Abstract
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.
Highlights
Heterogeneous catalysts have received considerable attention due to numerous applications in many areas of the chemical industry
We reported the synthesis of ZrO2/g-C3N4 by a mixing calcination method as a promising heterogeneous catalyst for the protection of hydroxyl groups and the preparation of α-aminophosphonate derivatives (Scheme 1A,B)
The ZrO2/g-C3N4 hybrids were prepared by direct heating of ZrO2 and melamine
Summary
Heterogeneous catalysts have received considerable attention due to numerous applications in many areas of the chemical industry. They offer several advantages, such as easy separation from the reaction medium, reusability without noticeable loss of activity, and affording desired products of high yield and purity [1]. While various attempts have been reported to improve the catalytic activity of zirconia [3], polymeric mesoporous graphitic carbon nitride (g-C3N4) has drawn more and more attention due its large surface area, high thermal and chemical stability, easy recyclability, and particular physical features. We reported the synthesis of ZrO2/g-C3N4 by a mixing calcination method as a promising heterogeneous catalyst for the protection of hydroxyl groups and the preparation of α-aminophosphonate derivatives (Scheme 1A,B). Protection of alcohols with hexamethyldisilazane (HMDS) catalyzed by ZrO2/g-C3N4 (A), and synthesis of α-aminophosphonates by ZrO2/g-C3N4 (B)
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