Alcohol
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This article is about the class of chemical compounds. For beverages containing these compounds, see Alcoholic beverage. For other uses, see Alcohol (disambiguation).
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Ball-and-stick model of the hydroxyl (-OH) functional group in an alcohol molecule (R3COH). The three "R's" stand for carbon substituents or hydrogen atoms.[1]
The hydroxyl (-OH) functional group with bond angle.
In chemistry, an alcohol is an organic compound in which the hydroxyl functional group (-OH) is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms.[2]
An important class of alcohols are the simple acyclic alcohols, the general formula for which is CnH2n+1OH. Of these ethanol (C2H5OH) is the alcohol found in alcoholic beverages; in common speech the word alcohol refers to ethanol.
Other alcohols are usually described with a clarifying adjective, as in isopropyl alcohol (propan-2-ol) or wood alcohol (methyl alcohol, or methanol). 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 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.
In everyday life "alcohol" without qualification usually refers to ethanol, or a beverage based on ethanol (as in the term "alcohol abuse").
Contents [hide]
1 Occurrence in nature
1.1 Human metabolites
2 Toxicity
2.1 Treatment
3 Nomenclature
3.1 Systematic names
3.2 Common names
3.2.1 Alkyl chain variations in alcohols
3.2.2 Simple alcohols
3.2.3 Higher alcohols
3.3 History and etymology
4 Physical and chemical properties
5 Applications
5.1 Alcoholic beverages
5.2 Antifreeze
5.3 Antiseptics
5.4 Fuels
5.5 Preservative
5.6 Solvents
6 Production
6.1 Ziegler and Oxo Processes
6.2 Hydration reactions
6.3 Biological routes
6.4 Laboratory synthesis
6.4.1 Substitution
6.4.2 Reduction
6.4.3 Hydrolysis
7 Reactions
7.1 Deprotonation
7.2 Nucleophilic substitution
7.3 Dehydration
7.4 Esterification
7.5 Oxidation
8 See also
9 Notes
10 References
11 External links
Occurrence in nature
Alcohol has been found outside the Solar System. It can be found in low densities in star and planetary-system-forming regions of space.[3]
Human metabolites
See also: Ethanol § Human metabolite and Methanol § Human metabolite
Studies have found trace quantities of endogenous alcohols of healthy volunteers from exhaled breath with a mean of 450 ppb methanol[4] and 244 ppb ethanol.[5] Fruit consumption is a source of endogenous methanol metabolized from pectin; One kilos of apple produces a mean of to 4.5 gram methanol.[6] However, methanol should never consumed on its own as it is poisonous to the central nervous system, and may cause blindness, coma, and death. These studies are not guidelines that intentional external consumptions of alcohols are healthy in quantities.
Toxicity
Main article: Alcoholic beverage § Alcohols
Ball-and-stick model of tert-Amyl alcohol, which is 20 times more intoxicating than ethanol and like all tertiary alcohols, cannot be metabolised to toxic aldehydes.[7][8][9]
Most significant of the possible long-term effects of ethanol. In addition, in pregnant women, it causes fetal alcohol syndrome.
Alcoholic beverages have been consumed by humans since prehistoric times for a variety of hygienic, dietary, medicinal, religious, and recreational reasons.
Primary alcohols (R-CH2-OH) can be oxidized either to aldehydes (R-CHO) (e.g. acetaldehyde) 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.
Ethanol's toxicity is largely caused by its primary metabolite, acetaldehyde (systematically ethanal)[10][11] and secondary metabolite, acetic acid.[11][12][13][14] All primary alcohols are broken down into aldehydes then to carboxylic acids whose toxicities are similar to acetaldehyde and acetic acid. Metabolite toxicity is reduced in rats fed N-acetylcysteine[10][15] and thiamine.[16]
Tertiary alcohols cannot be metabolized into aldehydes[17] 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.[medical citation needed] This makes them more suitable for recreational[18][19] and medicinal[20] use as the chronic harms are lower. Ethchlorvynol and tert-Amyl alcohol are good examples of tertiary alcohols which saw both medicinal and recreational use.[21][22]
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.[23] 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.[24][25]
Methanol itself, while poisonous (LD50 5628 mg/kg, oral, rat[26]), 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.[27][28]
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.[23][29][30]
Nomenclature
Systematic names
In the IUPAC system, the name of the alkane chain loses the terminal "e" and adds "ol", e.g., "methanol" and "ethanol".[31] When necessary, the position of the hydroxyl group is indicated by a number between the alkane name and the "ol": propan-1-ol for CH3CH2CH2OH, propan-2-ol for CH3CH(OH)CH3. Sometimes, the position number is written before the IUPAC name: 1-propanol and 2-propanol. If a higher priority group is present (such as an aldehyde, ketone, or carboxylic acid), then it is necessary to use the prefix "hydroxy",[31] for example: 1-hydroxy-2-propanone (CH3COCH2OH).[32]
The IUPAC nomenclature is used in scientific publications and where precise identification of the substance is important. 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 1st or 2nd carbon on the propane chain.
Alcohols are classified into 0°, primary (1°), secondary (2°; also italic abbreviated sec- or just s-), and tertiary (3°; also italic abbreviated tert- or just t-), based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl (OH) functional group. The primary alcohols have general formulas RCH2OH; secondary ones are RR'CHOH; and tertiary ones are RR'R"COH, where R, R', and R" stand for alkyl groups. Methanol (C H3O H or CH4O) is a 0° alcohol. Some sources include methanol as a primary alcohol,[33][34] including the 1911 edition of the Encyclopædia Britannica,[35] but this interpretation is less common in modern texts.
Some examples of simple alcohols and how to name them
Common names
Chemical Formula IUPAC Name Common Name
Monohydric alcohols
CH3OH Methanol Wood alcohol
C2H5OH Ethanol Alcohol
C3H7OH Isopropyl alcohol Rubbing alcohol
C4H9OH Butyl alcohol Butanol
C5H11OH Pentanol Amyl alcohol
C16H33OH Hexadecan-1-ol Cetyl alcohol
Polyhydric alcohols
C2H4(OH)2 Ethane-1,2-diol Ethylene glycol
C3H6(OH)2 Propane-1,2-diol Propylene Glycol
C3H5(OH)3 Propane-1,2,3-triol Glycerol
C4H6(OH)4 Butane-1,2,3,4-tetraol Erythritol, Threitol
C5H7(OH)5 Pentane-1,2,3,4,5-pentol Xylitol
C6H8(OH)6 Hexane-1,2,3,4,5,6-hexol Mannitol, Sorbitol
C7H9(OH)7 Heptane-1,2,3,4,5,6,7-heptol Volemitol
Unsaturated aliphatic alcohols
C3H5OH Prop-2-ene-1-ol Allyl alcohol
C10H17OH 3,7-Dimethylocta-2,6-dien-1-ol Geraniol
C3H3OH Prop-2-in-1-ol Propargyl alcohol
Alicyclic alcohols
C6H6(OH)6 Cyclohexane-1,2,3,4,5,6-hexol Inositol
C10H19OH 2 - (2-propyl)-5-methyl-cyclohexane-1-ol Menthol
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.[36]
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.[37]
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.[citation needed]
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."[38]
Like ethanol, butanol can be produced by fermentation processes. (However, the fermenting agent is a bacterium, Clostridium acetobutylicum, that feeds on cellulose, not sugars like the Saccharomyces yeast that produces ethanol.) Saccharomyces yeast are known to produce these higher alcohols at temperatures above 75 °F (24 °C).
History and etymology
The word alcohol appears in English as a term for a very fine powder in the 16th century. It was borrowed from French, which took it from medical Latin.
Ultimately the word is from the Arabic كحل (al-kuḥl, "kohl, a powder used as an eyeliner"). Al- is the Arabic definitive 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 sulfide Sb2S3 (hence the essence or "spirit" of the substance), which was used as an antiseptic, eyeliner, and cosmetic (see kohl (cosmetics)). 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.
The 1657 Lexicon Chymicum by William Johnson glosses the word as antimonium sive stibium. 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 first alcohol (today known as ethyl alcohol) was discovered by the tenth-century Persian alchemist al-Razi. The current Arabic name for alcohol (ethanol) is الغول al-ġawl – properly meaning "spirit" or "demon" – with the sense "the thing that gives the wine its headiness" (in the Qur'an sura 37 verse 47).[39] The term ethanol was invented 1838, modeled on the German word äthyl (Liebig), which is in turn based on Greek aither ether and hyle "stuff."[40]