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Radiochemistry for Preclinical Imaging Studies
Published in George C. Kagadis, Nancy L. Ford, Dimitrios N. Karnabatidis, George K. Loudos, Handbook of Small Animal Imaging, 2018
In contrast, when employing two different halogens in the substitution reaction, the equilibrium can be shifted toward completion as in the well-known Finkelstein reaction (Finkelstein 1910) on alkyl halides, employing Le Chatelier’s principle. In the original Finkelstein reaction, a solvent is employed that dissolves well both alkyl halides (reactant and product) and the sodium iodide (reactant), but the halide salt produced precipitates from the reaction solution. This physical removal of the side product drives the reaction toward completion. While the original Finkelstein reaction is applied to alkyl halides, an aromatic Finkelstein reaction with copper(I) or nickel(II) as catalyst has been developed and applied to 123I-labeled compounds more recently (Klapars and Buchwald 2002; Cant et al. 2012). Additionally, the substitution site of an aromatic ring may have to be activated by other substituents (Coenen et al. 2006). High specific activity can be achieved because excess chlorine or bromine precursor is easier to separate from the radioiodinated product than an isotopologue discussed earlier in the isotopic substitution approach (Eersels et al. 2005; Coenen et al. 2006).
Green synthesis of glycerol 1,3-bromo- and iodohydrins under solvent-free conditions
Published in Green Chemistry Letters and Reviews, 2019
Priscila Faustino dos Santos, Sara Raposo Benfica da Silva, Fernanda Priscila Nascimento Rodrigues da Silva, Jeronimo da Silva Costa, Jane Sayuri Inada, Vera Lúcia Patrocinio Pereira
The Finkelstein reaction is widely used in organic synthesis (41–50). It consists in the displacement of a leaving group under a C-sp3 (Cl, Br, I, OTs, OMs, etc.) by the action of a metallic halogenated nucleophile mainly acetone as solvent, where the new organic or inorganic metallic salt is insoluble (51, 52). Although the reaction has been considered to evolve via a mechanism SN2, it is an equilibrium process. Kinetic studies ratify that the reversibility of the reaction is not observed during transhalogenation due to the difference in the solubility between the salts involved in the process (53, 54). For example, NaI is highly soluble in acetone and when this is reacted with an alkyl chloride the NaCl formed is insoluble in acetone and precipitate, thus there is the equilibrium displacement in favour of the desired products (Le Châtelier’s principle) (55).