No abstract

In this study, an efficient catalyst based on graphitic carbon nitride nanosheets (CN) and copper(II) supported β-cyclodextrin (β-CD/Cu(II)) was synthesized and used for tandem oxidative amidation of benzylic alcohols. In this regard, CN was functionalized by β-CD/Cu(II) via 1,3-dibromopropane linker (CN-Pr-β-CD/Cu(II)). The prepared catalyst was characterized using FT-IR, XRD, FE-SEM, EDS, TGA, ICP-OES, BET, and TEM analyses. CN-Pr-β-CD/Cu(II) was subsequently applied in a direct oxidative amidation reaction and it was observed that different benzyl alcohols were converted to desire amides with good to excellent efficiency. This reaction was performed in the presence of amine hydrochloride salts, tert-butyl hydroperoxide (TBHP), and Ca2CO3 in acetonitrile (CH3CN) under nitrogen atmosphere. CN-Pr-β-CD/Cu(II) can be recycled and reused five times without significant reduction in reaction efficiency.

Recently, considerable attention has been devoted to heterogeneous catalysts. Generally, heterogeneous catalysts offer several advantages, such as mild reaction conditions, high throughput, and ease of work-up procedures. Among the heterogeneous catalysts investigated, polymeric mesoporous graphitic carbon nitrides (g-C3N4) have attracted much attention recently due to strong van der Waals interactions between the layers. g-C3N4 is chemically stable against acidic, basic, and organic solvents, and thermogravimetric analysis (TGA) also reveals that g-C3N4 is thermally stable even in air up to 600 °C, which can be attributed to its aromatic C-N heterocycles. More importantly, g-C3N4 is only composed of two earth-abundant elements: carbon and nitrogen. This not only suggests that it can be easily prepared at low cost, but also that its properties can be tuned by simple strategies without significant alteration of the overall composition. The last approach is considered to be the most efficient way to design high-performance heterogeneous catalysts utilizing g-C3N4 as a catalyst support. An interesting phenomenon is that the modification is mainly focused on metal oxides. Zirconia (ZrO2) is a physically rigid material with chemical inertness. It has high resistance against attacks by acids, alkalis, oxidants, and reductants. In this study, a ZrO2/g-C3N4 hybrid nanocomposite was shown to be an excellent catalyst for the conversion of alcohols and phenols into their corresponding trimethylsilyl ethers with hexamethyldisilazane (HMDS) under solvent-free conditions and for the synthesis of α-aminophosphonates. In addition, ZrO2/g-C3N4 could easily be recycled after separation from the reaction mixture without considerable loss in catalytic activity.