Alcohol

The formal name of an alcohol tells the number of hydroxyl (-OH) groups and the number of carbon atoms in the molecule, the names of any other atoms, and the attachment of the atoms in the molecule, although many older names are still used. Most simple alcohols end with the -ol suffix, added to the name of the molecule that had the same number of carbon atoms, but with a hydrogen atom in place of the hydroxyl group. Methanol, for example, has one carbon atom (like methane) and one hydroxyl group. Ethanol has two carbon atoms (like ethane) and one hydroxyl group. Two isomers of propanol exist (1-propanol and 2-propanol) because the hydroxyl group can be attached either at the end or in the middle of the three-carbon-atom chain. Rubbing alcohol contains mostly 2-propanol (also called isopropanol or isopropyl alcohol).

As the number of carbon atoms increases, the alcohol's solubility in water decreases. But as the number of hydroxyl groups grows, the solubility of the alcohol in water increases, as does its boiling point. Alcohols with two hydroxyl groups on adjacent carbon atoms are called glycols or diols. Ethylene glycol's properties of high water solubility, high boiling point, and low freezing point make it a good antifreeze for cars. These characteristics are due to the hydrogen bonding making the glycol associate firmly with water. Alcohols with more than three hydroxyl groups are called polyols. The sweetener sorbitol, often found in packaged baked goods and sugar-free gum, is a polyol with six carbon atoms and six hydroxyl groups in its molecules.

Most alcohols burn in air; ethanol has been frequently used as fuel. Methanol can sometimes be used as a fuel, though it evaporates too quickly for regular use in cars. Isopropyl alcohol is widely used in industry as a solvent for paints and chemical processes. In addition to its presence in alcoholic beverages, ethanol also is used as a solvent for food extracts such as vanilla, perfumes, and some types of paints and lacquers. Some alcohols can be ingested, although methanol is extremely toxic, and even ethanol is poisonous in large quantities. Glycerol, an alcohol with three carbon atoms and three hydroxyl groups in its molecules, has very low toxicity. It also possesses good moisturizing properties, so about 50% of the amount produced goes into foods and cosmetics.

Figure 1. Illustration by Hans & Cassidy. Courtesy of Gale Group.

Almost any organic chemical can be made by starting with the smaller alcohols, so both methanol and ethanol are in the top 50 industrial chemicals in the United States. Methanol occupies a particularly important place in industrial organic synthesis: it is used in the synthesis of organic chemicals such as formaldehyde (used to make various polymers), methyl-tert-butyl ether (the octane enhancer that replaced lead in unleaded gasoline), acetic acid, and synthetic gasoline, though this use has not yet become common.