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Acylation and Alkylation of Arenes
Benzene reacts with ethanoyl chloride.
a) Write a symbol equation for the reaction between benzene and ethanoyl chloride.
Answer
C6H6 + CH3COCl → C6H5COCH3 + HCl
b) Ethanoyl is not the electrophile that attacks the benzene. Write an equation showing the formation of the electrophile.
Answer
CH3COCl + AlCl3 → CH3CO+ + AlCl4–
c) Outline the mechanism for the reaction that forms the electrophile.
Answer
d) One of the species in the mechanism above is acting as a Lewis acid. State which species and explain your answer.
Answer
The AlCl3 behaves as a Lewis acid because it is accepting an electron pair from the CH3COCl.
e) Outline the mechanism for the reaction between the electrophile and benzene.
Answer
f) State the name of the catalyst and explain using the mechanisms above how it is behaving as a catalyst.
Answer
AlCl3 behaves as a catalyst.
In the first reaction, it reacts, forming AlCl4–. In the second reaction, the AlCl4– reacts with the benzene intermediate, helping to remove the hydrogen ion and reform the ring. In the process, AlCl4– becomes AlCl3 (and HCl is formed), regenerating the original catalyst.
g) Which of the following can be used as a replacement catalyst: iron chloride or ammonium chloride. Explain your answer.
Answer
Iron(III) chloride (FeCl3).
The iron in the FeCl3 can accept a pair of electrons due to having unfilled orbitals in its outer shell (Lewis acid behavior).
Propylbenzene can be formed from benzene.
a) State the name of the mechanism for this reaction.
Answer
Electrophilic Substitution
b) Write the overall equation for the reaction.
Answer
C6H6 + CH3CH2CH2Cl → C6H5CH2CH2CH3 + HCl
(Product can also be written as C6H5C3H7)
c) Write the equation for the reaction that forms the species that attacks the Benzene.
Answer
CH3CH2CH2Cl + AlCl3 → CH3CH2CH2+ + AlCl4–
d) Outline the mechanism for the reaction between benzene and the carbocation intermediate.
Answer
