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Preparation of Aldehydes and Ketones

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By oxidation of alcohols

We have already studied in alcohols and phenols that oxidation of alcohols converts 1° and 2° alcohols to aldehydes and ketones respectively when any one of the following is used :

Primary alcohols are oxidised to aldehydes

preparation of aldehydes from primary alcohols

Secondary alcohols are oxidised to ketones

preparation of ketones from secondary alcohols

From hydrocarbons

Ozonolysis of alkenes

Alkenes react with O3 in the presence of Zn and H2O to produce aldehydes or ketones depending upon the structure of alkene.

Ozonolysis of alkenes
Ozonolysis of alkenes
Ozonolysis of alkenes to give ketone

Ozonolysis is discussed in details in reactions of alkenes.

From hydration of alkynes

Alkynes undergo hydration according to Markovnikov's rule in the presence of catalyst HgSO4 and H2SO4 to give ketones.

preparation of ketones by hydration of alkynes

Exception : Ethyne gives aldehyde instead of ketones.

hydration of ethyne gives aldehydes not ketones

From acid chlorides

Rosenmund's reduction

Acid chloride is hydrogenated over catalyst Pd on BaSO4 and partially poisoned by the addition of Sulphur or quinoline to give aldehydes.

Rosenmund's reduction to prepare aldehydes

Important points regarding Rosenmund's reaction

Preparation of ketones

Treatment of acid chloride with dialkylcadmium [(R)2Cd] gives ketones.

ketones are prepared by treating acid chlorides with dialkylcadmium

From nitriles

  1. Nitriles are first reduced to corresponding imines with SnCl2 in the presence of HCl, which on hydrolysis give corresponding aldehydes. Preparation of aldehydes by this method is known as Stephen's reduction.
    preparation of aldehydes by stephen's reduction
    aldehydes can be prepared from nitriles
  2. Imines

    Imines contain carbon-nitrogen double bond and have the following structure :

    Structure of imines
  3. Nitriles can alternatively be reduced by diisobutylaluminium hydride (DiBAL-H) to imines, which on hydrolysis gives corresponding aldehydes.
    reduction of nitriles with diisobutylaluminiumhydride gives aldehydes
  4. Similarly, esters are also reduced to aldehydes with (DiBAL-H).
    Esters are reduced to aldehydes by DiBAL-H
  5. Treatment of nitriles with Grignard's reagents followed by hydrolysis yield ketones.
    preparation of ketones by reacting cyanide with grignard's reagent
    cyanide react with grignard reagents to give ketones

    Exception : HCN reacts with Grignard's reagents to form aldehyde (not ketone).

    hydrogen cyanide reacts with grignard reagents to give aldehydes and not ketones
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