Fluoro compounds are not prepared by electrophilic substitution due to the high reactivity of fluorine. Reactions with iodine are reversible, and the presence of an oxidizing agent (HNO₃, HIO₄) is needed to oxidize the HI formed during iodination, making the process irreversible.
Why is the preparation of fluoro compounds not suitable by electrophilic substitution, and what is the significance of the presence of an oxidizing agent in reactions with iodine?
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The preparation of fluoro compounds is not suitable by electrophilic aromatic substitution due to the high reactivity and strong nucleophilicity of fluoride ions. Fluoride ions can react with the electrophile in a highly reversible manner, leading to side reactions and mixtures of products. Instead, the Sandmeyer reaction or nucleophilic substitution methods are employed for the synthesis of aryl fluorides.
In reactions with iodine, the presence of an oxidizing agent, such as copper(I) chloride (CuCl), helps convert iodide ions to electrophilic iodine species, facilitating the iodination reaction. The oxidizing agent ensures the availability of the reactive iodine electrophile for substitution on the aromatic ring.