..... Click the link for more information. . In common usage the term alcohol usually refers to ethanol ethanol or ethyl alcohol, CH3CH2OH, a colorless liquid with characteristic odor and taste; commonly called grain alcohol or simply alcohol. Properties
Ethanol is a monohydric primary alcohol.
..... Click the link for more information. . The class of alcohols also includes methanol methanol, methyl alcohol, or wood alcohol, CH3OH, a colorless, flammable liquid that is miscible with water in all proportions. Methanol is a monohydric alcohol. It melts at −97.
..... Click the link for more information. ; the amyl, butyl, and propyl alcohols; the glycols glycol , dihydric alcohol in which the two hydroxyl groups are bonded to different carbon atoms; the general formula for a glycol is (CH2)n(OH)2.
..... Click the link for more information. ; and glycerol glycerol, glycerin, glycerine, or 1,2,3-propanetriol , CH2OHCHOHCH2OH, colorless, odorless, sweet-tasting, syrupy liquid. Glycerol is a trihydric alcohol. It melts at 17.
..... Click the link for more information. . An alcohol is generally classified by the number of hydroxyl groups in its molecule. An alcohol that has one hydroxyl group is called monohydric; monohydric alcohols include methanol, ethanol, and isopropanol isopropanol, isopropyl alcohol, or 2-propanol , (CH3)2CHOH, a colorless liquid that is miscible with water. It melts at −89°C; and boils at 82.3°C;. It is poisonous if taken internally.
..... Click the link for more information. . Glycols have two hydroxyl groups in their molecules and so are dihydric. Glycerol, with three hydroxyl groups, is trihydric. The monohydric alcohols are further classified as primary, secondary, or tertiary according to the number of carbon atoms bonded to the carbon atom to which the hydroxyl group is bonded. Many of the properties and reactions characteristic of alcohols are due to the electron charge distribution in the C-O-H portion of the molecule (see chemical bond chemical bond, mechanism whereby atoms combine to form molecules. There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the formation of an aggregate with sufficient stability to be regarded as
..... Click the link for more information. ). Chemical reactions involving the hydroxyl group in an alcohol molecule include: those in which the hydroxyl group is replaced as a whole, e.g., reaction of ethanol with hydrogen iodide to form ethyl iodide and water; those in which only the hydrogen in the hydroxyl group is replaced, e.g., the reaction of ethanol with sodium, an active metal, to form sodium ethoxide and hydrogen; and those in which the carbon-oxygen bond becomes a double bond to form an aldehyde aldehyde [alcohol + New Lat. dehydrogenatus=dehydrogenated], any of a class of organic compounds that contain the carbonyl group, and in which the carbonyl group is bonded to at least one hydrogen; the general formula for an aldehyde is RCHO, where R is
..... Click the link for more information. or ketone ketone , any of a class of organic compounds that contain the carbonyl group, C=O, and in which the carbonyl group is bonded only to carbon atoms. The general formula for a ketone is RCOR′, where R and R′ are alkyl or aryl groups.
..... Click the link for more information. depending on whether it is a primary or secondary alcohol. Alcohols are generally less volatile, have higher melting points, and are more soluble in water than the corresponding hydrocarbons (in which the -OH group is replaced with hydrogen). For example, at room temperature methanol is a liquid, while methane is a gas.
alcohol
Any of a class of common organic compounds that contain one or more hydroxyl groups (−OH) attached to one or more of the carbon atoms in a hydrocarbon chain. The number of other substituent groups (R) on that carbon atom make the alcohol a primary (RCH2OH), secondary (R2CHOH), or tertiary (R3COH) alcohol. Many alcohols occur naturally and are valuable intermediates in the synthesis of other compounds because of the characteristic chemical reactions of the hydroxyl group. Oxidation (see oxidation-reduction) of primary alcohols yields aldehydes and (if taken further) carboxylic acids; oxidation of secondary alcohols, ketones. Tertiary alcohols break down on oxidation. Alcohols generally react with carboxylic acids to produce esters. They may also be converted to ethers and olefins. Products of these numerous reactions include fats and waxes, detergents, plasticizers, emulsifiers, lubricants, emollients, and foaming agents. Ethanol (grain alcohol) and methanol (wood alcohol) are the best-known alcohols with one hydroxyl group. Glycols (e.g., ethylene glycol, or antifreeze) contain two hydroxyl groups, glycerol three, and polyols three or more. See also alcoholic beverage, alcoholism.
alcohol
alcohol [′al·kə‚hȯl]
Alcohol
a hydrocarbon derivative in which one or more hy-droxyl groups (—OH) are attached to saturated carbon atoms. Compounds in which the—OH groups are directly attached to an aromatic ring are called phenols, and those in which the—OH group is attached to a doubly bonded carbon are called enols.
Classification and nomenclature. Depending on the nature of the hydrocarbon radical, alcohols can be acyclic, or aliphatic (methyl alcohol, ethyl alcohol, allyl alcohol), alicyclic (cyclohex-anol), aliphatic-aromatic (benzyl alcohol), or heterocyclic. According to the number of—OH groups in the molecule, alcohols can be classified as monohydric (alcohols), dihydric (glycols), trihydric, tetrahydric, and polyhydric. The—OH groups can be attached to a primary carbon atom, shown as—CH2OH, a secondary carbon atom, shown as
or a tertiary carbon atom, shown as
According to the attachment, a monohydric alcohol would be described as primary, secondary, or tertiary.
The names of alcohols are usually derived from the names of the corresponding hydrocarbon radicals. For example, CH3—OH is called methyl alcohol, C2H5—OH is called ethyl alcohol, and C3H7—OH is called propyl alcohol. According to the system of nomenclature adopted by the International Union of Pure and Applied Chemistry, the suffix “ol” (also “diol,” “triol”) is added to the name of the corresponding hydrocarbon, and a number is used to indicate the number of the carbon atom to which the hydroxyl group is attached, for example, CH3—CH(OH)—CH3 (2-propanol) and HOCH2—CH2— CH2OH (1,3-propanediol). Derived names are sometimes used for secondary and tertiary alcohols. Some alcohols have familiar names; ethyl alcohol is commonly known as spirits of wine or grain alcohol, and methyl alcohol is called wood alcohol.
Some pharmaceutical substances are sometimes referred to as alcohols even though they bear no relation to this class of compounds. For example, boric, camphor, and salicyl alcohols are actually solutions of, respectively, boric acid, camphor, and salicylic acid.
Properties. The lower monohydric aliphatic alcohols are colorless liquids. Their higher homologs (beginning with C12) are solids. The C1-C3 alcohols have the characteristic alcohol odor and a burning taste; the C4-C5 alcohols have a sweet, suffocating odor, and they impart an unpleasant odor to fusel oil. The higher alcohols are odorless. The simplest glycols and glycerols are viscous liquids. In the liquid and solid states, there is hydrogen bonding between the alcohol molecules. This bonding results in abnormally high boiling points; for example, CH3OH boils at 64.7°C, while CH3SH boils at 6°C. Alcohols are readily soluble in many organic solvents and are themselves good solvents. The C(-C3 monohydric alcohols, the glycols up to C7, and glycerol are miscible with water in any proportions. The solubility of the C4-C5 alcohols in water is limited, and the higher alcohols are insoluble in water. Alcohols form azeotropic mixtures with water and a number of organic compounds. These mixtures are used, for example, in the production of absolute alcohol.
The chemical properties of alcohols derive from the presence of the hydroxyl group. Upon reaction with alkali and certain other metals, saltlike products called alcoholates are formed, such as C2H5ONa. The reaction of alcohols with acids yields esters, RCOOR’. Primary alcohols are oxidized under mild conditions to aldehydes, RCHO, and, subsequently, carboxylic acids, RCOOH. Secondary alcohols are oxidized to ketones, R—CO—R. Alcohols undergo dehydration with relative ease, and depending on the nature of the alcohol and the reaction conditions, form ethers, ROR, or olefins. The reaction of alcohols with PC15 and SOCl2 leads to the formation of such alkyl chlorides as RC1 and RC12.
Preparation and use. In industry, the hydrolysis of alkyl halides is used in the production of amyl alcohols and benzyl alcohol. The hydrolysis of the esters of alcohols made with sulfuric acid (alkyl sulfates) is an important step in the industrial production of isopropyl alcohol, ethyl alcohol, and (ert-butyl alcohol from olefins. Many alcohols are synthesized by the direct hydration of olefins in the presence of catalysts and by the reduction of such car-bony 1 compounds as aldehydes (obtained, for example, by the oxo process, that is, the addition of CO and H2 to olefins) and ketones, as well as by the reduction of carboxylic acids and the esters of these acids. The hydrogenation of carbon monoxide yields, for example, methyl, n-propyl, and isobutyl alcohols. Ethyl alcohol and certain other alcohols are produced by the fermentation of sugars by yeast, while certain higher alcohols are produced with the aid of organoaluminum compounds (Alfol process).
Alcohols are very common in nature in the free state and in the form of esters. For example, fats and oils are esters of glycerol, waxes are esters of the higher aliphatic alcohols, and phenylethyl alcohol and menthol are constituents of, respectively, rose oil and peppermint oil. Cetyl alcohol is found in beeswax, and the ester of benzyl alcohol and acetic acid (benzyl acetate) is a constituent of the essential oil of jasmine flowers.
Because of their many uses, alcohols form an important class of organic compounds. They serve as intermediates in the production of dyes, synthetic fibers, plastics, paints, varnishes, detergents, plasticizers, emulsifying agents, and pharmaceuticals. In addition to their use as solvents, alcohols are used in the production of alkylating agents. The lower aliphatic alcohols have a weak narcotic effect, and some alcohols, such as methyl alcohol and ethylene glycol, are toxic.
REFERENCE
Nesmeianov, A. N., and N. A. Nesmeianov, Nachala organicheskoi khimii, vols. 1–2. Moscow, 1969–70.V. N. FROSIN
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