Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl functional group (-OH) is bound to a carbon atom, usually connected to other carbon or hydrogen atoms.
An important class are the simple acyclic alcohols, the general formula for which is CnH2n+1OH. Of those, ethanol (C2H5OH) is the type of alcohol found in alcoholic beverages, and in common speech the word alcohol refers specifically 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 alcohols.

Simple alcohols

The most commonly used alcohol is ethanol, C2H5OH, with the ethane backbone. Ethanol has been produced and consumed by humans for millennia, in the form of fermented and distilled alcoholic beverages, and was isolated by the Persian alchemist Rāzi (Rhazes) around 900 AD. It is a clear flammable liquid that boils at 78.4 °C, which is used as an industrial solvent, car fuel, and raw material in the chemical industry. In the US and some other countries, because of legal and tax restrictions on alcohol consumption, ethanol destined for other uses often contains additives that make it unpalatable (such as Bitrex) or poisonous (such as methanol). Ethanol in this form is known generally as denatured alcohol; when methanol is used, it may be referred to as methylated spirits ("Meths") or "surgical spirits".
The simplest alcohol is methanol, CH3OH, which was formerly obtained by the distillation of wood and therefore is called "wood alcohol". It is a clear liquid resembling ethanol in smell and properties, with a slightly lower boiling point (64.7 °C), and is used mainly as a solvent, fuel, and raw material. Unlike ethanol, methanol is extremely toxic: one sip (as little as 10 ml) can cause permanent blindness by destruction of the optic nerve and 30 ml (one fluid ounce) is potentially fatal.[1]
Two other alcohols whose uses are relatively widespread (though not so much as those of methanol and ethanol) are propanol and butanol. Like ethanol, they 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.)
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".[2] 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",[2] for example: 1-hydroxy-2-propanone (CH3COCH2OH).

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 primary, secondary and tertiary, based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl group. Namely, 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. Ethanol and n-propyl alcohol are primary alcohols; isopropyl alcohol is a secondary one. The prefixes sec- (or s-) and tert- (or t-), conventionally in italics, may be used before the alkyl group's name to distinguish secondary and tertiary alcohols, respectively, from the primary one. For example, isopropyl alcohol is occasionally called sec-propyl alcohol, and the tertiary alcohol (CH3)3COH, or 2-methylpropan-2-ol in IUPAC nomenclature, is commonly known as tert-butyl alcohol or tert-butanol.

Physical and chemical properties

Alcohols have an odor that is often described as “biting” and as “hanging” in the nasal passages.
The hydroxyl group generally 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[3]). 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 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 (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 O-H group. With a pKa of around 16-19 they are generally 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.

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. 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.

Applications

Alcohols can be used as a beverage (ethanol only), as fuel and for many scientific, medical, and industrial utilities. Ethanol in the form of alcoholic beverages has been consumed by humans since pre-historic times. A 50% v/v solution of ethylene glycol in water is commonly used as an antifreeze.
Some alcohols, mainly ethanol and methanol, can be used as an alcohol 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.
Alcohols have applications in industry and science as reagents or solvents. Because of its low toxicity 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.
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 is also used as a preservative for specimens.
Alcohol gels have become common as hand sanitizers.

Production
Industrially alcohols are produced in several ways:
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 the conversion of invertase to glucose and fructose or the conversion of glucose to zymase and ethanol.
By direct hydration using ethylene (ethylene hydration)[5] or other alkenes from cracking of fractions of distilled crude oil.

Toxicity

Most significant of the possible long-term effects of ethanol. Additionally, in pregnant women, it causes fetal alcohol syndrome.
Ethanol in alcoholic beverages has been consumed by humans since prehistoric times for a variety of hygienic, dietary, medicinal, religious, and recreational reasons. The consumption of large doses of ethanol causes drunkenness (intoxication), which may lead to a hangover as its effects wear off. Depending upon the dose and the regularity of its consumption, ethanol can cause acute respiratory failure or death. Because ethanol impairs judgment in humans, it can be a catalyst for reckless or irresponsible behavior. The LD50 of ethanol in rats is 10.3 g/kg.[6]
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.[7] Similarly poisoning due to other alcohols such as ethylene glycol or diethylene glycol are due to their metabolites which are also produced by alcohol dehydrogenase.[8][9] 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.[7][10][11]
Methanol itself, while poisonous, has a much weaker sedative effect than ethanol. Some longer-chain alcohols such as n-propanol, isopropanol, n-butanol, t-butanol and 2-methyl-2-butanol do however have stronger sedative effects, but also have higher toxicity than ethanol.[12][13] These longer chain alcohols are found as contaminants in some alcoholic beverages and are known as fusel alcohols,[14][15] and are reputed to cause severe hangovers although it is unclear if the fusel alcohols are actually responsible.[16] Many longer chain alcohols are used in industry as solvents and are occasionally abused by alcoholics,[17][18] leading to a range of adverse health effects.[19]

References

Vale A (2007). "Methanol". Medicine 35 (12): 633–4. doi:10.1016/j.mpmed.2007.09.014.
^ a b William Reusch. "Alcohols". VirtualText of Organic Chemistry. http://www.cem.msu.edu/~reusch/VirtualText/alcohol1.htm#alcnom. Retrieved 2007-09-14.
^ Irena Majerza, Ireneusz Natkaniec (2006), ' Experimental and theoretical IR, R, and INS spectra of 2,2,4,4-tetramethyl-3-t-butyl-pentane-3-ol Journal of Molecular Structure, Volume 788, Issues 1-3, Pages 93-101 {{doi:10.1016/j.molstruc.2005.11.022}}
^ Global Status Report on Alcohol 2004
^ Lodgsdon, J.E. (1994). "Ethanol." In J.I. Kroschwitz (Ed.) Encyclopedia of Chemical Technology, 4th ed. vol. 9, p. 820. New York: John Wiley & Sons.
^ Robert S. Gable (2004). "Comparison of acute lethal toxicity of commonly abused psychoactive substances" (reprint). Addiction 99 (6): 686–696. doi:10.1111/j.1360-0443.2004.00744.x. http://web.cgu.edu/faculty/gabler/toxicity%20Addiction%20offprint.pdf.
^ a b Schep LJ, Slaughter RJ, Vale JA, Beasley DM (Sep 30 2009). "A seaman with blindness and confusion". BMJ 339: b3929. doi:10.1136/bmj.b3929. PMID 19793790. http://www.bmj.com/cgi/content/full/339/sep30_1/b3929.
^ Brent J (May 2009). "Fomepizole for ethylene glycol and methanol poisoning". N. Engl. J. Med. 360 (21): 2216–23. doi:10.1056/NEJMct0806112. ISSN 0028-4793. PMID 19458366.
^ Schep LJ, Slaughter RJ, Temple WA, Beasley DM (July 2009). "Diethylene glycol poisoning". Clin Toxicol (Phila) 47 (6): 525–35. doi:10.1080/15563650903086444. ISSN 1556-3650. PMID 19586352.
^ Zimmerman HE, Burkhart KK, Donovan JW. Ethylene glycol and methanol poisoning: diagnosis and treatment. Journal of Emergency Nursing. 1999 Apr;25(2):116-20. PMID 10097201
^ Lobert S. Ethanol, isopropanol, methanol, and ethylene glycol poisoning. Critical Care Nurse. 2000 December;20(6):41-7. PMID 11878258
^ McKee M, Suzcs S, Sárváry A, Adany R, Kiryanov N, Saburova L, Tomkins S, Andreev E, Leon DA. The composition of surrogate alcohols consumed in Russia. Alcoholism, Clinical and Experimental Research. 2005 October;29(10):1884-8. PMID 16269919
^ Bunc M, Pezdir T, Mozina H, Mozina M, Brvar M. Butanol ingestion in an airport hangar. Human and Experimental Toxicology. 2006 Apr;25(4):195-7. PMID 16696295
^ Woo KL. Determination of low molecular weight alcohols including fusel oil in various samples by diethyl ether extraction and capillary gas chromatography. Journal of AOAC International. 2005 September-October;88(5):1419-27. PMID 16385992
^ Lachenmeier DW, Haupt S, Schulz K. Defining maximum levels of higher alcohols in alcoholic beverages and surrogate alcohol products. Regulatory Toxicology and Pharmacology. 2008 Apr;50(3):313-21. PMID 18295386
^ Hori H, Fujii W, Hatanaka Y, Suwa Y. Effects of fusel oil on animal hangover models. Alcohol Clinical and Experimental Research. 2003 Aug;27(8 Suppl):37S-41S. PMID 12960505
^ Wiernikowski A, Piekoszewski W, Krzyzanowska-Kierepka E, Gomułka E. Acute oral poisoning with isopropyl alcohol in alcoholics. (Polish) Przeglad Lekarski. 1997;54(6):459-63. PMID 9333902
^ Mańkowski W, Klimaszyk D, Krupiński B. How to differentiate acute isopropanol poisoning from ethanol intoxication? -- a case report. (Polish) Przeglad Lekarski 2000;57(10):588-90. PMID 11199895
^ Bogomolova IN, Bukeshov MK, Bogomolov DV. The forensic medical diagnosis of intoxication of alcohol surrogates by morphological findings. (Russian) Sudebno Meditsinskaia Ekspertiza. 2004 September-October;47(5):22-5. PMID 15523882