The substitution of an aromatic amino group is possible via preparation of its diazonium salt and subsequent displacement with a nucleophile (Cl-, I-, CN-, RS-, HO-). Many Sandmeyer Reactions proceed under copper(I) catalysis, while the Sandmeyer-type reactions with thiols, water and potassium iodide don't require catalysis.
The Sandmeyer Reaction is a very important transformation in aromatic chemistry, because it can result in some substitution patterns that are not achievable by direct substitution.
Fluorination is possible by using the related Schiemann Reaction.
Mechanism of the Sandmeyer Reaction
Halo- and Azidodediazoniation of Arenediazonium Tetrafluoroborates with Trimethylsilyl Halides and Trimethylsilyl Azide and Sandmeyer-Type Bromodediazoniation with Cu(I)Br in [BMIM][PF6] Ionic Liquid
A. Hubbard, T. Okazaki, K. K. Laali, J. Org. Chem., 2008, 73, 316-319.
Unusually Stable, Versatile, and Pure Arenediazonium Tosylates: Their Preparation, Structures, and Synthetic Applicability
V. D. Filimonov, M. Trusova, P. Postnikov, E. A. Krasnokutskaya, Y. M. Lee, H. Y. Hwang, H. Kim, K.-W. Chi, Org. Lett., 2008, 10, 3961-3964.
Sulfonic Acid Based Cation-Exchange Resin: A Novel Proton Source for One-Pot Diazotization-Iodination of Aromatic Amines in Water
V. D. Filimonov, N. I. Semenischeva, E. A. Krasnokutskaya, A. N. Tretyakov, H. Y. Hwang, K.-W. Chi, Synthesis, 2008, 185-187.
A New, One-Step, Effective Protocol for the Iodination of Aromatic and Heterocyclic Compounds via Aprotic Diazotization of Amines
E. A. Krasnokutskaya, N. I. Semenischeva, V. D. Filimonov, P. Knochel, Synthesis, 2007, 81-84.