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:

  1. Monohydric
  2. Dihydric
  3. Trihydric
  4. Polyhydric

Based on the carbon to which OH group is attached alcohols are of 3 types:

  1. Primary alcohols
  2. Secondary alcohols
  3. 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

  1. It is a colourless liquid with characteristic smell.
  2. It has burning taste.
  3. 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).
  4. Its dissolution in H2O is exothermic and there is slight contraction in volume.
  5. Non ideal solution.

Chemical Reactions

The reactions of alcohols involve either cleavage of O - H bond or C - OH bond.