Theses and dissertations (Applied Sciences)
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Item Synthesis, characterization and antimicrobial evaluation of piperazinyl-quinolinyl-a-aminophosphonates(2019) Rajkoomar, Nikisha; Gengan, Robert Moonsamyα-Aminophosphonates (α-APs) is an important motif among heterocycles particularly in medicinal chemistry due to their reduced levels of cytotoxicity and structural resemblance to the corresponding α-amino acids. They are useful intermediates in synthetic organic processes and present with a broad spectrum of biological activities. Hence, there is an ongoing interest in the development of improved synthetic methods for the preparation of these α-APs. The complex molecules were initially synthesized in a step-wise reaction but this method suffered several drawbacks such as long reaction times and resulted in low yields. However, since the development of multi-component reactions (MCRs), three or more substrates can undergo an efficient one-pot reaction which results in higher product yields. The first step in the synthetic aspect of this study involved the preparation of a novel palladium supported strontium titanate (Pd-SrTiO3) material. Herein, an aqueous solution of strontium (II) nitrate was mixed with citric acid followed by reflux in an ethanolic solution of titanium (IV) butoxide. Thereafter, the dried solid was mixed with palladium (II) nitrate and this solution mixture was refluxed, filtered, calcined and subsequently dried. The characterization of Pd- SrTiO3 was undertaken with FT-IR, P-XRD, SEM, BET, SEM-EDX and Raman spectroscopic techniques. The synthesis of a series of novel -αAPs in a MCR system comprising an aldehyde, diethyl phosphate and selected aniline derivatives via the Kabachnik Fields reaction approach in the presence of catalytic amounts of Pd-SrTiO3 was investigated Twenty methyl piperazinyl-quinolinyl α-aminophosphonates (MPQ-α-APs) (4a-4t) were synthesized, purified and characterized by FT-IR, 1H-NMR, 13C-NMR, 31P-NMR, 2D-NMR and high resolution mass spectroscopic techniques. Valuable features of this routine included high yields, extensive substrate range, straight forward procedures and excellent catalytic properties. The cytotoxicity of 4d, 4e, 4f, 4m, 4q, 4r and 4s was evaluated using the Brine shrimp lethality assay. These compounds showed Artemia salina death < 50 % thereby suggesting their potential for other biological evaluation. The antimicrobial evaluation was conducted using the agar disc diffusion assay. The twenty MPQ-α-APs were assessed against Bacillus cereus , Staphylococcus aureus , Klebsiella pneumonia and Micrococcus luteus ; and three yeast cultures Candida albicans, Caraipa utilis and Saccharomyces cerevisiae. Compound 4m showed slight bacterial growth inhibition for the test species Bacillus cereus and Micrococcus luteus while compound 4r was marginally inhibitory to the growth of Staphylococcus aureus. Finally, the MPQ-α-APs were screened for their antioxidant activity by the DPPH assay. Compounds 4f and 4r demonstrated significant free radical scavenging potential of 94.24 % and 67.32 %, respectively. The remaining compounds showed low antioxidant activity within the range of 21 – 42 %.Item Synthesis, characterization and application of novel ionic liquids(2018) Arumugam, Vasanthakumar; Redhi, Gyanasivan Govindsamy; Gengan, Robert MoonsamyIonic liquids (ILs) or molten salts at room temperature presently experience significant attention in many areas of chemistry. The most attractive property is the “tenability” of the physical and chemical properties of ILs by varying structure. The use of ILs in solvents demands information about their behaviour in the presence of other compounds including organic solvents such as alcohols or carboxylic acids or water, commonly used for products extraction. In addition, the efficiency of chemical processes (synthesis, extractions and separations) is strongly influenced by the nature of ILs. In this study describes the synthesis and characterization of novel epoxy propyl substituted ionic liquids (ILs). The thermophysical properties of ILs and their binary mixtures with either water, alcohol or carboxylic acids were investigated and the results are discussed in terms of interactions through thermodynamic properties. Furthermore, 2-oxopyrrolidine (Pyr), 2-aminopicoline (Apic) and 1,4-diazabicyclo [2.2.2] octane (DABCO)-based dihydroxypropyl substituted ILs are synthesised and characterised successfully. These ILs were then used to synthesize and characterize a novel 4 th -generation multi-ionic IL. A significant application of this IL is the synthesis of a unique nanomaterial using magnetic iron nanoparticles, h-boron nitride and titanium dioxide. The nanomaterial was strategically used to reduce selected dyes and series of nitroanilines (NAs). The chapter 1 to 4 explains about the introduction, literature review, synthesis and thermophysical properties of ILs as well as thermodynamic properties of ILs. The fifth chapter of this study describe the synthesis, characterization and thermophysical properties of a novel 2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium chloride IL and its binary mixtures, with either water or ethanol. The density (ρ), and speed of sound (u), were measured for the above IL and its corresponding binary systems with either water or ethanol at different temperatures ranging from (293.15 to 313.15) K. The derived thermodynamic properties for instance excess molar volumes (V mE ), isentropic compressibility (k s ) deviation in isentropic compressibility (∆k s ) and intermolecular free length (L f ) were investigated from the ρ and u data, respectively. It is noted that V mE , k s ∆k s and L f values increase with increasing temperature. Derived properties such as V mE , and ∆k s data were fitted to the Redlich-Kister polynomial equation. The measured and calculated data were interpreted in terms of intermolecular interfaces and structural effects between similar and dissimilar molecules upon mixing (Paper: I) The chapter six describes the synthesis and characterization of 2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium salicylate and 2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium acetate ILs. These ILs and their binary mixtures with either water or methanol were then studied to determine their thermophysical properties. The temperature dependent ρ and u for IL, methanol, water, and their corresponding binary mixtures of {IL (1) + methanol or water (2)} were measured over the entire range of mole fractions at temperatures from T = (293.15 to 313.15) K in intervals of 5 K, under atmospheric pressure. The calculated thermodynamic properties such as V mE , k s ∆k s andL f , were derived from the investigated ρ and u data. The resulting experimental data for V mE , L f , and ∆k s , were well fitted to the Redlich-Kister polynomial equation. (Paper: II & III) The chapter seven reports the thermophysical properties of binary mixtures for the combination of 2′, 3′- epoxypropyl-N-methyl-2-oxopyrrolidinium chloride with carboxylic acids either ethanoic or propionic acids. The novel IL [EPMpyr] + [Cl] − was synthesized, and it has been mixed with ethanoic or propanoic acids. The influence of an epoxy group in this IL was more strongly affected with the acids, and their thermophysical properties at varied temperatures are discussed in term of density (ρ), viscosity (η), speed of sound (u), and refractive index (n) measurements. The ρ, u, η, and n of the IL, ethanoic acid, propanoic acid, and their corresponding binary mixtures {[EPMpyr] + [Cl] − (1) + ethanoic or propanoic acid (2)} were measured at T = (293.15-313.15) K and at P = 0.1 MPa. The theoretical thermodynamic properties of V mE , k s , ∆k s , and L f are calculated using experimental ρ and u data. The V mE and ∆k s values for both binary mixtures were found to be negative over the entire mole fraction range of compositions at all the investigated temperatures. These results suggest the existence of specific interactions between components in the molecules. The experimental data could be helpful to understand the molecular interactions between the IL and carboxylic acid combinations. The experimental data were fitted to the Redlich-Kister polynomial equation. This study is very important for industries because most of the ILs are viscous and have high pH values, so making their applications in industries are difficult. Hence these main disadvantages could be addressed and rectified simultaneously without drastically altering the nature of the IL by using various carboxylic acid combinations. Moreover, the thermophysical data and information about acid and IL mixtures will provide insight into the use of these ILs in acidic conditions, thereby enabling the development of processes for future industries. Additionally, the measurements of thermophysical properties were used to calculate thermodynamic properties, which lead to a better understanding of the interactions amongst unlike molecules and hydrogen bonds in binary mixtures. (Paper: IV) In summary, the first four publications describes the synthesis, characterization and thermophysical properties of 2′,3′-epoxypropyl substituted 2-oxopyrrolidinium cation-based novel ILs with various anions such as chloride, acetate and salicylate. These ILs were characterized by FTIR, 1 H NMR, 13 C NMR and elemental analysis to confirm the chemical structure of the ILs. The binary mixtures of ILs with either water or methanol or ethanol were carefully prepared. Experimental measurements of the thermophysical properties of ρ, u, η and n, selected solvents, and their binary mixtures at various temperatures, across the entire mole fraction ranges of ILs, were determine. Thermodynamic properties of V mE , k s , ∆k s and L f were calculated from ρ, and u data. These thermodynamic properties were correlated using the Redlich-Kister polynomial equation. Molecular interactions, especially H-bonding and other interaction effects that occur between ILs and molecular solvents were discussed. The chapter eight discusses the synthesis and characterization of novel 4 th generation amino trismethyl phosphonate (ATMP) based IL such as [DABCO, PYR, APIC-PDO] + [ATMP] - and their application to the synthesis and characterization of partially oxidized h-boron nitride modified nanomaterial with copper ferrite magnetic nanoparticles (NPs). This nanomaterial was characterized through various spectroscopic, microscopic and surface morphological techniques. Thereafter it was used as environmentally friendly heterogeneous catalyst for the reduction of a series of NAs and dyes such as 2-nitroaniline (2-NA), 3-nitroaniline (3-NA), 4-nitroaniline (4-NA), 4-nitro-1,2-phenylenediamine (4-NPD), methylene blue and allura red to their corresponding amino analogues. The rate constant, order of reaction, activation energy and constant ratio were calculated for each substrate. The order of reduction, was 4-NPD > 4-NA > 3-NA > 2-NA. Kinetic studies indicated either zero or pseudo-first order reactions. Furthermore, kinetic studies at various temperatures such as 25, 30, 40, 50 and 60 o C as well as the range of various quantities of catalyst such as 0.015, 0.030 and 0.045 ml (0.2mg/ml concentration) showed that either an increase in temperature or the amount of catalyst increased the rate of the reaction. It was found that the nanomaterial is an efficient catalyst in aqueous solution at ambient temperature, and the processes for recovery were simple. It was re-used more than seven times with negligible loss of its catalytic activity. It is envisaged that new industrial applications of the ILs and their nanomaterials will emanate in the future. (Paper: V) The chapter nine describes the synthesis, characterization and application to the reduction of NAs which were made using 2′,3′- epoxypropyl-N-methyl-2-oxopyrrolidinium salicylate IL, NiFe 2 O 4 NPs and titanium dioxide (TiO 2 ). Here IL was used as a bonding or capping agent to synthesize NiFe 2 O 4 NPs doped TiO 2 nanocomposite. This nanocomposite was characterized by various microscopic and surface morphological studies. The nanocomposite displayed a good catalytic activity for the reduction of 2-NA to 2-aminoaniline and can be recovered as well as recycled easily. (Paper: VI)Item Microwave synthesis and molecular re-arrangement of a grisadienone and its derivatives(2011) Ngcobo, Thandekile Sithembile; Gengan, Robert Moonsamy; Shode, F. O.ortho-Deoxygrisan (38), a spirodienone was synthesised from bisphenol (42) using both conventional and microwave assisted methods. The bisphenol (42) was synthesised from phenol (52) by conventional and microwave assisted methods. Benzophenone (43) was synthesised from compound (49) which in turn was synthesised from compound (53) by chromic acid oxidation in acetic anhydride or acetic acid. Compound (53) was synthesised from bisphenol (42) by mono-acetylation method.Acid-catalysed rearrangement of ortho-deoxygrisan (38) in the absence of light was investigated. Chromatography of the reaction mixture afforded compound (D) as a major component. Attempts to synthesise ortho-grisan (50) from benzophenone (43) were unsuccessful. Microwave assisted selenium dioxide oxidation of compound (53) gave a yellow compound C. The spectra of this compound were very similar to the spectra of ortho-deoxygrisan (38). However, selenium dioxide was reacted with compound (53) in the absence of microwave to give a yellow solid B. The 1H NMR spectral data of this compound led to the proposed structure B for it.Item Synthesis of bisquinolines through conventional and unconventional energy sources(2011) Makhanya, Talent Raymond; Gengan, Robert MoonsamyMalaria, the most prevalent parasitic disease, is considered a neglected disease owing to insufficient research and development in synthesis and therapy worldwide. Therapy failures are frequent and are due to a variety of factors such as the intrinsic characteristics of the disease, conditions of transmission, and the difficult control of spreading through tropical areas. Primary factors are the complexity of the parasite life cycle and the development of drug resistance. Another critical factor is the increasing number of immune-compromised patients that suffer from malaria and human immunodeficiency virus (HIV) co-infections. Most of the drugs currently available to treat malaria are quinoline derivatives modelled on the quinine molecule, found in the bark of Cinchona trees. Over the last 50 years the use of quinine has declined owing to the development of synthetic 4-aminoquinolines such as chloroquine. However, the malaria parasite is rapidly becoming resistant to the drugs currently available. Recently bisquinoline compounds were found more potent than chloroquine against both chloroquine-sensitive and resistant strains of malaria; this improved efficacy and prompted an increased interest in the design of these anti-malarial drugs. Although several synthetic methods are available to synthesise bisquinolines, we report the synthesis of bisquinolines from simple, readily available and cost- effective starting compounds. The synthesis was accomplished in four reaction steps using the Claisen condensation, Vilsmeir-Haack reaction, formation of a Schiff base and thermal cyclization, sequentially. We used a conventional energy source and microwave irradiation for the synthesis, wherever possible, of 2, 4-dichloro-3, 4'-biquinoline and 2, 4-dichloro-7'-methoxy-3, 4'-biquinoline. In the first step, 3-acyl-2, 4-dihydroxyquinoline is synthesised from an equimolar mixture of methyl-2-aminobenzoate and ethyl acetoacetate by microwave irradiation for 3 minutes; the yield is 90 % whereas by 6 hours refluxing the yield is 75 %. This is followed by the synthesis of 3-chloro-3-(2,4-dichloroquinolin-3yl) acrylaldehyde, by combining DMF and POCl3 at 00C to form the electrophile which reacts with 3-acyl-2,4-dihydroxyquinoline under microwave irradiation for 5 minutes; the yield is 65 % whereas by 6 hours refluxing the yield is 50 %. In the next step, several protocols to prepare a Schiff base 3-chloro-3-(2, 4-dichloroquinolin-3-yl) allylidene aniline are investigated with the best yield of 75% obtained by microwave irradiation for 5 minutes. Subsequently three aniline derivatives viz, 4-methoxyaniline, 4-chloroaniline and 4-methylaniline, are used as substrate to prepare 3-chloro-3-(2,4-dichloroquinolin-3-yl) allylidene-4-methoxyaniline, 3-chloro-3-(2 ,4-dichloroquinolin-3-yl) allylidene-4-methylaniline and 3-chloro-3-(2, 4-dichloroquinolin-3-yl) allylidene-4-chloro aniline at 68, 78 and 64 % yield, respectively. In the final step, 2, 4-dichloro-3, 4'-biquinoline is prepared; several methods were investigated, however, the best yield is 24 % which is obtained under alkaline conditions in the presence of K2CO3 and DMF by microwave irradiation for 10 minutes. The 2, 4-dichloro-7'-methoxy-3, 4'-biquinoline derivative is also prepared in 18 % yield under the same alkaline conditions. The outline of the total synthesis of bisquinoline is presented graphically below.