Benzene reacts with methanoyl chloride (HCOCl) in the presence of a catalyst - AQA - A-Level Chemistry - Question 8 - 2022 - Paper 2
Question 8
Benzene reacts with methanoyl chloride (HCOCl) in the presence of a catalyst.
08.1 Give an equation for the overall reaction when benzene reacts with methanoyl chlo... show full transcript
Worked Solution & Example Answer:Benzene reacts with methanoyl chloride (HCOCl) in the presence of a catalyst - AQA - A-Level Chemistry - Question 8 - 2022 - Paper 2
Step 1
08.1 Give an equation for the overall reaction when benzene reacts with methanoyl chloride. Name the organic product.
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Answer
The overall reaction can be represented as:
C6H6+HCOCl→C6H5CHO+HCl
The organic product formed in this reaction is benzaldehyde.
Step 2
08.2 Identify the catalyst needed in this reaction. Give an equation to show how the catalyst is used to form the electrophile, [HCO]⁺.
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Answer
The catalyst needed for this reaction is Aluminum chloride (AlCl₃).
The formation of the electrophile can be illustrated as follows:
HCOCl+AlCl3→[HCO]++[AlCl4]−
Step 3
08.3 Outline the mechanism for the reaction of benzene with the electrophile, [HCO]⁺.
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Answer
The mechanism proceeds in several steps:
Electrophilic Attack: An arrow from the benzene π electrons attacks the electrophile, [HCO]⁺, leading to the formation of a sigma complex (also known as an arenium ion).
Proton Loss: A proton is lost from the sigma complex, restoring the aromaticity of the benzene ring.
The final product is benzaldehyde with the release of a proton:
C6H5+HCO+→C6H5CHO
Key Points:
Initiation with the electrophile and deprotonation are crucial for restoring the aromaticity.
