關於酒精(English)

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.

Generally, the word alcohol, when used alone, usually refers to ethanol, also known as grain alcohol or (older) spirits of wine. Ethanol is a very strong and unique smelling, colorless, volatile liquid formed by the fermentation of sugars. It also often refers to any beverage that contains ethanol (see alcoholic beverage). It 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 forms of alcohol 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 chemical name of all alcohols.


[edit] Uses

[edit] Automotive
Main article: Alcohol as a fuel
Alcohol is often used as an automotive fuel. Ethanol and methanol can be made to burn more cleanly than gasoline or diesel. Alcohol was once used as an antifreeze in automobile radiators. To add to an internal combustion engine's performance, methanol may be injected into turbocharged and supercharged engines. This cools the air intake charge, providing a denser air charge.


[edit] Scientific, medical, and industrial
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.


[edit] 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. The consumption of large doses result 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 11,300 mg/kg.[2] This ratio would correspond to an 80kg (176.4lb) man drinking 65 shots of 80 proof alcohol, although the LD50 does not necessarily translate directly to humans. A more accurate but less precise figure would estimate the LD50 of the same 80kg (176.4lb) at about 15.5 shots of 80 proof alcohol.[3]

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.