Preparation of Ketones: Structure of Ketones, Reactions of Ketones (For CBSE, ICSE, IAS, NET, NRA 2022)

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What Are Ketones?

  • They constitute an important class of organic compounds containing the carbonyl group.
  • The removal of the alcohol, resulting from the reduction of a cheap aldehydes or ketone used as the oxidant, meets the problem of alcohol being less volatile than the corresponding carbonyl compound.
  • Ketones form the foundation for many building blocks. It can be used as paints, lacquers, textiles, solvents (manufacturing explosives) , etc.
  • It is also useful for tanning, preservation and in applications of hydraulic fluids.

Structure of Ketones

  • Ketone is a class of carbonyl compounds in which carbon atom and oxygen atom forms a covalent bond.
  • The rest of the two bonds join with the carbon atom or other radicals of hydrocarbons (aryl or alkyl group) .

Reactions of Ketones

  • Ketones are reactive compounds.
  • Though, they are less reactive in comparison to aldehydes even though ketones are closely related to aldehydes.
  • So, The similarity in nature is due to a carbonyl group which forms the basis of chemical reactivity for both the compounds (aldehydes and ketones) .

List of Preparation of Ketones

  • Ketones are an organic compound containing carbonyl groups (C = O) . The general formula for a ketone is R (C = O) R′, where R and R′ can be alkyl or aryl groups.
  • They are classified into two categories by their substituents:
  • symmetrical ketones: when two identical groups are attached to the carbonyl group
  • Asymmetrical ketones: when two different groups are appended to the carbonyl group
  • Many methods exist for the preparation of ketones at industrial scale and in laboratories. Standard methods include oxidation of alcohol, hydrocarbons, etc. Some general methods for the preparation of ketones are explained below:
    • Preparation of Ketones from Acyl Chlorides
    • Preparation of Ketones from Nitriles
    • Preparation of Ketones from Benzenes or Substituted Benzenes

Preparation of Ketones from Acyl Chlorides

Preparation of Ketones from Acyl Chlorides
  • Acyl chlorides upon treatment with Grignard reagent and a metal halide, yield ketones.
  • Ketone formation is possible by the treatment of acid chloride with di-alkyl cadmium [ (R) 2 Cd] . Cadmium chloride reacts with the Grignard reagent to form Dialkylcadmium. However, ketone formation is not possible by Rosenmund՚s Reaction.
  • Dialkylcadmium thus formed is further reacted with acyl chlorides to form ketones.

Preparation of Ketones from Nitriles

Preparation of Ketones from Nitriles
  • Treatment of nitriles with Grignard reagent upon further hydrolysis yields ketones.
  • Nitrile undergoes treatment with nitrile with Grignard reagent and further undergoes hydrolysis to form ketones.

Preparation of Ketones from Benzenes or Substituted Benzenes

Preparation of Ketones
  • Electrophilic aromatic substitution of a benzene ring with acid chlorides in the presence of a Lewis acid such as AlCl3 results in the formation of ketones.
  • This reaction is popularly known as Friedel Craft՚s acylation reaction.
  • Aromatic ketone formation is possible from benzene or substituted benzenes.
  • The most suitable preparation technique for an aromatic aldehyde is Friedel-Crafts acylation reaction.
  • In this reaction benzene or substituted benzenes undergoes treatment with an acid chloride or acid anhydride to form ketones.