benzen cl2

Question

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we know that halogenation of benzene adds a halogen lớn benzene in presence of a strong electrophile. but what if we use chlorine as a halogen but use an electrophile made out of a different halogen, lượt thích bromine?

asked Dec 29, 2022 at 11:07

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Oscar LanziOscar Lanzi 50.5k2 gold badges82 silver badges151 bronze badges · Accepted Answer

Typically mixing a halogen electrophile with a catalyst using a different halide ion is not done in Friedel-Crafts halogenations. Here's why in the case described in the question.

The electrophile could be changed through halogen displacement. Here, that would be chlorine reacting with $\ce{FeBr3}$, independently of the benzene, sánh the electrophile in subsequent reaction with benzene becomes bromine instead of chlorine. Since the chlorine could alternatively act as an electrophile first, you get a mixture of halobenzene products.
When the proton is displaced, it will combine with a halide ion abstracted from the halide molecule/complex anion. But that could be bromide instead of chloride, giving a mixed hydrogen halide product and altering the catalyst (and perhaps its solubility and Lewis acidity).

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So you risk mixing up the organic product, the displaced hydrogen halide and the catalyst. Don't go there. Match the halide ion in the catalyst with the halogen electrophile.