Abstract
The amide functional group is a crucial component of organic synthesis as evidenced by its widespread application in a variety of chemical products. As a result, there is a significant demand for the creation of innovative and effective catalytic procedures to produce amide bonds. The most commonly used procedure for the synthesis of amides are the reaction of an acyl chloride with an amine or the condensation of a carboxylic acid and an amine using an amide coupling reagent. These procedures have several drawbacks, including poor atom economy, the simultaneous generation of significant amounts of waste, time-consuming purifications, and the cost and toxicity of several amides coupling reagents used. Catalytic approaches for the direct formation of amides from non-activated carboxylic acids and amines have recently emerged as an area of interest.
Even though numerous catalytic procedures have been established, there is still a need for a more generic technique. An aminocarbonylation strategy, in which economical and widely accessible aryl halides are reacted with nitroarenes in the presence of a carbonyl source and a catalyst, provides an appealing alternate approach for obtaining amides derivatives. In this study, palladium nanoparticles supported on titanium dioxide were used as catalysts in the aminocarbonylation reactions. The mesoporous titanium dioxide support was successfully synthesised by the sol-gel method using titanium(IV) isopropoxide as a Ti precursor and pluronic (P123) as a surfactant. After the synthesis of the mesoporous support, the palladium nanoparticles were incorporated on the surface of the support through the deposition-precipitation method. The deposition of the metal was performed using sodium borohydride (NaBH4) solution as reducing agent.
Prior to the catalytic application of the synthesized supported-nanoparticles, the physical and chemical properties of the overall catalytic materials were analysed using various characterization techniques such as powder X-ray diffraction (p-XRD) for determining the crystallinity, Fourier transform infrared spectroscopy (FTIR) to determine the functional groups present in the catalyst, Brunauer-Emmett-Teller technique (BET) was used to determine the overall surface areas. Furthermore, scanning electron microscope (SEM) was used to determine the surface morphology, while transmission electron microscope (TEM) was used to determine the nanoparticle sizes and for defining the morphology of the nanoparticles. In addition, EDX was used
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to identify the elemental composition of the synthesized catalyst. The thermogravimetric analysis (TGA) was conducted to determine the thermal stability of the catalysts.
The characterization techniques used showed that the synthesized TiO2 support is an anatase phase and was found to be mesoporous in nature, exhibiting adequate structural and textural properties of mesoporous structure before and after the incorporation of the metal nanoparticles onto the surface of the support. The surface areas of the nanoparticles were found to be 114.53 m2/g for TiO2 and 103.39 m2/g for Pd/TiO2 respectively. The as-synthesized nanoparticles were found to be thermally stable at high temperature with a minimal weight loss attributed to the decomposition of the water molecules absorbed on the surface of the materials. The synthesized catalytic active supported Pd NPs was applied in the reductive aminocarbonylation reaction and exhibited a good catalytic activity and selectivity.