Catalysis lies at the heart of countless chemical protocols, from the academic research lab to the chemical industry. A variety of products such as medicines, fine chemicals, polymers, fibers, fuels, paints, lubricants and myriad other value added products essential for human being would not be feasible devoid catalysts. These active compounds arbitrate the mechanism by which chemical transformations take place, which enables the commercially viable creation of desired materials. Manufacturing protocols can be made economic, greener and more sustainable, by designing and vigilant use of catalysis, which reduces the chemical waste harmful to human health and the environment.
Why we need Nano-Catalyst?
Although attempt were made to make all active site on solid support accessible for reaction, allowing rates and selectivities comparable to those obtained with homogeneous catalysts, however only sites on the surface are available for catalysis, decreasing the overall reactivity of catalyst system. Another problem is the leaching of active molecule/complex from solid support because of breaking of bonds between metal and ligand during catalytic reactions, which again creates the problem of separation of trace metals from final product.
New catalyst systems that allow for rapid, selective chemical transformations with excellent product yield and with ease of catalyst separation and recovery is an urgent need for “greening" the chemical manufacturing processes.
Nanoparticles have emerged as sustainable alternatives to conventional materials, as robust, high-surface-area heterogeneous catalyst supports.2-8 Postsynthetic surface modification of magnetic nanoparticles imparts desirable chemical functionality and enables the generation of catalytic sites on the surfaces of ensuing metal-catalysts as well as organocatalysts. In view of their nano-size, the contact between reactants and catalyst increases dramatically thus mimicking the homogeneous catalysts. Their insoluble character coupled with paramagnetic nature, on the other hand, enables easy separation of these nano-catalysts from the reaction mixture using external magnet, which eliminates the requirement of catalyst filtration. These novel nano-catalysts bridge the gap between homogeneous and heterogeneous catalysis thus preserving the desirable attributes of both the systems.
Microwave Assisted Nano-Catalysis in Aqueous Medium:
In last few years, MW-assisted chemistry has blossomed into a matured and useful technique for a variety of applications. Although MW-assisted reactions in conventional solvents have developed rapidly, the center of attention has now shifted to the environmentally benign processes, which uses nano-catalyst and greener solvents such as water. It seems that combined approach by fusing microwave technique, nano-catalysis, and benign water as a reaction medium, can offer extraordinary synergistic effect with greater potential than these three components in isolation.
1. Polshettiwar, V.; Varma, R. S. Chem. Soc. Rev. 2008, 37, 1546.
2. Polshettiwar, V.; Varma, R. S. Chem. Eur. J. 2009, 15, 1582.
3. Polshettiwar, V.; Baruwati, B. ; Varma, R. S. ACS Nano 2009, 3, 728.
4. Polshettiwar, V.; Baruwati, B.; Varma, R. S. Chem. Commun. 2009, 1837.
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