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The classification and size order of polar solvents
Polar solvent
Polar solvent refers to the solvent containing polar groups such as hydroxyl or carbonyl, that is, the solvent molecule is a polar molecule. The polarity of the molecule is caused by the non coincidence of the centers of gravity of positive and negative charges in the molecule. The physical quantity used to characterize the polarity of molecules is dipole moment or dielectric constant. A large dielectric constant indicates a large polarity.
Chemical covalent bond can be divided into polar bond and nonpolar bond. Nonpolar bonds are common electron pairs that are not offset and appear in simple substances, such as O2; A polar bond is an offset of a common electron pair, such as HCl. When the offset is very strong, it seems that one side completely loses electrons and the other side gets electrons, which will become ionic bonds, such as NaCl.
The polarity of a compound depends on the functional groups and molecular structure contained in the molecule. The polarity of various compounds increases in the following order:
– CH3, – CH2 -, – CH =, – C III, – o-r, – S-R, – NO2, – n (R) 2, – ocor, – CHO, – COR, – NH2, – Oh, – COOH, – SO3H
Strong polar solvent
Methanol > ethanol > isopropanol
Medium polar solvent
Ethyl cyanide ＞ ethyl acetate ＞ chloroform ＞ dichloromethane ＞ ether ＞ toluene
Nonpolar solvent
Cyclohexane, petroleum ether, hexane, pentane
Polarity order of single solvent
Petroleum ether (small) → cyclohexane → carbon tetrachloride → trichloroethylene → benzene → toluene → dichloromethane → chloroform → ether → ethyl acetate → methyl acetate → acetone → n-propanol → methanol → pyridine → acetic acid (large)

Polar order of mixed solvents
Benzene: chloroform (1 + 1) → cyclohexane: ethyl acetate (8 + 2) → chloroform: acetone (95 + 5) → benzene: acetone (9 + 1) → benzene: ethyl acetate (8 + 2) → chloroform: ether (9 + 1) → benzene: methanol (95 + 5) → benzene: ether (6 + 4) → cyclohexane: ethyl acetate (1 + 1) → chloroform: ether (8 + 2) → chloroform: methanol (99 + 1) → benzene: methanol (9 + 1) → chloroform: acetone (85 + 15) → benzene: ether (4 + 6) → benzene: ethyl acetate (1 + 1) → chloroform: methanol (95 + 5) → chloroform: acetone (7 + 3) → benzene: ethyl acetate (3 + 7) → benzene: ether (1 + 9) → ether: methanol (99 + 1) → ethyl acetate: methanol (99 + 1) → benzene: acetone (1 + 1) → chloroform: methanol (9 + 1)
Note: benzene: methanol (95 + 5) means that 95 volumes of benzene are mixed with 5 volumes of methanol to form a mixed solvent
Common mixed solvents
Ethyl acetate / hexane: common concentration: 0 ~ 30%. However, it is sometimes difficult to completely remove the solvent on the rotary evaporator.
Ether / pentane system: it is commonly used when the concentration is 0 ~ 40%. It is very easy to remove on the rotary evaporator.
Ethanol / hexane or pentane: 5 ~ 30% is suitable for strong polar compounds.
Dichloromethane / hexane or pentane: 5 ~ 30%, which can be considered when other mixed solvents fail.
Comparison of functional group polarity
Alkanes (- CH3, – CH2 -) < olefins (- CH = ch -) < ethers (- O-CH3, – o-ch2 -) < nitro compounds (- NO2) < dimethylamine (ch3-n-ch3) < lipids (- coor) < ketones (- co -) < aldehydes (- CHO) < mercaptans (- SH) < amines (- NH2) < amides (- nhco-ch3) < alcohols (- OH) < phenols (- ar-oh) ＜ carboxylic acids (- COOH)
Common mobile phase polarity
Petroleum ether ＜ gasoline ＜ heptane ＜ hexane ＜ carbon disulfide ＜ xylene ＜ toluene ＜ chloropropane ＜ benzene ＜ bromoethane ＜ brominated benzene ＜ dichloroethane (DCM) < chloroform ＜ isopropyl ether ＜ nitromethane ＜ butyl acetate ＜ ether ＜ ethyl acetate ＜ n-pentane ＜ n-butanol ＜ phenol ＜ methylethanol ＜ TERT butanol ＜ tetrahydrofuran ＜ dioxane ＜ acetone ＜ ethanol ＜ acetonitrile ＜ methanol ＜ nitrogen dimethylformamide (DMF) ＜ water
Indicates the polarity of an organic solvent, which is related to its physicochemical properties, such as dielectric constant, dipole moment or refractive index. This representation regards all solvents as continuous acting media rather than discontinuous unity composed of various molecules, and does not take into account the special interaction between solvents and solutes.

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Under the environmental protection test, pentane is regarded as the best solution for cold storage panel?
On the aspect of environmental protection materials, the guidance catalogue of national industrial structure adjustment in 2011 clearly pointed out that the production and application of rigid polyurethane foam instead of HCFCs -141b (HCFC-141b) should be encouraged.
In 2014, HCFC-141b, the main foaming material of polyurethane, was granted a quota license for the first time. At the same time, the Ministry of environmental protection has also started the elimination of fluorine-containing foaming agents.
Then, the new regulations were issued. From January 1, 2019, except for the cold storage board industry, other ozone depleting industries could not use 141b, and the product was reduced by 30% per year in the cold storage board industry.
Professionals in the chemical industry pointed out that “using cyclopentane instead of HCFC-141b as foaming agent has undoubtedly become a mainstream scheme, and we expect 141b to be eliminated in less than three years.”
Similarly, many manufacturers use n-pentane as polyurethane foaming agent, which makes the foaming more uniform and the process more advantageous. Moreover, pentane has high safety requirements, and few enterprises can pass the safety assessment. These manufacturers spent 2 or 3 million on pentane technology reserve and based on environmental protection. With the support of the government, they passed safety assessment and environmental protection and based on environmental protection.
Experts in the field of foam blowing agents, David Zhang, Sales Manager of Junyuan Petroleum Group, also agreed: “at present, the best alternative is Pentane. Pentane must transform the foaming equipment, including foaming machine (gun head) and foaming fixture (heating system) The transformation of, intermediate tank, pre mixing system and storage tank needs to increase the ventilation and anti-static devices in the workshop, and the plant must use uninterruptible power supply, which will increase the burden of enterprises. ”