Preparation of Aldehydes from Methylbenzene (Etard and Gattermann-Koch Reactions)
Aromatic aldehydes are prepared from methylbenzene by the Etard reaction (chromyl chloride) or Gattermann-Koch reaction (CO, HCl, anhydrous AlCl3/CuCl).
What is Preparation of Aldehydes from Methylbenzene (Etard and Gattermann-Koch Reactions)?
A reaction where methylarenes are oxidized to the corresponding aldehydes using chromyl chloride.
Key formula / rule: Etard Reaction (Overall)
Key points
- To understand the mechanisms of Etard and Gattermann-Koch reactions.
- To identify the reagents and conditions required for these reactions.
- To differentiate between the Etard and Gattermann-Koch reactions.
- To apply these reactions for the synthesis of benzaldehyde from methylbenzene.
Common exam trap
Using strong oxidizing agents like KMnO4 or K2Cr2O7 which lead to over-oxidation to carboxylic acids.
Definitions
- Term
Etard Reaction
- Meaning
A reaction where methylarenes are oxidized to the corresponding aldehydes using chromyl chloride.
- Term
Gattermann-Koch Reaction
- Meaning
A formylation reaction that introduces a formyl group (-CHO) onto an aromatic ring using carbon monoxide and hydrogen chloride in the presence of a Lewis acid catalyst.
- Term
Chromyl Chloride
- Meaning
A reddish-brown liquid, CrO2Cl2, used as a selective oxidizing agent for converting methylarenes to benzaldehydes.
- Term
Formylation
- Meaning
The introduction of a formyl group (-CHO) into a molecule.
Learning objectives
To understand the mechanisms of Etard and Gattermann-Koch reactions.
To identify the reagents and conditions required for these reactions.
To differentiate between the Etard and Gattermann-Koch reactions.
To apply these reactions for the synthesis of benzaldehyde from methylbenzene.
Formulae
- Name
Etard Reaction (Overall)
- Note
Hydrolysis of the intermediate complex yields benzaldehyde.
- Expression
C6H5CH3 + 2CrO2Cl2 → [Intermediate Complex] → C6H5CHO
- Name
Gattermann-Koch Reaction
- Note
Generates formyl cation (HCO+) as the electrophile.
- Expression
C6H5CH3 + CO + HCl --(Anhydrous AlCl3/CuCl)-→ C6H5CHO + HCl
Prerequisites
Structure and nomenclature of aromatic hydrocarbons (methylbenzene).
Basic concepts of oxidation and reduction reactions.
Understanding of electrophilic aromatic substitution reactions.
Properties and reactivity of Lewis acids.
Common mistakes
Using strong oxidizing agents like KMnO4 or K2Cr2O7 which lead to over-oxidation to carboxylic acids.
Incorrectly handling anhydrous conditions required for Gattermann-Koch reaction.
Not controlling the stoichiometry or reaction time in Etard reaction, leading to byproducts.
Confusing the reagents and conditions for Etard and Gattermann-Koch reactions.
Keywords
Methylbenzene
Toluene
Benzaldehyde
Etard Reaction
Gattermann-Koch Reaction
Chromyl Chloride
Carbon Monoxide
Hydrogen Chloride
Lewis Acid
Oxidation
Formylation
Aromatic Aldehydes
Practice preview
Which reagent is used in Etard reaction for the preparation of benzaldehyde from toluene?…
easy
The reaction of toluene with chromyl chloride in carbon disulfide followed by hydrolysis yields benzaldehyde. This reaction is known as:…
medium
What is the product when toluene is treated with CO and HCl in the presence of anhydrous AlCl3/CuCl?…
medium