Aldehydes, Ketones and Carboxylic Acids: Aldehydes and Ketones, Preparation of Ketones (For CBSE, ICSE, IAS, NET, NRA 2023)

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  • Some important organic compounds containing carbonyl group are carboxylic acids, aldehydes, and ketones.
  • These molecules are highly polar and so have high boiling temperatures when compared to hydrocarbons as well as weak polar compounds such as ethers of comparable molecular masses.
  • The lower embers form hydrogen bonds with water and therefore are highly water-soluble.
  • While, higher members have big size hydrophobic carbon chain and are insoluble in water.

Aldehydes and Ketones

  • Both aldehydes and ketones contain a carbonyl group, a functional group with a carbon-oxygen double bond.
  • The names for aldehydes and ketone compounds are derived using similar nomenclature rules as for alkanes and alcohols, and include the class-identifying suffixes – al and – one, respectively:
Both Aldehydes and Ketones
  • Method of preparing aldehyde is by controlled oxidation of primary alcohols or dehydrogenation and cautious or controlled reduction of acyl halides.
  • In an aldehyde, the carbonyl group is bonded to at least one hydrogen atom. In a ketone, the carbonyl group is bonded to two carbon atoms:
The Aldehyde and Ketones
  • Aromatic halides may be produced by oxidation of Methylbenzene with chromyl chloride in presence of acetic anhydride
  • Formylation of arenes with carbon monoxide along with hydrochloric acid in the presence of anhydrous AlCl3
  • CuCl or hydrolysis of C7H6Cl2
  • As text, an aldehyde group is represented as – CHO; a ketone is represented as – C (O) – or – CO – .
  • In both aldehydes and ketones, the geometry around the carbon atom in the carbonyl group is trigonal planar; the carbon atom exhibits sp2 hybridization.
  • Two of the sp2 orbitals on the carbon atom in the carbonyl group are used to form σ bonds to the other carbon or hydrogen atoms in a molecule.
  • The remaining sp2 hybrid orbital forms a σ bond to the oxygen atom.
  • The unhybridized p orbital on the carbon atom in the carbonyl group overlaps a p orbital on the oxygen atom to form the π bond in the double bond.

Preparation of Ketones

  • Ketones are prepared by oxidizing secondary alcohols and the hydration of alkynes.
  • They can also be prepared by reacting acyl chloride with dialkylcadmium. Ketones, as well as aldehydes, can also be prepared by ozonolysis of alkenes.
  • 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.