Question

give five methods of preparation of aldehydes.​

Answer 1

Aldol Condensation.

Cannizzaro Reaction.

Finkelstien Reaction.

Friedel-Crafts Alkylation & Acylation.

Hoffmann Bromamide Reaction.

Answer 2

Five methods to prepare Aldehydes are explained below.

Explanation:

1) Oxidation of alcohol:

• Aldehydes are formed by the oxidation of primary alcohols, whereas secondary alcohol forms ketones.

$RCH_{2}OH+ KMnO_{4}/H^+$ → $RCHO$

2) Dehydrogenation of alcohols:

• This method is used in industries, when primary alcohol is passed through a metal catalyst, it gives out an aldehyde.

$C_{2}H_{5}OH+Cu (573K)$ → $CH_{3}CHO$

3) From hydrocarbons such as Alkenes:

• Alkenes are done ozonolysis and then the product is reacted with zinc dust and water.

$C_{2}H_{4}+O_{3}$ → $C_{2}H_{4}O_{3}+Zn/H_{2}O$ → $CH_{3}CHO$

4) Etard reaction:

• In this reaction, methylbenzene is reacted with chromyl chloride to form a benzaldehyde.

$C_{6}H_{5}CH_{3}+CrO_{2}Cl_{2}$ → $C_{6}H_{5}CHO$

5) Gatterman-Koch reaction:

• In this reaction, benzene is reacted with carbon monoxide and hydrogen chloride in the presence of aluminium chloride to form a benzaldehyde.

$C_{6}H_{5}+HCl+CO+AlCl_{3}$ → $C_{6}H_{5}CHO$