Lenonic acid, respectively (Scheme 1B). Recently, Back and coworkers have reported proof of formation of benzene peroxyselenonic acid within the epoxidation of cyclooctene promoted by selenonic acid/H2 O2 [11]. The oxidation of a diselenide is a lot more complex mainly because the cleavage of Se-Se bond along with the formation of seleninic products happens just after the addition of three equivalents of H2 O2 (Scheme 1C, first reaction). The seleninic goods may be additional oxidized to perseleninic derivatives (Scheme 1C, second reaction). The oxidation path of diselenides by H2 O2 or generally by peroxides was first proposed by Kice and Chiou [12], who described the formation of selenoxide and reduced species such water or alcohol molecules. As example, we can take into consideration diphenyl diselenide (1), which is essentially the most made use of catalyst in organic synthesis, but has also been thoroughly studied as antioxidant drug [13]. The addition of one equivalent of H2 O2 results in the formation of a selenoxide (two). Notably, selenium is often a stereogenic center and potentially two diastereoisomers with identical power kind. The addition of a second equivalent of H2 O2 may perhaps oxidize also the adjacent Se atom with all the formation of a diselenoxide (3) (Scheme two), which is not stable and also the selenium-selenium bond breaks. In truth, experimentally, the formation of benzene seleninic acid (four) has been detected. As a result, at a particular stage the inter-chalcogen bond of the diselenoxide could be hydrolized to benzene seleninic (4) and benzene selenenic (five) acids (Scheme three).Scheme two. Oxidation of diphenyl diselenide (1) by H2 O2 .Antioxidants 2021, 10,three ofScheme three. Hydrolysis of diphenyl diselenoxide (three).This latter product, like all selenenic derivatives, is experimentally elusive and has not been detected. Only when the selenium is protected by cradle-shaped molecular structure, selenenic acids could possibly be synthetized [14,15]. As option, each H2 O2 molecules can attack exactly the same Se atom forming a hydroxy perhydroxy species (six) (Scheme 4). This intermediate was by no means detected D-Sedoheptulose 7-phosphate References either, despite the fact that a nice study by Braga and co-workers postulated its formation [16]. Then, the hydroxy perhydroxy intermediate can oxidize the selenoxide to diselenoxide, in line with the mechanism described in Scheme five.Scheme four. Formation of hydroxy perhydroxy selenane (6).Scheme five. Oxidation of diphenyl selenoxide (two) by hydroxy perhydroxy selenane (six).Another intriguing aspect is the fact that the oxidation method of diphenyl diselenide is autocatalytic, as explained inside the mechanism sketched in Scheme 6 [17].Scheme 6. Autocatalytic mechanism of the oxidation by diphenyl diselenide by H2 O2 : 8 is decreased to four with concomitant oxidation of 1.Making use of an excess of H2 O2 , the benzene perseleninic acid (8, Scheme 6), which can be a strong oxidant, forms. This product is definitely the genuine oxidizing agent in organic reactions, when H2 O2 is employed in presence of a catalytic level of diphenyl diselenide (Scheme 1). Theoretical studies have played a vital role in understanding the intimate mechanistic features of the oxidation of organoselenides by H2 O2 . Nowadays, due to the N1-Methylpseudouridine site supercomputing facilities, quantum mechanical (QM) calculations, specifically Density Functional Theory (DFT) calculations, deliver an correct description with the prospective energy surface (PES). The reactions occur through the place in the minimum power points, corresponding towards the reactants and goods and, extra normally, towards the intermediates, at the same time as of the transition.
