ALCOHOLS

Alcohols or Alkanols are organic compounds with an -OH functional group.

Functional group is a group of atoms which is bonded to a carbon atom in an organic compound and which give distinct chemical properties to the compound.

The general formula of alcohol (alkyl alcohol) is C_nH_2n+1OH where n ≥ 1. Their names end up with suffix -ol.

IUPAC name	Molecular formula	Formula	Condensed formula	Common name
1 Methanol	CH₃OH	H-C-O-H	CH₃OH	Methyl alcohol
2 Ethanol	C₂H₅OH	H-C-C-O-H	CH₃CH₂OH	Ethyl alcohol
3 Propanol	C₃H₇OH	H-C-C-C-O-H	CH₃CH₂CH₂OH	Propyl alcohol
4 Butanol	C₄H₉OH	H-C-C-C-C-O-H	CH₃CH₂CH₂CH₂OH	Butyl alcohol

Nomenclature of Alcohols

Select the longer continuous carbon chain containing hydroxy group (OH group).
Number the carbon atoms in this longest chain beginning at the end nearest to the -OH group.
Name this longest chain by substituting the ending -ol for the -e of the corresponding alkane.

Isomerism in Alcohols

Isomerism in alcohols is caused by:

The branching of the carbon chain
The different locations of the OH group.

1. Butanol (C₄H₉OH)

CH₃CH₂CH₂CH₂OH - Butan-1-ol
CH₃CH₂CH(OH)CH₃ - Butan-2-ol
(CH₃)₂CHCH₂OH - 2-methylpropan-1-ol
(CH₃)₃COH - 2-methylpropan-2-ol

2. Pentanol (C₅H₁₁OH)

CH₃CH₂CH₂CH₂CH₂OH - Pentan-1-ol
CH₃CH₂CH₂CH(OH)CH₃ - Pentan-2-ol
CH₃CH₂CH(OH)CH₂CH₃ - Pentan-3-ol
(CH₃)₂CHCH₂CH₂OH - 3-methylbutan-1-ol
(CH₃)₂C(OH)CH₂CH₃ - 2-methylbutan-2-ol
CH₃CH₂CH(OH)CH(CH₃)₂ - 3-methylbutan-2-ol
(CH₃)₃CCH₂OH - 2,2-dimethylpropan-1-ol

Classification of Alcohols

The alcohols are classified into three groups:

Primary alcohols (1° - alcohols)
Secondary alcohols (2° - alcohols)
Tertiary alcohols (3° - alcohols)

(i) Primary Alcohols

These are the ones in which the carbon to which the OH group is attached is bonded to only one other carbon atom.

CH₃CH₂CH₂OH or H-C-C-C-OH

(ii) Secondary Alcohols

These are the ones in which the carbon to which the OH group is attached is bonded to two other carbon atoms.

CH₃CH(OH)CH₃ - propan-2-ol
CH₃CH₂CH(OH)CH₂CH₃ - pentan-3-ol

(iii) Tertiary Alcohols

These are the ones in which the carbon to which the OH group is attached is bonded to three other carbon atoms.

(CH₃)₃COH - 2-methylpropan-2-ol
CH₃CH₂C(OH)(CH₃)₂ - 2-methylbutan-2-ol

PREPARATION OF ALCOHOLS

Ethanol is produced through the fermentation of carbohydrates

Fermentation is the process in which large organic molecules are broken down into smaller molecules with the help of living organisms, especially yeasts.

Fermentation is the reaction where sugar is converted to alcohol/alkanol using biological catalyst/enzymes in yeast.

It involves three processes:

Conversion of starch to maltose using the enzyme diastase:

C₆H₁₀O₅(s) + H₂O(l) → C₁₂H₂₂O₁₁(aq) (maltose)
Hydrolysis of maltose to glucose using the enzyme maltase:

C₁₂H₂₂O₁₁(aq) + H₂O(l) → 2C₆H₁₂O₆(aq) (glucose)
Conversion of glucose to ethanol and carbon dioxide gas using the enzyme zymase:

C₆H₁₂O₆(aq) → 2C₂H₅OH(aq) + 2CO₂(g)

All enzymes involved are produced by yeast.
The optimum temperature for yeast to catalyze its process is 37°C.
If the ethanol content in the mixture rises to around 15%, the yeast is killed.
If a more concentrated solution of ethanol is required, the mixture is fractionally distilled.

PROPERTIES OF ETHANOL/ALCOHOL

(a) Physical Properties

Lower members of alcohols are liquid at room temperature (methanol, ethanol and propanol).
The solubility of alcohol in water decreases with increasing carbon chain.
They are colorless and volatile.
They are characterized by a distinct smell.
The melting point and boiling point increase with increase in molecular mass.

(b) Chemical Properties

Reaction with sodium:

2C₂H₅OH(aq) + 2Na(s) → H₂(g) + 2C₂H₅ONa(aq) (sodium ethoxide)
2CH₃OH(aq) + 2Na(s) → 2CH₃ONa(aq) + H₂(g)
Dehydration by concentrated H₂SO₄:

C₂H₅OH(l) → C₂H₄(g) + H₂O(l)
Oxidation reaction:

CH₃CH₂OH(aq) + [O] → CH₃CHO + H₂O(l) (ethanal)
In excess of [O], the aldehyde is oxidized to carboxylic acid:
CH₃CH₂OH(aq) + 2[O] → CH₃COOH + H₂O

[O] represents the oxygen from the oxidizing agent (K₂Cr₂O₇/KMnO₄ - acidified).
Combustion of alcohol:

CH₃CH₂OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)
Reaction with carboxylic acid (Esterification reaction):

CH₃COOH + CH₃OH → CH₃COOCH₃ + H₂O (methyl ethanoate)
C₂H₅COOH + CH₃OH → C₂H₅COOCH₃ + H₂O (methyl propanoate)

An alcohol reacts with organic acids to form sweet smelling compounds called esters.

Uses of Ethanol

It is used in alcoholic drinks.
It is used as fuel.
Ethanol is a good solvent for gums and paints.
It is used in the manufacture of other organic chemicals like acetaldehyde, chloroform, etc.

HARMFUL EFFECTS OF ALCOHOL

Excessive consumption of alcohol leads to addiction. ADDICTION is a situation whereby someone becomes dependent on alcohol. A person who is addicted to alcohol cannot stay for long time without drinking. A person who is addicted to alcohol is termed as an alcoholic.

The following are some of the negative effects of alcohol in the society:

Neglecting families and other relationships. The neglected family suffers financial difficulties which could lead to divorce.
Children from neglected families can also get involved in criminal activities.
Alcoholics are sometimes violent and may cause injuries to other people.

Health Problems Associated with Alcoholism

Damage of the liver.
Damage of the brain cells.
Damage to the heart due to destruction of heart muscles.
Alcohol is a diuretic, that is, it stimulates production of urine.
Excessive consumption of alcohol by pregnant women may lead to defects in an unborn baby.
The alcoholic may develop anemia if he or she does not eat well.

Important Summary

General formula: C_nH_2n+1OH

The general formula can be represented as R-OH where R stands for alkyl group.