Ethyl alcohol

Ethyl alcohol, also known as ethanol or grain alcohol, is a flammable, colorless chemical compound, one of the alcohols that is most often found in alcoholic beverages. In common parlance, it is often referred to simply as alcohol. Its chemical formula is C₂H₅OH.

This article is mostly about ethanol as a chemical compound. For beverages containing ethanol, see alcoholic beverage. For the use of ethanol as a fuel, see alcohol fuel.

History

Ethanol has been known to humans since prehistory as the active ingredient of alcoholic beverages. Its isolation as a relatively pure compound was probably achieved first by Persian alchemists who developed the art of distillation, such as Geber (721–815) and Al-Razi (864–930).

Production

Ethanol for use in alcoholic beverages is produced by fermentation: it is a product of sugar metabolism in certain species of yeast in the absence of oxygen. The process of culturing yeast under conditions to produce alcohol is referred to as brewing. Yeasts can grow in the presence of up to only about 14% alcohol, but the concentration of alcohol in the final product can be increased by distillation.

For a mixture of ethanol and water, there is a maximum boiling azeotrope at 96% ethanol and 4% water. For this reason, fractional distillation of ethanol-water mixtures (of less than 96% ethanol) cannot yield ethanol purer than 96%. Therefore, 95% ethanol in water is a fairly common solvent.

To produce absolute ethanol, a small amount of benzene is added, and the mixture is again fractionally distilled. Benzene forms a tertiary azeotrope with water and ethanol to remove the last of the water, and a binary azeotrope with ethanol removes most of the benzene. The resulting ethanol is water free, for processes that require it. However, several ppm of benzene remains, so consumption by humans leads to distinctive liver damage.

Ethanol for industrial use is often made from petroleum feedstocks, typically by the catalytic hydration of ethylene with sulfuric acid as catalyst. This process is cheaper than the production by fermentation.

Ethanol for industrial use is normally made unfit for human consumption ("denatured") by the inclusion of small amounts of substances that are either toxic (such as methanol) or unpleasant (such as denatonium), thus avoiding the applicable taxes or inventory controls. Denatured ethanol has the UN number UN 1987 and toxic denatured ethanol has UN 1986.

Use

Ethanol is used as a fuel (often mixed with gasoline) and in a wide variety of industrial processes. Ethanol is also used in antifreeze products for its low melting point.

It is easily soluble in water in all proportions with a slight overall decrease in volume when the two are mixed. Absolute ethanol and 95% ethanol are themselves good solvents, somewhat less polar than water and used in perfumes, paints and tinctures. Other proportions of ethanol with water or other solvents can also be used as a solvent. Alcoholic drinks have a large variety of tastes because various flavor compounds are dissolved during brewing.

A solution of 70–85% of ethanol is commonly used as a disinfectant. It kills organisms by denaturing their proteins and dissolving their lipids and is effective against most bacteria and fungi, and many viruses, but is ineffective against bacterial spores. Because of this disinfectant property, alcoholic beverages can be stored for a long time.

The hydroxyl group on the ethanol molecule is an extremely weak acid, but upon treatment alkali metal or a very strong base, an H⁺ can be removed to form an ethoxide ion, C₂H₅O^-.

Hazards

• Ethanol and mixtures with water greater than about 50% ethanol are flammable and easily ignited, although there are some solvents and organic compounds which are even more flammable.

• Although ethanol is not highly toxic, death from ethyl alcohol consumption is possible when blood alcohol level reaches 0.4%. A blood level of 0.5% or more is commonly fatal. Levels of even less than 0.1% can cause intoxication, with unconciousness often occurring at 0.3–0.4%. The legal limits for driving are about 0.08–0.10% in most states, with a trend toward lowering the limit in recent years. Methyl alcohol or methanol, on the other hand, is very toxic.

See also

• Energy directory compiles various energy technologies and issues featured at Wikipedia, with emphasis on clean, renewable energy systems.
• alcohol fuel
• alcoholic beverages
• biodiesel
• denatured alcohol
• methanol
• propyl alcohol

External links

• Alcohol in Arabic sources (Geber but no mention of Al-Razi).