I declare that the matter embodied 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 guidance of Associate Professor Dr. This is to certify that Harjyoti Thakuria has been working under my supervision since July, 2006 as a regular registered doctor. This is to certify that Harjyoti Thakuria has satisfactorily completed all the courses required for the Ph.D.
I am grateful to the head of the Department of Chemistry and all the faculty members, staff and technical assistants, scientific officer who offered help directly or indirectly at different stages during my research work. I am also grateful to Central Instrument Facility of IITG, Center for Nanotechnology, Department of Physics, Department of chemical engineering without their help it will not be possible to do my research work so smoothly.
Catalysis
Catalysis is inhibited when the reactant or catalyst is removed or modified by any of several types of agents (inhibitors). Single-phase catalysis (for example, the catalyst is dispersed in a liquid solution or gas mixture with the reactants) is homogeneous; that is heterogeneous in more than one phase (for example, the reactants are liquids and the catalyst is a solid). Chemisorption, a form of heterogeneous catalysis, often involves bonding between the solid surface of the catalyst and the reactant, changing the nature of the chemisorbed molecules.
The net free energy change of a reaction is the same whether a catalyst is used or not; the catalyst simply makes activation easier. The presence of the catalyst opens up a different reaction pathway (shown in red) with lower activation energy.
Types of catalysts
One of the main objectives of green chemistry is to develop environmentally acceptable routes to important biological products. The use of a reaction system in which the catalyst is in a different phase from that of the substrate and products allows easy removal of the catalyst from the reaction mixture via filtration, centrifugation or decantation. Co3O4, a mixed valence compound with a normal spinel structure, is the most stable phase in the Co–O system and one of the most important transition metal oxides with gas sensing behavior and solar energy reflective properties [1.28].
In particular, when preparing nanopowders in the liquid phase, the viscosity increases dramatically due to the huge specific surface area of the product. A surfactant has been used to reduce the viscosity of the suspension and to stabilize the suspension of nanopowders [1,47].
Green synthetic methodologies
The aim is not only to optimally control the size, shape, morphology and polydispersity of the crystals, but also to fabricate new organic/inorganic composite materials with interesting electrical, magnetic and optical properties. Among them, the chemical solution route offers the preparation of nanosized materials a promising option due to its simplicity, practicality, large scale, controllability, and low cost. To obtain nanoparticles with a narrow size distribution via the reactive precipitation method, a high degree of supersaturation and a uniform spatial concentration distribution of the solute are indispensable, and micromixing is a key factor to meet these requirements [1.45].
Solid state reaction is a green reaction and can be accelerated by heating, shaking, milling of the reaction mixture and irradiation with ultrasound, making it a very ideal synthetic process. Benzodiazepines are interesting compounds because they belong to an important class of the pharmacologically prominent 1,5-benzodiazepines that have been widely used as anticonvulsant, anti-anxiety, analgesic, sedative, antidepressant, hypnotic and anti-inflammatory drugs [1.79].
Development, Characterization and Application of Heterogeneous
Materials
Physical measurements
Synthesis of MOF from Nitrilotriacetic acid (NTA) and Bicine [N,N-bis (2-
Bicine (0.326 g, 2 mmol) and freshly prepared copper hydroxide (1 mmol, 0.097 g) were thoroughly ground with a pestle in an open mortar at room temperature in air.
Gel Mediated synthesis of Transition metal hydroxide and oxide
The gel was then washed several times with water to remove excess amount of salts attached to it. The gel was then placed in hot water and filtered hot to remove the organic materials. The resulting hydroxides were washed with ethanol to get rid of the organic matter attached to it and air dried before characterization.
Metal hydroxide was heated in an oven at 600°C for about 5 hours to obtain corresponding oxides.
Results and discussion
- MOF from Nitrilotriacetic acid (NTA) and Bicine [N,N-bis(2-hydroxyethyl)
- Gel mediated Copper Hydroxide and Copper Oxide
- Gel mediated Cobalt Hydroxide and Cobalt Oxide
- Gel mediated Nickel Hydroxide and Nickel Oxide
- Gel mediated Mangnese Hydroxide and Manganese Oxide
- General procedure for N-formylation
- General procedure for acylation of amines, alcohols and phenols
- General procedure for Friedel Craft acylation
A crystal water molecule (O10) forms strong hydrogen bonds with neighboring metal-coordinated water molecules as well as with the coordinated O atom of the carboxylic acid group. Each of the crystal water molecules is hydrogen bonded to the four neighboring molecules in an almost tetrahedral arrangement. Two of the alternate rectangular voids in the 2D rectangular network are filled with these water molecules.
The FT-IR spectrum of complex 2 shows (Figure 2.10) a broad band centered at 3500 cm–1 due to the presence of water molecules, which also disappears when heated, as for complex 1. The magnetic moment of the Cu(II) complex is 1.51 BM showing the presence of an unpaired electron. The FT-IR spectrum of the complex shows two strong and sharp bands at 3310 cm-1 and.
The robustness of the framework is reflected in the thermogravimetric analysis of complex 3, which shows negligible weight loss up to about 140oC. It also shows an exothermic peak at 370oC due to the decomposition of the complex as shown in (Figure 2.14). PXRD pattern (Figure 2.19) confirms the crystalline bulk of the copper oxide and the mineral phase is confirmed to be tenorite (PDF no.
From the SEM image (Figure 2.21), we found that cobalt oxide formed similar structure to the cobalt hydroxide, but smaller in size. In the presence of agarose gel and gelatin aggregates of small spherical particles of 10-20 nm are observed (Figure 2.22). Thermal decomposition leads in all cases to the formation of porous aggregates of spherical balls with a diameter range of 100-150 nm (Figure 2.25).
Results and discussion
- Metal oxide catalyzed N- formylation of amine
- Metal oxide catalyzed acylation of amines
- Metal oxide catalyzed acylation of phenols
- Metal oxide catalyzed acylation of alcohols
- Metal oxides catalyzed Friedel Craft acylation
The reaction conditions were standardized after performing the N-formylation of aniline in different amounts of metal oxide catalyst (Table 2.3) and reaction time. Both aromatic amine possessing electron donating and electron withdrawing groups (Table 2.4, entries 1-50) and aliphatic amine (Table 2.4, entries 51-55) proceed smoothly and give N-formylated products in excellent yield. The catalytic activity of the transition metal oxides as heterogeneous catalyst for N-acylation of amine is summarized in Table 6.
As shown in Table 2.7, the reaction of aniline (1 mmol) as a standard with acetic anhydride (1 mmol) was investigated under different solvent-free reaction conditions. Acylation of aromatic amines containing both electron-donating and electron-withdrawing groups (Table 2.8, entries 1 – 35) were efficient TH. In any case, when we used other transition metal oxides as heterogeneous catalysts, as shown in Table 10, we obtained better results regarding the porous ZnO.
The catalytic activity of the recovered catalyst was investigated as shown in table 2.13. In each case, after 2-3 reuses of this catalyst, almost >90% was easily recovered from the reaction mixture by simple washing with dichloromethane, retaining their catalytic properties. activity. To the best of our knowledge, these reactions have never been reported using this type of macroporous transition metal oxides as a heterogeneous catalyst. Catalytic activity of the recovered catalyst was investigated as shown in the Table 2.17. In each case, after two and three recycles of this catalyst, nearly >90% was easily recovered from the reaction mixture by simple washing with dichloromethane.
In any case, when we used other transition metal oxides as heterogeneous catalysts, as shown in the table, we got a better result. It is clear from Table 2.19 that only Cr2O3 and CoO catalyzed the Friedel Craft reaction, while the other oxides, namely CuO, NiO and Mn2O3, could not catalyze this reaction. Acylation of heterocyclic compounds such as furan (Table 2.20, entries 7 and 8) forms a 2-acylated product in excellent yield.
In the case of benzene and anthracene (Table 2.20, entries 5, 6, 9 and 10), since they are inherently less reactive, they therefore give much less yield. Here, the catalytic activity of the recovered catalyst was also investigated as shown in Table 2.21. In each case, after two and three reuses of these catalysts, nearly >90% was readily recovered from the reaction mixture by simple washing with dichloromethane.
Solid-State Synthesis of Some Heterocyclic Compounds of Medicinal
- Materials
- Analysis and Measurements …
- General procedure for the synthesis of 2,3-dihydro-1,5-benzodiazepines
- General procedure for the synthesis of 1,4-Dihydro-quinoxaline-2,3-dione
- General Procedure for synthesis of benzimidazole/2-mercaptobenzimidazole
- Results and discussion
- Synthesis of 2,3-dihydro-1,5-benzodiazepine
- Synthesis of Quinoxaline-2,3-dione
- Synthesis of Benzimidazole derivatives
Details of the substrates used, products obtained, reaction times and yields are given in Table 3.2. After completion of the reaction, the melt was washed with water and the desired product was crystallized from water at low temperature. The reaction was carried out at room temperature using acetone and o-phenylenediamine in the presence of a catalytic amount of an organic acid.
No product was obtained in the absence of acid under similar reaction conditions at room temperature. Therefore, it can accept one proton in the presence of acid, which is reflected in the solid state structure. As shown in Figure 3.3, the crystal structure of 1a consists of two crystallographically independent heterocyclic ring molecules in an asymmetric unit.
However, the three-dimensional arrangement of molecules in the crystal lattice is unique and quite attractive. We report simple solid-phase milling of the two reactants at RT in an open atmosphere to obtain the product in good yield (Scheme 3.2). Given the problems encountered in the synthesis of quinoxaline, a relatively more versatile but simplified procedure was perceived.
A wide range of o-phenylene diamine derivatives were screened to determine the scope of the current reaction protocol and the results are summarized in Table 3.2. It is generally observed that the presence of electron withdrawing groups in the aromatic ring increases the yield of the reaction by reducing the reaction time. The structures of the products were determined from their spectral data (1H NMR, IR and MS). The plausible condensation mechanism is depicted in Figure 3.9.
We also performed X-ray powder diffraction and FT-IR analysis of hydrated as well as dehydrated crystals to confirm the role of water of crystallization. The operational simplicity of the procedure is also attractive, offering a wide scope in organic synthesis.
