Methods of Preparation of Haloarenes

Direct halogenations

Chlorobenzene is prepared by direct chlorination of benzene in the presence of Lewis acid catalysts such as FeCl₃.

From benzene diazonium chloride

Chlorobenzene is prepared by the Sandmeyer reaction or the Gattermann reaction using benzene diazonium chloride.

Sandmeyer reaction

When an aqueous solution of benzene diazonium chloride is warmed with Cu₂Cl₂ in HCl, chlorobenzene is formed.

Preparation of iodobenzene

Iodobenzene is prepared by warming benzene diazonium chloride with aqueous KI solution.

\[\ce{\underset{(\underset{\underset{chloride}{benzene diazonium}}{Sandmeyer rection)}}{C6H5N2Cl + Kl} ->[warm] \underset{Iodo benzene}{C6H5I + N2 + KCl}}\]

Preparation of fluorobenzene

Aryl fluorides are prepared by

When a diazonium salt is treated with fluoroboric acid (HBF), the diazonium fluoro borate precipitates out of solution. If this precipitated salt is filtered and then heated, it decomposes to give the aryl fluoride.

Commercial preparation of chloro benzene (Raschig process)

Chlorobenzene is commercially prepared by passing a mixture of benzene vapour, air and HCl over heated cupric chloride. This reaction is called the Raschig process.