Green chemistry concept in polyethylene glycol applications
Green chemistry is a hotspot and frontier in the field of chemistry research. The development of green environmentally friendly chemical systems and environmentally friendly synthetic methods have attracted people's attention. One of the contents of green chemistry research is to replace traditional volatile organic solvents with clean and environmentally friendly reaction media. Some new water, supercritical fluids and ionic liquids have been developed. Among them, water is the most environmentally friendly solvent, but many organic substances are insoluble in water, and some chemical reactions strictly require a water-free environment, which greatly limits the application of water. Supercritical fluids have the advantage of being non-toxic, chemically inert, and non-volatile as a reaction medium, but supercritical fluids require high pressure environments and expensive equipment. The characteristics of low vapor pressure and good stability, as well as the characteristics of adjustable polarity in chemical reactions in recent years, have attracted attention. However, ionic liquids are expensive and the toxicity is unknown, and there are also insufficient applications. Polyethylene Glycol PEG is a polymer with a relative molecular mass of several hundred to several thousand. A relative molecular mass of less than 600 is a colorless viscous liquid with relative molecular mass.
More than 800 is a white solid, it is non-toxic, non-volatile, good thermal stability, recyclable, cheap and easy to obtain. It is also a hydrophilic polymer that is easily dissolved in water, methylene chloride, alcohol, toluene and acetone to form a mixed solvent with these solvents, the most common being the PEG-H2O system. However, it is not soluble in n-hexane, cyclohexane, isopropanol and diethyl ether, so these solvents can be used to precipitate PEG for separation purposes. Due to these characteristics, PEG is considered to be an environmentally friendly new type of green organic solvent. In the organic synthesis reaction, atomic economy is also the focus of attention. Molecularly immobilized catalysts are commonly used in macroporous resins. Such polymer-supported catalysts tend to occur in heterogeneous reactions due to poor solubility. The yield is low, the reaction time is long, and the kinetic behavior is different from that of single-phase systems. . PEG is a soluble polymer-supported catalyst, which allows the reaction to be carried out in a single-phase system. The separation and recovery of the catalyst is achieved by the "homogeneous reaction, two-phase separation" method. The advantages of PEG in organic synthesis and the traditional reaction solvent Compared with (DMF, DMSO, CH3CN, etc.), the use of PEG as a reaction medium can accelerate the reaction rate and increase the yield. Thanks to PEG, it is not only an effective reaction medium, but also a phase transfer catalyst for the reaction. The PEG-supported organic catalysts have high catalytic performance, and the supported chiral ligands give relatively high enantioselectivity to the main products of the chiral reaction. In addition, these supported catalysts can be used in multiple cycles. The response of PEG will continue to attract further exploration of PEG as a solvent.And the support of the catalyst, and the grafting functionalization with the ionic liquid with the advantages of stable and almost no volatility; and the application in combination with microwave technology and biochemistry, which helps to improve the yield of the organic reaction and optimize Reaction time; while PEG as the medium of reaction, it will be more inclined to recycle some expensive metal catalysts。