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, the molecules of which have undergone changes, 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 is as follows: 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 isomerism of the carbon skeleton and functional group.

Monohydric alcohols exhibit such physical properties :

1. Alcohols containing up to 15 carbon atoms are liquids, and 15 or more are solids.
2. The solubility in water depends on the molecular weight, the higher it is, the alcohol is less soluble in water. Thus, lower alcohols (up to propanol) are mixed with water in any proportions, while the higher alcohols are practically insoluble in it.
3. The boiling point also increases with increasing atomic mass, for example, t bp. CH3OH = 65 ° C, and t is boiling. C2H5OH = 78 ° C.
4. The higher the boiling point, the lower the volatility, i.e. The substance evaporates poorly.

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 alcohol and water.

Monohydric alcohols are able to enter into such chemical reactions:

1. Burning - the flame is bright, heat is released: C2H5OH + 3O2 - 2CO2 + 2H2O.
2. Replacement - the interaction of alkanols with active metals, reaction products are unstable compounds - alcoholates, - capable of decomposing water: 2C2H5OH + 2K - 2C2N5OK + H2.
3. Interaction with hydrohalic acids: C2H5OH + HBr-C2H5Br + H2O.
4. Esterification with organic and inorganic acids, as a result of which an ether is formed.
5. Oxidation, which produces aldehydes or ketones.
6. Dehydration. This reaction occurs when heated by a catalyst. Intramolecular dehydration in lower alcohols occurs according to Zaitsev's rule, the result of this reaction is the formation of water and unsaturated hydrocarbon. When intermolecular dehydration reaction products are ethers and water.

Having considered the chemical properties of alcohol, it can be concluded that monohydric alcohols are amphoteric compounds, They can react with alkali metals, exhibiting weak acid properties, and with hydrogen halides, showing basic properties. All chemical reactions proceed with the disruption of the bond O-H or C-O.

Thus, the limiting monohydric alcohols are complex compounds with one OH group that do not have free valences after the formation of a CC bond and exhibit weakly acid and base properties. Due to their physical and chemical properties, they have found wide application in organic synthesis, in the production of solvents, additives to fuel, as well as in the food industry, medicine, cosmetology (ethanol).