Class 12 Chemistry Notes – Methods of preparation of Alcohols

From Haloalkanes:-

When HaloAlkanes (alkyl halides) are heated with aqueous sodium or Potassium Hydroxide, they forms alcohols

From Alkenes:-

Alcohols can be produced from Alkenes by their Hydration, by passing alkenes through concentrated H₂SO₄ and then hydrolysis with boiling water gives alcohols.

Mechanism: – it involves following steps

(i) Electrophilic attack by hydroxyl union on alkenes gives a carbocation intermediate :-

 

(ii) Nucleophilic attack by water on 2⁰ carbocation

 

(iii) Deprotonation or loss of proton to form alcohol

 

From Hydroboration – oxidation :- B₂H₆ (Diborane) if C- deficient molecule it acts as an electrophilic and react with alkenes to form trialkylborates  which on subsequent oxidation with alkaline H₂O₂ gives alcohols

From Carbonyl Compounds:-

• By reduction of aldehyde and ketones.

R – CHO reacting with H2/Ni or Na/ C₂H₅OH giving R – CH₂ OH.

Aldehyde or LiAlH₄ or NaBH₄  1^o alcohol

• By reduction of Carboxylic acids and esters:-

 

From Oxy-Mercuration DeMercuration of alkene:-

By simple addition of water to alkene reagent used in this process is mercuric acetate

 

Form Grignard Reagents:-

Regents are alkyl or aryl magnesium halides (R – MgX)

Process:-

 

Basic magnesium halide

 

Example : From aldehyde gives alcohol

 

Hydrolysis of ester

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