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.
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 Islamic alchemists who developed the art of distillation, such as Geber (721-815) and Al-Razi (864-930).
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.
Ethanol is used as a fuel 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 and is itself a good solvent, used in perfumes, paints and tinctures. 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.