Solvent 37431 225852047 2008-07-15T18:22:13Z 76.100.230.227 /* Solutions and solvation */ {{otheruses}} A '''solvent''' is a liquid or gas that dissolves a solid, liquid, or gaseous [[solute]], resulting in a [[solution]]. The most common solvent in everyday life is [[water]]. Most other commonly-used solvents are [[organic chemistry|organic]] ([[carbon]]-containing) chemicals. These are called ''organic solvents''. Solvents usually have a low [[boiling point]] and evaporate easily or can be removed by [[distillation]], leaving the dissolved substance behind. To distinguish between solutes and solvents, solvents are usually present in the greater amount. Solvents can also be used to [[solvent extraction|extract]] [[soluble]] compounds from a mixture, the most common example is the brewing of [[coffee]] or [[tea]] with hot water. Solvents are usually clear and colorless liquids and many have a characteristic [[odor]]. The [[concentration]] of a solution is the amount of compound that is dissolved in a certain volume of solvent. The ''[[solubility]]'' is the maximal amount of compound 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 paint thinners (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 in chemical syntheses. The use of inorganic solvents (other than water) is typically limited to research chemistry and some technological processes. == Solutions and solvation == When one substance is disolved into another, a solution is formed.<ref>Tinoco, Sauer, Wang & Puglisi, ''Physical Chemistry'' Prentice Hall 2002 p. 134</ref> This is opposed to a mixture where one compound is added to another and no bonds are formed, a way to think of mixtures and solutions is to compare a cup of water with sand mixed in versus a soda where all of the ingredients are uniform to create a new substance. No residue is left in the bottom. The mixing is referred to as miscibility, whereas the ability to disolve one compound into another is known as solubility. However, in addition to mixing, both substances in the solution can interact with each other in specific ways. Solvation describes these interactions. When something is dissolved, molecules of the solvent arrange itself around molecules of the solute. Heat is evolved and entropy is decreased making the solution more thermodynamically stable than the solute alone. This arranging is mediated by the respective chemical properties of the solvent and solute, such as hydrogen bonding, dipole moment and polarizability.<ref>Lowery, T.H. and Richardson, K.S., ''Mechanism and Theory in Organic Chemistry'', Harper Collins Publishers 3rd ed. 1987 p. 181-183 .</ref> == Solvent classifications == Solvents can be broadly classified into two categories ''polar''/''non-polar'' and ''protic''/''aprotic''. Generally, the [[dielectric constant]] of the solvent provides a rough measure of a solvent's polarity. Solvents with a dielectric constant of less than 15 are generally considered nonpolar.<ref>Lowery, T.H. and Richardson, K.S., ''Mechanism and Theory in Organic Chemistry'', Harper Collins Publishers 3rd ed. 1987 p. 177.</ref> 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.<ref>Lowery, T.H. and Richardson, K.S., ''Mechanism and Theory in Organic Chemistry'', Harper Collins Publishers 3rd ed. 1987 p. 177.</ref> 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 m'''Y''' scale'' measures polarity in terms of solvent influence on buildup of positive charge of a solute during a chemical reaction. ''Kosower's '''Z''' scale'' measures polarity in terms of the influence of the solvent on [[Ultraviolet|uv]] absorption maxima of a salt, usually [[pyridinium]] [[iodide]] or the pyridinium [[zwitterion]].<ref>Kosower, E.M. "An introduction to Physical Organic Chemistry" Wiley: New York, 1969 p. 293</ref> ''Donor number and donar acceptor scale'' measures polarity in terms of how a solvent interacts with specific substances, like a strong [[Lewis acid]] or a strong Lewis base.<ref>Gutmann, V. ''Coord. Chem. Rev.'' 1976, 18 225</ref> The polarity, dipole moment, polarizability and [[hydrogen bonding]] of a solvent determines what type of [[Chemical compound|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 chemistry|inorganic]] [[salt]]s (e.g. [[table salt]]) dissolve only in very polar solvents like water, while strongly non-polar compounds like [[oil]]s or [[wax]]es 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 a-protic=== Solvents with a [[relative static permittivity]] greater than 15 can be further divided into protic and aprotic. Protic solvents solvate [[anion]]s (negatively charged solutes) strongly via [[hydrogen bonding]]. Water is a protic solvent. Aprotic solvents such as [[acetone]] or [[dichloromethane]] tend to have large [[dipole moment]]s (separation of partial positive and partial negative charges within the same molecule) and solvate positively charged species via their negative dipole.<ref>Lowery, T.H. and Richardson, K.S., ''Mechanism and Theory in Organic Chemistry'', Harper Collins Publishers 3rd ed. 1987 p. 183.</ref> In [[chemical reaction]]s the use of polar protic solvents favors the [[SN1 reaction|S<sub>N</sub>1]] [[reaction mechanism]], while polar aprotic solvents favor the [[SN2 reaction|S<sub>N</sub>2]] reaction mechanism. == Solvent effects== === Boiling point === Another 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 ranges below 100 °C *Medium Boilers: Boiling ranges between 100 °C and 150 °C *High Boilers: Boiling ranges above 150 °C === Density === 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: many [[halogen]]ated 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 [[partition coefficient|partitioning]] compounds between solvents and water in a [[separatory funnel]] during chemical syntheses. ==Health and safety== === Fire === 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 [[explosion|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 temperature]]s which increase greatly the fire risk associated with these solvents. The autoignition temperature of carbon disulfide is below 100°C (212°F), so as a result objects such as [[steam]] pipes, [[light bulb]]s, [[hotplate]]s and recently extinguished [[bunsen burner]]s are able to ignite its vapours. === Peroxide formation === [[Ether]]s like [[diethyl ether]] and [[tetrahydrofuran]] (THF) can form highly explosive [[organic peroxide]]s upon exposure to oxygen and light, THF is normally more able to form such [[peroxide]]s 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 Fe<sup>2+</sup> ion to an Fe<sup>3+</sup> 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 [[distillation|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]] is removed as well. === Health effects === Many solvents can lead to a sudden loss of consciousness if [[inhalation|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]] 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 [[Volatile substance abuse|glue sniffing]], often with harmful long term health effects like [[neurotoxicity]] or [[cancer]]. [[Methanol]] can cause internal damage to the [[eye]]s, including permanent blindness. 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. Many chemists make a point of not drinking [[beer]]/[[wine]]/other alcoholic drinks if they know that they have been exposed to an aromatic solvent.{{Fact|date=February 2007}} === Environmental contamination === 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 [[aquifer]]s are affected. === Chronic health effects === Some solvents including chloroform and [[benzene]] (an ingredient of [[gasoline]]) are [[carcinogen]]ic. Many others can damage internal organs like the [[liver]], the [[kidneys]], or the [[brain]]. ==== General precautions==== * Avoiding being exposed to solvent vapors by working in a [[fume hood]], or with local exhaust ventilation (LEV), or in a well ventilated area * Keeping the storage containers tightly closed * Never using open flames near flammable solvents, use electrical heating instead * Never flush flammable solvents down the drain, read safety data sheets for proper disposal information * Avoiding the inhalation of solvent vapors * Avoiding contact of the solvent with the skin &mdash; many solvents are easily absorbed through the skin. They also tend to dry the skin and may cause sores and wounds. == 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 [[density]] of nonpolar solvents that are heavier than water is bolded. <!-- Here is a table of data; skip past it to edit the text. --> {| border="1" cellpadding="5" cellspacing="0" align="center" ! align="center" | Solvent ! align="center" | [[Chemical Formula]] ! align="center" | [[Boiling point]] ! align="center" | [[Dielectric constant]] ! align="center" | [[Density]]<!-- ### Non-Polar Solvents ### --> |- bgcolor="#DDDDDD" | align="center" colspan="5" | '''Non-Polar Solvents''' |- bgcolor="#DDDDDD" | align="center" | [[Hexane]] | align="center" | CH<sub>3</sub>-CH<sub>2</sub>-CH<sub>2</sub>-CH<sub>2</sub>-CH<sub>2</sub>-CH<sub>3</sub> | align="center" | 69 °C | align="center" | 2.0 | align="center" | 0.655 g/ml |- bgcolor="#DDDDDD" | align="center" | [[Benzene]] | align="center" | C<sub>6</sub>H<sub>6</sub> | align="center" | 80 °C | align="center" | 2.3 | align="center" | 0.879 g/ml |- bgcolor="#DDDDDD" | align="center" | [[Toluene]] | align="center" | C<sub>6</sub>H<sub>5</sub>-CH<sub>3</sub> | align="center" | 111 °C | align="center" | 2.4 | align="center" | 0.867 g/ml |- bgcolor="#DDDDDD" | align="center" | [[Diethyl ether]] | align="center" | CH<sub>3</sub>CH<sub>2</sub>-O-CH<sub>2</sub>-CH<sub>3</sub> | align="center" | 35 °C | align="center" | 4.3 | align="center" | 0.713 g/ml |- bgcolor="#DDDDDD" | align="center" | [[Chloroform]] | align="center" | CHCl<sub>3</sub> | align="center" | 61 °C | align="center" | 4.8 | align="center" | '''1.498 g/ml''' |- bgcolor="#DDDDDD" | align="center" | [[Ethyl acetate]] | align="center" | CH<sub>3</sub>-C(=O)-O-CH<sub>2</sub>-CH<sub>3</sub> | align="center" | 77 °C | align="center" | 6.0 | align="center" | 0.894 g/ml |- bgcolor="#FFCCFF" | align="center" colspan="5" | '''Polar Aprotic Solvents''' |- bgcolor="#FFCCFF" | align="center" | [[1,4-Dioxane]] | align="center" | <u>/-CH<sub>2</sub>-CH<sub>2</sub>-O-CH<sub>2</sub>-CH<sub>2</sub>-O-\</u> | align="center" | 101 °C | align="center" | 2.3 | align="center" | '''1.033 g/ml''' |- bgcolor="#FFCCFF" | align="center" | [[Tetrahydrofuran]] (THF) | align="center" | <u>/-CH<sub>2</sub>-CH<sub>2</sub>-O-CH<sub>2</sub>-CH<sub>2</sub>-\</u> | align="center" | 66 °C | align="center" | 7.5 | align="center" | 0.886 g/ml |- bgcolor="#FFCCFF" | align="center" | [[Dichloromethane]] (DCM) | align="center" | CH<sub>2</sub>Cl<sub>2</sub> | align="center" | 40 °C | align="center" | 9.1 | align="center" | '''1.326 g/ml''' <!-- ### Polar Aprotic Solvents ### --> |- bgcolor="#FFCCFF" | align="center" | [[Acetone]] | align="center" | CH<sub>3</sub>-C(=O)-CH<sub>3</sub> | align="center" | 56 °C | align="center" | 21 | align="center" | 0.786 g/ml |- bgcolor="#FFCCFF" | align="center" | [[Acetonitrile]] (MeCN) | align="center" | CH<sub>3</sub>-C≡N | align="center" | 82 °C | align="center" | 37 | align="center" | 0.786 g/ml |- bgcolor="#FFCCFF" | align="center" | [[Dimethylformamide]] (DMF) | align="center" | H-C(=O)N(CH<sub>3</sub>)<sub>2</sub> | align="center" | 153 °C | align="center" | 38 | align="center" | 0.944 g/ml |- bgcolor="#FFCCFF" | align="center" | [[Dimethyl sulfoxide]] (DMSO) | align="center" | CH<sub>3</sub>-S(=O)-CH<sub>3</sub> | align="center" | 189 °C | align="center" | 47 | align="center" | '''1.092 g/ml'''<!-- ### Polar Protic Solvents ### --> |- bgcolor="#FFCCCC" | align="center" colspan="5" | '''Polar Protic Solvents''' |- bgcolor="#FFCCCC" | align="center" | [[Acetic acid]] | align="center" | CH<sub>3</sub>-C(=O)OH | align="center" | 118 °C | align="center" | 6.2 | align="center" | '''1.049 g/ml''' |- bgcolor="#FFCCCC" | align="center" | [[Butanol|''n''-Butanol]] | align="center" | CH<sub>3</sub>-CH<sub>2</sub>-CH<sub>2</sub>-CH<sub>2</sub>-OH</sub> | align="center" | 118 °C | align="center" | 18 | align="center" | 0.810 g/ml |- bgcolor="#FFCCCC" | align="center" | [[Isopropanol]] (IPA) | align="center" | CH<sub>3</sub>-CH(-OH)-CH<sub>3</sub> | align="center" | 82 °C | align="center" | 18 | align="center" | 0.785 g/ml |- bgcolor="#FFCCCC" | align="center" | [[1-Propanol|''n''-Propanol]] | align="center" | CH<sub>3</sub>-CH<sub>2</sub>-CH<sub>2</sub>-OH</sub> | align="center" | 97 °C | align="center" | 20 | align="center" | 0.803 g/ml |- bgcolor="#FFCCCC" | align="center" | [[Ethanol]] | align="center" | CH<sub>3</sub>-CH<sub>2</sub>-OH</sub> | align="center" | 79 °C | align="center" | 24 | align="center" | 0.789 g/ml |- bgcolor="#FFCCCC" | align="center" | [[Methanol]] | align="center" | CH<sub>3</sub>-OH | align="center" | 65 °C | align="center" | 33 | align="center" | 0.791 g/ml |- bgcolor="#FFCCCC" | align="center" | [[Formic acid]] | align="center" | H-C(=O)OH | align="center" | 100 °C | align="center" | 58 | align="center" | '''1.21 g/ml''' |- bgcolor="#FFCCCC" | align="center" | [[Water (molecule)|Water]] | align="center" | H-O-H | align="center" | 100 °C | align="center" | 80 | align="center" | 1.000 g/ml</table> == See also == {{wiktionary|solvent}} * [[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 fluid]]s, [[ionic liquid]]s and [[deep eutectic solvent]]s * [[Water pollution]] * Solvents are often refluxed with an appropriate [[desiccant]] prior to distillation to remove water * [[Occupational health]] ==References== <references/> ==External links== * [http://www.speckanalytical.co.uk/products/Tips/bps.html Table] Properties of common organic solvents * [http://www.usm.maine.edu/~newton/Chy251_253/Lectures/Solvents/Solvents.html Table and text] O-Chem Lecture * [http://virtual.yosemite.cc.ca.us/smurov/orgsoltab.htm Tables] Properties and toxicities of organic solvents {{Reaction mechanisms}} [[Category:Soil contamination]] [[Category:Solvents| ]] [[Category:Solutions]] [[Category:Chemical compounds]] [[ar:مذيب]] [[bs:Otapalo]] [[ca:Dissolvent]] [[cs:Rozpouštědlo]] [[da:Opløsningsmiddel]] [[de:Lösungsmittel]] [[et:Lahusti]] [[es:Disolvente]] [[fa:حلال]] [[fr:Solvant]] [[ko:용매]] [[it:Solvente]] [[he:תמיסה#הממס]] [[lt:Tirpiklis]] [[nl:Oplosmiddel]] [[ja:溶媒]] [[no:Løsemiddel]] [[nn:Løysemiddel]] [[pl:Rozpuszczalnik]] [[pt:Solvente]] [[ro:Diluanţi]] [[ru:Растворители]] [[simple:Solvent]] [[sk:Rozpúšťadlo]] [[sr:Растварач]] [[fi:Liuotin]] [[sv:Lösningsmedel]] [[th:ตัวทำละลาย]] [[zh:溶剂]]