Question

Why isn’t FeBr₃ used as a catalyst in the first step of the synthesis of 1,3,5-tribromobenzene?

Short answer

Due to excess Br⁺ ions, FeBr₃ is not used as a catalyst in the first step of synthesizing 1,3,5-tribromobenzene.

Step-by-step solution

Reactions of arene diazonium salt

An iodo substituent replaces the diazonium group if potassium iodide is added to a solution comprising the diazonium ion.

The treatment of arene diazonium chloride with fluoroboric acid leads to substituting the fluorine group in the place of the diazonium group.

The reason why FeBr3 is not used as a catalyst in the first step of synthesizing 1,3,5-tribromobenzene

The amine group of aniline is a strong activating substituent. It contributes electrons to the ring by resonance due to the lone pair of electrons on nitrogen. It reacts with bromine to form 2,4,6-tribromoaniline.

The amine group of 2,4,6-tribromoaniline is converted to arenediazonium salt. It reacts with hypophosphoric acid to produce 1,3,5-tribromobenzene. Hence, FeBr₃ is not used as a catalyst in the first step of synthesizing 1,3,5-tribromobenzene.