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Alcohol:
In chemistry, an alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group. The general formula for a simple acyclic alcohol is CnH2n+1OH.

The word alcohol was introduced into the English language circa 1543 from the Arabic: ??????, "al-gu?l". In layman's terms, it usually refers to ethanol, also known as grain alcohol or (older) spirits of wine, or to any alcoholic beverage. Ethanol is a colorless, volatile liquid with a mild odor which can be obtained by the fermentation of sugars. (Industrially, it is more commonly obtained by ethylene hydration—the reaction of ethylene with water in the presence of phosphoric acid.) Ethanol is the most widely used depressant in the world, and has been for thousands of years. This sense underlies the term alcoholism (addiction to alcohol).

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 "official" IUPAC chemical name of all alcohols.

There are three major subsets of alcohols: primary (1°), secondary (2°) and tertiary (3°), based upon the number of carbon atoms the C-OH group's carbon (shown in red) is bonded to. Ethanol is a simple 'primary' alcohol. The simplest secondary alcohol is isopropyl alcohol (propan-2-ol), and a simple tertiary alcohol is tert-butyl alcohol (2-methylpropan-2-ol).

Simple Alcohols:
The simplest and most commonly used alcohols are methanol and ethanol. Methanol was formerly obtained by the distillation of wood and called "wood alcohol." It is now a cheap commodity, the chemical product of carbon monoxide reacting with hydrogen under high pressure. Methanol is intoxicating but not directly poisonous. It is toxic by its breakdown (toxication) by the enzyme alcohol dehydrogenase in the liver by forming formic acid and formaldehyde which cause permanent blindness by destruction of the optic nerve.

Apart from its familiar role in alcoholic beverages, ethanol is also used as a highly controlled industrial solvent and raw material. To avoid the high taxes on ethanol for consumption, additives are added to make it unpalatable (such as denatonium benzoate—"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".

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". 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", for example: 1-hydroxy-2-propanone (CH3COCH2OH).

Common names for alcohols usually takes name of the corresponding alkyl group and add the word "alcohol", e.g. methyl alcohol, ethyl alcohol or 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)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.

Primary alcohol (1°)- Have general formulas RCH2OH Secondary alcohol (2°)- Have general formulas RR'CHOH Tertiary alcohol (3°)- Have general formulas RR'RCOH Hydrogen bond strength order: 1°>2°>3° Boiling point order: 1°>2°>3° Acidity order: 1°>2°>3°.

Etymology:
The word alcohol appears in English in the 16th century, loaned via French from medical Latin, ultimately from the Arabic al-ku?l. al is Arabic for the definitive article, the in English. ku?l was the name given to 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 and eyeliner.

Physical and Chemical Properties:
The hydroxyl group generally makes the alcohol molecule polar. Those groups can form hydrogen bonds to one another and to other compounds. 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+.

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.

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:

1. 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.
2. By direct hydration using ethylene (ethylene hydration or other alkenes from cracking of fractions of distilled crude oil. It usually uses a catalyst of phosphoric acid under high temperature and pressure of 50-120.
3. Methanol is produced from synthesis gas, where carbon monoxide and 2 equivalents of hydrogen gas are combined to produce methanol using a copper, zinc oxide and aluminium oxide catalyst at 250°C and a pressure of 50-100 atm.

Endogenous:
It is inevitable that all humans always have some amount of alcohol in their bodies at all times, even if they never drink alcoholic beverages in their lives. This is because of a process called endogenous ethanol production. Many of the bacteria in the intestines use alcohol fermentation as a form of respiration. This metabolic method produces alcohol as a waste product, in the same way that metabolism results in the formation of carbon dioxide and water. Thus, human bodies always contain some quantity of alcohol produced by these benign bacteria.

Laboratory Synthesis: Several methods exist for the preparation of alcohols in the laboratory.
1. 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).
2. 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.
3. Alkenes engage in an acid catalysed hydration reaction using concentrated sulfuric acid as a catalyst which 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.
4. Grignard reagents react with carbonyl groups to secondary and tertiary alcohols. Related reactions are the Barbier reaction and the Nozaki-Hiyama reaction.
5. Noyori asymmetric hydrogenation is the asymmetric reduction of ß-keto-esters .
6. Amines can be converted to diazonium salts which are then hydrolyzed.

Toxicity:
Alcohol, specifically ethanol, is a potent central nervous system depressant, with a range of side effects. The amount and circumstances of consumption play a large part in determining the extent of intoxication; for example, consuming alcohol after a heavy meal is less likely to produce visible signs of intoxication than consumption on an empty stomach.[citation needed] Hydration also plays a role, especially in determining the extent of hangovers. The concentration of alcohol in blood is usually measured in terms of the blood alcohol content.

Alcohol has a biphasic effect on the body, which is to say that its effects change over time.[1] Initially, alcohol generally produces feelings of relaxation and cheerfulness, but further consumption can lead to blurred vision and coordination problems. Cell membranes are highly permeable to alcohol, so once alcohol is in the bloodstream it can diffuse into nearly every biological tissue of the body. After excessive drinking, unconsciousness can occur and extreme levels of consumption can lead to alcohol poisoning and death (a concentration in the blood stream of 0.55% will kill half of those affected). Death can also occur through asphyxiation by vomit. An appropriate first aid response to an unconscious, drunken person is to place them in the recovery position.

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. The consumption of large doses results in drunkenness or intoxication (which may lead to a hangover as the effect wears off) and, depending on the dose and regularity of use, can cause acute respiratory failure or death and with chronic use has medical repercussions. Because alcohol impairs judgment, it can often be a catalyst for reckless or irresponsible behavior. The LD50 of ethanol in rats is 10,300 mg/kg.

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.

An effective treatment to prevent formaldehyde toxicity after methanol 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. Remaining formaldehyde will be converted to formic acid and excreted.

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. These longer chain alcohols are found as contaminants in some alcoholic beverages and are known as fusel alcohols, and are reputed to cause severe hangovers although it is unclear if the fusel alcohols are actually responsible. Many longer chain alcohols are used in industry as solvents and are occasionally abused by alcoholics, leading to a range of adverse health effects.

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