Alcohols
Alcohols are the organic compounds with -OH group as the functional group. They are monoalkyl derivatives of water.
Based on the number of OH groups alcohols are classified as:
- Monohydric
- Dihydric
- Trihydric
- Polyhydric
Based on the carbon to which OH group is attached alcohols are of 3 types:
- Primary alcohols
- Secondary alcohols
- Tertiary alcohols
Isomerism in Alcohols
They exhibit chain, position, functional isomerism.
Ethyl Alcohol: C2H5OH
Preparation
1. By the hydrolysis of ethyl halide (industrial method): Ethyl halide on hydrolysis with aqueous sodium hydroxide or potassium hydroxide gives ethyl alcohol.
2. By the hydrolysis of ester: Hydrolysis of ethyl acetate with aqueous alkali gives ethyl alcohol.
3. By the hydration of Ethylene (industrial method): Ethylene on reaction with conc. sulphuric acid at 75 - 80°C gives ethyl alcohol.
4. By the reduction of Acetaldehdye (CH3-CHO): Acetaldehyde on reduction with Hydrogen and Nickel or Lithium aluminum hydride gives ethyl alcohol.
5. From Grignard reagent and formaldehyde: Methyl magnesium halide on reaction with formaldehyde followed by hydrolysis gives ethyl alcohol.
Physical Properties
- It is a colourless liquid with characteristic smell.
- It has burning taste.
- It forms hydrogen bonds with water and also with it itself therefore it exists as associated liquid, soluble in water and boiling point is very high (78.1 °C).
- Its dissolution in H2O is exothermic and there is slight contraction in volume.
- Non ideal solution.
Chemical Reactions
The reactions of alcohols involve either cleavage of O - H bond or C - OH bond.