction. In order to improve the knowledge system of acetonitrile properties, the scattered acetonitrile extraction methods in the literature were summarized and Shared, so as to apply these properties to our practical work.

1. several situations in which acetonitrile is not mutually soluble with water

1.1 Salt and acetonitrile-water system

The phase separation between acetonitrile and water can be seen by adding inorganic salt or organic salt in the homogeneous transparent solution of acetonitrile and water. Since the density of acetonitrile is lower than that of water, the upper phase is rich in acetonitrile (with a small amount of water) and the lower phase is poor in acetonitrile (mainly water).

This salt-induced acetonitrile phase separation is called acetonitrile salting out. The addition of salt has a strong hydration effect, and salt binds more water molecules, resulting in a significant decrease in the number of free water molecules that would otherwise interact with acetonitrile, resulting in phase separation. In this way, substances originally dissolved in the aqueous phase can be extracted into the acetonitrile-rich phase during the phase separation process. Such an extraction method is called acetonitrile salting out extraction.

The main salts used as initiators of phase separation include sodium chloride, calcium chloride, zinc sulfate, ammonium sulfate, magnesium sulfate, tetrabutyl ammonium perchlorate, etc. The type of salts will affect the extraction recovery. It should be pointed out that organic solvents that can produce phase separation under the induction of salt in a solution that is originally mutually soluble with water are not only limited to acetonitrile, but also have such properties as ethanol, isopropanol, acetone, etc. However, acetonitrile as the sample matrix can be well matched with the acetonitrile-based mobile phase analyzed by REVERsed-phase liquid chromatography, so acetonitrile salting out extraction method is particularly popular.

1.2 Sugar and acetonitrile-water system

In 2008, Wang of the University of Illinois reported a separation of acetonitrile-water phase caused by sugar. When monosaccharides (glucose, xylose, arabinose, or fructose) or disaccharides (sucrose or maltose) above a certain threshold are added to acetonitrile-aqueous solutions, significant phase separation is observed.

Polysaccharides do not have such properties of initiating phase separation. Other organic solvents commonly miscible with water (such as methanol, ethanol, n-propanol, isopropanol, acetone) do not have the properties of separation from water caused by sugar. The upper phase was rich acetonitrile phase and the lower phase was poor acetonitrile phase. The extraction method based on this phenomenon is called acetonitrile extraction.

1.3 Low temperature and acetonitrile-water system

In 1999 Yoshida and his colleagues reported a cryogenic separation of acetonitrile from water. Separation of acetonitrile and water was observed when the solution formed with water (volume ratio: 1:1) was placed at -20 °C for 20 min. The extraction method based on this phenomenon is called acetonitrile low temperature extraction.

Generally, the temperature of phase separation is controlled from -40°C to -40°C, because the melting point of acetonitrile is -45°C, and within the experimental temperature range, the acetonitrile rich phase is liquid, while the water-rich phase is mostly solid.

The experiment confirmed that most common organic solvents miscible with water at room temperature are not capable of phase separation with water at low temperature. Compared with the other two acetonitrile extraction methods, acetonitrile low-temperature extraction does not require the introduction of a third party phase initiator, so the system is relatively simple and will not pollute the subsequent separation and analysis work. In addition, low temperature extraction also avoids the chemical changes of temperature sensitive molecules caused by higher temperature, making the analysis results more reliable.

1.4 Hydrophobic solvent and acetonitrile-Water body

The addition of a hydrophobic and acetonitrile-soluble organic solvent (such as chloroform, dichloromethane, toluene) to the homogeneous acetonitrile-water system can induce the phase separation of acetonitrile-water system. The extraction method based on this is called solvon-induced phase-change extraction.

2, the conclusion

“Is acetonitrile and water mutually soluble under any conditions?” The question seems so simple that it has long been settled in existing textbooks. However, with the rapid development of information technology, it is more convenient for us to consult literature materials and update knowledge content with The Times.