Properties of alcohols
Alcohols are organic compounds having a functional group OH- attached to a saturated carbon atom (sp3). Compounds of the hydroxyl group with sp2-hybridization are divided into phenols - with aromatic hydrocarbons, and enols - with aliphatic hydrocarbons.
Alcohols can be considered as derivatives of water. Physical and chemical properties of alcohols due to the presence of a hydroxyl group. The high electronegativity of oxygen causes the polarity of the O-H bond, which allows alcohols to form hydrogen bonds.
Hydrogen bonding is the cause of the high boiling point and water solubility of alcohols with low molecular weight mass. With the growth of the carbon skeleton, the solubility of alcohols in water decreases and the solubility in organic substances increases connections. The physical properties of phenols are similar to the physical properties of alcohols.
Alcohols are divided into primary, secondary and tertiary, according to the number of hydrocarbon groups attached to the atom carbon associated with the OH group.
Reactions of alcohols
There are four types of reaction with alcohols: with acid and base, oxidation and substitution.
Obtaining alcohols
There are a huge number of different ways to obtain alcohols from other compounds, but in industry the largest the applications were presented below.
From aldehydes and ketones
The best way to prepare alcohols are reactions with Grignard reagents (formula R-Mg-X and Ar-Mg-X). Group Mg-X has a weak positive charge, group R or Ar has a weak negative charge. Due to the breaking of the pi bond in the carbonyl group, carbon gets a positive charge, oxygen gets a negative one. Thus, the Mg-X group joins oxygen, group R/Ar - to carbon. The formed compound is treated with a weak hydrochloric acid solution, the result is alcohol and digalogenated magnesium.
Mechanism of production of alcohols from aldehydes and ketones:
RR-C=O + Rδ--(Mg-X)δ+ → RR-C(-R)-O-Mg-X
RR-C(-R)-O-Mg-X + H+Cl- → RRR-C-OH + MgClX
Made of carbon monoxide
The most important alcohols in the industry are methanol and ethanol. At the moment, a large amount of methanol is being produced catalytic reduction of carbon monoxide in the presence of hydrogen:
In the presence of Cu-ZnO-Cr2, O3 at a temperature of 250°C, 50-100 atm
CO + 2H2 → CH3OH
Ethanol is obtained by hydration of ethylene or fermentation of sugar from starch, barley or other cereals:
In the presence of yeast:
C6H12O6 → 2CH3CH2OH + 2CO2
To date, most ethanol is produced by catalytic hydration of ethylene with acid. Sulfuric acid forms alkylseric acid, which is then diluted with water and heated, which causes the hydrolysis process:
C2H4 + H+[OSO3H]- → CH3CH2OSO3H
CH3CH2OSO3H + H2O → CH3CH2OH + H2SO4
Esters
The formula of ether (ether) is R-O-R and Ar-O-R. An oxygen atom that binds two carbon groups.
The electronegativity of oxygen in ether molecules creates a dipole moment, which increases the boiling point of ethers compared to the corresponding alkanes. Since oxygen is not connected to the hydrogen atom in ethers, the boiling point of alcohols is much higher than the boiling point of ethers.
Esters, with the exception of dimethyl ether and methyl ethyl ether, are insoluble in water. For example, diethyl ether it is used to separate organic compounds from aqueous solutions without reacting with ionic compounds.
Diethyl ether is used as a solvent of nitrocellulose, which is used in paints and explosives. Tert-butylmethyl ether is used to increase the octane number.
Phenols
Preparation of phenols
Phenol is obtained by the nucleophilic substitution reaction of a chlorobenzene molecule (Doe method). The process consists in alkaline hydrolysis at high temperature and pressure:
weak NaOH solution, 300°, 200 atm
C6H6Cl → C6H6O-Na+
HCl
C6H6O-Na+ → C6H6OH
Application of phenols
Phenol and its derivatives are important in industry, in particular, medicines such as aspirin and epinephrine are obtained from phenols.
The first disinfection preparations were phenols. All phenols have bactericidal properties, which are enhanced with each alkyl group attached to the ring. Phenols with six alkyl groups have the best bactericidal properties, for example hexylresorcinol (1,3-dioxy-4-n-hexylbenzene, C12H18O2). Phenol is a measure for the "strength" of a bactericidal actions of other drugs.
Chlorophenols are widely used for disinfection, against bacteria and fungi. For example, pentachlorophenol is an excellent fungicide that preserves wood and protects it from termites and humidity.
Classification of alcohols
By the number of hydroxyl groups
Monatomic
(one group -OH), for example, methanol CH3OH, ethanol C2H5he, propanol WITH 3H7OH.
Polyatomic
(two or more groups -HE). for example, ethylene glycol HO–CH2–CH2–OH, glycerin HO–CH2–CH(OH)–CH2–OH.
Diatomic alcohols with two OH groups at the same carbon atom R-CH(OH)2 are unstable and, splitting off the water, they immediately turn into aldehydes R–CH =O.
By the nature of the carbon atom
Aliphatic alcohols are divided into primary, secondary and tertiary (depending on which atom a carbon bound hydroxy group.
>In polyatomic alcohols, primary, secondary and tertiary alcohol groups are distinguished. For example, a triatomic molecule glycerin alcohol contains two primary alcohol (HO–CH2–) and one secondary alcohol (–CH(OH)–) groups.
Primary
R–CH2–OH
Secondary
R2CH–OH
Tertiary
R3C–OH
According to the structure of the hydrocarbon radical
Limit values
marginal or alkanols (CH3OH, CH3CH2–OH).
Unsaturated
unsaturated, or alkenols (CH2=CH–CH2–OH) and alkynols (CH≡S-CH2HE).
Unsaturated alcohols with an OH group with a carbon atom connected to another atom by a double bond are very unstable and are immediately isomerized into aldehydes or ketones. For example, vinyl alcohol CH2=CH–OH turns into acetic aldehyde CH3–CH=O.
Aromatic
(C6H5CH2–OH) - not to be confused with phenols! Ar-OH.
In aromatic alcohols, the hydroxyl group is not bound to the carbon atom of the benzene ring. Compounds in which the hydroxyl group is bound to the benzene ring are called phenols.
The classification of alcohols is diverse and depends on which feature of the structure is taken as a basis.
