Studies on metal complexes with acylhydrazones based on heterocyclic carbonyl compounds

Dept.of Applied Chemistry, Cochin University of Science and Technology

Studies on the Synthesis and Transformations of a Few 2(3H)- and 3(2H)-Furanones

The thesis entitled studies on the synthesis and transformations of a few 2(3H)- and 3(2H)- furanones. Furanones represent an interesting class of heterocyclic compounds, which constitute the central ring system of many natural products. The derivatives of furan is divided, depending on their structure 2(3H)-furanones(I), 2(5H)-furanones(II), and 3(2H)-furanones(III). Systems I&II are unsatured gama lactones known as ‘butenolides’. Compounds of this type also known as ‘crotonolactones’ based on the parent crotonic acid. In conclusion a number of 2(3H)-and 3(2H)- furanones were synthesized from dibenzoylalkene precursors and were characterized on the basis of spectral analytical and X-ray data. On direct irradiation 3,3-bis(4-chloropheneyl)-5-aryl-3H-furan -2-ones underwent decarbonylation to yield the corresponding alpha, beta- unsaturated carbonyl compounds and upon sensitized irradiation they underwent dimersation arising through a 2+2 cycloaddition reaction. Our studies on 3(2H)-furanones revealed that these compounds are thermally stable, while they undergo extensive decomposition to intractable mixtures under the influence of light. Similarly, the novel dibenzoylalkenes- type systems containing hetroatomatic rings synthesized by us also underwent extensive decomposition under the influence of heat. Some of the 3(2H)-furanones synthesized by us exhibit remarkable anti-proliferative activity.

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.

Synthesis of dimethyl acetal of ketones: design of solid acid catalysts for one-pot acetalization reaction

The synthesis of dimethyl acetals of carbonyl compounds such as cyclohexanone, acetophenone, and benzophenone has successfully been carried out by the reaction between ketones and methanol using different solid acid catalysts. The strong influence of the textural properties of the catalysts such as acid amount and adsorption properties (surface area and pore volume) determine the catalytic activity. The molecular size of the reactants and products determine the acetalization ability of a particular ketone. The hydrophobicity of the various rare earth exchanged Mg–Y zeolites, K-10 montmorillonite clay, and cerium exchanged montmorillonite (which shows maximum activity) is more determinant than the number of active sites present on the catalyst. The optimum number of acidic sites as well as dehydrating ability of Ce3+-montmorillonite and K-10 montmorillonite clays and various rare earth exchanged Mg–Y zeolites seem to work well in shifting the equilibrium to the product side.

Synthesis, spectral and structural studies of transition metal complexes of N(4)-substituted semicarbazones

The thesis is an introduction to our attempts to evaluate the coordination behaviour of a few compounds of our interest. Semicarbazones and their metal complexes have been an active area of research during the past years because of the beneficial biological activities of these substances. Tridentate NNO semicarbazone systems formed from heterocyclic and aromatic carbonyl compounds and their transition metal complexes are well-authenticated compounds in this field and their synthesis and characterization are well desirable. Hence, we decided to develop a research program aimed at the synthesis and characterization of novel semicarbazones derived from 2-benzoylpyridine and 2-acetylpyridine and their transition metal complexes. In addition to various physicochemical methods of analysis, single crystal X—Ray diffraction studies were also used for the characterization of the complexes.

Transition metal complexes of some N4-phenylsemicarbazones: crystal structures and spectral studies

The unusual coordination modes of semicarbazones when bound to metals, the wide applications and structural diversity of metal complexes of semicarbazones provoked us to synthesize and characterize the tridentate ONO and NNO-donor semicarbazones and their transition metal complexes. This work is focused on the studies on complexes of three N4-phenylsemicarbazones synthesized by changing the carbonyl compounds. This work is concerned with the studies of two new semicarbazones, 2- formylpyridine-N4-phenylsemicarbazone (HL1) and 3-ethoxysalicylaldehyde- N4-phenylsemicarbazone (H2L2) and a reported semicarbazone 2-benzoylpyridine-N4-phenylsemicarbazone (HL3) [29]. The compositions of these semicarbazones were determined by the CHN analyses and IR, UV and NMR spectral studies were used for the characterization of these compounds. The molecular structure of 3-ethoxysalicylaldehyde-N4-phenylsemicarbazone (H2L2) was obtained by single crystal X-ray diffraction studies. Also, we have synthesized Cu(II), Cd(II), Zn(II) and Ni(II) complexes of these three semicarbazones. The complexes were characterized by various spectroscopic techniques, magnetic and conductivity studies. We could isolate single crystals of some complexes of all metals suitable for X-ray diffraction studies. This thesis is divided into six chapters.

The ligating versatility of halides and pseudohalides in copper(II) complexes- monomers, dimers and chains”

The work embodied in this thesis was carried out by the author in the Department of Applied Chemistry, CUSAT, Kochi, during the period 2008-2013. The thesis brings to light, our attempts to evaluate the coordination behavior of some compounds of interest. The biological activities of semicarbazones and their metal complexes have been an active area of research during the past years because of their significant role in naturally occurring biological systems. Tridentate NNO and ONO semicarbazone systems formed from heterocyclic and aromatic carbonyl compounds and their transition metal complexes are well-authenticated compounds in this field and their synthesis, crystal structures and spectral studies are well desirable. Hence, we decided to develop a research program aimed at the syntheses, crystal structures and spectral studies of copper complexes with halides and pseudohalides. In addition to single crystal X-ray diffraction studies, various physico-chemical methods of analysis were also used for the characterization of the complexes

Thermal degradation studies on Edible Oil during Deep Fat Frying Process

Deep fat frying process is one of the widely followed cooking practices throughout the world. Cooking oils serve as a medium for frying food for transferring heat and makes fried food tasty and palatable. Frying process is a most complex process involving numerous physicochemical changes which are complicated to understand. Frying leads to thermal degradation of oil through thermo-oxidation, hydrolysis, and polymerization. Hydrolysis results in formation of free fatty acids whereas oxidation process produces hydroperoxides and small molecular carbonyl compounds. This whole process leads to the formation of polar compounds and degradation of antioxidants that further degrades frying oil. Eventually, through mass transfer process these degradation products accumulate into fried food and reduce the nutritional quality of both oil and food. Thus, the frying process is of research interest calls for detailed systematic study which is chosen for the present study. The primary objective of this study is to understand the mechanism of degradation and characterization ofdegraded products which helps in arriving at the limits for frying oil utilization in terms of number of frying cycles. The mechanistic studies and the knowledge on the degraded products help to understand the way to retard the deterioration of oil for stability and enhancement of frying cycles. The study also explores the formation of the predominant polar compounds and their structural elucidation through mass spectrometry. Oxidation of oil is another important factor that ignites the degradation phenomena. One of the best ways to increase thermal stability of any oil is addition of potent antioxidants. But, most of the natural and synthetic antioxidants are unstable and ineffective at frying temperatures. Therefore, it is necessary to screen alternative antioxidants for their activity in the refined oils which are devoid of any added antioxidants. In this context, this study discussed the efficacy of several natural and synthetic antioxidants to retard the formation of polar compounds and thermooxidation during prolonged frying conditions. Similarly, the advantage of blending of two different oils to improve the thermal stability was explored. The present study brings out the total picture on the type of degradation products formed during frying and the ways of retarding the determination to improve upon the stability of the oil and enhancement of frying cycles.

Transition metal complexes of some N4-phenylsemicarbazones: crystal structures and spectral studies

The work embodied in this thesis was carried out by the author in the Department of Applied Chemistry, CUSAT, Kochi, during the period 2009-2012. The thesis is an introduction to our attempts to evaluate the coordination behavior of some compounds of our interest. The biological activities of semicarbazones and their metal complexes have been an active area of research during the past years because of their significant role in naturally occurring biological systems. Tridentate NNO and ONO semicarbazone systems formed from heterocyclic and aromatic carbonyl compounds and their transition metal complexes are wellauthenticated compounds in this field and their synthesis, crystal structures and spectral studies are well desirable. Hence, we decided to develop a research program aimed at the syntheses, crystal structures and spectral studies of new N4- phenylsemicarbazones derived from 2-formylpyridine and 3-ethoxysalicylaldehyde and their transition metal complexes and new transition metal complexes of 2- benzoylpyridine-N4-phenylsemicarbazone. In addition to various physicochemical methods of analysis, single crystal X-ray diffraction studies were also used for the characterization of the complexes.

Novel1, 3-Dipolar Cycloaddition Reactions of Acyclic Carbonyl Ylides and Related Chemistry

The thesis entitled novel 1,3-dipolar cycloaddition reactions of acyclic carbonyl ylides and related chemistry embodies the results of the investigations carried out to explore the reactivity of acyclic carbonyl ylides,generated by the reaction of dicarbomethoxy carbine and aldehydes towards dipolarophiles such as activated styrenes,1,2-and 1,4-quinones. In conclusion ,we have explored the reactivity pattern of acyclic carbonyl ylides derived from dicarbomethoxycarbene and aldehyde towards activated styrenes with a view to develop a stereoselective synthesis of highly substituted tetrahydrofuran derivatives. It was also found that the ylide could be trapped by various 1,2-and 1,4-diones to form dioxolane derivatives. It is noteworthy that the cycloaddition is highly region- and stereoselective. With isatins the ylide preferentially adds to the more electrone deficient carbonyl group making it regiospecific. Hetrocyclic compounds are of pivotal importance in organic chemistry, and enormous efforts have been devoted to develop new methodologies for their synthesis. It is noteworthy in this context that, 1,3-dipolar cycloaddition reaction,otherwise called Huisgen reaction, constitutes one of the most efficient methods for the synthesis of five membered heterocycles. Among the various dipoles, carbonyl ylides have received substiancial attention in recent years largely due to their utility in the synthesis of a wide range of oxygen hetrocycles, which are often found as structural subunits of many bioactive natural products.

Preparation, Characterisation And Microwave Dielectric Properties Of Anbn-1o3n (N=5,6,8) Type Perovskite Compounds

The present study on the preparation , characterization and microwave dielectric properties of AnBn-1O3n (N=5,6,8) type perovskite compounds. The explored ceramics show dielectric constant between 11 and 54,quality factor in the range 2400 to 88900 GHz and Tf in the range -73 to +231ppm/0C.Most of the investigated cation deficient hexagonal perovskites show intermediate dielectric constant with high quality factors. This study gives a general introduction about material, scientific and technological aspects of DRs.Three important ,€r ,Q and Tf, used for the DR characterization are described. The relationship of the above parameters with the fundamental material characteristics is discussed. Different modes are excited when a DR is excited with suitable microwave spectrum of frequencies .A description of analytical determination of frequencies and construction of mode charts used for sample design and mode identification are also discussed. In this study several ceramics are developed for DR purposes, very little attention has been paid to grow the single crystals. It might be due to the fact that the difficulties and time involved in the growth of single crystals, big enough to function as microwave resonators make them expensive .However single crystals of these materials may have very high Q values. It is also possible that a better understanding of the dielectric properties in relation to the structure can be arrived using single crystals. Hence one of the future directions of dielectric resonator research should be to grow good quality single crystals of the above materials.

A Novel Accelerator Combination for the Low Temperature Curing of Silica-Filled NBR Compounds

Zinc salts of ethyl, isopropyl, and butyl xanthates were prepared in the laboratory. The effect of these xanthates in combination with zinc diethyldithiocarbamate (ZDC) on the vulcanization of silica-filled NBR compounds has been studied at different temperatures. The cure times of these compounds were compared with that of NBR compounds containing tetramethylthiuram disulphide/dibenzthiazyl disulphide. The rubber compounds with the xanthates and ZDC were cured at various temperatures from 60 to 150°C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density, elongation at break, compression set, abrasion resistance, flex resistance, heat buildup, etc. were evaluated. The properties showed that zinc salt of xanthate/ZDC combination has a positive synergistic effect on the cure rate and mechanical properties of NBR compounds.

Synergism of Xanthate/Dithiocarbamate Accelerator in Carbon Black Filled NR Compounds

Zinc salts of ethyl, isopropyl and butyl xanthates were prepared in the laboratory. The effect of these xanthates with zinc diethyldithiocarbamate (ZDC) on the vulcanization of HAF filled NR compound has been studied at different temperatures. The rubber compounds with the three xanthate accelerators and ZDC were cured at various temperatures from 60°C to 150°C. The sheets were moulded and properties such as tensile strength , tear strength , cross-link density, elongation -at-break, compression set, heat build up, abrasion resistance, flex resistance , etc. were evaluated . The properties showed that zinc xanthate/ZDC accelerator combination has a positive synergistic effect on the mechanical properties of NR compounds. The curing of HAF filled NR compound containing zinc xanthate /ZDC is slightly slower than the curing of the corresponding gum compounds . It is observed that, by gradually increasing the amount of the accelerator, the cure time of black filled NR compound can be made equal to that of the gum compou

Use of Amine Terminated Liquid Natural Rubber as a Plasticiser in Filled NR andNBR Compounds

Amine Terminated Liquid Natural Rubber (ATNR) was used as a plasticiser in filled NR and NBR compounds replacing oil/DOP. The scorch time and cure time were found to be lowered when ATNR was used as the plasticiser. ATNR was found to improve the mechanical properties like tensile strength, tear strength and modulus of the vulcanizates . The ageing resistance of the vulcanizates containing ATNR was superior compared to the vulcanizates containing oil/DOP.