HPLC > Solvent Polarity Index
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In chemistry, a protic solvent is a solvent that has a hydrogen atom bound to an oxygen (as in a hydroxyl group), a nitrogen (as in an amine group) or a fluorine (as in hydrogen fluoride). In general terms, any solvent that contains a labileH+ is called a protic solvent. The molecules of such solvents readily donate protons (H+) to reagents. Conversely, aprotic solvents cannot donate hydrogen.
What's the chemical difference between DMF and DMSO? Based on polarity index, DMSO and DMF have values of 7.2 and 6.4 respectively. Hence, they have comparable polarity with DMSO slightly. Start studying ID solvent as polar protic or aprotic. Learn vocabulary, terms, and more with flashcards, games, and other study tools.
Polar protic solvents are often used to dissolve salts. In general, these solvents have high dielectric constants and high polarity.
Common characteristics of protic solvents :
Examples include water, most alcohols, formic acid, hydrogen fluoride, and ammonia. Polar protic solvents are favorable for SN1 reactions, while polar aprotic solvents are favorable for SN2 reactions.
Polar aprotic solvents are solvents that lack an acidic hydrogen. Consequently, they are not hydrogen bond donors. These solvents generally have intermediate dielectric constants and polarity. Although discouraging use of the term 'polar aprotic', IUPAC describes such solvents as having both high dielectric constants and high dipole moments, an example being acetonitrile. Other solvents meeting IUPAC's criteria include pyridine, ethyl acetate, DMF, HMPA, and DMSO.[1]
Common characteristics of aprotic solvents:
The criteria are relative and very qualitative. A range of acidities are recognized for aprotic solvents. Their ability to dissolve salts depends strongly on the nature of the salt.
Polar aprotic solvents are generally incompatible with strong bases, such as Grignard reagents or t-butyllithium. These reagents require ethers, not nitriles, amides, sulfoxides, etc. The strong base may even deprotonate them ( such as methyl anion as a base having a pKaH of 50, and sulfoxides have pKa of approximately 35.
The solvents are qualitatively grouped into non-polar, polar aprotic, and polar protic solvents, often ranked by dielectric constant.
Solvent | Chemical formula | Boiling point | Dielectric constant | Density | Dipole moment (D) |
---|---|---|---|---|---|
Non-polar solvents | |||||
Hexane | CH3-CH2-CH2-CH2-CH2-CH3 | 69 °C | 2.0 | 0.655 g/mL | 0.00 D |
benzene | C6H6 | 80 °C | 2.3 | 0.879 g/ml | 0.00 D |
toluene | C6H5CH3 | 111 °C | 2.4 | 0.867 g/mL | 0.36 D |
1,4-dioxane | (CH2CH2O)2 | 101 °C | 2.3 | 1.033 g/mL | 0.45 D |
chloroform | CHCl3 | 61 °C | 4.8 | 1.498 g/mL | 1.04 D |
diethyl ether | (CH3CH2)2O | 35 °C | 4.3 | 0.713 g/mL | 1.15 D |
Polar aprotic solvents | |||||
dichloromethane (DCM) | CH2Cl2 | 40 °C | 9.1 | 1.3266 g/mL | 1.60 D |
N-methylpyrrolidone | CH3NC(O)C3H6 | 202 °C | 32.2 | 1.028 g/mL | 4.1 D |
tetrahydrofuran (THF) | C4H8O | 66 °C | 7.5 | 0.886 g/mL | 1.75 D |
ethyl acetate (EtOAc) | CH3CO2CH2CH3 | 77 °C | 6.0 | 0.894 g/mL | 1.78 D |
acetone[note 1] | CH3C(O)CH3 | 56 °C | 21 | 0.786 g/mL | 2.88 D |
dimethylformamide (DMF) | HC(O)N(CH3)2 | 153 °C | 38 | 0.944 g/mL | 3.82 D |
acetonitrile (MeCN) | CH3CN | 82 °C | 37 | 0.786 g/mL | 3.92 D |
dimethyl sulfoxide (DMSO) | CH3S(O)CH3 | 189 °C | 47 | 1.092 g/mL | 3.96 D |
propylene carbonate (PC) | C4H6O3 | 242 °C | 64 | 1.205 g/mL | 4.90 D |
Polar protic solvents | |||||
formic acid | HCO2H | 101 °C | 58 | 1.21 g/mL | 1.41 D |
n-butanol | CH3CH2CH2CH2OH | 118 °C | 18 | 0.810 g/mL | 1.63 D |
isopropanol (IPA) | (CH3)2CH(OH) | 82 °C | 18 | 0.785 g/mL | 1.66 D |
nitromethane[note 2] | CH3NO2 | 101°C | 35.87 | 1.1371 g/mL | 3.56 D |
ethanol (EtOH) | CH3CH2OH | 79 °C | 24.55 | 0.789 g/mL | 1.69 D |
methanol (MeOH) | CH3OH | 65 °C | 33 | 0.791 g/mL | 1.70 D |
Acetic acid (AcOH) | CH3CO2H | 118 °C | 6.2 | 1.049 g/mL | 1.74 D |
Water | H2O | 100 °C | 80 | 1.000 g/mL | 1.85 D |
note 1 Acetone is subject to keto-enol tautomerism to the enol form (propen-2-ol) and can therefore exhibit a protic behavior. |
note 2 Although the hydrogen is bonded to the carbon, the carbon is next to a positively charged nitrogen and it is double bonded to an oxygen. |
Africaan's chemical press.2010.pg405