Final answer:
The halogenation of benzene with bromine is an electrophilic aromatic substitution reaction that uses an iron catalyst to facilitate the substitution of a hydrogen atom with a bromine atom, producing bromobenzene.
Step-by-step explanation:
The mechanism for a halogenation of benzene with bromine involves an electrophilic aromatic substitution reaction. Benzene, being stabilized by electron delocalization in its aromatic ring, reacts with bromine in the presence of a catalyst such as iron (Fe) or iron(III) bromide (FeBr3). The catalyst polarizes the bromine molecule, making one of the bromine atoms more positive. Benzene behaves as a nucleophile and its pi electrons attack this electrophilic bromine to form a non-aromatic sigma complex intermediate, which quickly loses a proton to reform the stable aromatic ring, ultimately substituting one hydrogen atom on the benzene ring with a bromine atom. The product of this reaction is bromobenzene and hydrogen bromide. It should be noted that when halogenating benzene, the presence of an iron catalyst is essential to proceed with formation of the aryl halide.