Question

Describe a method for the preparation of haloarenes from benzene.

Answer 1

Method for preparation of haloarenes from benzene:

1. Electrophilic substitution method: Haloarenes are prepared by direct halogenation of benzene using halogens (Cl₂, Br₂) in the presence of a catalyst such as ferric halides (FeCl₃, FeBr₃).
   Reaction details: The catalyst generates an electrophilic halogen species. Benzene undergoes electrophilic substitution, where one hydrogen is replaced by a halogen atom.
   Example equation: \[\mathrm{C_6H_6} + \mathrm{Cl_2} \xrightarrow{\mathrm{FeCl_3}} \mathrm{C_6H_5Cl} + \mathrm{HCl}\]
2. Alternative method (Sandmeyer reaction): Involves conversion of aniline to diazonium salt followed by reaction with cuprous halides (e.g., CuCl) to substitute nitrogen by halogen.
   \[ \mathrm{C}_6\mathrm{H}_5\mathrm{N}_2^+ \mathrm{Cl}^- + \mathrm{CuCl} \rightarrow \mathrm{C}_6\mathrm{H}_5\mathrm{Cl} + \mathrm{N}_2\]
3. Gattermann reaction: Preparation of haloarenes by reaction of diazonium salt with halogen acid and cuprous halide catalyst.

Thus, benzene can be converted to haloarenes primarily by electrophilic substitution or via diazonium salts (Sandmeyer/Gattermann reactions).