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Alcohol

of the hydroxyl (-OH) functional group in an alcohol molecule (R3COH). The three "R's" stand for carbon substituents or hydrogen atoms.]] In chemistry, an alcohol is any organic compound in which the hydroxyl functional group (– O H) is bound to a saturated carbon atom. The term alcohol originally referred to the primary alcohol ethanol (ethyl alcohol), which is used as a drug and is the main alcohol present in alcoholic beverages. The suffix -ol appears in the IUPAC chemical name of all substances where the hydroxyl group is the functional group with the highest priority; in substances where a higher priority group is present the prefix hydroxy- will appear in the International Union of Pure and Applied Chemistry (IUPAC) name. The suffix -ol in non-systematic names (such as paracetamol or cholesterol) also typically indicates that the substance includes a hydroxyl functional group and, so, can be termed an alcohol. But many substances, particularly sugars (examples glucose and sucrose) contain hydroxyl functional groups without using the suffix. An important class of alcohols, of which methanol and ethanol are the simplest members is the saturated straight chain alcohols, the general formula for which is CnH2n+1OH.

History

Rhazes (854 CE – 925 CE), was a Persian{{Citation | last =Robinson | first =Victor | year =1944 | date = | publication-date = | title =The story of medicine | edition = | series = | place = | publication-place =New York | publisher =New Home Library | volume = | pages = | isbn = | doi = | oclc = | url = }}{{Citation | last =Porter | first =Dorothy | publication-date =1999 | date = | year =2005 | title =Health, civilization, and the state: a history of public health from ancient to modern times | edition = | volume = | series = | publication-place = | place =New York | publisher=Routledge | pages = | page =25 | isbn =0-415-20036-9 | doi = | oclc = | url =| pmc =2560849}} polymath, physician, alchemist, and philosopher who discovered numerous compounds and chemicals including "alcohol" by developing several chemical instruments and methods of distillation.

Nomenclature

Etymology

The word "alcohol" is from the Arabic kohl (), a powder used as an eyeliner.http://www.etymonline.com/index.php?allowed_in_frame=0&search=alcohol Al- is the Arabic definite article, equivalent to the in English. Alcohol was originally used for the very fine powder produced by the sublimation of the natural mineral stibnite to form antimony trisulfide , hence the essence or "spirit" of this substance. It was used as an antiseptic, eyeliner, and cosmetic. The meaning of alcohol was extended to distilled substances in general, and then narrowed to ethanol, when "spirits" was a synonym for hard liquor. Bartholomew Traheron, in his 1543 translation of John of Vigo, introduces the word as a term used by "barbarous" ( Moorish) authors for "fine powder." Vigo wrote: "the barbarous auctours use alcohol, or (as I fynde it sometymes wryten) alcofoll, for moost fine poudre.""alcohol, n." OED Online. Oxford University Press, September 2016. Web. 15 November 2016. The 1657 Lexicon Chymicum, by William Johnson glosses the word as "antimonium sive stibium." Lexicon Chymicum By extension, the word came to refer to any fluid obtained by distillation, including "alcohol of wine," the distilled essence of wine. Libavius in Alchymia (1594) refers to "vini alcohol vel vinum alcalisatum". Johnson (1657) glosses alcohol vini as "quando omnis superfluitas vini a vino separatur, ita ut accensum ardeat donec totum consumatur, nihilque fæcum aut phlegmatis in fundo remaneat." The word's meaning became restricted to "spirit of wine" (the chemical known today as ethanol) in the 18th century and was extended to the class of substances so-called as "alcohols" in modern chemistry after 1850. The term ethanol was invented 1892, based on combining the word ethane with "ol" the last part of "alcohol".Proc. Chem. Soc. 8 July 1892, page 128 "As ol is indicative of an OH derivative, there seems no reason why the simple word acid should not connote carboxyl, and why al should not connote COH; the names ethanol ethanal and ethanoic acid or simply ethane acid would then stand for the OH, COH and COOH derivatives of ethane."

Systematic names

IUPAC nomenclature is used in scientific publications and where precise identification of the substance is important, especially in cases where the relative complexity of the molecule does not make such a systematic name unwieldy. In the IUPAC system, in naming simple alcohols, the name of the alkane chain loses the terminal "e" and adds "ol", e.g., as in "methanol" and "ethanol". When necessary, the position of the hydroxyl group is indicated by a number between the alkane name and the "ol": propan-1-ol for , propan-2-ol for . If a higher priority group is present (such as an aldehyde, ketone, or carboxylic acid), then the prefix "hydroxy" is used, e.g., as in 1-hydroxy-2-propanone ().Organic chemistry IUPAC nomenclature. Alcohols Rule C-201. In cases where the OH functional group is bonded to an sp2 carbon on an aromatic ring the molecule is known as a phenol, and is named using the IUPAC rules for naming phenols. Organic Chemistry Nomenclature Rule C-203: Phenols

Common names

In other less formal contexts, an alcohol is often called with the name of the corresponding alkyl group followed by the word "alcohol", e.g., methyl alcohol, ethyl alcohol. Propyl alcohol may be n-propyl alcohol or isopropyl alcohol, depending on whether the hydroxyl group is bonded to the end or middle carbon on the straight propane chain. As described under systematic naming, if another group on the molecule takes priority, the alcohol moiety is often indicated using the "hydroxy-" prefix. Alcohols are then classified into primary, secondary (sec-, s-), and tertiary (tert-, t-), based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl functional group. (The respective numeric shorthands 1°, 2°, and 3° are also sometimes used in informal settings.) The primary alcohols have general formulas RCH2OH. The simplest primary alcohol is methanol (CH3OH), for which R=H, and the next is ethanol, for which R=CH3, the methyl group. Secondary alcohols are those of the form RR'CHOH, the simplest of which is 2-propanol (R=R'=CH3). For the tertiary alcohols the general form is RR'R"COH. The simplest example is tert-butanol (2-methylpropan-2-ol), for which each of R, R', and R" is CH3. In these shorthands, R, R', and R" represent substituents, alkyl or other attached, generally organic groups.

Alkyl chain variations in alcohols

Short-chain alcohols have alkyl chains of 1–3 carbons. Medium-chain alcohols have alkyl chains of 4–7 carbons. Long-chain alcohols (also known as fatty alcohols) have alkyl chains of 8–21 carbons, and very long-chain alcohols have alkyl chains of 22 carbons or longer.

Simple alcohols

"Simple alcohols" appears to be a completely undefined term. However, simple alcohols are often referred to by common names derived by adding the word "alcohol" to the name of the appropriate alkyl group. For instance, a chain consisting of one carbon (a methyl group, CH3) with an OH group attached to the carbon is called "methyl alcohol" while a chain of two carbons (an ethyl group, CH2CH3) with an OH group connected to the CH2 is called "ethyl alcohol." For more complex alcohols, the IUPAC nomenclature must be used. Simple alcohols, in particular ethanol and methanol, possess denaturing and inert rendering properties, leading to their use as anti-microbial agents in medicine, pharmacy, and industry.

Higher alcohols

Encyclopædia Britannica states, "The higher alcohols—those containing 4 to 10 carbon atoms—are somewhat viscous, or oily, and they have heavier fruity odours. Some of the highly branched alcohols and many alcohols containing more than 12 carbon atoms are solids at room temperature." Like ethanol, butanol can be produced by fermentation processes. Saccharomyces yeast are known to produce these higher alcohols at temperatures above . The bacterium Clostridium acetobutylicum can feed on cellulose to produce butanol on an industrial scale.

Applications

(15+), in litres of pure ethanol]] Alcohol has a long history of several uses worldwide. It is found in alcoholic beverages sold to adults, as fuel, and also has many scientific, medical, and industrial uses. The term alcohol-free is often used to describe a product that does not contain alcohol.
  • Alcoholic beverages, typically containing 3–40% alcohol by volume, have been produced and consumed by humans since pre-historic times. Natural fermentation also produces trace amounts of other alcohols such as 2-methyl-2-butanol and γ-hydroxybutyric acid (GHB), which have psychoactive effects similar to alcohol when used as a drug.
  • Antifreeze commonly includes a 50% v/v (by volume) solution of ethylene glycol in water.
  • Medical: Ethanol can be used as an antiseptic to disinfect the skin before injections are given, often along with iodine. Ethanol-based soaps are becoming common in restaurants and are convenient because they do not require drying due to the volatility of the compound. Alcohol based gels have become common as hand sanitizers.
  • Alcohol fuel: Some alcohols, mainly ethanol and methanol, can be used as fuel. Fuel performance can be increased in forced induction internal combustion engines by injecting alcohol into the air intake after the turbocharger or supercharger has pressurized the air. This cools the pressurized air, providing a denser air charge, which allows for more fuel, and therefore more power.
  • Preservative: Alcohol is often used as a preservative for biological specimens in the fields of science and medicine.
  • Solvent: Hydroxyl groups (-OH), found in alcohols, are polar and therefore hydrophilic (water loving) but their carbon chain portion is non-polar which make them hydrophobic. The molecule increasingly becomes overall more nonpolar and therefore less soluble in the polar water as the carbon chain becomes longer. Methanol has the shortest carbon chain of all alcohols (one carbon atom) followed by ethanol (two carbon atoms.) Alcohols have applications in industry and science as reagents or solvents. Because of its relatively low toxicity compared with other alcohols and ability to dissolve non-polar substances, ethanol can be used as a solvent in medical drugs, perfumes, and vegetable essences such as vanilla. In organic synthesis, alcohols serve as versatile intermediates.

Toxicity

, which is 20 times more intoxicating than ethanol and like all tertiary alcohols, cannot be metabolised to toxic aldehydes.]] Ethanol is thought to cause harm partly as a result of direct damage to DNA caused by its metabolites. . In addition, in pregnant women it may cause fetal alcohol syndrome.]] Ethanol's toxicity is largely caused by its primary metabolite, acetaldehyde (systematically ethanal) and secondary metabolite, acetic acid. Many primary alcohols are metabolized into aldehydes then to carboxylic acids whose toxicities are similar to acetaldehyde and acetic acid. Metabolite toxicity is reduced in rats fed N-acetylcysteine and thiamine. Although the mechanism is unclear, a meta-analysis of 572 studies have shown increased cancer risk from consumption of ethanol.http://www.otago.ac.nz/news/news/otago617874.html Tertiary alcohols cannot be metabolized into aldehydes and as a result they cause no hangover or toxicity through this mechanism. Some secondary and tertiary alcohols are less poisonous than ethanol, because the liver is unable to metabolize them into toxic by-products. This makes them more suitable for pharmaceutical use as the chronic harms are lower. Ethchlorvynol and tert-amyl alcohol are tertiary alcohols which have seen both medicinal and recreational use. Other alcohols are substantially more poisonous than ethanol, partly because they take much longer to be metabolized and partly because their metabolism produces substances that are even more toxic. Methanol (wood alcohol), for instance, is oxidized to formaldehyde and then to the poisonous formic acid in the liver by alcohol dehydrogenase and formaldehyde dehydrogenase enzymes, respectively; accumulation of formic acid can lead to blindness or death. Likewise, poisoning due to other alcohols such as ethylene glycol or diethylene glycol are due to their metabolites, which are also produced by alcohol dehydrogenase. Methanol itself, while poisonous ( LD50 5628 mg/kg, oral, rat), has a much weaker sedative effect than ethanol. Isopropyl alcohol is oxidized to form acetone by alcohol dehydrogenase in the liver, but has occasionally been abused by alcoholics, leading to a range of adverse health effects.

Treatment

An effective treatment to prevent toxicity after methanol or ethylene glycol ingestion is to administer ethanol. Alcohol dehydrogenase has a higher affinity for ethanol, thus preventing methanol from binding and acting as a substrate. Any remaining methanol will then have time to be excreted through the kidneys.

Physical and chemical properties

Alcohols have an odor that is often described as "biting" and as "hanging" in the nasal passages. Ethanol has a slightly sweeter (or more fruit-like) odor than the other alcohols. In general, the hydroxyl group makes the alcohol molecule polar. Those groups can form hydrogen bonds to one another and to other compounds (except in certain large molecules where the hydroxyl is protected by steric hindrance of adjacent groups ). This hydrogen bonding means that alcohols can be used as protic solvents. Two opposing solubility trends in alcohols are: the tendency of the polar OH to promote solubility in water, and the tendency of the carbon chain to resist it. Thus, methanol, ethanol, and propanol are miscible in water because the hydroxyl group wins out over the short carbon chain. Butanol, with a four-carbon chain, is moderately soluble because of a balance between the two trends. Alcohols of five or more carbons such as pentanol and higher are effectively insoluble in water because of the hydrocarbon chain's dominance. All simple alcohols are miscible in organic solvents. Because of hydrogen bonding, alcohols tend to have higher boiling points than comparable hydrocarbons and ethers. The boiling point of the alcohol ethanol is 78.29 °C, compared to 69 °C for the hydrocarbon hexane (a common constituent of gasoline), and 34.6 °C for diethyl ether. Alcohols, like water, can show either acidic or basic properties at the -OH group. With a pKa of around 16-19, they are, in general, slightly weaker acids than water, but they are still able to react with strong bases such as sodium hydride or reactive metals such as sodium. The salts that result are called alkoxides, with the general formula RO− M+. Meanwhile, the oxygen atom has lone pairs of nonbonded electrons that render it weakly basic in the presence of strong acids such as sulfuric acid. For example, with methanol: Alcohols can be oxidised to give aldehydes, ketones or carboxylic acids, or they can be dehydrated to alkenes. They can react with carboxylic acids to form ester compounds, and they can (if activated first) undergo nucleophilic substitution reactions. The lone pairs of electrons on the oxygen of the hydroxyl group also makes alcohols nucleophiles. For more details, see the reactions of alcohols section below. As one moves from primary to secondary to tertiary alcohols with the same backbone, the hydrogen bond strength, the boiling point, and the acidity typically decrease.

Occurrence in nature

Ethanol occurs naturally as a byproduct of the metabolic process of yeast. As such, ethanol will be present in any yeast habitat. Ethanol can commonly be found in overripe fruit. Methanol is produced naturally in the anaerobic metabolism of many varieties of bacteria, and is commonly present in small amounts in the environment. Alcohols have been found outside the Solar System at low densities in star-forming regions of interstellar space. Giant cloud of space alcohol found labnews.co.uk/

Production

Ziegler and oxo processes

In the Ziegler process, linear alcohols are produced from ethylene and triethylaluminium followed by oxidation and hydrolysis.Jürgen Falbe, Helmut Bahrmann, Wolfgang Lipps, Dieter Mayer "Alcohols, Aliphatic" in Ullmann's Encyclopedia of Chemical Technology Wiley-VCH Verlag; Weinheim, 2002. An idealized synthesis of 1-octanol is shown: Al(C2H5)3 + 9 C2H4 → Al(C8H17)3 Al(C8H17)3 + 3 O + 3 H2O → 3 HOC8H17 + Al(OH)3 The process generates a range of alcohols that are separated by distillation. Many higher alcohols are produced by hydroformylation of alkenes followed by hydrogenation. When applied to a terminal alkene, as is common, one typically obtains a linear alcohol: RCH=CH2 + H2 + CO → RCH2CH2CHO RCH2CH2CHO + 3 H2 → RCH2CH2CH2OH Such processes give fatty alcohols, which are useful for detergents.

Hydration reactions

Low molecular weight alcohols of industrial importance are produced by the addition of water to alkenes. Ethanol, isopropanol, 2-butanol, and tert-butanol are produced by this general method. Two implementations are employed, the direct and indirect methods. The direct method avoids the formation of stable intermediates, typically using acid catalysts. In the indirect method, the alkene is converted to the sulfate ester, which is subsequently hydrolyzed. The direct hydration using ethylene ( ethylene hydration) or other alkenes from cracking of fractions of distilled crude oil. Hydration is also used industrially to produce the diol ethylene glycol from ethylene oxide.

Biological routes

Ethanol is obtained by fermentation using glucose produced from sugar from the hydrolysis of starch, in the presence of yeast and temperature of less than 37 °C to produce ethanol. For instance, such a process might proceed by the conversion of sucrose by the enzyme invertase into glucose and fructose, then the conversion of glucose by the enzyme complex zymase into ethanol (and carbon dioxide). Several of the benign bacteria in the intestine use fermentation as a form of anaerobic metabolism. This metabolic reaction produces ethanol as a waste product, just like aerobic respiration produces carbon dioxide and water. Thus, human bodies contain some quantity of alcohol endogenously produced by these bacteria. In rare cases, this can be sufficient to cause " auto-brewery syndrome" in which intoxicating quantities of alcohol are produced.

Substitution

Primary alkyl halides react with aqueous NaOH or KOH mainly to primary alcohols in nucleophilic aliphatic substitution. (Secondary and especially tertiary alkyl halides will give the elimination (alkene) product instead). Grignard reagents react with carbonyl groups to secondary and tertiary alcohols. Related reactions are the Barbier reaction and the Nozaki-Hiyama reaction.

Reduction

Aldehydes or ketones are reduced with sodium borohydride or lithium aluminium hydride (after an acidic workup). Another reduction by aluminiumisopropylates is the Meerwein-Ponndorf-Verley reduction. Noyori asymmetric hydrogenation is the asymmetric reduction of β-keto-esters.

Hydrolysis

Alkenes engage in an acid catalysed hydration reaction using concentrated sulfuric acid as a catalyst that gives usually secondary or tertiary alcohols. The hydroboration-oxidation and oxymercuration-reduction of alkenes are more reliable in organic synthesis. Alkenes react with NBS and water in halohydrin formation reaction. Amines can be converted to diazonium salts, which are then hydrolyzed. The formation of a secondary alcohol via reduction and hydration is shown:

Reactions

Deprotonation

Alcohols behave as weak acids, undergoing deprotonation, but strong bases are required. The deprotonation reaction to produce an alkoxide salt is performed with a strong base such as sodium hydride or sodium metal. 2 R-OH + 2 NaH → 2 R-O−Na+ + 2 H2 2 R-OH + 2 Na → 2 R-O−Na+ + H2 Water is similar in pKa to many alcohols, so with sodium hydroxide an equilibrium exists, which usually lies to the left: R-OH + NaOH ⇌ R-O−Na+ + H2O (equilibrium to the left) The acidity of alcohols is strongly affected by solvation. In the gas phase, alcohols are more acidic than is water.

Nucleophilic substitution

The OH group is not a good leaving group in nucleophilic substitution reactions, so neutral alcohols do not react in such reactions. However, if the oxygen is first protonated to give R−OH2+, the leaving group ( water) is much more stable, and the nucleophilic substitution can take place. For instance, tertiary alcohols react with hydrochloric acid to produce tertiary alkyl halides, where the hydroxyl group is replaced by a chlorine atom by unimolecular nucleophilic substitution. If primary or secondary alcohols are to be reacted with hydrochloric acid, an activator such as zinc chloride is needed. In alternative fashion, the conversion may be performed directly using thionyl chloride. 1 Alcohols may, likewise, be converted to alkyl bromides using hydrobromic acid or phosphorus tribromide, for example: 3 R-OH + PBr3 → 3 RBr + H3PO3 In the Barton-McCombie deoxygenation an alcohol is deoxygenated to an alkane with tributyltin hydride or a trimethylborane-water complex in a radical substitution reaction.

Dehydration

Alcohols are themselves nucleophilic, so R−OH2+ can react with ROH to produce ethers and water in a dehydration reaction, although this reaction is rarely used except in the manufacture of diethyl ether. More useful is the E1 elimination reaction of alcohols to produce alkenes. The reaction, in general, obeys Zaitsev's Rule, which states that the most stable (usually the most substituted) alkene is formed. Tertiary alcohols eliminate easily at just above room temperature, but primary alcohols require a higher temperature. This is a diagram of acid catalysed dehydration of ethanol to produce ethene: A more controlled elimination reaction is the Chugaev elimination with carbon disulfide and iodomethane.

Esterification

To form an ester from an alcohol and a carboxylic acid the reaction, known as Fischer esterification, is usually performed at reflux with a catalyst of concentrated sulfuric acid: R-OH + R'-COOH → R'-COOR + H2O In order to drive the equilibrium to the right and produce a good yield of ester, water is usually removed, either by an excess of H2SO4 or by using a Dean-Stark apparatus. Esters may also be prepared by reaction of the alcohol with an acid chloride in the presence of a base such as pyridine. Other types of ester are prepared in a similar manner for example, tosyl (tosylate) esters are made by reaction of the alcohol with p- toluenesulfonyl chloride in pyridine.

Oxidation

Primary alcohols (R-CH2-OH) can be oxidized either to aldehydes (R-CHO) or to carboxylic acids (R-CO2H), while the oxidation of secondary alcohols (R1R2CH-OH) normally terminates at the ketone (R1R2C=O) stage. Tertiary alcohols (R1R2R3C-OH) are resistant to oxidation. The direct oxidation of primary alcohols to carboxylic acids normally proceeds via the corresponding aldehyde, which is transformed via an aldehyde hydrate (R-CH(OH)2) by reaction with water before it can be further oxidized to the carboxylic acid. via aldehydes and aldehyde hydrates]] Reagents useful for the transformation of primary alcohols to aldehydes are normally also suitable for the oxidation of secondary alcohols to ketones. These include Collins reagent and Dess-Martin periodinane. The direct oxidation of primary alcohols to carboxylic acids can be carried out using potassium permanganate or the Jones reagent.

See also

Notes

References

External links

"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Alcohol, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Alcohol&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany