Methods of Preparation

(1) Direct halogenation: benzene + Cl2 over a Lewis-acid catalyst (FeCl3) gives chlorobenzene + HCl. (2) From benzene diazonium chloride: (i) Sandmeyer reaction -- aqueous benzenediazonium chloride warmed with Cu2Cl2/HCl gives chlorobenzene + N2; the same transformation using copper powder instead of Cu2Cl2 is called the Gattermann reaction. (3) Iodobenzene: benzenediazonium chloride warmed with aqueous KI gives iodobenzene + N2 + KCl. (4) Fluorobenzene: benzenediazonium chloride + fluoroboric acid (HBF4) gives diazonium fluoroborate, which on heating gives fluorobenzene + BF3 + N2 -- the Balz-Schiemann reaction. (5) Commercial (Raschig proces …