Alcohols are derivatives of hydrocarbons, in the molecules of which one or more hydrogen atoms near a saturated carbon atom is replaced by a hydroxy group - OH. It has been experimentally proved that the number of hydroxyls in an alcohol molecule cannot exceed the number of hydrocarbon atoms. Depending on the nature of the radical, acyclic (aliphatic) and cyclic alcohols are distinguished; by the number of hydroxyl groups - mono-, di-, tri- and polyhydric alcohols; by saturation - saturated and unsaturated; the localization of the hydroxyl group in the hydrocarbon chain is primary, secondary and tertiary alcohols.
Polyhydric alcohols are derivatives of alkanes, in the molecules of which more than three hydrogen atoms are replaced by hydroxy groups - OH. Polyhydric alcohols as derivatives of monosaccharides are characterized by optical isomerism and isomerism of position in the hydrocarbon chain of the OH group. Optical isomerism is associated with the ability of certain groups of organic substances in solutions to exhibit optical activity. The optical activity of substances is determined using a polarimeter.
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, and a purple chelate complex forms.
Polyhydric alcohols: key representatives
C4H6 (OH) 4 tetrahydric alcohols are called tetrites, C5H7 (OH) 5 pentatomic alcohols are pentites, and C6H8 (OH) 6 hexatomic alcohols are called hexites. In each such group, individual alcohols are distinguished, which have historical names: erythritol, arabitol, sorbitol, xylitol, dulcite, beckoning, etc.
Obtaining 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 rowan fruits.
Polyhydric alcohols are optically active compounds that are highly soluble in water. The IR and UV spectra have absorption bands typical of OH groups of monohydric alcohols. The chemical properties of alcohols are due to the presence of an OH group. In the interaction of these substances with alkaline earth metals , alcoholates are formed - sugar. During the oxidation of hydroxyl, which is localized near the first carbon atom (C1), monosaccharides are formed.
Polyhydric alcohols: key representatives
Erythritol 2 () 22 - crystalline substance, melts at 121.5 ° . 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 2 () 3 - sweet crystals, well soluble in water, melt at a temperature of 61.5 degrees. Said alcohol can be synthesized by reduction of xylose. Xylitol is used in the food industry in the manufacture of food products for diabetics, as well as in the production of alkyd resins, drying oils and surfactants.
Pentaerythritol C (CH2OH) 4 is a solid substance that is poorly soluble in water. Obtained by reacting formaldehyde with acetaldehyde in the presence of Ca (OH) 2. It is used in the production of polyesters, alkyd resins, tetrapentaerythritol, surfactants, plasticizers to obtain polyvinyl chloride, synthetic oils. It exhibits narcotic properties.
It attracts 2 () 42 - a sweet substance that tastes sweet, melts at a temperature of 165 degrees. Contained in mosses, mushrooms, algae, higher plants. They are used as a diuretic and as a component of cosmetic products (ointments).
D-Sorbitol 2 () 42 - melts at a temperature of 96 degrees. The fruits of mountain ash are rich in this alcohol. Sorbitol is obtained by restoring glucose. The specified alcohol is an intermediate in the synthesis of vitamin C, has a diuretic effect, is used as a substitute for sucrose for diabetics.