Monohydric alcohols, their physical and chemical properties

Alcohols are a separate class of organic compounds that contain one or more hydroxyl groups in their composition. Depending on the number of OH groups, these oxygen-containing compounds are divided into monohydric alcohols, triatomic, etc. Most often, these complex substances are considered as derivatives of hydrocarbons whose molecules have undergone changes, because one or more hydrogen atoms are replaced by a hydroxyl group.

The simplest representatives of this class are monohydric alcohols, the general formula of which looks like this: R-OH or

Cn + H 2n + 1OH.

The homologous series of these compounds begins with methyl alcohol or methanol (CH3OH), followed by ethanol (C2H5OH), then propanol (C3H7OH), etc.

Alcohol is characterized by the isomerism of the carbon skeleton and functional group.

Monohydric alcohols exhibit such physical properties :

1. Alcohols containing up to 15 carbon atoms - liquids, 15 and more - solids.
2. The solubility in water depends on the molecular weight; the higher it is, the alcohol is less soluble in water. So, lower alcohols (before propanol) are mixed with water in any proportions, and higher ones are practically insoluble in it.
3. The boiling point also increases with increasing atomic mass, for example, t bales. CH3OH = 65 ° C, and t bales. 25 = 78 ° .
4. The higher the boiling point, the lower the volatility, i.e. the substance does not evaporate well.

These physical properties of saturated alcohols with one hydroxyl group can be explained by the appearance of an intermolecular hydrogen bond between individual molecules of the compound itself or of alcohol and water.

Monohydric alcohols are able to enter into such chemical reactions:

1. Combustion - the flame is bright, heat is released: 25 + 32 - 22 + 22.
   
2. Substitution is the interaction of alkanols with active metals, the reaction products are unstable compounds - alcoholates, - capable of decomposing water: 225 + 2 - 225 + 2.
3. Reaction with hydrohalic acids: 25 + HBr - 25Br + 2.
4. Esterification with organic and inorganic acids, resulting in the formation of ether.
5. Oxidation, which produces aldehydes or ketones.
6. Dehydration. This reaction occurs when heated with a catalyst. Intramolecular dehydration in lower alcohols occurs according to the Zaitsev rule, the result of this reaction is the formation of water and an unsaturated hydrocarbon. In intermolecular dehydration, the reaction products are ethers and water.

Having examined the chemical properties of alcohol, we can conclude that monohydric alcohols are amphoteric compounds, because they can react with alkali metals, exhibiting weak acidic properties, and with hydrogen halides, exhibiting basic properties. All chemical reactions proceed with an O — H or C — O bond break.

Thus, saturated monohydric alcohols are complex compounds with one OH group that do not have free valencies after the formation of the C — C bond and exhibit weak properties of both acids and bases. Due to their physical and chemical properties, they are widely used in organic synthesis, in the production of solvents, fuel additives, as well as in the food industry, medicine, cosmetology (ethanol).