First Example of Organocatalysis by Polystyrene-Supported PAMAM Dendrimers: Highly Efficient and Reusable Catalyst for Knoevenagel Condensations

This paper describes the first use of polystyrene-supported poly(amidoamine) (PAMAM) dendrimers as heterogeneous basic organocatalysts for carbon–carbon bond formation. Polystyrene-supported PAMAM dendrimers of first, second and third generations have been used as reusable base catalysts in Knoevenagel condensations of carbonyl compounds with active methylene compounds. The reactions proceed in short periods of time and with 100% selectivity. This novel catalyst eliminates the use of aromatic and halogenated solvents, as well as complex purification processes. The catalysts can be recycled ten times.

Organocatalysis by poly(amidoamine) dendrimers; Knoevenagel and Mannich reactions catalyzed in water

Knoevenagel condensation between carbonyl compounds and active methylene compounds as well as three component Mannich reaction between aldehydes, ketones and amines proceeded smoothly in water with good to excellent yield and high selectivity in the presence of zero and first generation poly(amidoamine) (PAMAM) dendrimers. The products and the catalyst were separated by simple biphasic extraction. The catalyst was found to be reusable.

Factors Underlying Heterogeneous Individual Growth in Macrobrachium rosenbergii and the Effect of Size Heterogeneity on Economic Feasibility of Farming in Kuttanad ( Kerala )

School of Industrial Fisheries, Cochin University of Science and Technology

Catalysis By Some Pillared Montmorillonites

In the present study, we have prepared and evaluated the physical and chemical properties and catalytic activities of various single, mixed and modified pillared montmorillonites. The single oxide pillared clays include AI-, Fe- and Cr-pillared montmorillonites. The mixed oxide pillared montmorillonites such as Fe-AI and Cr-AI pillared systems with various Fe(Cr)/Al ratios are also prepared. Modification of iron-pillared system is done by vanadia impregnation. Characterisation using various physico-chemical techniques and a detailed study of acidic properties are also carried out. Major part of our work is oriented to evaluate the catalytic activity of the pillared systems towards certain important catalytic reactions. Our samples are found to be excellent catalysts for the reactions namely Friedel-Crafts benzylation and benzoylation, methylation of aniline and catalytic wet peroxide oxidation of phenol.

New supported transition metal complexes: synthesis, characterization and application as catalysts for oxidation/hydrodesulphurization reactions

This thesis deals with the synthesis and charcterisation of some supported transition metal complexes and their catalytic properties. Two industrially important reactions were carried out: i) cyclohexanol oxidation and ii) hydrodesulphurization of diesel. Thesis is divided into nine chapters. An overview of the heterogenised homogeneous systems is given in Chapter 1. Chapter 2 deals with the materials and methods used for the preparation and characterisation. Details regarding the synthesis and characterisation of zeolite encapsulated transition metal complexes are given in Chapter 3 to Chapter 7. In Chapter 8, the results of catalytic activity studies of the cyclohexanol oxidation using the zeolite encapsulated complexes are presented. Details of preparation of hydrodesulphurization catalysts through the molecular designed dispersion method, their characterization and catalytic activity studies are presented in Chapter 9. References are given at the end of the thesis.

Studies on some supported transition metal complex and metal oxide catalysts for oxidation reactions

Zeolite encapsulated transition metal complexes have received wide attention as an effective heterogenized system that combines the tremendous activity of the metal complexes and the attractive features of the zeolite structure. Zeolite encapsulated complexes offer a bright future for attempts to replace homogeneous systems retaining its catalytic activity and minimizing the technical problems. especially for the partial oxidation of organic compounds. Studies on some zeolite encapsulated transition metal complexes are presented in this thesis. The ligands selected are technically important in a bio-mimetic or structural perspective. Attempts have been made in this study to investigate the composition, structure and stability of encapsulated complexes using available techniques. The catalytic activity of encapsulated complexes was evaluated for the oxidation of some organic compounds. The recycling ability of the catalyst as a result of the encapsulation was also studied.Our studies on Cu-Cr/Al2O3, a typical metal oxide catalyst. illustrate the use of design techniques to modify the properties of such conventional catalysts. The catalytic activity of this catalyst for the oxidation of carbon monoxide was measured. The effect of additives like Ce02 or Ti02 on the activity and stability of this system was also investigated. The additive is potent to improve the activity and stability ofthe catalyst so as to be more effective in commercial usage.

Surface Properties and Catalytic Activity of Ferrospinels Containing Cobalt, Nickel and Copper

The present study describes the surface properties and catalytic activities of ferrospinels containing Co, Ni and Cu prepared by the low temperature route. Various physico-chemical methods have been adopted to characterise the systems. The reactions carried out are the Friedel-Crafts benzoylation of aromatics and the cyclohexanol decomposition. We have attempted the sulphate modification of the ferrites and have studied the surface and catalytic properties of the sulphated analogues.The work is presented in six chapters, the last chapter giving the summary and conclusions of the results presented earlier. Our samples prove as potential catalysts for the benzoylation of aromatics , for which truly heterogeneous catalysts are rare. Again , the materials show remarkable dehydration/dehydrogenation activities during cyclohexanol decomposition. There is plenty of scope for research in this field, especially in the development of environmentally benign catalysts for acylation reactions.

Solid acid-catalyzed dehydration/Beckmann rearrangement of aldoximes: towards high atom efficiency green processes

Rare earth metal ion exchanged (La3+, Ce3+, RE3+) KFAU-Y zeolites were prepared by simple ion-exchange methods and have been characterized using different physico-chemical techniques. In this paper a novel application of solid acid catalysts in the dehydration/ Beckmann rearrangement of aldoximes; benzaldoxime and 4-methoxybenzaldoxime is reported. Dehydration/Beckmann rearrangement reactions of benzaldoxime and 4-methoxybenzaldoxime is carried out in a continuous down flow reactor at 473K. 4-Methoxybenzaldoxime gave both Beckmann rearrangement product (4-methoxyphenylformamide) and dehydration product (4-methoxybenzonitrile) in high overall yields. The difference in behavior of the aldoximes is explained in terms of electronic effects. The production of benzonitrile was near quantitative under heterogeneous reaction conditions. The optimal protocol allows nitriles to be synthesized in good yields through the dehydration of aldoximes. Time on stream studies show a fast decline in the activity of the catalyst due to neutralization of acid sites by the basic reactant and product molecules.

A comparative study of medium and large pore zeolites in alkylation reactions

In this thesis an attempt has been made to compare the catalytic activity of some medium and large pore zeolites in a few alkylation and acylation reactions. The work reported in the present study is basically centered around the following zeolites namely, ZSM-5, mordenite, zeolite Y and beta. The major reactions carried out were benzoylation of o-xylene, propionylation of toluene and anisole and benzylation of 0xylene.The programme involves the synthesis, modifications and characterization of the zeolite catalysts by various methods. The influence of various parameters such as non-framework cations, Si/AI ratio of zeolites, temperature of the reaction, catalyst concentration, molar ratio of the reactants and recycling of the catalysts were also examined upon the conversion of reactants and the formation of the desired products in the alkylation / acylation reactions.The general conclusions drawn by us from the results obtained are summarized in the last chapter of the thesis. Zeolite beta offers interesting opportunities as a potential catalyst in alkylation reactions and the area of catalysis by medium and large pore zeolites is very fascinating and there is plenty of scope for further research in this field. Moreover, zeolite based catalysts are effective in meeting current industrial processing and more stringent environment pollution limits.

Organic Reactions Catalysed by Modified Clays

Department of Applied Chemistry, Cochin University of Science and Technology

Catalysis by Polymer Supported Dendrimers, their Metal Complexes and Nanoparticle Conjugates

The present thesis has described the development of some heterogeneous catalysts based on polymer supported dendrimers. Attachment of dendrimers to crosslinked polymer produced new catalysts with combined benefits of both dendrimers and heterogeneous catalysts. These were used as heterogeneous catalysts in selected reactions. All possible attempts were taken to avoid halogenated and aromatic solvents and toxic reagents. In short the present work has dealt with development of environmental friendly catalysts based on dendrimers.