Synthesis, Structural Evaluation and Studies of

I hereby declare that the matter contained in this thesis is the result of investigations carried out by me in the Department of Chemistry, Indian Institute of Technology Guwahati, India under the supervision of Professor Mihir K, Chaudhuri, FASc., FNA and co-supervision of Dr. It is certified that the work contained in the thesis entitled "Synthesis, Structure Evaluation and Reactivity Studies of Heteroperoxovanadates (V) And Development of Solid Acid Catalysts for Organic Transformations" by Saitanya K Bharadwaj, a student in the Department of Chemistry, Indian Institute for Technology, Guwahati for the award of the degree of Doctor of Philosophy was conducted under my supervision/ . co-supervision and that this work has not been submitted elsewhere for a degree. I would like to thank all faculty members of Department of Chemistry of IIT Guwahati for their valuable suggestions.

The introductory chapter of the thesis presents an overview of various aspects of peroxovanadium chemistry with special reference to haloperoxidase activity and insulin mimesis, and a brief description of the importance of heterogeneous catalysis for organic transformations. VHPO possesses trigonal bipyramidal geometry around the native vanadium and a distorted tetragonal structure in the active (peroxo-intermediate) form. Structural characterization has revealed that vanadate is covalently bound to Nε of the imidazolyl moiety of a histidine amino acid, and further through hydrogen bonds to a variety of amino acid side chains (e.g. Arg, His, Ser, Lys) and water interstitial in the vicinity of the active center.

After laying the foundation as indicated above, the scope of work in the current Ph.

Materials and Methods

An internal comparison of the results is made to enable us to comment on their relative efficacy. Taking cues from bromoperoxidase activity and keeping in mind environmental safety in relation to the knowledge and experience we have gained in peroxovanadium chemistry, it became possible to develop newer and more environmentally friendly brominating agents, e.g. tribromides, "bromine store" and bromination protocols from a solution of KBr or NH4Br. work, like my predecessor, it has been possible to extract bromine from "bitter". Two solid acid catalysts have been developed by controlled heating and boiling of aluminum or titania with phosphoric acid over a temperature range of 200-2200C. The catalysts were characterized by chemical analysis as well as IR analysis, powder XRD, SEM/EDAX, TG/DTG.

Two of the earliest discrete diperoxovanadate(V) compounds, potassium oxodiperoxo(pyridine-2-carboxylato)vanadate(V) and potassium oxodiperoxo(3-hydroxypyridine-2-carboxylato)vanadate(V), had been shown to improve membrane fluidity and increase the rate of glucose uptake [68]. To this end, a number of ligands have been used in the exploration of vanadium chemistry. The exact color of the solution depended on the pH (a deep yellow color would indicate that too little K2CO3 had been used, while colorless solution would indicate that too much K2CO3 had been used).

The crystal parameters for the compounds are presented in the experimental part of the respective chapters. A pH value of 5.5 or 6 was found to be favorable for the successful synthesis of target complexes. Comparison of different bond lengths of compound (1) with ImzH[VO(O2)2Imz] is shown in Table 3.1.6.

DFT calculations have been performed to investigate the structural and electronic properties of the complexes (1)-(3). The coordination of peroxide leads to the appearance of the corresponding νas(VO2) and νs(VO2) at approx. This change has been attributed to the coordination of the acidic ligand to the vanadium (V) centers [46].

Each of the compounds was used for the reactions and repeated reactions were carried out to achieve the optimal conditions. Accordingly, the reactivity of the synthesized compounds has been studied for the oxidation of bromide and the results are listed in Table 3.4.1. In nature, the vanadium-dependent bomboperoxidase enzyme catalyzes the oxidation of bromide by hydrogen peroxide, followed by bromination of the organic substrates.

By starting from the bromoperoxidase activity and keeping environmental safety in mind, in connection with the knowledge and experience we gained in peroxovanadium chemistry [2], it was possible to develop newer and environmentally friendly brominating agents, i.e. tribromides, the "storehouse for bromine". and bromination protocols from a solution of KBr or NH4Br [3]. The mixture was stirred at the prescribed temperature until the lump solidified and then the temperature was reduced to about 1000C. The whole was then placed in a vacuum desiccator and cooled to ambient temperature It was found that the pattern of the catalyst matched well with that of aluminum trishydrogen phosphate [47].

Figure 1 Ortep diagrams of anion of compound 1 and 3

Newer Heteroperoxovanadates (V): Synthesis, Structure and

Synthesis, structural delineation and DFT investigation of Oxo-peroxo-

• Results and Discussion
• Conclusion

Synthesis and structural delineation of Oxo-peroxo-citrato-vanadate (V)

• Results and Discussion
• Conclusion

Synthesis and structural investigation of Oxo-peroxo- µ-hydroxo and µ-

• Results and Discussion
• Conclusion

Studies of Reactivity of Newer Peroxovanadates (V)

• Results and Discussion
• Conclusion

Oxidative Extraction of Bromide from Sea Bittern and Bromination of

Extraction of Bromide from Sea Bittern: An Eco-friendly Bio-mimetic

• Results and Discussion
• Conclusion

A detailed experimental procedure for bromide extraction was presented in this section. Tetrabutyl ammonium tribromide (TBATB), benzyltrimethyl ammonium tribromide (BTMATB), cetyltrimethylammonium tribromide (CTMATB), tetraethylammonium tribromide (TEATB), and tetramethylammonium tribromide (TMATB) were all prepared from seawater and characterized.

Direct Bromination of Phenol with Sea Bittern

• Results and Discussion
• Conclusion

Therefore, only suitable experimental conditions will lead to the successful synthesis of the target compounds. The XRD patterns of the catalyst and a fresh sample of TiO2 are shown in Figure 5.6.

Table 1.1 Vaska’s classification of peroxo complexes

Development of sewer solid acid catalysts for organic transformations

Experimental

The sources of chemicals and solvents, the methods for quantitative determination of elements and the details of all the equipment used for physico-chemical studies have been described in Chapter 2. The catalyst was prepared by taking a mixture of alumina (neutral) (Loba Chemie, India) and phosphoric acid (96%) (E. Merck) in a silica boat maintaining the molar ratio of Al: H3PO4 as 1: 3 and heated at 200-2200C on a hot sand bath. The catalyst thus prepared was finally transferred and stored in an airtight sample vial.

The heating was then interrupted, and when the temperature dropped to approx. 100°C, the catalyst was transferred to a vacuum desiccator. After completion of the reaction, the reaction mixture was extracted with ethyl acetate and washed with 5% aqueous solution of sodium bicarbonate (2.5 mL) followed by water (5 mL) and dried with anhydrous sodium sulfate. Evaporation of the solvent followed by column chromatography of the crude mixture on silica gel using n-hexane and ethyl acetate (95:5) as eluent gave pure products, namely 2-nitrobromobenzene and 4-nitrobromobenzene in the ratio 25:75 in overall yield 75%.

After the completion of the reaction, the product was extracted with ethyl acetate, washed sequentially with 5% aqueous sodium bicarbonate solution (2.5 mL) and water (5 mL), and then dried with anhydrous Na2SO4. Evaporation of the solvent followed by column chromatography of the crude mixture on silica gel using n-hexane and ethyl acetate (95:5) as eluent afforded 2-nitro toluene and 4-nitro toluene in the ratio 48:52 as clean. In the case of solid substrates, acetonitrile (3-5 mL) was used as solvent. e) General experimental procedure for the catalytic sulfoxidation reaction.

While methanol was used as a solvent for hydrogen peroxide, acetonitrile was used for nitric acid oxidations. After completion of the reaction, the product was extracted with ethyl acetate and washed with 5% aqueous sodium bicarbonate solution (2.5 mL) followed by water (5 mL) in the cases of nitric acid oxidation, while for those of hydrogen peroxide oxidation. washing was done with water only. Evaporation of the solvent followed by column chromatography on silica gel using n-hexane and ethyl acetate (95:5) as eluent gave the corresponding sulfoxide and sulfone in the ratio of 95:5 and 98:2, respectively, for hydrogen peroxide and acid nitric with overall yields of 85% and 90%.

Results and Discussion

• Preparation and characterization of catalysts
• Nitration of organic compounds with nitric acid
• Phosphate impregnated titania catalyzed chemoselective sulfoxidation

EDAX analysis gave a qualitative composition of the catalyst in good agreement with elemental analysis values. The average crystallite size of the fresh titanium oxide sample and the catalyst was calculated from the XRD patterns using the Scherrer equation [51]. It was found that the crystallite sizes of the first and TiO2 present in the catalyst are 62.15 nm and 41.54 nm, respectively.

A comparison of this with that of the fresh TiO2 sample shows an increase in particle size in the case of the catalyst. While column 3 of Table 5.2 represents the isolated yield and reaction time for Catalyst-A, the same is shown for Catalyst-T in Column 4. As is clear, aromatic compounds with electron-donating group (Table 5.2, entries and 14) are easily subjected to Figure 5.8 Scanning electron micrographs of (a) Catalyst- T with magnification of 10 µm and.

Also, the deactivated aromatic compounds underwent nitration in good yields (Table 5.2, entries 6 and 7), however, with a relatively longer time. Notably, polyaromatic hydrocarbons such as naphthalene, anthracene, phenanthrene (Table 5.2, entries 8, 9, and 10) underwent smooth and regioselective nitrations under the same experimental conditions. Thus the reaction of benzaldehyde (Table 5.2, entry 16) provided benzoic acid while 2-hydroxy benzaldehyde (Table 5.2, entry 17) and 2,4-dihydroxy benzaldehyde (Table 5.2, entry 18) underwent nitration.

Similarly, the reaction of phenylmethyl sulfide (Table 5.2, entry 19) gave the corresponding sulfoxide quantitatively, while dibenzothiophene (DBT) (Table 5.2, entry 20) and pyridine (Table 5.2, entry 21) both gave oxidized products. It is clear that the catalyst worked well up to the third cycle; then the yield started to decrease due to leaching of the catalyst (Table 5.3). The comparative reactivity of sulfide and the corresponding sulfoxide was also investigated to ensure the selectivity of the catalyst (Table 2).

Although hydrogen peroxide and nitric acid by themselves can oxidize benzylphenyl sulfides (Table 5.7, entries 1 and 2), the reactions are slow and thus require the need for a catalyst for activation. The reaction can be scaled up (5 g) to give a good yield (Table 5.5, entry 5), showing its prospect for preparative scale use.

Table 5.1 Desorption and adsorption of pore volume of TiO 2 and Catalyst-T

Conclusions

Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part A: Theory and Applications in Inorganic Chemistry. Ipure=999 Assumed by taking the reference of pure TiO2 [51] Scherer's equation for average crystallite size. Figures 5.S4 (a) FTIR spectrum of pyridine-n-oxide, (b) FTIR spectrum of 3-nitropyridine and (c) 1H NMR spectrum of 3-nitropyridine.

Figure 5.S12 (a) FTIR spectrum of standard DMSO, (b) FTIR spectrum of DMSO obtained from the reaction, and (c) GCMS profile of DMSO.