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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Synthesis and study of dibenzodihydroxy-26-crown-8

Amoozgar, Zohreh January 2007 (has links)
The objective of this research was to synthesis dibenzo-dihydroxy-26-crown-8 (1) as an ionophore for variety of chemosensors. Complexation of the ionophore (1) to a cation would cause a change of conformation. The conformational changes could affect fluorescence, UV spectra and/or Carbon-13 NMR of the chemosensor, depending on the fluorophores attached to the hydroxyl groups of crown 1 and/ or the identity of the ion. Several synthetic routes for crown 1 formation are given in the proposed synthetic procedure. Bis-1,2[2-hydroxyethoxy]benzene (17), bis-1,2[2-(3-chloro-2-hydroxypropoxy)ethoxy]benzene (18), bis-1,2[2-(2,3-epoxypropoxy)ethoxy]benzene (19) and bis-1,2[2(3-chloro-2-oxopropoxy)ethoxy]benzene (22) were synthesized. The reaction of 17 and 19 was attempted in the presence of SnC14, basic and acidic conditions, and in several solvents. The reaction of 17 and 22, and the reaction of 17 and 1,3-dichloroacetone were attempted in various reaction conditions. Crown 1 may have formed in the reaction of 17 and 19 in methylene chloride/ toluene in the presence of SnCl4 as the Lewis acid. / Department of Chemistry
2

The synthesis and study of a crown ether functionalized with both phosphine and phenol groups

Crabill, Todd W. January 2005 (has links)
This study has resulted in a crown ether functionalized with both phosphine and phenol groups, 5-diphenylphosphino-1,3-xylyl-18-crown-5. The target molecule was obtained from a six step synthesis. 4-Bromophenol was treated in sequence with formaldehyde, dimethylsulfate, and phosphorus tribromide producing 4-bromo-2,6-bis(bromomethyl)anisole. The main intermediate, 5-diphenylphosphino-1,3-xylyl-18-crown-5, was obtained by treating 4-bromo-2,6-bis(bromomethyl)anisole in sequence with tetraethylene glycol, lithium iodide, and methyldiphenyl phosphonite. The lithium iodide cleaved the anisole-to-methyl group bond, and the methyldiphenyl phosphonite provided the phosphine group for the crown ether following a lithium bromine exchange reaction. The 31P NMR of the phosphine crown ether showed a single signal at 6 -5.9, showing consistency of a single product. The IH NMR of the phosphine crown ether in deuterated chloroform showed signals at 6 3.55-3.7 (crown CH2), 6 4.6 (benzylic CH2), 6 7.1 (d, J = 7.o Hz, crown aromatic CH2), and 6 7.2-7.4 (noncrown aromatic CH2). / Department of Chemistry
3

The synthesis and study of 5-oxime-2-methoxy-1,3-xylyl-18-crown-5

Acord, Douglas A. January 2009 (has links)
Access to abstract permanently restricted to Ball State community only / Access to thesis permanently restricted to Ball State community only / Department of Chemistry
4

Fluorescent molecular sensors based on photoresponsive modified β-cyclodextrin and crown ethers for detecting organic molecules and metal ions in water

Ncube, Phendukani 09 December 2013 (has links)
D.Phil. (Chemistry) / The problem of maintaining good quality of water for domestic use and for aquatic life remains a challenge. Water sources are often contaminated with pollutants from natural sources such as volcanic eruptions and by human activities such as manufacturing industries, mining, water-purification processes, agricultural activities and a vast number of other activities. Water-purification processes used by municipal authorities are designed to remove most of the pollutants but some trace amounts will always remain and have been detected in drinking water and treated waste water reservoirs. These trace amounts pose a threat to human health and the well-being of aquatic life. The detection of these trace amounts of pollutants is often carried out by laboratory-based techniques that require sophisticated, expensive instruments and often require extensive sample preparation and pre-concentration. Simple, quick and in-field detection methods are necessary especially for remote small communities with limited or no access to laboratories. Optical detection systems offer hope as a solution to this problem. In this work newly developed fluorescence-based molecular sensors for the detection of pollutants in water were developed, characterised and tested for their sensing abilities towards organic and inorganic pollutants. The fluorescent probes for organic pollutants were designed based on the host-guest chemistry of the cyclodextrin molecule. Azo dye-modified β-cyclodextrins were synthesised and linked via ethylene glycol and epichlorohydrin to produce the sensors that were then tested for their sensing response towards chlorophenols and small aliphatic chlorinated alkanes which are often formed during the disinfection of water in the purification process. The sensor molecules were characterised by UV-Vis, FT-IR and 1D and 2D NMR spectroscopy. The amount of cyclodextrin in each sensor molecule was quantified using the anthrone method (67%) as well as by 1H-NMR spectroscopy (72%). To demonstrate the host-guest interaction of the sensor molecules, isothermal titration calorimetry (ITC) was used. ITC measurements showed that modifying β-cyclodextrin and using linkers did not alter its host-guest interaction with guest molecules as demonstrated by the stoichiometry, n, stability (or binding or association) constant (K) and thermodynamic parameters of the interaction. The sensor molecule linked via ethylene glycol showed selectivity towards 4- chlorophenol among the chlorophenols investigated and has the potential to be used in a sensor for the detection of 4-chlorophenol. The sensor molecule linked via epichlorohydrin showed sensitivity towards chloroform, a typical disinfection by-product. These experimental results showed that the sensor molecules could be used for quick on-field detection of chlorinated organic compounds in water. Sensor molecules for inorganic pollutants were based on the complex formation of crown ethers with metal ions. The sensor was formed by modifying a dibenzo-18- crown-6 ether molecule with an azo dye. The sensor was then characterised using UV-Vis spectrophotmetry, FT-IR and NMR spectroscopies as well as mass spectrometry and CHNS elemental analysis. The sensor molecule was then subjected to different metal ions and the fluorescence change of the probe observed. Interestingly, the sensor was highly sensitive and selective to mercury (II) and Cu (II) ions in water. Mercury (II) is one of the most hazardous heavy metals among the heavy-metal ions found in environmental waters and its early detection in water sources is important. The synthesised molecular sensor can therefore be incorporated into a simple hand-held gadget with a light source and be used for on-field detection of mercury (II) ions in remote areas.
5

Asymmetric induction in reactions of chiral carboxylic esters and silyl enol ethers

Evans, Melanie Daryl January 1998 (has links)
Several camphor and pinane derivatives have been synthesised and evaluated for use as chiral auxiliaries in asymmetric synthesis. Various blocking groups have been attached to the camphor skeleton in attempts to improve stereofacial selectivity; these include α-methoxybenzyl and xylyl groups, and novel stereoisomeric ketal moieties derived from meso- and (R,R)-(-)-2,3-butanediol. Benzylation reactions carried out on the lithium enolates of ester derivatives of the camphor-derived chiral auxiliaries afforded α-benzylated products in 5-60% diastereomeric excess. Stereochemical aspects have been explored using high resolution NMR, X-ray crystallographic and computer modelling techniques, and hydrolysis of selected α-benzylated products has permitted the diasteroselective bias to be confirmed. Opposite configurations at the new stereogenic centre are clearly favoured by the xylyl and ketal blocking groups - an observation rationalised in terms of the presence or absence of chelating potential in the blocking group. Baylis-Hillman reactions carried out on a series of specially prepared camphor-derived acrylic esters containing the ketal blocking group exhibited both low diastereoselectivities (0-30% d.e.) and very long reaction times. Chiral silyl enol ethers, synthesised using both pinane and camphor derivatives as chiral auxiliaries, showed up to 20% diastereomeric excess in MCPBA oxidation, alkylation and Mukaiyama reactions. Attempts to bring the prochiral centre in the silyl enol ether substrates closer to the chiral auxiliary, and thus improve the stereofacial selectivity, proved unsuccessful. The silyl enol ether derivatives, however, display interesting fragmentation patterns in their electron impact mass spectra, which were investigated using a combination of high resolution MS, comparative low resolution MS and metastable peak analysis.
6

Complexation of metal salts with phosphorus-containing poly(arylene ether)s

Bonaplata Revilla, Elena 21 July 2009 (has links)
Poly(arylene ether phosphine oxide)s (PEPO) are a recently identified subset of an important macromolecular series which includes industrially important high performance thermoplastics, such as the polysulfones, e.g. UDEL@ and polyether ketones, e.g. PEEK@, PEKK@, etc. The PEPO materials show an elevated glass transition temperature, high thermal and oxidative stability, improved solubility, and increased flame resistance. It has been demonstrated that a variety of metal salts including metals such as iron, zinc, cobalt, and copper, can be complexed at a molecular level with the phosphoryl group in films of these polymers producing novel transparent metal/polymer "composites". A procedure for obtaining homogeneous films from solutions of the metal halide complexed polymers has been developed. FTIR experiments as well as Tl phosphorus (31 P) NMR measurements were conducted to demonstrate the existance of metal complexation in the solid state. The effect of the chemical composition of the chain, type of metal salt, molar concentration of the metal salt, and heating cycle were investigated and found to influence properties of the films such as solubility, glass transition temperature, thermal stability, and storage mexiulus. Additionally, linear poly(arylene ether phosphine oxide)s were reduced to different extents to the corresponding phosphine containing polymers. Properties such as intrinsic One of these phosphine polymers was subsequently used in the generation of a rhodium catalyst for the hydroformylation of octene-l. The utilization of polymer-supported catalysts has important advantages such as catalyst recovery and the ease of separation of the product. The catalyst activity of the polymeric rhodium complex was studied as a function of reaction time as well as ligand to rhodium ratio. For a phosphorus/rhodium ratio of two these heterogeneous catalysts suffer in tenns of reaction rate in relation to their homogeneous counterparts. However, at phosphorus/rhodium ratios of approximately eight the reaction is almost quantitative after three hours, and the selectivity is greatly improved over that of monomeric homogeneous catalysts for the same P/Rh ratio. / Master of Science
7

Chemistry Of Thio And Seleno Metallates In Organic Synthesis

Saravanan, V 06 1900 (has links)
Thio metallates are known for many years for their utility in many processes. They have been established as versatile reagents in organic synthesis. However the heavier metal chalcogenides, though known for many years, have been ignored for a long time. In this thesis the results of the development of tetraethylammonium tetraselenotungstate [EttN]2Wse4 1 as a new class of selenium transfer reagent have been described. The thesis also deals with the chemistry of benzyltriethylammonium tetrathiomolybdate, [BnEt3N]2MoS4,2 in the synthesis of diselenides and thio esters. The thesis entitled "Chemistry of Thio and Seleno Metallates in Organic Synthesis" is divided into four Chapters. Chapter 1 In this chapter a detailed studies of alkylation of tetraethylammonium tetraselenotungstate (EuN)2WSe4,1 with a variety of alkyl halides, benzylic halides and acyl halides to yield the corresponding diselenides in excellent yields are described. (structural Formula) Scheme 1 Various carbohydrate-derived diselenides were also prepared by treating the sugar bromides with tetraethylammonium tetraselenotungstate 1 (Scheme 2). An attempt was made to synthesize seleno lactones from co- bromo acyl halides. This reaction mainly furnished the corresponding diacyl diselenides (Scheme 3). The reaction of 1 with aryldiazonium tetrafluoroborates led to the formation of corresponding diselenides or mono selenides depending on the substitution on the aromatic ring (Scheme 4). (structural formula) Scheme 2 (structural formula) Scheme 3 (structural formula) Scheme 4 Chapter 2 In this chapter a general methodology for the formation of the diselenide bond has been extended to the synthesis of a number of redox- switched crown ethers of various ring size using the reagents tetraethylammonium tetraselenotungstate (Et4N)2WSe4 t 1 and benzyltriethylammonium tetrathiomolybdate, [BnEt3NJ2MoS4,2 (Scheme 5). (structural formula) Scheme 5 The association constants for the binding of silver and potassium ions with the diselena crown ethers were determined. This methodology is very useful for obtaining selenacrown ethers under very mild conditions and also without using high dilution conditions. Chapter 3 In this chapter a general methodology for the facile conversion of amides and lactams to the corresponding seleno amides and selenolactams is described. A number of amides and lactams were converted into their selenocarbonyl derivatives in excellent yield via the formation of Vilsmeier intermediates followed by treatment with tetraethylammonium tetraselenotungstate (EuN^WSe4,1 (Scheme .6). (structural formula( Scheme 6 Chapter 4 In this chapter, a general method for the synthesis of thioesters is described. The reaction of p- nitrophenyl esters and disulfides with benzyltriethylammonium tetrathiomolybdate (PhCH2NEt3)2MoS4,2 furnished the corresponding thio esters in good yield (Scheme (7). The intramolecular version of this reaction furnished dimeric thiolactones as the major product (Scheme 8) (structural formula) Scheme 7 (structural formula) Scheme 8 (for structural formula pl see the original document)

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