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A solvent (from the , "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for polar molecules, and the most common solvent used by living things; all the ions and proteins in a cell are dissolved in water within the cell.

Major uses of solvents are in paints, paint removers, inks, and dry cleaning. Specific uses for solvents are in (e.g. tetrachloroethylene); as (, ); as nail polish removers and solvents of glue (, , ); in spot removers (, petrol ether); in detergents (); and in (). Solvents find various applications in chemical, , oil, and gas industries, including in chemical syntheses and purification processes

Some solvents are highly toxic and emit volatile organic compounds. Biobased solvents are usually more expensive, but ideally less toxic and . Biogenic raw materials usable for solvent production are for example lignocellulose, and , but also waste and byproducts from other industries (such as , and ).


Solutions and solvation
When one substance is dissolved into another, a solution is formed.
(2025). 9780130266071, Prentice Hall. .
This is opposed to the situation when the compounds are like sand in water. In a solution, all of the ingredients are uniformly distributed at a molecular level and no residue remains. A solvent-solute mixture consists of a single phase with all solute molecules occurring as solvates (solvent-solute complexes), as opposed to separate continuous phases as in suspensions, emulsions and other types of non-solution mixtures. The ability of one compound to be dissolved in another is known as solubility; if this occurs in all proportions, it is called .

In addition to mixing, the substances in a solution interact with each other at the molecular level. When something is dissolved, molecules of the solvent arrange around of the solute. is involved and is increased making the solution more thermodynamically stable than the solute and solvent separately. This arrangement is mediated by the respective chemical properties of the solvent and solute, such as , dipole moment and .Lowery and Richardson, pp. 181–183 Solvation does not cause a chemical reaction or chemical configuration changes in the solute. However, solvation resembles a coordination complex formation reaction, often with considerable energetics (heat of solvation and entropy of solvation) and is thus far from a neutral process.

When one substance dissolves into another, a solution is formed. A solution is a homogeneous mixture consisting of a solute dissolved into a solvent. The solute is the substance that is being dissolved, while the solvent is the dissolving medium. Solutions can be formed with many different types and forms of solutes and solvents.


Solvent classifications
Solvents can be broadly classified into two categories: polar and non-polar. A special case is elemental mercury, whose solutions are known as amalgams; also, other exist which are liquid at room temperature.

Generally, the dielectric constant of the solvent provides a rough measure of a solvent's polarity. The strong polarity of water is indicated by its high dielectric constant of 88 (at 0 °C). Solvents with a dielectric constant of less than 15 are generally considered to be nonpolar.Lowery and Richardson, p. 177.

The dielectric constant measures the solvent's tendency to partly cancel the field strength of the electric field of a immersed in it. This reduction is then compared to the of the charged particle in a vacuum. Heuristically, the dielectric constant of a solvent can be thought of as its ability to reduce the solute's effective internal charge. Generally, the dielectric constant of a solvent is an acceptable predictor of the solvent's ability to dissolve common , such as salts.


Other polarity scales
Dielectric constants are not the only measure of polarity. Because solvents are used by chemists to carry out chemical reactions or observe chemical and biological phenomena, more specific measures of polarity are required. Most of these measures are sensitive to chemical structure.

The Grunwald–Winstein m Y scale measures polarity in terms of solvent influence on buildup of positive charge of a solute during a chemical reaction.

's Z scale measures polarity in terms of the influence of the solvent on -absorption maxima of a salt, usually or the pyridinium .Kosower, E.M. (1969) "An introduction to Physical Organic Chemistry" Wiley: New York, p. 293

Donor number and donor acceptor scale measures polarity in terms of how a solvent interacts with specific substances, like a strong or a strong Lewis base.

The Hildebrand parameter is the square root of cohesive energy density. It can be used with nonpolar compounds, but cannot accommodate complex chemistry.

Reichardt's dye, a dye that changes color in response to polarity, gives a scale of ET(30) values. ET is the transition energy between the ground state and the lowest excited state in kcal/mol, and (30) identifies the dye. Another, roughly correlated scale ( ET(33)) can be defined with .

Gregory's solvent ϸ parameter is a quantum chemically derived charge density parameter. This parameter seems to reproduce many of the experimental solvent parameters (especially the donor and acceptor numbers) using this charge decomposition analysis approach, with an electrostatic basis. The ϸ parameter was originally developed to quantify and explain the Hofmeister series by quantifying polyatomic ions and the monatomic ions in a united manner.

The polarity, dipole moment, polarizability and of a solvent determines what type of compounds it is able to dissolve and with what other solvents or liquid compounds it is . Generally, polar solvents dissolve polar compounds best and non-polar solvents dissolve non-polar compounds best; hence " like dissolves like". Strongly polar compounds like (e.g. ) or ionic compounds, like inorganic salts (e.g. ) dissolve only in very polar solvents like water, while strongly non-polar compounds like or dissolve only in very non-polar organic solvents like . Similarly, water and (or and vegetable oil) are not with each other and will quickly separate into two layers even after being shaken well.

Polarity can be separated to different contributions. For example, the Kamlet-Taft parameters are dipolarity/polarizability ( π*), hydrogen-bonding acidity ( α) and hydrogen-bonding basicity ( β). These can be calculated from the wavelength shifts of 3–6 different solvatochromic dyes in the solvent, usually including Reichardt's dye, and diethylnitroaniline. Another option, Hansen solubility parameters, separates the cohesive energy density into dispersion, polar, and hydrogen bonding contributions.


Polar protic and polar aprotic
Solvents with a dielectric constant (more accurately, relative static permittivity) greater than 15 (i.e. polar or polarizable) can be further divided into and aprotic. Protic solvents, such as , solvate (negatively charged solutes) strongly via . Polar aprotic solvents, such as or , tend to have large dipole moments (separation of partial positive and partial negative charges within the same molecule) and solvate positively charged species via their negative dipole.Lowery and Richardson, p. 183. In chemical reactions the use of polar protic solvents favors the SN1 reaction mechanism, while polar aprotic solvents favor the SN2 reaction mechanism. These polar solvents are capable of forming hydrogen bonds with water to dissolve in water whereas non-polar solvents are not capable of strong hydrogen bonds.


Physical properties

Properties table of common solvents
The solvents are grouped into , polar , and polar solvents, with each group ordered by increasing polarity. The of solvents which exceed those of water are bolded.

CH3CH2CH2CH2CH3 36.1 1.840.6260.00
CH3CH2CH2CH2CH2CH3 69 1.880.6550.00

C6H6
80.12.30.8790.00
H3C(CH2)5CH398.381.920.6800.0
C6H5-CH31112.380.8670.36
1,4-Dioxane
C4H8O2
101.12.31.0330.45
CH3CH2-O-CH2CH3 34.6 4.30.7131.15
(THF)
C4H8O
667.50.8861.75
CHCl3 61.2 4.811.4981.04
(DCM)CH2Cl2 39.6 9.11.32661.60

CH3-C(=O)-O-CH2-CH3
77.16.020.8941.78

CH3-C(=O)-CH3
56.1210.7862.88
Dimethylformamide (DMF)
H-C(=O)N(CH3)2
153380.9443.82
(MeCN)CH3-C≡N 82 37.50.7863.92
Dimethyl sulfoxide (DMSO)
CH3-S(=O)-CH3
18946.71.0923.96
CH3-NO2 100–103 35.871.13713.56
Propylene carbonateC4H6O3 240 64.01.2054.9

NH3 -33.3 170.674 (at -33.3 °C)1.42

H-C(=O)OH
100.8581.211.41
CH3CH2CH2CH2OH 117.7 180.8101.63
Isopropyl alcohol (IPA)
CH3-CH(-OH)-CH3
82.6180.7851.66
n-PropanolCH3CH2CH2OH 97 200.8031.68
CH3CH2OH 78.2 24.550.7891.69
CH3OH 64.7 330.7911.70

CH3-C(=O)OH
1186.21.0491.74
Water
H-O-H
100801.0001.85
The ACS Green Chemistry Institute maintains a tool for the selection of solvents based on a principal component analysis of solvent properties.


Hansen solubility parameter values
The Hansen solubility parameter (HSP) values
(2007). 9781420006834, CRC Press. .
are based on dispersion bonds (δD), (δP) and (δH). These contain information about the inter-molecular interactions with other solvents and also with polymers, pigments, , etc. This allows for rational formulations knowing, for example, that there is a good HSP match between a solvent and a polymer. Rational substitutions can also be made for "good" solvents (effective at dissolving the solute) that are "bad" (expensive or hazardous to health or the environment). The following table shows that the intuitions from "non-polar", "polar aprotic" and "polar protic" are put numerically – the "polar" molecules have higher levels of δP and the protic solvents have higher levels of δH. Because numerical values are used, comparisons can be made rationally by comparing numbers. For example, acetonitrile is much more polar than acetone but exhibits slightly less hydrogen bonding.

CH3-(CH2)3-CH314.50.00.0
CH3-(CH2)4-CH314.90.00.0
CH3-(CH2)5-CH315.30.00.0
/-(CH2)6-\16.80.00.2
C6H618.40.02.0
C6H5-CH318.01.42.0
C2H5-O-C2H514.52.94.6
CHCl317.83.15.7
1,4-Dioxane/-(CH2)2O(CH2)2O-\17.51.89.0
CH3-C(=O)-O-C2H515.85.37.2
/-(CH2)4-O-\16.85.78.0
CH2Cl217.07.37.1
CH3-C(=O)-CH315.510.47.0
CH3-C≡N15.318.06.1
DimethylformamideH-C(=O)-N(CH3)217.413.711.3
DimethylacetamideCH3-C(=O)-N(CH3)216.811.510.2
DimethylimidazolidinoneC5H10N2O18.010.59.7
C6H12N2O17.89.59.3
N-Methylpyrrolidone/-(CH2)3-N(CH3)-C(=O)-\18.012.37.2
Propylene carbonateC4H6O320.018.04.1
C5H5N19.08.85.9
/-(CH2)4-S(=O)2-\19.216.29.4
Dimethyl sulfoxideCH3-S(=O)-CH318.416.410.2
CH3-C(=O)-OH14.58.013.5
CH3-(CH2)3-OH16.05.715.8
(CH3)2-CH-OH15.86.116.4
n-PropanolCH3-(CH2)2-OH16.06.817.4
C2H5-OH15.88.819.4
CH3-OH14.712.322.3
HO-(CH2)2-OH17.011.026.0
HO-CH2-CH(OH)-CH2-OH17.412.129.3
H-C(=O)-OH14.610.014.0
WaterH-O-H15.516.042.3
If, for environmental or other reasons, a solvent or solvent blend is required to replace another of equivalent solvency, the substitution can be made on the basis of the Hansen solubility parameters of each. The values for mixtures are taken as the of the values for the neat solvents. This can be calculated by , a spreadsheet of values, or HSP software.
(2025). 9780955122026, Hansen-Solubility. .
A 1:1 mixture of and 1,4 dioxane has δD, δP and δH values of 17.8, 1.6 and 5.5, comparable to those of at 17.8, 3.1 and 5.7 respectively. Because of the health hazards associated with toluene itself, other mixtures of solvents may be found using a full HSP dataset.


Boiling point
ethylene dichloride83.48
pyridine115.25
methyl isobutyl ketone116.5
methylene chloride39.75
isooctane99.24
carbon disulfide46.3
carbon tetrachloride76.75
o-xylene144.42

The boiling point is an important property because it determines the speed of evaporation. Small amounts of low-boiling-point solvents like , , or acetone will evaporate in seconds at room temperature, while high-boiling-point solvents like water or dimethyl sulfoxide need higher temperatures, an air flow, or the application of for fast evaporation.

  • Low boilers: boiling point below 100 °C (boiling point of water)
  • Medium boilers: between 100 °C and 150 °C
  • High boilers: above 150 °C


Density
Most organic solvents have a lower than water, which means they are lighter than and will form a layer on top of water. Important exceptions are most of the solvents like or will sink to the bottom of a container, leaving water as the top layer. This is crucial to remember when partitioning compounds between solvents and water in a separatory funnel during chemical syntheses.

Often, is cited in place of density. Specific gravity is defined as the density of the solvent divided by the density of water at the same temperature. As such, specific gravity is a unitless value. It readily communicates whether a water-insoluble solvent will float (SG < 1.0) or sink (SG > 1.0) when mixed with water.

Pentane0.626
Petroleum ether0.656
Hexane0.659
Heptane0.684
Diethyl amine0.707
Diethyl ether0.713
Triethyl amine0.728
tert-Butyl methyl ether0.741
Cyclohexane0.779
tert-Butyl alcohol0.781
Isopropanol0.785
Acetonitrile0.786
Ethanol0.789
Acetone0.790
Methanol0.791
Methyl isobutyl ketone0.798
Isobutyl alcohol0.802
1-Propanol0.803
Methyl ethyl ketone0.805
2-Butanol0.808
Isoamyl alcohol0.809
1-Butanol0.810
Diethyl ketone0.814
1-Octanol0.826
p-Xylene0.861
m-Xylene0.864
Toluene0.867
Dimethoxyethane0.868
Benzene0.879
Butyl acetate0.882
1-Chlorobutane0.886
Tetrahydrofuran0.889
Ethyl acetate0.895
o-Xylene0.897
Hexamethylphosphorus triamide0.898
2-Ethoxyethyl ether0.909
N, N-Dimethylacetamide0.937
0.943
N, N-Dimethylformamide0.944
2-Methoxyethanol0.965
Pyridine0.982
Propanoic acid0.993
Water1.000
2-Methoxyethyl acetate1.009
Benzonitrile1.01
1-Methyl-2-pyrrolidinone1.028
Hexamethylphosphoramide1.03
1,4-Dioxane1.033
Acetic acid1.049
Acetic anhydride1.08
Dimethyl sulfoxide1.092
Chlorobenzene1.1066
Deuterium oxide1.107
Ethylene glycol1.115
Diethylene glycol1.118
Propylene carbonate1.21
Formic acid1.22
1,2-Dichloroethane1.245
Glycerin1.261
Carbon disulfide1.263
1,2-Dichlorobenzene1.306
Methylene chloride1.325
Nitromethane1.382
2,2,2-Trifluoroethanol1.393
Chloroform1.498
1,1,2-Trichlorotrifluoroethane1.575
Carbon tetrachloride1.594
Tetrachloroethylene1.623


Multicomponent solvents
Multicomponent solvents appeared after World War II in the , and continue to be used and produced in the post-Soviet states. These solvents may have one or more applications, but they are not universal preparations.


Solvents
50%, 18%, 12%, 10%, 10%.
toluene 50%, ethanol 15%, butanol 10%, butyl- or 10%, 8%, 7%
butyl- or amyl acetate 29.8%, ethyl acetate 21.2%, butanol 7.7%, toluene or 41.3%
butyl acetate 50%, ethanol 10%, butanol 20%, toluene 20%
ethyl cellosolve 30%, butanol 20%, 50%
ethyl cellosolve 20%, butanol 30%, xylene 50%
90%, butanol 10%
butyl acetate 20%, butanol 80%
toluene 62%, acetone 26%, butyl acetate 12%.
xylene 85%, acetone 15%.
toluene 60%, butyl acetate 30%, xylene 10%.
50%, toluene 50%.
solvent 50%, xylene 35%, acetone 15%.
toluene 50%, ethyl cellosolve 30%, acetone 20%.
toluene 34%, cyclohexanone 33%, acetone 33%.
butanol 60%, ethanol 40%.
xylene 90%, butyl acetate 10%.
ethanol 64%, ethylcellosolve 16%, toluene 10%, butanol 10%.
toluene 25%, xylene 25%, butyl acetate 18%, ethyl cellosolve 17%, butanol 15%.
toluene 60%, butyl acetate 30%, xylene 10%.
white spirit 70%, xylene 30%.
ethanol 75%, butanol 25%.
xylene 50%, acetone 20%, butanol 15%, ethanol 15%.
petroleum spirits 70%, ethanol 20%, acetone 10%.
petroleum spirits 50%, ethanol 20%, acetone 20%, ethyl cellosolve 10%.
petroleum spirits 50%, acetone 30%, ethanol 20%.
absolute alcohol (99.8%) 95%, ethyl acetate 5%


Thinners
butanol 50%, xylene 50%
butanol 95%, xylene 5%
xylene 90%, butanol 10%
ethanol 65%, butyl acetate 30%, ethyl acetate 5%.
cyclohexanone 50%, ethanol 50%.
xylene 60%, butyl acetate 20%, ethyl cellosolve 20%.
toluene 50%, butyl acetate (or amyl acetate) 18%, butanol 10%, ethanol 10%, ethyl acetate 9%, acetone 3%.


Safety

Fire
Most organic solvents are or highly flammable, depending on their volatility. Exceptions are some chlorinated solvents like and . Mixtures of solvent vapors and air can . Solvent vapors are heavier than air; they will sink to the bottom and can travel large distances nearly undiluted. Solvent vapors can also be found in supposedly empty drums and cans, posing a hazard; hence empty containers of volatile solvents should be stored open and upside down.

Both and have exceptionally low autoignition temperatures which increase greatly the fire risk associated with these solvents. The autoignition temperature of carbon disulfide is below 100 °C (212 °F), so objects such as pipes, , , and recently extinguished are able to ignite its vapors.

In addition some solvents, such as methanol, can burn with a very hot flame which can be nearly invisible under some lighting conditions. This can delay or prevent the timely recognition of a dangerous fire, until flames spread to other materials.


Explosive peroxide formation
like and (THF) can form highly explosive upon exposure to oxygen and light. THF is normally more likely to form such peroxides than diethyl ether. One of the most susceptible solvents is diisopropyl ether, but all ethers are considered to be potential peroxide sources.

The heteroatom () stabilizes the formation of a which is formed by the abstraction of a atom by another free radical. The carbon-centered free radical thus formed is able to react with an oxygen molecule to form a peroxide compound. The process of peroxide formation is greatly accelerated by exposure to even low levels of light, but can proceed slowly even in dark conditions.

Unless a is used which can destroy the peroxides, they will concentrate during , due to their higher . When sufficient peroxides have formed, they can form a , shock-sensitive solid at the mouth of a container or bottle. Minor mechanical disturbances, such as scraping the inside of a vessel, the dislodging of a deposit, or merely twisting the cap may provide sufficient energy for the peroxide to or explode violently.

Peroxide formation is not a significant problem when fresh solvents are used up quickly; they are more of a problem in laboratories which may take years to finish a single bottle. Low-volume users should acquire only small amounts of peroxide-prone solvents, and dispose of old solvents on a regular periodic schedule.

To avoid explosive peroxide formation, ethers should be stored in an airtight container, away from light, because both light and air can encourage peroxide formation.

A number of tests can be used to detect the presence of a peroxide in an ether; one is to use a combination of iron(II) sulfate and potassium thiocyanate. The peroxide is able to the Fe2+ ion to an Fe3+ ion, which then forms a deep-red coordination complex with the .

Peroxides may be removed by washing with acidic iron(II) sulfate, filtering through , or from /. Alumina degrades the peroxides but some could remain intact in it, therefore it must be disposed of properly. The advantage of using sodium/benzophenone is that and oxygen are removed as well.


Health effects
General health hazards associated with solvent exposure include toxicity to the nervous system, reproductive damage, liver and kidney damage, respiratory impairment, cancer, hearing loss, and .


Acute exposure
Many solvents can lead to a sudden loss of consciousness if in large amounts. Solvents like and have been used in medicine as , , and for a long time. Many solvents (e.g. from or solvent-based glues) are abused recreationally in glue sniffing, often with harmful long-term health effects such as or . Fraudulent substitution of 1,5-pentanediol by the psychoactive 1,4-butanediol by a subcontractor caused the product recall.

(grain alcohol) is a widely used and abused psychoactive drug. If ingested, the so-called "toxic alcohols" (other than ethanol) such as , 1-propanol, and metabolize into toxic aldehydes and acids, which cause potentially fatal metabolic acidosis. The commonly available alcohol solvent methanol can cause permanent blindness or death if ingested. The solvent 2-butoxyethanol, used in , can cause and metabolic acidosis.


Chronic exposure
Chronic solvent exposures are often caused by the inhalation of solvent vapors, or the ingestion of diluted solvents, repeated over the course of an extended period.

Some solvents can damage internal organs like the , the , the , or the . The cumulative brain effects of long-term or repeated exposure to some solvents is called chronic solvent-induced encephalopathy (CSE).

Chronic exposure to organic solvents in the work environment can produce a range of adverse neuropsychiatric effects. For example, occupational exposure to organic solvents has been associated with higher numbers of painters suffering from . Ethanol has a effect when taken in combination with many solvents; for instance, a combination of / and ethanol causes greater / than either substance alone.

Some organic solvents are known or suspected to be cataractogenic. A mixture of aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, , , and were found to greatly increase the risk of developing in the lens of the eye.


Environmental contamination
A major pathway of induced health effects arises from spills or leaks of solvents, especially chlorinated solvents, that reach the underlying soil. Since solvents readily migrate substantial distances, the creation of widespread soil contamination is not uncommon; this is particularly a health risk if are affected. can occur from sites with extensive subsurface solvent contamination.


See also
  • | Refurbishment |
  • Free energy of solvation
  • IARC
  • Solvents are often refluxed with an appropriate prior to distillation to remove water. This may be performed prior to a chemical synthesis where water may interfere with the intended reaction
  • List of water-miscible solvents
  • Occupational health
  • Partition coefficient (log P) is a measure of differential solubility of a compound in two solvents
  • Solvent systems exist outside the realm of ordinary organic solvents: Supercritical fluids, and deep eutectic solvents
  • Volatile Organic Compound


Bibliography


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