Dictionary
a liquor or brew containing alcohol as the active agent "alcohol (or drink) ruined him" any of a series of volatile hydroxyl compounds that are made from hydrocarbons by distillation
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Wikipedia
In general usage, alcohol (from Arabic language Arabic ''al-ghawl'' !الغو&# 1604;)? refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see ''alcoholic beverage''). This sense underlies the term alcoholism (addiction to alcohol). Other forms of alcohol are usually described with a clarifying adjective, as in ''isopropyl alcohol'' or by the suffix ''-ol'', as in ''isopropanol''.In chemistry, alcohol is a more general term, applied to any organic compound in which a hydroxyl group (''-oxygenOhydrogenH'') is bound to a carbon atom, which in turn is bound to other hydrogen and/or carbon atoms. The general formula for a simple acyclic alcohol is !CnH< sub>2n+1OH? .As a Medicationdrug, common alcohol (ethanol) is known to have a depressantdepressing effect that decreases the responses of the central nervous system.
Structure - The functional group of an alcohol is a hydroxyl group bonded to an sp3 hybridized carbon. It can therefore be regarded as a derivative of water_(molecule)water, with an alkyl group replacing one of the hydrogens. If an aryl group is present rather than an alkyl, the compound is generally called a phenol rather than an alcohol. The oxygen in an alcohol has a bond angle of around 109° (c.f. 104.5° in water), and two nonbonded electron pairs. The O-H bond in methanol (CH3OH) is around 96 picometres long.
Primary, secondary, and tertiary alcohols - There are three major subsets of alcohols- 'primary' (1°), 'secondary' (2°) and 'tertiary' (3°), based upon the number of carbons the C-OH carbon (shown in red) is bonded to. Methanol is the simplest 'primary' alcohol. The simplest secondary alcohol is isopropanol (propan-2-ol), and a simple tertiary alcohol is ''tert''-butanol (2-methylpropan-2-ol).
Methanol & ethanol - The simplest and most commonly used alcohols are methanol and ethanol (common names methyl alcohol and ethyl alcohol, respectively), which have the structures shown above.Methanol was formerly obtained by the distillation of wood, and was called "wood alcohol". It is now a cheap commodity chemical produced by the high pressure reaction of carbon monoxide with hydrogen. In common usage, "alcohol" often refers simply to ethanol or "grain alcohol". Methylated spirits ("Meths"), also called "surgical spirits", is a form of ethanol rendered undrinkable by the addition of methanol. Aside from its major use in alcoholic beverages, ethanol is also used (though highly controlled) as an industrial solvent and raw material.
Uses - Alcohols are in wide use in industry and science as reagents, solvents, and alcohol as a fuelfuels. Ethanol and methanol can be made to burn more cleanly than gasoline or diesel. Because of its low toxicity and ability to dissolve non-polar substances, ethanol is often used as a solvent in medical drugs, perfumes, and vegetable essences such as vanilla. In organic synthesis, alcohols frequently serve as versatile intermediates. Ethanol is also commonly used in beverages after fermentation to promote flavor or induce a euphoric intoxication commonly known as "drunkenness" or "being drunk".
Sources - Many alcohols can be created by fermentation of fruits or cerealgrains with yeast, but only ethanol is commercially produced this way, chiefly for alcohol as a fuelfuel and alcoholic beveragedrink. Other alcohols are generally produced by synthetic routes from natural gas, petroleum, or coal feed stocks, for example via acid catalyzed hydration reactionhydration of alkenes. For more details see #Chemistry of alcoholsChemistry of alcohols
Nomenclature -
Systematic names - In the IUPAC nomenclatureIUPAC system, the name of the alkane chain loses the terminal "e" and adds "ol", e.g. "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 !CH3CH&l t;sub>2CH2OH,? Isopropyl alcoholpropan-2-ol for !CH3CH(O H)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", for example: 1-hydroxy-2-propanol !(CH3COC H2OH).? Some examples of simple alcohols and how to name them: Common names for alcohols usually take the name of the corresponding alkyl group and add the word "alcohol", e.g. methyl alcohol, ethyl alcohol or Butyl''tert''-butyl 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. Isopropyl alcohol is also occasionally called ''sec''-propyl alcohol.As mentioned above alcohols are classified as primary (1°), secondary (2°) or tertiary (3°), and common names often indicate this in the alkyl group prefix. For example !(CH3)&l t;sub>3COH? is a tertiary alcohol is commonly known as ''tert''-butyl alcohol. This would be named 2-methylpropan-2-ol under IUPAC rules, indicating a propane chain with methyl and hydroxyl groups both attached to the middle (#2) carbon.An alcohol with two hydroxyl groups is commonly called a "glycol", e.g. !HO-CH2- CH2-OH? is ethylene glycol. The IUPAC name is ethane-1,2-diol, "diol" indicating two hydroxyl groups, and 1,2 indicating their bonding positions. Geminal glycols (with the two hydroxyls on the same carbon atom), such as ethane-1,1-diol, are generally unstable. For three or four groups, "triol" and "tetraol" are used.
Etymology - The word "alcohol" almost certainly comes from the Arabic language (the "al-" prefix being the Arabic definite article); however, the precise origin is unclear. It was introduced into Europe, together with the art of distillation and the substance itself, around the 12th century by various European authors who translated and popularized the discoveries of Islamic alchemyalchemists. A popular theory, found in many dictionaries, is that it comes from !الكح&# 1604;? = ''ALKHL'' = ''al-kuhul'', originally the name of very finely powdered antimony sulfide antimony!Sb2sulf urS3 used as an antiseptic and eyeliner. The powder is prepared by sublimation (physics)sublimation of the natural mineral stibnite in a closed vessel. According to this theory, the meaning of ''alkuhul'' would have been first extended to distilled substances in general, and then narrowed to ethanol. This conjectured etymology has been circulating in England since 1672 at least (Oxford English DictionaryOED).However, this derivation is suspicious since the current Arabic name for alcohol, !الكح&# 1608;ل? = ''ALKHWL'' = ''al???'', does not derive from ''al-kuhul''. The Qur'an in verse 37:47 uses the word !الغو&# 1604;? = ''ALGhWL'' = ''al-ghawl'' — properly meaning "spirit" ("spiritual being") or "demon" — with the sense "the thing that gives the wine its headiness". The word ''al-ghawl'' also originated the English languageEnglish word "ghoul", and the name of the star Algol. This derivation would, of course, be consistent with the use of "spirit" or "spirit of wine" as synonymous of "alcohol" in most Western languages. (Incidentally, the etymology "alcohol" = "the devil" was used in the 1930s by the United StatesU.S. Temperance movementTemperance Movement for propaganda purposes.)According to the second theory, the popular etymology and the spelling "alcohol" would not be due to generalization of the meaning of ''ALKHL'', but rather to Western alchemists and authors confusing the two words ''ALKHL'' and ''ALGhWL'', which have indeed been transliterated in many different and overlapping ways.
Physical and chemical properties - The hydroxyl group generally makes the alcohol molecule polar moleculepolar. Those groups can form hydrogen bonds to one another and to other compounds. Two opposing solubility trends in alcohols are: the tendency of the polar OH to promote solubility in water, and 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 (amyl alcoholPentanol and higher) are effectively insoluble because of the hydrocarbon chain's dominance. Because of hydrogen bonding, alcohols tend to have higher boiling points than comparable hydrocarbons and ethers. All simple alcohols are miscible in organic solvents. This hydrogen bonding means that alcohols can be used as protic solvents.The lone pairs of electrons on the oxygen of the hydroxyl group also makes alcohols nucleophiles.Alcohols, like water, can show either acidic or basic properties at the O-H group. With a pKapKa of around 16-19 they are generally slightly weaker acids than water (molecule)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 AlkylRO- MetalM+. Meanwhile the oxygen atom has lone pairs of nonbonded electrons that render it weakly Base_(chemistry)basic in the presence of strong acids such as sulfuric acid. For example, with methanol: Alcohols can also undergo oxidation to give aldehydes, ketones or carboxylic acids, or they can be dehydrated to alkenes. They can react to form ester compounds, and they can (if activated first) undergo nucleophilic substitution reactions. For more details see the #Chemistry of alcohols section below.
Toxicity - Alcohols often have an odor described as 'biting' that 'hangs' in the nasal passages. Ethanol in the form of alcoholic beverages has been consumed by humans since pre-historic times, for a variety of hygienic, dietary, medicinal, religious, and recreational reasons. While infrequent consumption of ethanol in small quantities may be harmless or even beneficial, larger doses result in a state known as drunkenness or intoxication and, depending on the dose and regularity of use, can cause acute respiratory failure or death and with chronic use has medical repercussions.Other alcohols are substantially more poisonous than ethanol, partly because they take much longer to be metabolized, and often their metabolism produces even more toxic substances. Methanol, or ''wood alcohol'', for instance, is oxidized by alcohol dehydrogenase enzymes in the liver to the poisonous formaldehyde, which can cause blindness or death. Interestingly, an effective treatment to prevent formaldehyde toxicity after methanol ingestion is to administer ethanol. This will bind to alcohol dehydrogenase, preventing methanol from binding and thus acting as a substrate. Any formaldehyde will be converted to formic acid and excreted before it causes damage.
Chemistry of alcohols -
Preparation -
Laboratory - There are three common methods: From alkyl halides: react with aqueous Sodium hydroxideNaOH or Potassium hydroxideKOH (mainly 1° alcohols).:R-Br + KOH → R-OH + KBr From aldehydes or ketones: reduction with sodium borohydride or lithium aluminium hydride.:R-CHO - O → R-OH From alkenes: an acid catalysed hydration reaction using concentrated sulfuric acid as a catalyst (gives usually 2° or 3° !alcohols).:C2H42SO< ;sub>4? (l) → !C2H< sub>5-HSO4:CH5< ;/sub>-HSO4? + H2O → !C2H< sub>5OH? + !H2SO< ;sub>4? The formation of a secondary alcohol via the last two methods is shown:
Industrial - Fermentation: using glucose produced from sugar from the hydrolysis of starch, in the presence of yeast and temperature of <37°C to produce !ethanol.:C12H2211? → !C6H< sub>12O? + !C6H< sub>12O:Invertase? → glucose + !fructose:C6H12 O6? + H2O → !C2H< sub>5OH? + !CO2:Glu cose? → zymase + ethanol Direct hydration reactionhydration: using ethene or other alkenes from cracking of fractions of distilled crude oil. Uses a catalyst of phosphoric acid under high temperature and pressure. Methanol from water gas: It is manufactured from Syngassynthesis gas, where CO + 2 H2 are combined to produce methanol using a CopperCu, ZnO and Aluminium oxide!Al2O< ;sub>3? catalyst at 250°C and a pressure of 50-100 atm.:CO - + H2 + H2O (g) → !CH3OH
Reactions - See the #Physical and chemical propertiesphysical and chemical properties section above for a general overview.
Deprotonation - Alcohols can behave as weak acids, undergoing deprotonation. The deprotonation reaction to produce an alkoxide salt is either performed with a strong base such as sodium hydride or butyllithium''n''-butyllithium, or with sodium or potassium metal.: 2 R-OH + 2 Sodium hydrideNaH → 2 !R-O-Na& lt;sup>+? + Hydrogen!H2&uarr ;:? 2 R-OH + 2SodiumNa → !2R-O−Na+ :? e.g. 2 Ethanol!CH3CH&l t;sub>2-OH? + 2 Na → 2 !CH3-CH& lt;sub>2-O−Na< ;sup>+Water? is similar in pKapKa to many alcohols, so with sodium hydroxide there is an equilibrium set up which usually lies to the left:: R-OH + Sodium hydroxideNaOH <=> !R-O-Na& lt;sup>+? + H2O (equilibrium to the left)
Nucleophilic substitution - The hydroxylOH 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_(molecule)water) is much more stable, and 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. If primary or secondary alcohols are to be reacted with hydrochloric acid, an activator such as zinc chloride is needed. Alternatively 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 + !H3PO< ;sub>3In? the Barton-McCombie deoxygenation an alcohol is deoxygenated to an alkane with organotintributyltin hydride or a organoboranetrimethylborane-water complex in a radical substitution reaction.
Dehydration reactionDehydration - Alcohols are themselves nucleophilic, so !R−OH2+? can react with ROH to produce ethers and water, 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 generally 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 requre a higher temperature.This is a diagram of acid catalysed dehydration of ethanol to produce ethene:
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 ! |
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Alcohol and Alcoholism
Journal published by th Medical Council on Alcoholism. Summaries and full text articles available online.
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