Alcohol refers to a class of chemical compounds, all of which consist of chemically bonded atoms of carbon, hydrogen, and oxygen. All alcohol molecules contain at least one hydroxyl group. A hydroxyl group is a specific arrangement of atoms in which a hydrogen atom is bonded to an oxygen atom. In alcohol molecules, the oxygen atom in the hydroxyl group is, in turn, bonded to a carbon atom.
People commonly use the word alcohol to refer to such beverages as beer, wine, and liquors. But there are many types of alcohols, and they have a variety of uses. This article discusses the chemical properties and commercial uses of several alcohols. For information on alcoholic beverages, see Alcoholic beverage.
Methanol,
also called methyl alcohol or wood alcohol, is the simplest of the alcohols. It has one hydroxyl group. Methanol is a highly toxic, colorless liquid. It boils at 149 °F (65 °C) and freezes at -137 °F (-94 °C).
Methanol originally was produced from wood, but it is now commercially produced primarily from methane, the chief component of natural gas. The majority of commercially produced methanol is converted to formaldehyde, a chemical used to make plastics. As an industrial solvent (substance that dissolves other substances), methanol is important in the manufacture of paints and varnishes. Methanol also functions as a fuel-line antifreeze for automobiles, and it serves as an ingredient in the production of other chemicals. Methanol can be used as a motor fuel, but it is more expensive than other fuels. See Methanol.
Ethanol,
also called ethyl alcohol, is the alcohol found in alcoholic beverages. Ethanol is also used for a variety of other purposes. It serves as a solvent for chemical reactions and for lacquers, varnishes, and stains. It is also important in the preparation of chemicals used as detergents, flavorings, and fragrances. As a gasoline additive, ethanol improves vehicle performance and reduces emissions of dangerous pollutants. Some motor vehicles are designed to run on fuels of 85 percent or more ethanol. Several automakers manufacture a number of flexible fuel vehicles, which can run on gasoline, fuel of 85 percent ethanol, or any mixture of the two.
Ethanol is produced by several methods. For example, ethanol used in beverages is produced by fermenting fruits, grains, or vegetables. However, most ethanol used for commercial purposes is made by heating ethylene and water under pressure in the presence of a phosphoric acid catalyst (see Catalysis). Ethylene is a gas that is a component of crude oil.
The U.S. government controls and taxes the production and distribution of ethanol in the United States and taxes ethyl alcohol used in alcoholic beverages. For this reason, ethanol manufacturers in the United States denature (make unfit to drink) most of the ethanol that will be used for purposes other than alcoholic drinks. Manufacturers denature ethanol by mixing it with methanol or other poisonous chemicals.
Ethanol boils at 172 °F (78 °C) and freezes at -173 °F (-114 °C). It has one hydroxyl group.
Propanol,
or propyl alcohol, has one hydroxyl group. There are two forms of propanol, called isomers. Isomers have the same kind and number of atoms. However, they have different molecular structures and therefore different chemical and physical properties. For example, one of the isomers of propanol, called normal propanol, 1-propanol, or n propyl alcohol, boils at 208 °F (98 °C) and freezes at -195 °F (-126 °C). But the other isomer, known as isopropanol, 2-propanol, or isopropyl alcohol, boils at 181 °F (83 °C) and freezes at -126 °F (-88 °C).
Normal propanol is made commercially from ethylene and synthesis gas, a mixture of hydrogen and carbon monoxide, in the presence of a rhodium or cobalt catalyst. Propyl alcohol is used to prepare other chemicals, and it is used as a solvent for sticky substances called resins.
Isopropanol is produced by reaction of the gas propylene, a component of crude oil, with water in the presence of an acid or metal catalyst. Isopropanol is mainly used to produce acetone, a common industrial solvent. It is also used as a rubbing alcohol, and in cosmetics and lotions.
Ethanediol,
or ethylene glycol, is a highly toxic alcohol that is used mainly as an antifreeze in automobile radiators. It is produced by the reaction of ethylene with water and oxygen in the presence of a silver oxide catalyst. Ethanediol has a boiling point of 388 °F (198 °C) and a freezing point of -9 °F (-13 °C). It has two hydroxyl groups.
Other alcohols
include plasticizer alcohols, which have 6 to 11 carbon atoms. Plasticizers are used in the manufacture of plastics, and they give these substances flexibility.
Alcohols that have more than 11 carbon atoms are called detergent alcohols. Manufacturers use these alcohols to make detergents, soaps, and shampoos. In combination with other chemicals, these alcohols have the ability to dissolve dirt and grease in water in a process called emulsification.
See also Antifreeze; Ethanol; Glycerol; Solvent.
