Alcohols are derivatives of hydrocarbons, inmolecules of which one or several hydrogen atoms near a saturated carbon atom are replaced by a hydroxy group - OH. It has been experimentally proven that the amount of hydroxyls in an alcohol molecule cannot exceed the number of hydrocarbon atoms. Depending on the nature of the radical, there are acyclic (aliphatic) and cyclic alcohols; by the number of hydroxyl groups - one-, two-, three-and polyhydric alcohols; saturation - saturated and unsaturated; the localization of the hydroxyl group in the hydrocarbon chain is primary, secondary and tertiary alcohols.
Polyhydric alcohols - derivatives of alkanes, inmolecules of which more than three hydrogen atoms are replaced by hydroxyl groups - OH. Optical isomerism and position isomerism in the hydrocarbon chain of an OH group are characteristic of polyatomic alcohols as derivatives of monosaccharides. Optical isomerism is associated with the ability of some groups of organic substances in solutions to exhibit optical activity. Optical activity of substances is determined using a polarimeter.
Qualitative reaction to polyhydric alcohols
The most common qualitative responseon polyhydric alcohols is their interaction with copper hydroxide. During the reaction, the hydroxide dissolves, and a purple chelate complex is formed.
Polyhydric alcohols: key representatives
C4H6 (OH) 4 tetrahydric alcohols are calledtetrites, pentaatomic C5H7 (OH) 5 - pentites, six-atom alcohols C6H8 (OH) 6 - hexites. In each such group, separate alcohols are distinguished, which have historical names: erythritol, arabitol, sorbitol, xylitol, dulcite, lures, etc.
Getting polyatomic alcohols
These alcohols are synthesized by reducingmonosaccharides, condensation of aldehydes with formaldehyde in an alkaline medium. Very often polyhydric alcohols are obtained from natural raw materials. Some alcohols are extracted from the fruits of mountain ash.
Polyhydric alcohols - optically activecompounds, well soluble in water. In the IR and UV spectra, the absorption bands are typical for OH groups of monohydric alcohols. The chemical properties of alcohols are due to the presence of the OH group. When these substances interact with alkaline earth metals, alcoholates form - saharaty. The oxidation of hydroxyl, which is localized near the first carbon atom (C1), forms monosaccharides.
Polyhydric alcohols: key representatives
Erythritol HOCH2 (CHON) 2CH2OH - crystallinesubstance melts at 121.5 ° C. The indicated alcohol is found in lichens and mosses. Erythritol can be obtained due to the reduction of 1,3-butadiene and erythrosis. The specified alcohol is used in the manufacture of explosive compounds, quick-drying paints, emulsifiers.
Xylitol HOCH2 (CHON) 3CHOH — sweet crystals,well soluble in water, melt at a temperature of 61.5 degrees. The specified alcohol can be synthesized by reduction of xylose. Xylitol is used in the food industry in the manufacture of food for diabetics, as well as in the manufacture of alkyd resins, drying oils and surfactants.
Pentaerythritol C (CH2OH) 4 - solid, badsoluble in water. Obtained by reacting formaldehyde with acetaldehyde in the presence of Ca (OH) 2. Used in the manufacture of polyesters, alkyd resins, tetrapentaerythritol, surfactants, plasticizers for the production of polyvinyl chloride, synthetic oils. Shows narcotic properties.
Mannit HOHN2 (SNON) 4CH2OH - sweet to the tastesubstance melts at 165 degrees. Contained in mosses, mushrooms, algae, higher plants. Used as a diuretic and as a component of cosmetic products (ointments).
D-Sorbitol HOCH2 (CHON) 4CH2OH - melts attemperature of 96 degrees. This alcohol is rich in the fruits of mountain ash. Sorbitol is obtained when glucose is reduced. The specified alcohol is an intermediate product in the synthesis of vitamin C, exhibits a diuretic effect, is used as a substitute for sucrose for diabetics.
