Oxidative coupling reactions enable the direct formation of a new bond from two C–H or heteroatom–H bonds without the need for special activating or leaving groups, and are thus interesting in the context of green chemistry. In order to attain high atom economy and sustainability, it is desirable to conduct these reactions catalytically with oxygen or air as terminal oxidant. Here, a representative overview of such reactions is given, illustrating the substrate scope and the variety of catalyst systems. Additionally, mechanisms and general strategies to utilise oxygen in such reactions are discussed
A Brønsted acid catalyzed C-H functionalization via Intermediate PeroxideS (CHIPS), generated photochemically, allows the oxidative coupling of indole derivatives with a variety of nitrogen nucleophiles. The reaction can be performed in one pot and requires only visible light, elemental oxygen, a Brønsted acid and a photosensitizer. The method can be applied to an efficient synthesis of some biologically active compounds.
The acid-catalyzed reactions of photochemically generated tetrahydrocarbazole peroxides with anilines have been studied experimentally and computationally to identify the underlying reaction mechanism. The kinetic data indicate a reaction order of one in the hydroperoxide and zero in the aniline. Computational investigations using density functional theory support the experimental findings and predict an initial tautomerization between an imine and enamine substructure of the primarily generated tetrahydrocarbazole peroxide to be the rate controlling step. The enamine tautomer then loses hydrogen peroxide upon protonation, generating a stabilized allylic carbocation that is reversibly trapped by solvent or aniline to form the isolated products.
In present study, the anodizing of aluminium was carried out in sulphuric acid/tartaric acid electrolyte system to increase pitting corrosion resistance. The corrosion resistance of the oxide coating of aluminium was determined by potentiodynamic polarization test. The surface morphology was investigated using scanning electron microscope before and after the corrosion test. It was found that anodic oxide coating obtained in sulphuric acid/tartaric acid showed higher pitting corrosion resistance.
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