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Many electrophilic aromatic halogenations require the presence of aluminum trihalide (halide-chloride or bromide) as a catalyst. Why is it unnecessary to include an aluminum trihalide in the electrophillic aromatic bromination reaction of acetanilide with molecular bromide?

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Answer: The aluminium trihalide assists in the heterolytic bond fission of the bromine molecule.

Step-by-step explanation:

The electrophilic aromatic bromination of acetalinide with molecular bromine requires the formation of Br+. This specie is formed when an Aluminum trihalide reacts with bromine. The Br-Br bond breaks heterolytically such that charged species are produced. This Br+ participates in the electrophilic aromatic substitution and AlX4- is formed where X4 shows a tetrahalide complex of aluminium

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