Alcohols (Alkanols)

Alcohol Database German Version French Version

1) Alcohol is the common name for the alcohol ethanol (ethyl alcohol), contained in alcoholic beverages (spirits). See also alcoholic fermentation and spirits.

2) Chemical group of the Alkanols, which contain one or more hydroxyl groups in the molecule, see scheme of alkanols.

From the chemical structure it has to be distinguish between primary alcohols (like methanol, ethanol, 1-propanol, 1-butanol ...), secondary alcohols (like 2-propanol, 2-butanol ...) and tertiary alcohols (like tert. butanol) as representatives with only one single hydroxyl group, also called univalent alcohols. Primarily means that the C-atom that is connected with the hydroxyl group has only one alkyl residue (rsp. none with methanol), with secondary alcohols there are two alkyl residues and according to three alkyl residues with tertiary alcohols. See scheme of alkanols.

Important connections with more than one hydroxyl groups are ethylenglycol (two OH-groups = diol, a bivalent alcohol) and the glycerol (three OH-groups = triol, a trivalent alcohol). With diols, whose hydroxyl groups are bound at asymmetrically substituted carbon atoms, spatially different arrangements exist, which are called as chirale isomers,. These possesses a great importance to the purposeful synthesis of optically active natural substances, which are often physiologically effective only in a defined stereochemistry. See scheme of alkanols and alcohol database.

The nomenclature of the alcohols results from the name of the basis hydrocarbon,attaching the ending "-ol". If different isomers are possible, the position of the OH-group (hydroxyl group) is indicated by placing in front Arabic numerals. Chirale centers are represented by placing the position as Arabic numeral and the optical direction of rotation in front, designation by the letters R rsp. S, in round parentheses (example: (2S, 5S)-2,5-Hexandiol). See scheme of alkanols.

By the polarity of the hydroxyl group the formation of hydrogen bonds is possible. Therefore melting and boiling points of the alcohols are clearly increased and the solubility of the short-chained alcohols in polar solvents - especialy water - conditionally opposite the appropriate alkanes, which decreases with increasing length of the hydrocarbon chain.

Synthesis of the alcohols

The synthesis of the primary and secondary alcohols under maintaining the carbon chain can take place via reduction of the aldehydes rsp. ketones. The reduction of prochiralic ketones with NADH (by means of alcohol and ADH regenerates in situ) permits the representation of optically active alcohols, which are important parent compounds for the pharmaceutical industry. Secondary and tertiary alcohols can be received by water addition to alkenes. A general possible synthesis procedure under simultaneous extension of the hydrocarbon chain offers the Grignard procedure. See synthesis.

Phenols

Substances which contain the hydroxyl group bound at an aromatic ring system doesn't belong to the alcohols. This chemical substance class is called phenols, which are higher reactive than alcohols because of more acid like behavior of the phenolic hydroxyl group.