Finkelstein reaction iodination

Halide exchange from the lower halides to iodine is often desirable due to the higher reactivity of iodides in nucleophilic substitutions, reductions, organometallic or radical reactions (Scheme 30). Conversion of chlorides and bromides to iodides with sodium iodide in acetone is called the Finkelstein reaction. This halide exchange is an equilibrium process, which is shifted to the iodinated products due to precipitation of the less soluble sodium bromide or chloride from acetone. Best results are obtained when the reaction mixture is free of water. 

One of these consists in the substitution of iodine for the ester group attached to the primary carbon atom as the result of prolonged heating with sodium iodide in acetone solution (Finkelstein s reagent (20]). The reaction appears likely to consist in breaking the C—O linkage ... 

A Finkelstein substitution with practical utility was reported some years ago (Fig. 34).130 An co-bromo fatty acid undergoes halogen exchange with radioactive Na 23i to provide the labelled iodo acid, used as a tracer for the medical exploration of cardiac metabolism. The sonochemical reaction conducted in butanone provides quantitative yields of the expensive and thermally labile product, and the presence of water in the solvent, up to 7%, is tolerated. In comparison, the usual method requires heating at ca. 180 C and anhydrous conditions, and the purity of the product is much less satisfactory. It can be noticed that the unusually high temperature of the sonochemical reaction, close to the solvent boiling point, makes an interpretation hazardous. A second case of a Finkelstein substitution, a mesylate-iodine exchange, was published recently without experimental detail. i... 

Vinyl bromides can be converted into vinyl iodides using a Finkelstein-type reaction (Example 7.28) [146]. The process was copper catalyzed and used sodium iodide as a source of nucleophilic iodine. While only a single example was listed, this procedure has the potential to be very attractive to the synthetic community due to operational simplicity. 

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