Seleninic add

Baeyer-Villiger Oxidation of Ketones in Fluorinated Alcohol Solvents - Catalysis by Arsonic and Seleninic Adds... 

It was noted in Sections 4.3.2.2 and 4.3.2.3 that arsonic acids and seleninic adds are efficient catalysts for the epoxidation of alkenes. For both types of catalyst, significant enhancement of catalyst activity and selectivity was observed in fluorinated alcohol solvents compared to, for example, 1,4-dioxane. 

Seleninic acids Seleninic adds of the type used for alkene epoxidation (c Section 4.3.2.3) have also been employed as catalysts for the Baeyer-VUhger oxidation of ketones with hydrogen peroxide, mainly by Syper [57] and by Sheldon et al. [58,59]. In most cases, halogenated solvents such as dichloromethane or l,2-didiloroethane were used. In a study of solvent effects, Sheldon et cd. observed that, once again, TFE and in particular 1,1,1,3,3,3-hexafluoro-2-propanol are superior to dichloromethane with regard to selectivity and rate [58]. However, the effects are not as pronounced as in the case of alkene epoxidation (e.g., a factor of about 2 in rate between dichloromethane and HFIP, and 1.3 for TFE). The Baeyer-Villiger oxidation of a series of ketones and aldehydes was studied in TFE, and the results are summarized in Table 4.3 [58]. 

The catalysts applied to alkene epoxidation in fluorinated alcohol solvents can be subdivided into those which are metal/chalconide-based and those which are purely organic in nature (Scheme 4.5). The former comprise arsanes/arsane oxides [27,28], arsonic acids [29, 30], seleninic acids/diselenides ]31-35], and rhenium compounds such as Re207 and MTO (methylrhenium trioxide) ]36,37]. As shown in Scheme 4.5, their catalytic activity is ascribed to the intermediate formation of, for example, perseleninic/perarsonic adds or bisperoxorhenium complexes. In other words, their catalytic effect is due to the equilibrium transformation of hydrogen peroxide to kmetically more active peroxidic spedes. 

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