ALCOHOL

any of a class of organic compounds characterized by one or more hydroxyl (OH) groups attached to a carbon atom of an alkyl group (hydrocarbon chain). Alcohols may be considered as derivatives of water (H2O) in which one of the hydrogen atoms has been replaced by an alkyl group. Alcohols are among the most common organic compounds and are valuable intermediates in the synthesis of other compounds. Alcohols may be classified according to which carbon of the alkyl group is bonded to the hydroxyl group. In primary alcohols (RCH2OH), the oxygen of the hydroxyl group is bonded to a carbon atom bearing at least two hydrogen atoms. In secondary alcohols (R2CHOH), the hydroxyl group is bonded to a carbon attached to two other carbons, while in tertiary alcohols (R3COH) it is bonded to a carbon attached to three other carbon atoms. Most alcohols are colourless liquids or solids at room temperature: primary alcohols with fewer than 12 carbon atoms are liquid; those with 12 or more carbon atoms are solid. Polyhydric alcohols (those with more than one hydroxyl group) usually have the consistency of syrup. Alcohols with complex arrangements of carbon atoms, such as sterols, are usually solids. Alcohols of low molecular weight are highly soluble in water. With increasing molecular weight, alcohols become less soluble in water and their boiling points, vapour pressures, densities, and viscosities increase. Primary alcohols may be oxidized to aldehydes or further to carboxylic acids, and secondary alcohols may be oxidized to ketones. When tertiary alcohols are oxidized, they decompose, breaking carbon-carbon bonds. Alcohols generally react with carboxylic acids to produce estersneutral organic compounds found in fats and oils. Alcohols can also be converted to ethers and olefinic hydrocarbons. Adding hydroxyl groups to an alcohol without increasing the number of carbon atoms changes many of its properties. In some cases, it may enhance sweetness, and the resultant alcohols are used as sweeteners. Alcohols with 8 to 12 carbon atoms have a characteristic roselike or lilylike odour and are used in making perfumes. In general, the most important industrial use of alcohols is as chemical intermediates, chiefly because alcohols can readily be converted into a large number of other compounds. This is done by simple chemical reactions to yield products such as fats and waxessurface active agents used in detergents, plasticizers, emulsifiers, lubricants, emollients, and foaming agents. Alcohols are among the more abundantly produced organic chemicals in industry. Some, such as ethanol and methanol, are utilized in great quantities. Ethanol, CH3CH2OH, also called ethyl alcohol, or grain alcohol, can be made by fermentation from the carbohydrates found in fruits, molasses, grains, and other agricultural products. It is also made industrially from ethylene, CH2=CH2. Ethanol is used in toiletries and pharmaceuticals and to sterilize hospital instruments. It is, moreover, the alcohol in alcoholic beverages. The anesthetic ether is also made from ethanol. Methanol, also known as methyl alcohol, wood alcohol, or carbinol, can be manufactured from hardwood or from hydrogen and carbon monoxide (CO). It is used as a solvent, as a raw material for the manufacture of formaldehyde and special resins, in special fuels, in antifreeze, and for cleaning metals. Methanol and ethanol are good fuels for automobile engines because they have high octane ratings and low pollution emission, though their solvent properties can cause problems by dissolving certain materials used in modern fuel systems. Gasohol, a solution of 10 percent ethanol in gasoline, is an alternative fuel that can be used in most automobiles without the solvency problem.