Methods leading to polyvalent iodine compounds

Aryl iodides are exceptional among the aromatic halogen compounds in that they form a series of derivatives in which the iodine exhibits a covalency greater than one. Some typical interconversions for which experimental conditions are given (Expts 6.31 to 6.36) are summarised below. 

Two polyvalent iodine compounds arising from o-iodobenzoic acid have been found to be useful synthetic reagents. Thus oxidation of the iodo acid (7) with potassium persulphate, followed by the addition of benzene and treatment with potassium iodide gives the iodonium iodide (8) which is converted into diphenyliodonium-2-carboxylate [DPIC (9)] with aqueous alkali (Expt 6.35).16 

DIPC has been used as a benzyne precursor17 into which it decomposes at 160— 220 °C. At lower temperatures (80-100°C) and in the presence of copper(n) acetate, it reacts with amino and phenolic nucleophiles to give ort/io-substituted benzoic acids.16 

The periodinane (10) may also be prepared from o-iodobenzoic acid by oxidation with potassium bromate and then treatment with acetic anhydride18 (see Expt 6.36 for detailed formulation). It should be noted that the organic derivatives of pentacoordinate iodine(v) are termed periodinanes.18b This compound (the systematic name is l,l,l-triacetoxy-2,l-benzoxiodol-3(3//)-one) has found use as an oxidant of primary alcohols to aldehydes and alicyclic ketones to secondary alcohols it is claimed to have advantages over the chromium-based oxidation reagents. 

Experiment 6.31 (DICHLOROIODO)BENZENE (Iodobenzene dichloride) Phi + Cl2----- PhICl2 

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Methods leading to polyvalent iodine compounds (Expts 6.31 to 6.36). 

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