Chemical properties of alcohols

Derivatives of hydrocarbons with one or more hydrogen atoms in the molecule substituted by -OH (hydroxyl group or hydroxy group) are alcohols. The chemical properties are determined by the hydrocarbon radical and the hydroxyl group. Alcohols form a separate homologous series, in it each subsequent representative differs from the previous term by the homologous difference corresponding to = CH2. All substances of this class can be represented by the formula: R-OH. For single-atom limit compounds, the general chemical formula has the form CnH2n + 1OH. According to the international nomenclature, names can be formed from a hydrocarbon with the addition of the end -ol (methanol, ethanol, propanol and so on).

This is a very diverse and extensive class of chemical compounds. Depending on the number of -OH groups in the molecule, it is divided into single-, two-triatomic and so on-polyatomic compounds. The chemical properties of alcohols also depend on the content of hydroxy groups in the molecule. These substances are neutral and do not dissociate into ions in water, such as strong acids or strong bases. However, they can be weakly manifested as acidic (they decrease with increasing molecular weight and branching of the hydrocarbon chain in the series of alcohols), and the basic (grow with increasing molecular weight and branching of the molecule) properties.

The chemical properties of alcohols depend on the type and spatial arrangement of the atoms: the molecules are with the isomerism of the chain and the isomerism of position. Depending on the maximum number of single bonds of the carbon atom (bonded to the hydroxy group) with other carbon atoms (with 1, 2 or 3), primary (normal), secondary or tertiary alcohols are distinguished. In primary alcohols, the hydroxyl group is attached to the primary carbon atom. In secondary and tertiary - to secondary and tertiary, respectively. Starting with propanol, isomers appear that differ in the position of the hydroxyl group: propyl alcohol C3H7-OH and isopropyl alcohol CH3- (CHOH) -CH3.

There are several basic reactions that characterize the chemical properties of alcohols:

1. When reacting with alkali metals or their hydroxides (the deprotonation reaction), alcoholates are formed (the hydrogen atom is replaced by a metal atom), methylates, ethylates, propylates are obtained depending on the hydrocarbon radical, and so on, for example, sodium propylate: 2CH3CH2OH + 2Na → 2CH3CH2ONa + H2 ↑.
2. When reacting with concentrated hydrohalic acids, halogen derivatives of hydrocarbons are formed: HBr + CH3CH2OH ↔CH3CH2Br + H2O. This reaction is reversible. As a result, the nucleophilic substitution of the hydroxyl group by a halogen ion occurs.
3. Alcohols can be oxidized to carbon dioxide, to aldehydes or to ketones. The alcohols burn in the presence of oxygen: 3O2 + C2H5OH → 2CO2 + 3H2O. Under the action of a strong oxidizing agent (chromic acid, potassium permanganate , etc.), primary alcohols are converted to aldehydes: C2H5OH → CH3COH + H2O, and secondary ones to ketones: CH3- (CHOH) -CH3 → CH3- (CHO) -CH3 + H2O.
4. The dehydration reaction proceeds with heating in the presence of dehydrating substances (zinc chloride, sulfuric acid and so on). As a result, alkenes are formed: C2H5OH → CH2 = CH2 + H2O.
5. The esterification reaction also occurs when heated in the presence of dehydrating compounds, but, unlike the previous reaction, at a lower temperature and with the formation of ethers: 2C2H5OH → C2H5-O-C2H5O. With sulfuric acid, the reaction occurs in two stages. First, the sulfuric acid ether is formed: C2H5OH + H2SO4 → C2H5O-SO2OH + H2O, then when heated to 140 ° C and in excess of alcohol, diethyl ether (often called sulfuric ether) is formed: C2H5OH + C2H5O-SO2OH → C2H5-O-C2H5O + H2SO4 .

The chemical properties of polyhydric alcohols, by analogy with their physical properties, depend on the type of hydrocarbon radical that forms the molecule, and, of course, the amount of hydroxyl groups in it. For example, ethylene glycol CH3OH-CH3OH (boiling point 197 ° C), which is a 2-atom alcohol, is a colorless liquid (has a sweetish taste) that mixes with H2O, as well as lower alcohols in any ratio. Ethylene glycol, like its higher homologues, enter into all the reactions characteristic of monohydric alcohols. Glycerin CH2OH-CHOH-CH2OH (boiling point 290 ° C) is the simplest representative of 3 atomic alcohols. It is a thick, sweet-to-taste liquid that is heavier than water, but mixes with it in any proportions. It dissolves in alcohol. For glycerol and its homologues, all reactions of monohydric alcohols are also characteristic.

The chemical properties of alcohols determine the directions of their application. They are used as a fuel (bioethanol or biobutanol and others), as solvents in various industries; As a raw material for the production of surfactants and detergents; For synthesis of polymeric materials. Some representatives of this class of organic compounds are widely used as lubricants or hydraulic fluids, as well as for the manufacture of drugs and biologically active substances.