Protic solvent
Encyclopedia
In chemistry
a protic solvent is a solvent
that has a hydrogen
atom bound to an oxygen
(as in a hydroxyl
group) or a nitrogen
(as in an amine
group). In general terms, any molecular solvent that contains dissociable H+ is called a protic solvent. The molecules of such solvents can donate an H+ (proton). However, aprotic solvents cannot donate hydrogen.
Polar protic solvents are solvents that share ion dissolving power with aprotic solvents but have an acidic hydrogen. In general, these solvents have high dielectric constant
s and high polarity
.
Common characteristics of protic solvents :
Examples are water, methanol
, ethanol
, formic acid
, hydrogen fluoride
, and ammonia
.
Polar aprotic solvents are solvents that share ion dissolving power with protic solvents but lack an acidic hydrogen. These solvents generally have intermediate dielectric constant
s and polarity
.
Common characteristics of aprotic solvents:
Examples are dimethyl sulfoxide
, dimethylformamide
, dioxane and hexamethylphosphorotriamide, tetrahydrofuran
.
Polar protic solvents are favorable for SN1 reactions, while polar aprotic solvents are favorable for SN2 reactions.
Apart from solvent effects
, polar aprotic solvents may be essential for reactions that use strong bases, such as reactions involving Grignard reagents or n-butyllithium
. If a protic solvent were to be used, the reagent would be consumed by a side-reaction with the solvent.
An example of a dipolar aprotic solvent is methylpyrrolidone
.
. The properties of solvents that exceed those of water are bolded.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
a protic solvent is a solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
that has a hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
atom bound to an oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
(as in a hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
group) or a nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
(as in an amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
group). In general terms, any molecular solvent that contains dissociable H+ is called a protic solvent. The molecules of such solvents can donate an H+ (proton). However, aprotic solvents cannot donate hydrogen.
Polar protic solvents are solvents that share ion dissolving power with aprotic solvents but have an acidic hydrogen. In general, these solvents have high dielectric constant
Dielectric constant
The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...
s and high polarity
Chemical polarity
In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
.
Common characteristics of protic solvents :
- solvents display hydrogen bonding
- solvents have an acidic hydrogen (although they may be very weak acids)
- solvents are able to stabilize ionIonAn ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s- cations by unshared free electron pairs
- anions by hydrogen bonding
Examples are water, methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
, ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
, formic acid
Formic acid
Formic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early...
, hydrogen fluoride
Hydrogen fluoride
Hydrogen fluoride is a chemical compound with the formula HF. This colorless gas is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the...
, and ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
.
Polar aprotic solvents are solvents that share ion dissolving power with protic solvents but lack an acidic hydrogen. These solvents generally have intermediate dielectric constant
Dielectric constant
The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...
s and polarity
Chemical polarity
In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
.
Common characteristics of aprotic solvents:
- solvents do not display hydrogen bonding
- solvents do not have an acidic hydrogen
- solvents are able to stabilize ionIonAn ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s
Examples are dimethyl sulfoxide
Dimethyl sulfoxide
Dimethyl sulfoxide is an organosulfur compound with the formula 2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water...
, dimethylformamide
Dimethylformamide
Dimethylformamide is an organic compound with the formula 2NCH. Commonly abbreviated as DMF , this colourless liquid is miscible with water and the majority of organic liquids. DMF is a common solvent for chemical reactions...
, dioxane and hexamethylphosphorotriamide, tetrahydrofuran
Tetrahydrofuran
Tetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor...
.
Polar protic solvents are favorable for SN1 reactions, while polar aprotic solvents are favorable for SN2 reactions.
Apart from solvent effects
Solvent effects
In chemistry, Solvent effects is the group of effects that a solvent has on chemical reactivity. Solvents can have an effect on solubility, stability and reaction rates and choosing the appropriate solvent allows for thermodynamic and kinetic control over a chemical reaction.-Effects on...
, polar aprotic solvents may be essential for reactions that use strong bases, such as reactions involving Grignard reagents or n-butyllithium
N-Butyllithium
n-Butyllithium is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene...
. If a protic solvent were to be used, the reagent would be consumed by a side-reaction with the solvent.
An example of a dipolar aprotic solvent is methylpyrrolidone
Methylpyrrolidone
N-Methyl-2-pyrrolidone is a chemical compound with 5-membered lactam structure. It is a clear to slightly yellow liquid miscible with water and solvents like ethyl acetate, chloroform, benzene and lower alcohols or ketones. It also belongs to the class of dipolar aprotic solvents which includes...
.
Properties of common solvents
The solvents are grouped into non-polar, polar aprotic, and polar protic solvents and ordered by increasing polarity. The polarity is given as the dielectric constantDielectric constant
The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...
. The properties of solvents that exceed those of water are bolded.
| Solvent | Chemical Formula Chemical formula A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound.... |
Boiling point Boiling point The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.... |
Dielectric constant Dielectric constant The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum... |
Density Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight... |
Dipole moment Bond dipole moment The bond dipole moment uses the idea of electric dipole moment to measure the polarity of a chemical bond within a molecule. The bond dipole μ is given by:\mu = \delta \, d.... (D Debye The debye is a CGS unit of electric dipole momentElectric dipole moment is defined as charge times displacement: Historically the debye was defined as the dipole moment resulting from two charges of opposite sign but an equal magnitude of 10-10 statcoulomb10-10 statcoulomb is approximately 0.2083... ) |
|---|---|---|---|---|---|
| Non-Polar Solvents | |||||
| Hexane Hexane Hexane is a hydrocarbon with the chemical formula C6H14; that is, an alkane with six carbon atoms.The term may refer to any of four other structural isomers with that formula, or to a mixture of them. In the IUPAC nomenclature, however, hexane is the unbranched isomer ; the other four structures... |
CH3-CH2-CH2-CH2-CH2-CH3 | 69 °C | 2.0 | 0.655 g/ml | 0.00 D |
| Benzene Benzene Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6.... |
C6H6 | 80 °C | 2.3 | 0.879 g/ml | 0.00 D |
| Toluene Toluene Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic... |
C6H5-CH3 | 111 °C | 2.4 | 0.867 g/ml | 0.36 D |
| 1,4-Dioxane 1,4-Dioxane 1,4-Dioxane, often called dioxane because the other isomers of dioxane are rare, is a heterocyclic organic compound. It is a colorless liquid with a faint sweet odor similar to that of diethyl ether. It is classified as an ether. This colorless liquid is mainly used as a stabilizer for the solvent... |
/-CH2-CH2-O-CH2-CH2-O-\ | 101 °C | 2.3 | 1.033 g/ml | 0.45 D |
| Chloroform Chloroform Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous... |
CHCl3 | 61 °C | 4.8 | 1.498 g/ml | 1.04 D |
| Diethyl ether Diethyl ether Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor... |
CH3CH2-O-CH2-CH3 | 35 °C | 4.3 | 0.713 g/ml | 1.15 D |
| Polar Chemical polarity In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in... Aprotic Solvents |
|||||
| Dichloromethane Dichloromethane Dichloromethane is an organic compound with the formula CH2Cl2. This colorless, volatile liquid with a moderately sweet aroma is widely used as a solvent. Although it is not miscible with water, it is miscible with many organic solvents... (DCM) |
CH2Cl2 | 40 °C | 9.1 | 1.3266 g/ml | 1.60 D |
| Tetrahydrofuran Tetrahydrofuran Tetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor... (THF) |
/-CH2-CH2-O-CH2-CH2-\ | 66 °C | 7.5 | 0.886 g/ml | 1.75 D |
| Ethyl acetate Ethyl acetate Ethyl acetate is the organic compound with the formula CH3COOCH2CH3. This colorless liquid has a characteristic sweet smell and is used in glues, nail polish removers, and cigarettes... (EtOAc) |
CH3-C(=O)-O-CH2-CH3 | 77 °C | 6.0 | 0.894 g/ml | 1.78 D |
| Acetone Acetone Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory... |
CH3-C(=O)-CH3 | 56 °C | 21 | 0.786 g/ml | 2.88 D |
| Dimethylformamide Dimethylformamide Dimethylformamide is an organic compound with the formula 2NCH. Commonly abbreviated as DMF , this colourless liquid is miscible with water and the majority of organic liquids. DMF is a common solvent for chemical reactions... (DMF) |
H-C(=O)N(CH3)2 | 153 °C | 38 | 0.944 g/ml | 3.82 D |
| Acetonitrile Acetonitrile Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture... (MeCN) |
CH3-C≡N | 82 °C | 37 | 0.786 g/ml | 3.92 D |
| Dimethyl sulfoxide Dimethyl sulfoxide Dimethyl sulfoxide is an organosulfur compound with the formula 2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water... (DMSO) |
CH3-S(=O)-CH3 | 189 °C | 47 | 1.092 g/ml | 3.96 D |
| Polar Chemical polarity In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in... Protic Protic Protić is a Serbian surname. It may refer to:* Milorad B. Protić, an astronomer* Miodrag B. Protić, a painter* Stojan Protić, Yugoslav political figure... Solvents |
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| Formic acid Formic acid Formic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early... |
H-C(=O)OH | 101 °C | 58 | 1.21 g/ml | 1.41 D |
| n-Butanol N-Butanol n-Butanol or n-butyl alcohol or normal butanol is a primary alcohol with a 4-carbon structure and the molecular formula C4H9OH. Its isomers include isobutanol, 2-butanol, and tert-butanol... |
CH3-CH2-CH2-CH2-OH | 118 °C | 18 | 0.810 g/ml | 1.63 D |
| Isopropanol (IPA) | CH3-CH(-OH)-CH3 | 82 °C | 18 | 0.785 g/ml | 1.66 D |
| n-Propanol | CH3-CH2-CH2-OH | 97 °C | 20 | 0.803 g/ml | 1.68 D |
| Ethanol Ethanol Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a... (EtOH) |
CH3-CH2-OH | 79 °C | 30 | 0.789 g/ml | 1.69 D |
| Methanol Methanol Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol... (MeOH) |
CH3-OH | 65 °C | 33 | 0.791 g/ml | 1.70 D |
| Acetic acid Acetic acid Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell... (AcOH) |
CH3-C(=O)OH | 118 °C | 6.2 | 1.049 g/ml | 1.74 D |
| Water | H-O-H | 100 °C | 80 | 1.000 g/ml | 1.85 D |