Polyhydric alcohols: characterization, production and use

Alcohols are derivatives of hydrocarbons, in molecules of which one or several hydrogen atoms near the saturated carbon atom is replaced by a hydroxy group - OH. It has been experimentally proved that the amount of hydroxyl in an alcohol molecule can not exceed the number of hydrocarbon atoms. Depending on the nature of the radical, acyclic (aliphatic series) and cyclic alcohols are distinguished; By the number of hydroxyl groups - single, double, triple and polyhydric alcohols; By saturation - saturated and unsaturated; Place of localization of the hydroxyl group in the hydrocarbon chain - primary, secondary and tertiary alcohols.

Polyhydric alcohols are alkane derivatives, in molecules of which more than three hydrogen atoms are replaced by hydroxy groups - OH. For polyhydric alcohols as derivatives of monosaccharides, optical isomerism and isomerism of position in the hydrocarbon chain of the OH group are characteristic. Optical isomerism is associated with the ability of some groups of organic substances in solutions to exhibit optical activity. The optical activity of substances is determined by means of a polarimeter.

A qualitative reaction to polyhydric alcohols

The most common qualitative reaction to polyhydric alcohols is their interaction with copper hydroxide. During the reaction, the hydroxide dissolves, thus forming a chelate complex of violet color.

Polyhydric alcohols: main representatives

The tetrahalic alcohols C4H6 (OH) 4 are called tetrites, pyatomic C5H7 (OH) 5 -pentites, hexahydrates of C6H8 (OH) 6 hexahydric alcohols. In each such group, separate alcohols are distinguished, which have historical names: erythritol, arabite, sorbitol, xylitol, dulcite, manite, etc.

Preparation of polyhydric alcohols

These alcohols are synthesized by reduction of monosaccharides, 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 are optically active compounds that are readily soluble in water. IR and UV spectra have absorption bands typical for OH groups of monohydric alcohols. The chemical properties of alcohols are due to the presence of an OH group. When these substances interact with alkaline-earth metals , alcoholates are formed-saccharates. In the oxidation of hydroxyl, which is localized near the first carbon atom (C1), monosaccharides are formed.

Polyhydric alcohols: main representatives

Erythritol HOCH2 (CHOH) 2CH2OH - a crystalline substance, melts at 121.5 ° C. This alcohol is found in lichens and mosses. Erythritol can be obtained by reduction of 1,3-butadiene and erythrose. This alcohol is used in the manufacture of explosives, quick-drying paints, emulsifiers.

Xylitol HOCH2 (CHOH) 3CHON - sweet crystals, readily soluble in water, melt at a temperature of 61.5 degrees. This alcohol can be synthesized by reduction of xylose. Xylitol is used in the food industry for the manufacture of food for diabetics, as well as for the production of alkyd resins, drying oils and surfactants.

Pentaerythritol C (CH2OH) 4 is a solid that is poorly soluble in water. Obtained by reacting formaldehyde with acetaldehyde in the presence of Ca (OH) 2. Used in the production of polyesters, alkyd resins, tetrapentaerythritol, surfactants, plasticizers for the production of polyvinyl chloride, synthetic oils. It shows narcotic properties.

Manitol НОСН2 (СНОН) 4СН2ОН - sweet taste of the substance, melts at a temperature of 165 degrees. Contained in mosses, mushrooms, algae, higher plants. Applied as a diuretic and as a component of cosmetic products (ointments).

D-sorbitol HOCH2 (CHOH) 4CH2OH - melts at a temperature of 96 degrees. This alcohol is rich in fruits of mountain ash. Sorbitol is produced by the reduction of glucose. This alcohol is an intermediate product in the synthesis of vitamin C, has a diuretic effect, is used as a substitute for sucrose for diabetics.