The reactivity of Au and AuBi nanoparticles supported on activated carbon AC was investigated in the direct oxidation of glucose to glucaric acid. The catalysts were very active, regardless of the Au nanoparticles size, but the catalyst with the smallest average particle diameter was the least selective to glucaric acid because of the enhanced consecutive oxidative degradation of the intermediately formed gluconic acid. The reaction network included the fast oxidation of glucose to gluconic acid, which was the only primary product, and its consecutive oxidation into either glucaric acid or lighter mono and dicarboxylic acids. The best glucaric acid yield obtained with a AuBi/AC catalyst (Au/Bi 3:1) was 31 %, with 18 % residual gluconic acid. The control of reaction parameters was essential to achieving the best selectivity. Specifically, the glucose concentration turned out to be a critical parameter in relation to O2 pressure and to glucose/metal ratio.
The aerobic oxidative CÀC bond cleavage of vicinal diols catalyzed by vanadium amino triphenolates is described. Our results show that CÀC bond cleavage can be performed in different solvents, under an air or oxygen atmosphere, with a large variety of glycols (cyclic or linear, with aromatic or aliphatic substituents) affording the corresponding carbonyl derivatives with high chemoselectivity.Reactions can be performed with as little as 10 ppm of catalyst reaching TON up to 81,000 and TOFs of up to 4150 h À1 . A reaction mechanism, rationalized by density functional theory calculations, is also proposed.
The mechanism of the oxidation of cyclohexanone with an aqueous solution of hydrogen peroxide has been investigated. Experiments revealed the preliminary formation of an intermediate, identified as cyclohexylidene dioxirane, in equilibrium with the ketone, followed by formation of 1-hydroperoxycyclohexanol (Criegee adduct). Computational analysis with explicit inclusion of up to two water molecules rationalized the formation of the dioxirane intermediate via addition of the hydroperoxide anion to the ketone and revealed that this species is not involved in the formation of the Criegee adduct. The direct addition of hydrogen peroxide to the ketone is predicted to be favored over hydrolysis of the dioxirane, the latter in competition with ring opening to carbonyl oxide followed by hydration. However, dioxirane may account for the formation of the bis-hydroperoxide derivative.
The inside cover picture, provided by Giulia Licini, Carles Bo and coworkers illustrates the highly chemoselective aerobic oxidative cleavage of 1,2‐diols to the corresponding carbonyl derivatives catalyzed by vanadium‐aminotriphenolate complexes. This catalytic method works with a large variety of glycols, linear or cyclic, with aromatic or aliphatic substituents. Pre‐association of the substrate to the metal center, followed by a two‐electron oxidation mechanism, yields the carbonyl derivatives and a reduced VIII metal complex, which is rapidly oxidized back to the catalyst by O2. Details of this work can be found in the full paper on pages 3281–3291 (E. Amadio, J. González‐Fabra, D. Carraro, W. Denis, B. Gjoka, C. Zonta, K. Bartik, F. Cavani, S. Solmi, C. Bo, G. Licini, Adv. Synth. Catal. 2018, 360, 3281–3291; DOI: 10.1002/adsc.201800050).
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