A solvent (from the Latin solvō, “I loosen, untie, I solve”) 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. Common uses for organic solvents are in dry cleaning (e.g., tetrachloroethylene), as a paint thinner (e.g., toluene, turpentine), as nail polish removers and glue solvents (acetone, methyl acetate, ethyl acetate), in spot removers (e.g., hexane, petrol ether), in detergents (citrus terpenes), in perfumes (ethanol), and nail polish, (part of how it stays on nails) and in chemical synthesis. The use of inorganic solvents (other than water) is typically limited to research chemistry and some technological processes.
In 2005, the worldwide market for solvents had a total volume of around 17.9 million tons, which led to a turnover of about €8,000,000,000.
- 1 Solutions and solvation
- 2 Solvent classifications
- 3 Physical properties of common solvents
- 4 Health and safety
- 5 See also
- 6 References
- 7 Bibliography
- 8 External links
Solutions and solvation
When one substance is dissolved into another, a solution is formed. This is opposed to the situation when the compounds are insoluble and one of them precipitate like sand in water. In solution, all of the ingredients are uniformly distributed at a molecular level and no residue remains. The mixing is referred to as miscibility, whereas the ability to dissolve one compound into another is known as solubility. However, in addition to mixing, both substances in the solution interact with each other. When something is dissolved, molecules of the solvent arrange themselves around molecules of the solute. Heat is involved and entropy is increased making the solution more thermodynamically stable than the solute alone. This arrangement is mediated by the respective chemical properties of the solvent and solute, such as hydrogen bonding, dipole moment and polarizability.
Solvents can be broadly classified into two categories: polar and non-polar. Generally, the dielectric constant of the solvent provides a rough measure of a solvent's polarity. The strong polarity of water is indicated, at 20 °C, by a dielectric constant of 80.10;. Solvents with a dielectric constant of less than 15 are generally considered to be nonpolar. Technically, the dielectric constant measures the solvent's ability to reduce the field strength of the electric field surrounding a charged particle immersed in it. This reduction is then compared to the field strength of the charged particle in a vacuum. In laymen's terms, dielectric constant of a solvent can be thought of as its ability to reduce the solute's internal charge.
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.
The Grunwald Winstein mY scale measures polarity in terms of solvent influence on buildup of positive charge of a solute during a chemical reaction.
Donor number and donor acceptor scale measures polarity in terms of how a solvent interacts with specific substances, like a strong Lewis acid or a strong Lewis base.
The polarity, dipole moment, polarizability and hydrogen bonding of a solvent determines what type of compounds it is able to dissolve and with what other solvents or liquid compounds it is miscible. As a rule of thumb, polar solvents dissolve polar compounds best and non-polar solvents dissolve non-polar compounds best: "like dissolves like". Strongly polar compounds like sugars (e.g., sucrose) or ionic compounds, like inorganic salts (e.g., table salt) dissolve only in very polar solvents like water, while strongly non-polar compounds like oils or waxes dissolve only in very non-polar organic solvents like hexane. Similarly, water and hexane (or vinegar and vegetable oil) are not miscible with each other and will quickly separate into two layers even after being shaken well.
Polar protic and polar aprotic
Solvents with a relative static permittivity greater than 15 can be further divided into protic and aprotic. Protic solvents solvate anions (negatively charged solutes) strongly via hydrogen bonding. Water is a protic solvent. Aprotic solvents such as acetone or dichloromethane 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. In chemical reactions the use of polar protic solvents favors the SN1 reaction mechanism, while polar aprotic solvents favor the SN2 reaction mechanism.
Physical properties of common solvents
Properties table 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 constant. The properties of solvents that exceed those of water are bolded.
Solvent Chemical formula Boiling point Dielectric constant Density Dipole moment Non-polar solvents Pentane CH3-CH2-CH2-CH2-CH3 36 °C 1.84 0.626 g/ml 0.00 D Cyclopentane C5H10 40 °C 1.97 0.751 g/ml 0.00 D Hexane CH3-CH2-CH2-CH2-CH2-CH3 69 °C 1.88 0.655 g/ml 0.00 D Cyclohexane C6H12 81 °C 2.02 0.779 g/ml 0.00 D Benzene C6H6 80 °C 2.3 0.879 g/ml 0.00 D Toluene C6H5-CH3 111 °C 2.38 0.867 g/ml 0.36 D 1,4-Dioxane /-CH2-CH2-O-CH2-CH2-O-\ 101 °C 2.3 1.033 g/ml 0.45 D Chloroform CHCl3 61 °C 4.81 1.498 g/ml 1.04 D Diethyl ether CH3CH2-O-CH2-CH3 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 Tetrahydrofuran (THF) /-CH2-CH2-O-CH2-CH2-\ 66 °C 7.5 0.886 g/ml 1.75 D Ethyl acetate CH3-C(=O)-O-CH2-CH3 77 °C 6.02 0.894 g/ml 1.78 D Acetone CH3-C(=O)-CH3 56 °C 21 0.786 g/ml 2.88 D Dimethylformamide (DMF) H-C(=O)N(CH3)2 153 °C 38 0.944 g/ml 3.82 D Acetonitrile (MeCN) CH3-C≡N 82 °C 37.5 0.786 g/ml 3.92 D Dimethyl sulfoxide (DMSO) CH3-S(=O)-CH3 189 °C 46.7 1.092 g/ml 3.96 D Polar protic solvents Formic acid H-C(=O)OH 101 °C 58 1.21 g/ml 1.41 D n-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 CH3-CH2-OH 79 °C 24.55 0.789 g/ml 1.69 D Methanol CH3-OH 65 °C 33 0.791 g/ml 1.70 D Acetic acid 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
There's another powerful way to look at these same solvents. By knowing their Hansen solubility parameter values (HSPiP), which are based on δD=dispersion bonds, δP=polar bonds and δH=hydrogen bonds, you know important things about their inter-molecular interactions with other solvents and also with polymers, pigments, nanoparticles etc. so you can do two things. First, you can create rational formulations knowing, for example, that there is a good HSP match between a solvent and a polymer. Second, you can make rational substitutions for "good" solvents (they dissolve things well) that are "bad" (for the environment, for health, for cost etc.). 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. So acetonitrile is much more polar than acetone but slightly less hydrogen bonding.
Solvent Chemical formula δD Dispersion δP Polar δH Hydrogen bonding Non-polar solvents Hexane CH3-CH2-CH2-CH2-CH2-CH3 14.9 0.0 0.0 Benzene C6H6 18.4 0.0 2.0 Toluene C6H5-CH3 18.0 1.4 2.0 Diethyl ether CH3CH2-O-CH2-CH3 14.5 2.9 4.6 Chloroform CHCl3 17.8 3.1 5.7 1,4-Dioxane /-CH2-CH2-O-CH2-CH2-O-\ 17.5 1.8 9.0 Polar aprotic solvents Ethyl acetate CH3-C(=O)-O-CH2-CH3 15.8 5.3 7.2 Tetrahydrofuran (THF) /-CH2-CH2-O-CH2-CH2-\ 16.8 5.7 8.0 Dichloromethane CH2Cl2 17.0 7.3 7.1 Acetone CH3-C(=O)-CH3 15.5 10.4 7.0 Acetonitrile (MeCN) CH3-C≡N 15.3 18.0 6.1 Dimethylformamide (DMF) H-C(=O)N(CH3)2 17.4 13.7 11.3 Dimethyl sulfoxide (DMSO) CH3-S(=O)-CH3 18.4 16.4 10.2 Polar protic solvents Acetic acid CH3-C(=O)OH 14.5 8.0 13.5 n-Butanol CH3-CH2-CH2-CH2-OH 16.0 5.7 15.8 Isopropanol CH3-CH(-OH)-CH3 15.8 6.1 16.4 n-Propanol CH3-CH2-CH2-OH 16.0 6.8 17.4 Ethanol CH3-CH2-OH 15.8 8.8 19.4 Methanol CH3-OH 14.7 12.3 22.3 Formic acid H-C(=O)OH 14.6 10.0 14.0 Water H-O-H 15.5 16.0 42.3
Consider a simple example of rational substitution. Suppose for environmental reasons we needed to replace the chlorinated solvent, chloroform, with a solvent (blend) of equal solvency using a mixture of two non-chlorinated solvents from this table. Via trial-and-error, a spreadsheet or some software such as HSPiP we find that a 50:50 mix of toluene and 1,4 dioxane is a close match. The δD of the mixture is the average of 18.0 and 17.5 = 17.8. The δP of the mixture is the average of 1.4 and 1.8 = 1.6 and the δH of the mixture is the average of 2.0 and 9.0 = 5.5. So the mixture is 17.8, 1.6, 5.5 compared to Chloroform at 17.8, 3.1, 5.7. Because Toluene itself has many health issues, other mixtures of solvents can be found using a full Hansen solubility parameter dataset.
Solvent Boiling point (°C) ethylene dichloride 83.48 pyridine 115.25 methyl isobutyl ketone 116.5 methylene chloride 39.75 isooctane 99.24 carbon disulfide 46.3 carbon tetrachloride 76.75 o-xylene 144.42
An important property of solvents is boiling point. This also determines the speed of evaporation. Small amounts of low-boiling solvents like diethyl ether, dichloromethane, or acetone will evaporate in seconds at room temperature, while high-boiling solvents like water or dimethyl sulfoxide need higher temperatures, an air flow, or the application of vacuum for fast evaporation.
- Low boilers: boiling temperature below 100 °C (boiling point of water)
- Medium boilers: between 100 °C and 150 °C
- High boilers: above 150 °C
Most organic solvents have a lower density than water, which means they are lighter and will form a separate layer on top of water. An important exception: most of the halogenated solvents like dichloromethane or chloroform will sink to the bottom of a container, leaving water as the top layer. This is important to remember when partitioning compounds between solvents and water in a separatory funnel during chemical syntheses.
Often, specific gravity 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.
Solvent Specific gravity Pentane 0.626 Petroleum ether 0.656 Hexane 0.659 Heptane 0.684 Diethyl amine 0.707 Diethyl ether 0.713 Triethyl amine 0.728 Tert-butyl methyl ether 0.741 Cyclohexane 0.779 Tert-butyl alcohol 0.781 Isopropanol 0.785 Acetonitrile 0.786 Ethanol 0.789 Acetone 0.790 Methanol 0.791 Methyl isobutyl ketone 0.798 Isobutyl alcohol 0.802 1-Propanol 0.803 Methyl ethyl ketone 0.805 2-Butanol 0.808 Isoamyl alcohol 0.809 1-Butanol 0.810 Diethyl ketone 0.814 1-Octanol 0.826 p-Xylene 0.861 m-Xylene 0.864 Toluene 0.867 Dimethoxyethane 0.868 Benzene 0.879 Butyl acetate 0.882 1-Chlorobutane 0.886 Tetrahydrofuran 0.889 Ethyl acetate 0.895 o-Xylene 0.897 Hexamethylphosphorus triamide 0.898 2-Ethoxyethyl ether 0.909 N,N-Dimethylacetamide 0.937 Diethylene glycol dimethyl ether 0.943 N,N-Dimethylformamide 0.944 2-Methoxyethanol 0.965 Pyridine 0.982 Propanoic acid 0.993 Water 1.000 2-Methoxyethyl acetate 1.009 Benzonitrile 1.01 1-Methyl-2-pyrrolidinone 1.028 Hexamethylphosphoramide 1.03 1,4-Dioxane 1.033 Acetic acid 1.049 Acetic anhydride 1.08 Dimethyl sulfoxide 1.092 Chlorobenzene 1.1066 Deuterium oxide 1.107 Ethylene glycol 1.115 Diethylene glycol 1.118 Propylene carbonate 1.21 Formic acid 1.22 1,2-Dichloroethane 1.245 Glycerin 1.261 Carbon disulfide 1.263 1,2-Dichlorobenzene 1.306 Methylene chloride 1.326 Nitromethane 1.382 2,2,2-Trifluoroethanol 1.393 Chloroform 1.498 1,1,2-Trichlorotrifluoroethane 1.575 Carbon tetrachloride 1.594 Tetrachloroethylene 1.623
Health and safety
Most organic solvents are flammable or highly flammable, depending on their volatility. Exceptions are some chlorinated solvents like dichloromethane and chloroform. Mixtures of solvent vapors and air can explode. 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 flash fire hazard; hence empty containers of volatile solvents should be stored open and upside down.
Both diethyl ether and carbon disulfide 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 steam pipes, light bulbs, hotplates and recently extinguished bunsen burners are able to ignite its vapours.
Explosive peroxide formation
Ethers like diethyl ether and tetrahydrofuran (THF) can form highly explosive organic peroxides upon exposure to oxygen and light, THF is normally more able to form such peroxides than diethyl ether. One of the most susceptible solvents is diisopropyl ether.
The heteroatom (oxygen) stabilizes the formation of a free radical which is formed by the abstraction of a hydrogen atom by another free radical. The carbon centred free radical thus formed is able to react with an oxygen molecule to form a peroxide compound. A range of tests can be used to detect the presence of a peroxide in an ether; one is to use a combination of iron sulfate and potassium thiocyanate. The peroxide is able to oxidize the Fe2+ ion to an Fe3+ ion which then form a deep red coordination complex with the thiocyanate. In extreme cases the peroxides can form crystalline solids within the vessel of the ether.
Unless the desiccant used can destroy the peroxides, they will concentrate during distillation due to their higher boiling point. When sufficient peroxides have formed, they can form a crystalline and shock sensitive solid precipitate. When this solid is formed at the mouth of the bottle, turning the cap may provide sufficient energy for the peroxide to detonate. Peroxide formation is not a significant problem when solvents are used up quickly; they are more of a problem for laboratories which take years to finish a single bottle. Ethers have to be stored in the dark in closed canisters in the presence of stabilizers like butylated hydroxytoluene (BHT) or over sodium hydroxide.
Peroxides may be removed by washing with acidic iron(II) sulfate, filtering through alumina, or distilling from sodium/benzophenone. Alumina does not destroy the peroxides; it merely traps them. The advantage of using sodium/benzophenone is that moisture and oxygen are removed as well.
Many solvents can lead to a sudden loss of consciousness if inhaled in large amounts. Solvents like diethyl ether and chloroform have been used in medicine as anesthetics, sedatives, and hypnotics for a long time. Ethanol (grain alcohol) is a widely used and abused psychoactive drug. Diethyl ether, chloroform, and many other solvents (e.g., from gasoline or glues) are used recreationally in glue sniffing, often with harmful long term health effects like neurotoxicity or cancer. Methanol can cause permanent blindness and death. It is also dangerous because it burns with an invisible flame.
It is interesting to note that ethanol has a synergistic effect when taken in combination with many solvents. For instance a combination of toluene/benzene and ethanol causes greater nausea/vomiting than either substance alone.
Chronic exposure to organic solvents in the work environment can produce a range of adverse neuropsychiatric effects and, occupational exposure to organic solvents has been associated with higher numbers of painters regularly exposed to high levels of organic solvents suffering from alcoholism.
- Avoid being exposed to solvent vapors by working in a fume hood, or with local exhaust ventilation (LEV), or in a well ventilated area
- Keep the storage containers tightly closed
- Never use open flames near flammable solvents; use electrical heating instead
- Never flush flammable solvents down the drain; read safety data sheets for proper disposal information
- Avoid the inhalation of solvent vapors
- Avoid contact of the solvent with the skin — many solvents are easily absorbed through the skin. They also tend to dry the skin and may cause sores and wounds.
A major pathway to induce health effects arises from spills or leaks of solvents that reach the underlying soil. Since solvents readily migrate substantial distances, the creation of widespread soil contamination is not uncommon; there may be about 5000 sites worldwide that have major subsurface solvent contamination; this is particularly a health risk if aquifers are affected.
- 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, ionic liquids and deep eutectic solvents
- Water model
- Water pollution
- Solvents are often refluxed with an appropriate desiccant prior to distillation to remove water. This may be performed prior to a chemical synthesis where water may interfere with the intended reaction.
- Occupational health
- Free energy of solvation
- ^ Tinoco, Sauer, Wang & Puglisi, Physical Chemistry Prentice Hall 2002 p. 134 ISBN 0130266078
- ^ Lowery and Richardson, pp. 181-183
- ^ a b Lowery and Richardson, p. 177.
- ^ Kosower, E.M. "An introduction to Physical Organic Chemistry" Wiley: New York, 1969 p. 293
- ^ Gutmann, V. (1976). "Solvent effects on the reactivities of organometallic compounds". Coord. Chem. Rev. 18 (2): 225. doi:10.1016/S0010-8545(00)82045-7.
- ^ Lowery and Richardson, p. 183.
- ^ a b Solvent Properties - Boiling Point
- ^ Dielectric Constant
- ^ a b Steven Abbott and Charles M. Hansen Hansen Solubility Parameters in Practice, ISBN 0955122023 (2008)
- ^ a b Charles M. Hansen Hansen solubility parameters: a user's handbook CRC Press, 2007, ISBN 0849372488
- ^ Selected solvent properties - Specific Gravity
- ^ U.S. Department of Labor > Occupational Safety & Health Administration > Solvents Page current as of: 29 August 2007
- ^ Lundberg I, Gustavsson A, Högberg M, Nise G (June 1992). "Diagnoses of alcohol abuse and other neuropsychiatric disorders among house painters compared with house carpenters". Br J Ind Med 49 (6): 409–15. PMC 1012122. PMID 1606027. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1012122.
- Lowery, T.H. and Richardson, K.S., Mechanism and Theory in Organic Chemistry, Harper Collins Publishers 3rd ed. 1987 ISBN 0063640449
-  Solvents in Europe.
- Table and text O-Chem Lecture
- Tables Properties and toxicities of organic solvents
Basic reaction mechanisms Nucleophilic substitution Elimination reaction Related topics Chemical kinetics Articles related to solutions Solution Concentration
and related quantities
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