3.  Methods used for the preparation of Aldehydes only

Methods used for the preparation of Aldehydes only

Rosenmund's reduction :

Here acid chlorides are reduced to aldehyde with H₂ in boiling xylene using palladium as a catalyst supported on barium sulphate.

Note :

(a) Pd Catalyst is poisoned by BaSO₄ to check further reduction of aldehyde to alcohol.

(b) Formaldehyde cannot be obtained by this method because HCOCl is unstable at common temperature.

(c) Reaction with acid chloride and dialkyl cadmium we can obtain ketone.

Stephen's reduction :

Oxo-process :

It is also called as carbonylation here alkene reacts with water gas at high temperature and pressure in the presence of cobalt carbonyl catalyst to give aldehyde.

Reimer-Teimann Reaction :

By this method phenolic aldehyde is prepared

From esters or nitrile :

DIBAL–H : Diisobutyl aluminium hydride [AlH(i-Bu)₂] is a reducing agent.

From hydrocarbons :

By oxidation of methyl benzene and its derivative using chromyl chloride (CrO₂Cl₂)

This reaction is called Etard reaction.

By oxidation of methyl benzene and its derivative using chromic oxide (CrO₃) in acetic anhydride:

By Gatterman-Koch reaction :