Alkenes - ester polymeric solvents thermodynamic interactions - Part 1
- Scheepers, Jacques J., Muzenda, Edison
- Authors: Scheepers, Jacques J. , Muzenda, Edison
- Date: 2012
- Subjects: Activity coefficients , Esters , Alkenes , Thermodynamics , Solubility
- Type: Article
- Identifier: uj:6274 , http://hdl.handle.net/10210/8914
- Description: This work focused on the interactions between ester solvents and volatile organic compounds of alkene in nature. Infinite dilution activity coefficients of alkenes in various fatty acid ester solvents were predicted in order to study and thermodynamically understand the nature and effect of the bond interactions involved. Activity coefficients were computed using Microsoft Excel model specifically designed for this purpose. The ester solvent chain length and saturation influenced the solubility of alkene organics. Saturated and longer ester chains gave better absorption performance. Alkenes were found to be more soluble than their alkane counterparts of similar carbon count.
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- Authors: Scheepers, Jacques J. , Muzenda, Edison
- Date: 2012
- Subjects: Activity coefficients , Esters , Alkenes , Thermodynamics , Solubility
- Type: Article
- Identifier: uj:6274 , http://hdl.handle.net/10210/8914
- Description: This work focused on the interactions between ester solvents and volatile organic compounds of alkene in nature. Infinite dilution activity coefficients of alkenes in various fatty acid ester solvents were predicted in order to study and thermodynamically understand the nature and effect of the bond interactions involved. Activity coefficients were computed using Microsoft Excel model specifically designed for this purpose. The ester solvent chain length and saturation influenced the solubility of alkene organics. Saturated and longer ester chains gave better absorption performance. Alkenes were found to be more soluble than their alkane counterparts of similar carbon count.
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Alkenes - ester polymeric solvents thermodynamic interactions - part 2
- Scheepers, Jacques J., Muzenda, Edison, Belaid, Mohamed
- Authors: Scheepers, Jacques J. , Muzenda, Edison , Belaid, Mohamed
- Date: 2012
- Subjects: Activity coefficients , Esters , Alkenes , Thermodynamics
- Type: Article
- Identifier: uj:5341 , http://hdl.handle.net/10210/9581
- Description: This paper is a continuation of our work reported previously [1] on the interaction between ester solvents and alkene volatile organic compounds (VOCs). The interactions were presented inform of infinite dilution activity coefficients. A Microsoft Excel spreadsheet for the modified UNIFAC Dortmund group contribution method [2] was designed and used in computing the required phase equilibrium. The size of the solvent molecule (biodiesel) relative to the VOC molecule influenced the thermodynamic interactions. The degree of ester (biodiesel) bond saturation influenced the ease in which cyclic VOCs interacted with the solvent compared to their straight chain counterparts. The location of branches such as methyl branches in relation to the double-bonded carbons had an impact on the predicted infinite dilution activity coefficients.
- Full Text:
- Authors: Scheepers, Jacques J. , Muzenda, Edison , Belaid, Mohamed
- Date: 2012
- Subjects: Activity coefficients , Esters , Alkenes , Thermodynamics
- Type: Article
- Identifier: uj:5341 , http://hdl.handle.net/10210/9581
- Description: This paper is a continuation of our work reported previously [1] on the interaction between ester solvents and alkene volatile organic compounds (VOCs). The interactions were presented inform of infinite dilution activity coefficients. A Microsoft Excel spreadsheet for the modified UNIFAC Dortmund group contribution method [2] was designed and used in computing the required phase equilibrium. The size of the solvent molecule (biodiesel) relative to the VOC molecule influenced the thermodynamic interactions. The degree of ester (biodiesel) bond saturation influenced the ease in which cyclic VOCs interacted with the solvent compared to their straight chain counterparts. The location of branches such as methyl branches in relation to the double-bonded carbons had an impact on the predicted infinite dilution activity coefficients.
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Biphenolate and cyclopentadienyl-derived complexes of zirconium and titanium as catalysts for the polymerisation of alpha olefins
- Authors: Van Zyl, Aletta
- Date: 2012-09-04
- Subjects: Oligomers , Polymerization , Zirconium , Alkenes , Titanium
- Type: Thesis
- Identifier: uj:3459 , http://hdl.handle.net/10210/6852
- Description: M.Sc. , An annual production of approximately 46 million metric tons of polyolefins worldwide, emphasizes the industrial importance of this product and the polymerisation process. Olefins are the basic building block of the petrochemical industry and are therefore readily available and cheap. Reactivity of olefins decreases from ethylene to propylene to 1-octene and makes the study of polymerisation catalysts more complex, seeing that the activity of a catalyst differs from monomer to monomer. In this study zirconocene complexes with bridged cyclopentadienyl ligands have been prepared and investigated as , possible catalysts for the polymerisation of higher aolefins. Fulvenes have been reductively coupled and used as ligands for zirconium complexes. Steric bulk of the substituents on the ligand have been increased and changes in the polymeric products have been studied. The tacticty, endgroups and chain lengths of the polyolefins have been investigated. There is currently a considerable interest in the development of 'non-metallocene' catalysts as alternatives for the polymerisation and oligomerisation of a-olefins. Chelating diamide complexes of Group 4 metals have been the focus of much attention and these compounds have shown moderate to high reactivity. However, only a few examples of the corresponding chelating alkoxides are known. In this study, alkoxide complexes of zirconium and titanium have been prepared with Schiff bases as ligands. These complexes have been evaluated as polymerisation catalysts and the products have been studied. The titanium complexes were more active than the zirconium analogues. The narrow molecular weight distribution of the polyolefins gave evidence that these catalysts are single-sited catalysts.
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- Authors: Van Zyl, Aletta
- Date: 2012-09-04
- Subjects: Oligomers , Polymerization , Zirconium , Alkenes , Titanium
- Type: Thesis
- Identifier: uj:3459 , http://hdl.handle.net/10210/6852
- Description: M.Sc. , An annual production of approximately 46 million metric tons of polyolefins worldwide, emphasizes the industrial importance of this product and the polymerisation process. Olefins are the basic building block of the petrochemical industry and are therefore readily available and cheap. Reactivity of olefins decreases from ethylene to propylene to 1-octene and makes the study of polymerisation catalysts more complex, seeing that the activity of a catalyst differs from monomer to monomer. In this study zirconocene complexes with bridged cyclopentadienyl ligands have been prepared and investigated as , possible catalysts for the polymerisation of higher aolefins. Fulvenes have been reductively coupled and used as ligands for zirconium complexes. Steric bulk of the substituents on the ligand have been increased and changes in the polymeric products have been studied. The tacticty, endgroups and chain lengths of the polyolefins have been investigated. There is currently a considerable interest in the development of 'non-metallocene' catalysts as alternatives for the polymerisation and oligomerisation of a-olefins. Chelating diamide complexes of Group 4 metals have been the focus of much attention and these compounds have shown moderate to high reactivity. However, only a few examples of the corresponding chelating alkoxides are known. In this study, alkoxide complexes of zirconium and titanium have been prepared with Schiff bases as ligands. These complexes have been evaluated as polymerisation catalysts and the products have been studied. The titanium complexes were more active than the zirconium analogues. The narrow molecular weight distribution of the polyolefins gave evidence that these catalysts are single-sited catalysts.
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Die oligomerisasie van Sasol alfa-olefienfraksies
- Authors: Ranwell, Alta
- Date: 2014-07-23
- Subjects: Oligomers , Alkenes
- Type: Thesis
- Identifier: uj:11798 , http://hdl.handle.net/10210/11521
- Description: M.Sc. , The development of synthetic lubricants was the logical result of high demands being made by modern technology, the exhaustion of natural mineral oil sources and the search for environmentally friendly substances. Alpha olefins are products of the Sasol Fischer-Tropsch process and are currently part of the wider petrol pool. Substantial value can be added to the alpha olefins by the production of high value polyalphaolefins (PADs). This project was aimed at finding explanations for previous unsuccessful attempts to produce acceptable PADs from Sasol feedstreams. High priority was given to the modification of experimental procedures to produce a synthetic oil that conforms to specific standards. Oxygenates, aromatics and "other than alpha" olefins (branched, internal and cyclic olefins) were identified as problem components in the Sasol feedstream. These compounds led to early termination of oligomerisation and in the presence of BF3 , unwanted compounds were even incorporated into the PAD products. The feedstream was thus purified by distillation and a MeDH/H2D extraction procedure. As a result, better reaction control (with regard to oligomer distribution) was gained and the product quality improved. Reaction conditions were optimised and basic reaction models (to predict oligomer distributions) were developed. It became clear however, that product quality did not only depend on oligomer distribution, but also on the specific structures present in the various oligomers. GC analyses showed that each oligomer consists of a great number of isomers - even more than can be explained in terms of the classic cationic mechanism for oligomerisation. GC-MS analyses could not successfully distinguish between different branched isomers, because of the complexity of the mixture. Summary The question was asked whether the complex mixture has already been formed during the primary oligomerisation process, or at a later stage by skeletal rearrangements. Research work indicated that one can distinguish between a primary (normal oligomerisation) process, and a secondary process (skeletal rearrangement). It became clear that the secondary process is favoured by specific reaction conditions (e.g. long reaction times and high co-catalyst concentrations). The formation of isomers increased under these conditions and product quality was adversely affected. The possibility to produce PAD products from Sasol feedstreams identical to commercial products still exists, and necessitate further research work.
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- Authors: Ranwell, Alta
- Date: 2014-07-23
- Subjects: Oligomers , Alkenes
- Type: Thesis
- Identifier: uj:11798 , http://hdl.handle.net/10210/11521
- Description: M.Sc. , The development of synthetic lubricants was the logical result of high demands being made by modern technology, the exhaustion of natural mineral oil sources and the search for environmentally friendly substances. Alpha olefins are products of the Sasol Fischer-Tropsch process and are currently part of the wider petrol pool. Substantial value can be added to the alpha olefins by the production of high value polyalphaolefins (PADs). This project was aimed at finding explanations for previous unsuccessful attempts to produce acceptable PADs from Sasol feedstreams. High priority was given to the modification of experimental procedures to produce a synthetic oil that conforms to specific standards. Oxygenates, aromatics and "other than alpha" olefins (branched, internal and cyclic olefins) were identified as problem components in the Sasol feedstream. These compounds led to early termination of oligomerisation and in the presence of BF3 , unwanted compounds were even incorporated into the PAD products. The feedstream was thus purified by distillation and a MeDH/H2D extraction procedure. As a result, better reaction control (with regard to oligomer distribution) was gained and the product quality improved. Reaction conditions were optimised and basic reaction models (to predict oligomer distributions) were developed. It became clear however, that product quality did not only depend on oligomer distribution, but also on the specific structures present in the various oligomers. GC analyses showed that each oligomer consists of a great number of isomers - even more than can be explained in terms of the classic cationic mechanism for oligomerisation. GC-MS analyses could not successfully distinguish between different branched isomers, because of the complexity of the mixture. Summary The question was asked whether the complex mixture has already been formed during the primary oligomerisation process, or at a later stage by skeletal rearrangements. Research work indicated that one can distinguish between a primary (normal oligomerisation) process, and a secondary process (skeletal rearrangement). It became clear that the secondary process is favoured by specific reaction conditions (e.g. long reaction times and high co-catalyst concentrations). The formation of isomers increased under these conditions and product quality was adversely affected. The possibility to produce PAD products from Sasol feedstreams identical to commercial products still exists, and necessitate further research work.
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Die vorming van sure op 'n seolietkatalisator tydens die isomerisasie van 1-hekseen
- Authors: Loggenberg, Peter Matthews
- Date: 2014-02-13
- Subjects: Zeolites , Alkenes , Isomerization , Catalysis
- Type: Thesis
- Identifier: uj:3969 , http://hdl.handle.net/10210/9328
- Description: M.Sc. (Chemistry) , The isomerization of short chain olefins on a catalyst containing a H-X zeolite (HZ-1) produces mainly branched olefins at 400°C. At SASOL the catalyst is also used to reduce organic acids present in the feed. Amarked increase in the acid concentration over a period of time has been reported. Other impurities in the reactor feed include short chain alcohols, aldehydes and ketones. This study consisted of kinetic experiments which concentrated on the formation of acids from ketones and aldehydes during the isomerization of 1-hexene on 60/80 mesh HZ-1. The formation of acetic and propionic acid from methyl ethyl ketone was observed. It was also shown that n-butyrealdehyde forms formic acet ic, propionic and n-butyric acid at 400°C. The presence of n-buthanol during the reaction of methyl ethyl ketone enhanced the formation of acid. A supplementary study showed the formation of only acetic acid from acetone. The study of the formation of acids from a 5% methyl ethyl ketone/5% n-buthanol at 400, 300, 250, 200 and 150°C showed an overall decrease in the acid concentration with a lowering in temperature. These results showed the development of a definite maximum in the acid production. The formation of formic acid was also observed at 200 and 150°C. Amechanism for the formation of acids from ketones is proposed and discussed. Other than existing mechanisms this explains the formation of formic, acetic and propionic acid from methyl ethyl ketone. The mechanism includes Bronsted and Lewis acid sites. During this study a method was developed for the analysis of trace quantities of organic acids present in the reaction product. Ion exclusion chromatography was used for the quantitative determination of the different types of acids. Surface studies with nitrogen adsorptics showed a drastic decrease in the surface area during the reactions. Pore volume studies showed remarkably the loss of macropores' with a pore diameter bigger than 3,6 nm. Pikinometry showed the existance of micropores which were unaffected by the reactions. Aneutron activation analysis of HZ-l showed the presence of a great variety of transition elements mainly Scandium, Cobalt and Iron.
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- Authors: Loggenberg, Peter Matthews
- Date: 2014-02-13
- Subjects: Zeolites , Alkenes , Isomerization , Catalysis
- Type: Thesis
- Identifier: uj:3969 , http://hdl.handle.net/10210/9328
- Description: M.Sc. (Chemistry) , The isomerization of short chain olefins on a catalyst containing a H-X zeolite (HZ-1) produces mainly branched olefins at 400°C. At SASOL the catalyst is also used to reduce organic acids present in the feed. Amarked increase in the acid concentration over a period of time has been reported. Other impurities in the reactor feed include short chain alcohols, aldehydes and ketones. This study consisted of kinetic experiments which concentrated on the formation of acids from ketones and aldehydes during the isomerization of 1-hexene on 60/80 mesh HZ-1. The formation of acetic and propionic acid from methyl ethyl ketone was observed. It was also shown that n-butyrealdehyde forms formic acet ic, propionic and n-butyric acid at 400°C. The presence of n-buthanol during the reaction of methyl ethyl ketone enhanced the formation of acid. A supplementary study showed the formation of only acetic acid from acetone. The study of the formation of acids from a 5% methyl ethyl ketone/5% n-buthanol at 400, 300, 250, 200 and 150°C showed an overall decrease in the acid concentration with a lowering in temperature. These results showed the development of a definite maximum in the acid production. The formation of formic acid was also observed at 200 and 150°C. Amechanism for the formation of acids from ketones is proposed and discussed. Other than existing mechanisms this explains the formation of formic, acetic and propionic acid from methyl ethyl ketone. The mechanism includes Bronsted and Lewis acid sites. During this study a method was developed for the analysis of trace quantities of organic acids present in the reaction product. Ion exclusion chromatography was used for the quantitative determination of the different types of acids. Surface studies with nitrogen adsorptics showed a drastic decrease in the surface area during the reactions. Pore volume studies showed remarkably the loss of macropores' with a pore diameter bigger than 3,6 nm. Pikinometry showed the existance of micropores which were unaffected by the reactions. Aneutron activation analysis of HZ-l showed the presence of a great variety of transition elements mainly Scandium, Cobalt and Iron.
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Imidazolyl- and pyrazolyl-salicylaldimine transition metal complexes and their applications in olefin transformation reactions
- Authors: Yankey, Margaret
- Date: 2011-05-16T06:45:25Z
- Subjects: Salicylates , Transition metal complexes , Alkenes , Catalysts , Heck reaction , Ligands
- Type: Thesis
- Identifier: uj:7064 , http://hdl.handle.net/10210/3627
- Description: M.Sc. , This study deals with the synthesis of nitrogen-donor imidazolyl- and pyrazolyl-salicylaldimine compounds, their reactions with selected transition metals and applications as catalysts for Heck coupling reactions of aryl halides with butyl acrylate, ethylene polymerization reactions and reactions of higher α-olefins. Imidazole-based salicylaldimine compounds 2,4-di-tert-butyl-6-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L1) and 4-tert-butyl-2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L2) were prepared by Schiff base condensation reaction of histamine dihydrochloride with 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 5-tert-butyl-2-hydroxybenzaldehyde respectively. The compounds were characterized by 1H, 13C{1H} NMR and IR spectroscopy; and high resolution mass spectrometry (HRMS). Compounds 2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L3), 2,4-di-tert-butyl-6-{[2-(3,5-dimethyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L4), 2,4-di-tert-butyl-6-[(2-pyrazol-1-yl-ethylimino)-methyl]-phenol (L5) and 2,4-di-tert-butyl-6-{[2-(3,5-diphenyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L6) were synthesized according to literature procedure. Reactions of L1-L3 with [PdCl2(MeCN)2] yielded complexes 2.1-2.3 respectively. Ligand L1 was also complexed with [FeCl2] and [CoCl2] to give complexes 2.4 and 2.5 respectively, while complexes 2.6-2.15 were synthesized by reactions of L1, L2 and L4-L6 with [VCl3] and [CrCl3(THF)3]; all in a ratio of 1:1. The palladium(II) complexes (2.1-2.3) were characterized by 1H, 13C{1H} NMR and IR spectroscopy, mass spectrometry and elemental analysis, while complexes 2.4-2.15 were characterized by IR spectroscopy, mass spectrometry and elemental analysis due to their paramagnetic nature. The structures of complexes 2.1 and 2.4 were confirmed by single crystal X-ray diffraction analysis. All the complexes formed were mononuclear.
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- Authors: Yankey, Margaret
- Date: 2011-05-16T06:45:25Z
- Subjects: Salicylates , Transition metal complexes , Alkenes , Catalysts , Heck reaction , Ligands
- Type: Thesis
- Identifier: uj:7064 , http://hdl.handle.net/10210/3627
- Description: M.Sc. , This study deals with the synthesis of nitrogen-donor imidazolyl- and pyrazolyl-salicylaldimine compounds, their reactions with selected transition metals and applications as catalysts for Heck coupling reactions of aryl halides with butyl acrylate, ethylene polymerization reactions and reactions of higher α-olefins. Imidazole-based salicylaldimine compounds 2,4-di-tert-butyl-6-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L1) and 4-tert-butyl-2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L2) were prepared by Schiff base condensation reaction of histamine dihydrochloride with 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 5-tert-butyl-2-hydroxybenzaldehyde respectively. The compounds were characterized by 1H, 13C{1H} NMR and IR spectroscopy; and high resolution mass spectrometry (HRMS). Compounds 2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L3), 2,4-di-tert-butyl-6-{[2-(3,5-dimethyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L4), 2,4-di-tert-butyl-6-[(2-pyrazol-1-yl-ethylimino)-methyl]-phenol (L5) and 2,4-di-tert-butyl-6-{[2-(3,5-diphenyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L6) were synthesized according to literature procedure. Reactions of L1-L3 with [PdCl2(MeCN)2] yielded complexes 2.1-2.3 respectively. Ligand L1 was also complexed with [FeCl2] and [CoCl2] to give complexes 2.4 and 2.5 respectively, while complexes 2.6-2.15 were synthesized by reactions of L1, L2 and L4-L6 with [VCl3] and [CrCl3(THF)3]; all in a ratio of 1:1. The palladium(II) complexes (2.1-2.3) were characterized by 1H, 13C{1H} NMR and IR spectroscopy, mass spectrometry and elemental analysis, while complexes 2.4-2.15 were characterized by IR spectroscopy, mass spectrometry and elemental analysis due to their paramagnetic nature. The structures of complexes 2.1 and 2.4 were confirmed by single crystal X-ray diffraction analysis. All the complexes formed were mononuclear.
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Lanthanide organic frameworks of Azole type linkers as catalysts for the epoxidation of olefins
- Authors: Belay, Yonas Habtegiorghies
- Date: 2018
- Subjects: Alkenes , Catalysis , Azoles
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/416766 , uj:35269
- Description: Abstract: The aim of the project is the synthesis of lanthanum metal organic frameworks with azole based linkers as catalysts for the oxidation of olefins to aldehydes and epoxides. The organic struts of azole based linkers 4-((1-(4-carboxyphenyl)-1H-1,2,3-triazol-4-yl)methoxy)-3- methoxybenzoic acid (18), 5-((1-(4-carboxyphenyl)-1H-1,2,3-triazol-4- yl)methoxy)isophthalic acid (23), 5-(4-((3,5-dicarboxyphenyl)methyl)-1H-1,2,3-1-yl) isophthalic acid (26) and 4,4ˈ-(2H-tetrazole-2,5-diyl)dibenzoic acid (28) were successfully synthesized using copper-catalyzed click chemistry reaction of azides and alkynes. Their structures were confirmed using nuclear magnetic resonance spectroscopy (NMR), high resolution electrospray ionization mass spectrometry (ESI-MS), and elemental analysis. The metal organic frameworks were synthesized by mixing lanthanum nitrate hexahydrate and the azole based linker organic struts in dimethylformamide solvent using solvothermal technique. Other synthesis methods such as solvent evaporation and diffusion techniques were also attempted for the synthesis of crystalline metal organic frameworks. The slow evaporation method of synthesis provided UJMOF-1 (La-triazole 18 MOF) as a crystalline product suitable for single X-ray diffraction analysis. All the attempted synthesis methods for UJMOF-2, UJMOF-3 and UJMOF-4 did not provide crystalline product suitable for single crystal X-ray diffraction analysis. However, the solvothermal synthesis for all the MOFs provided microcrystalline powder solid products. The products were characterized using different characterization techniques such as acid digestion 1H NMR, EA, IR, ESI-MS, SEM-EDX, PXRD, ICP-OES, BET, TGA and DSC methods, which provided substantial support for the formation of the proposed lanthanum based metal organic frameworks. The MOFs showed good catalytic activities for the oxidation of olefins to aldehydes and epoxides, using hydrogen peroxide and tert-butyl hydroperoxide, respectively, as oxidizing agents in the presence and absence of additives after heating at 70-80 °C in acetonitrile solvent for 24 hours. , Ph.D. (Chemistry)
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- Authors: Belay, Yonas Habtegiorghies
- Date: 2018
- Subjects: Alkenes , Catalysis , Azoles
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/416766 , uj:35269
- Description: Abstract: The aim of the project is the synthesis of lanthanum metal organic frameworks with azole based linkers as catalysts for the oxidation of olefins to aldehydes and epoxides. The organic struts of azole based linkers 4-((1-(4-carboxyphenyl)-1H-1,2,3-triazol-4-yl)methoxy)-3- methoxybenzoic acid (18), 5-((1-(4-carboxyphenyl)-1H-1,2,3-triazol-4- yl)methoxy)isophthalic acid (23), 5-(4-((3,5-dicarboxyphenyl)methyl)-1H-1,2,3-1-yl) isophthalic acid (26) and 4,4ˈ-(2H-tetrazole-2,5-diyl)dibenzoic acid (28) were successfully synthesized using copper-catalyzed click chemistry reaction of azides and alkynes. Their structures were confirmed using nuclear magnetic resonance spectroscopy (NMR), high resolution electrospray ionization mass spectrometry (ESI-MS), and elemental analysis. The metal organic frameworks were synthesized by mixing lanthanum nitrate hexahydrate and the azole based linker organic struts in dimethylformamide solvent using solvothermal technique. Other synthesis methods such as solvent evaporation and diffusion techniques were also attempted for the synthesis of crystalline metal organic frameworks. The slow evaporation method of synthesis provided UJMOF-1 (La-triazole 18 MOF) as a crystalline product suitable for single X-ray diffraction analysis. All the attempted synthesis methods for UJMOF-2, UJMOF-3 and UJMOF-4 did not provide crystalline product suitable for single crystal X-ray diffraction analysis. However, the solvothermal synthesis for all the MOFs provided microcrystalline powder solid products. The products were characterized using different characterization techniques such as acid digestion 1H NMR, EA, IR, ESI-MS, SEM-EDX, PXRD, ICP-OES, BET, TGA and DSC methods, which provided substantial support for the formation of the proposed lanthanum based metal organic frameworks. The MOFs showed good catalytic activities for the oxidation of olefins to aldehydes and epoxides, using hydrogen peroxide and tert-butyl hydroperoxide, respectively, as oxidizing agents in the presence and absence of additives after heating at 70-80 °C in acetonitrile solvent for 24 hours. , Ph.D. (Chemistry)
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Mechanistic study on tertiary phosphine complexes of ruthenium as olefin metathesis catalysts.
- Authors: Oosthuizen, Sharon
- Date: 2008-05-15T13:28:00Z
- Subjects: Phosphine , Alkenes , Chemical kinetics , Reactivity (Chemistry) , Metathesis (Chemistry) , Ruthenium , Transition metal catalysts , Complex compounds synthesis
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/374346 , uj:1717 , http://hdl.handle.net/10210/405
- Description: Ruthenium carbene complexes, with the general structure, [LL’Ru=CHR], are commonly known as Grubbs type catalysts, named after the discoverer of these metathesis catalysts. The discovery was quite revolutionary, since the catalysts proved to be easy to handle, tolerant towards various functional groups and more stable with regard to air and water than previous transition metal catalysts. Another important advantage was that all types of olefin metathesis reactions could be initiated without the help of co-catalysts or promoters. Today Grubbs type catalysts find wide application in especially organic and synthetic chemistry. A well-known example is the SHOP-process which produces long chain -olefins, while other important applications include the synthesis of macro-cyclic and cyclic olefins. The current study involved experimental and theoretical work to investigate various aspects comprising synthetic procedures, reactivity, kinetics, geometry and electronic properties of the complexes. Results are discussed briefly in the following paragraphs. The first aim of the project was to synthesise a Grubbs type catalyst. Initial efforts were focused on the preparation of a first generation catalyst through various methods. This included modifying the reported method for the synthesis of [(PPh3)2Cl2Ru=CH-CH=CMe2] to yield [(PPh2Cy)2Cl2Ru=CHCH= CMe2] instead; a phosphine exchange reaction with the complex [(PPh3)2Cl2Ru=CH-CH=CMe2] and free phosphine PPh2Cy; and utilising the analogue arsine ligand, AsPh3, to synthesise [(AsPh3)2Cl2Ru=CHCH=CMe2]; but unfortunately no success was achieved. However, it was possible to synthesise a novel second generation Grubbs type catalyst, [(IMesH2)(PPh2Cy)Cl2Ru=CHPh], through the phosphine exchange reaction of [(IMesH2)(NC5H5)2Cl2Ru=CHPh] and PPh2Cy. The new complex was tested in kinetic reaction studies and phosphine exchange reactions. Results showed that [(IMesH2)(PPh2Cy)Cl2Ru=CHPh] was catalytically active for the ring closing metathesis of commercial diethyl diallylmalonate. The reaction was first order with regard to the olefin, contrary to the second order kinetic results reported for similar reactions catalysed by first generation Grubbs catalysts. The phosphine exchange reactions were very successful and a rate constant could be determined. The rate constant was independent of the free phosphine concentration and activation parameters had relatively large, positive values; results indicative of a dissociative mechanism. These findings are in correlation with literature reports. A kinetic investigation was done on the catalyst-olefin coordination involving the functionalized olefins vinyl acetate, allyl acetate and allyl cyanide; and the first generation Grubbs catalyst, [(PCy3)2Cl2Ru=CHPh]. A two-step rate law, similar to an interchange mechanism, was determined. Phobcat, [(PhobCy)2Cl2Ru=CHPh], is modified first generation Grubbs type catalyst with rigid bicyclic phosphine rings which was recently developed by the Sasol Homogeneous Metathesis Group. In the current study Phobcat was compared to Grubbs1-PCy3 in the cross metathesis reaction of 1-octene. Results showed that Phobcat was up to 60% more active and had a 5 hour longer lifetime than Grubbs 1-PCy3. Theoretical studies were done on the three functionalized olefins of the earlier experimental study to gain fundamental understanding of steric and electronic influences on these catalyst-olefin systems. Without exception, coordination via the heteroatom of the olefin was significantly more favourable than coordination via the double bond functionality. This result indicates that metathesis of these olefins is highly unlikely, since the stable heteroatom coordination will suppress the parallel Ru=C/C=C interaction which is compulsory for the metathesis reaction. Orbital studies highlighted the difference between coordination of acetate and cyanide, but no trend of an electronic nature could be recognised. , Prof. A. Roodt
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- Authors: Oosthuizen, Sharon
- Date: 2008-05-15T13:28:00Z
- Subjects: Phosphine , Alkenes , Chemical kinetics , Reactivity (Chemistry) , Metathesis (Chemistry) , Ruthenium , Transition metal catalysts , Complex compounds synthesis
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/374346 , uj:1717 , http://hdl.handle.net/10210/405
- Description: Ruthenium carbene complexes, with the general structure, [LL’Ru=CHR], are commonly known as Grubbs type catalysts, named after the discoverer of these metathesis catalysts. The discovery was quite revolutionary, since the catalysts proved to be easy to handle, tolerant towards various functional groups and more stable with regard to air and water than previous transition metal catalysts. Another important advantage was that all types of olefin metathesis reactions could be initiated without the help of co-catalysts or promoters. Today Grubbs type catalysts find wide application in especially organic and synthetic chemistry. A well-known example is the SHOP-process which produces long chain -olefins, while other important applications include the synthesis of macro-cyclic and cyclic olefins. The current study involved experimental and theoretical work to investigate various aspects comprising synthetic procedures, reactivity, kinetics, geometry and electronic properties of the complexes. Results are discussed briefly in the following paragraphs. The first aim of the project was to synthesise a Grubbs type catalyst. Initial efforts were focused on the preparation of a first generation catalyst through various methods. This included modifying the reported method for the synthesis of [(PPh3)2Cl2Ru=CH-CH=CMe2] to yield [(PPh2Cy)2Cl2Ru=CHCH= CMe2] instead; a phosphine exchange reaction with the complex [(PPh3)2Cl2Ru=CH-CH=CMe2] and free phosphine PPh2Cy; and utilising the analogue arsine ligand, AsPh3, to synthesise [(AsPh3)2Cl2Ru=CHCH=CMe2]; but unfortunately no success was achieved. However, it was possible to synthesise a novel second generation Grubbs type catalyst, [(IMesH2)(PPh2Cy)Cl2Ru=CHPh], through the phosphine exchange reaction of [(IMesH2)(NC5H5)2Cl2Ru=CHPh] and PPh2Cy. The new complex was tested in kinetic reaction studies and phosphine exchange reactions. Results showed that [(IMesH2)(PPh2Cy)Cl2Ru=CHPh] was catalytically active for the ring closing metathesis of commercial diethyl diallylmalonate. The reaction was first order with regard to the olefin, contrary to the second order kinetic results reported for similar reactions catalysed by first generation Grubbs catalysts. The phosphine exchange reactions were very successful and a rate constant could be determined. The rate constant was independent of the free phosphine concentration and activation parameters had relatively large, positive values; results indicative of a dissociative mechanism. These findings are in correlation with literature reports. A kinetic investigation was done on the catalyst-olefin coordination involving the functionalized olefins vinyl acetate, allyl acetate and allyl cyanide; and the first generation Grubbs catalyst, [(PCy3)2Cl2Ru=CHPh]. A two-step rate law, similar to an interchange mechanism, was determined. Phobcat, [(PhobCy)2Cl2Ru=CHPh], is modified first generation Grubbs type catalyst with rigid bicyclic phosphine rings which was recently developed by the Sasol Homogeneous Metathesis Group. In the current study Phobcat was compared to Grubbs1-PCy3 in the cross metathesis reaction of 1-octene. Results showed that Phobcat was up to 60% more active and had a 5 hour longer lifetime than Grubbs 1-PCy3. Theoretical studies were done on the three functionalized olefins of the earlier experimental study to gain fundamental understanding of steric and electronic influences on these catalyst-olefin systems. Without exception, coordination via the heteroatom of the olefin was significantly more favourable than coordination via the double bond functionality. This result indicates that metathesis of these olefins is highly unlikely, since the stable heteroatom coordination will suppress the parallel Ru=C/C=C interaction which is compulsory for the metathesis reaction. Orbital studies highlighted the difference between coordination of acetate and cyanide, but no trend of an electronic nature could be recognised. , Prof. A. Roodt
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Nano-space confinement of pre-selective catalysts for hydroformylation of 1-octene
- Authors: Vunain, Ephraim
- Date: 2015-08-12
- Subjects: Rhodium catalysts , Alkenes , Hydroformylation , Nanochemistry
- Type: Thesis
- Identifier: uj:13835 , http://hdl.handle.net/10210/14155
- Description: Ph.D. (Chemistry) , Rhodium-catalyzed hydroformylation is one of the most important industrial processes for the production of linear and branch aldehydes. Aldehydes serve as intermediates in the production of various fine chemicals. Rh-based homogeneous catalysts for aldehydes production have demonstrated high yields and selectivity. Catalyst separation and recovery of expensive Rh-metal from reaction mixtures is a challenge to this process. With increasing industrial demand for highly selective processes, homogeneous catalysis could well be extensively employed if catalyst recovery from products and recyclability could be accomplished more efficiently and economically. The above problems justify the investigation of immobilized (heterogenized) catalysts by both academia and industry. This would solve the separation problem by making it possible to separate the catalyst from the reaction medium with simple filtration techniques and to regenerate the catalyst for reuse. Moreover, the ease of recovery of catalyst from products and reusability can minimize the impact of the process on the environment. Immobilization of metal complexes on solid supports is an effective approach to overcome the limitations of homogeneous catalysis. Support materials such as Mobil Composite Material (MCM-41) and Santa Barbara Amorphous type material (SBA-15) are attractive candidates for immobilizing metal complexes because of their high surface area, adjustable pore sizes, large pore volumes and high surface silanol groups. In the present work, mesoporous silica supports, MCM-41 and SBA-15 were synthesized. Rhodium(I) complex species, trans-aquacarbonyl bis(triphenylphosphine) [Rh(CO)(OH2)(PPh3)2]OTf and trans-aquacarbonyl bis{tris-(m-sulfonphenyl)-phosphine} [Rh(CO)(OH2)(TPPTS)2]OTf were synthesized as catalyst precursors and anchored onto the mesoporous MCM-41 and SBA-15 framework structure via an electrostatic method to form immobilized (heterogenized) catalysts. The support and catalyst were characterized using a range of solid-state techniques. Results showed that the structural integrity of the catalyst supports was maintained after immobilization. Results also revealed a strong interaction between rhodium complex species and the inner walls of the ordered mesoporous materials, thus leading to the formation of stable heterogenized catalysts. In addition, immobilized catalysts constrained the pores, thus leading to a confinement effect, which enhanced activity and regioselectivity in the hydroformylation process. Selected immobilized catalysts were...
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- Authors: Vunain, Ephraim
- Date: 2015-08-12
- Subjects: Rhodium catalysts , Alkenes , Hydroformylation , Nanochemistry
- Type: Thesis
- Identifier: uj:13835 , http://hdl.handle.net/10210/14155
- Description: Ph.D. (Chemistry) , Rhodium-catalyzed hydroformylation is one of the most important industrial processes for the production of linear and branch aldehydes. Aldehydes serve as intermediates in the production of various fine chemicals. Rh-based homogeneous catalysts for aldehydes production have demonstrated high yields and selectivity. Catalyst separation and recovery of expensive Rh-metal from reaction mixtures is a challenge to this process. With increasing industrial demand for highly selective processes, homogeneous catalysis could well be extensively employed if catalyst recovery from products and recyclability could be accomplished more efficiently and economically. The above problems justify the investigation of immobilized (heterogenized) catalysts by both academia and industry. This would solve the separation problem by making it possible to separate the catalyst from the reaction medium with simple filtration techniques and to regenerate the catalyst for reuse. Moreover, the ease of recovery of catalyst from products and reusability can minimize the impact of the process on the environment. Immobilization of metal complexes on solid supports is an effective approach to overcome the limitations of homogeneous catalysis. Support materials such as Mobil Composite Material (MCM-41) and Santa Barbara Amorphous type material (SBA-15) are attractive candidates for immobilizing metal complexes because of their high surface area, adjustable pore sizes, large pore volumes and high surface silanol groups. In the present work, mesoporous silica supports, MCM-41 and SBA-15 were synthesized. Rhodium(I) complex species, trans-aquacarbonyl bis(triphenylphosphine) [Rh(CO)(OH2)(PPh3)2]OTf and trans-aquacarbonyl bis{tris-(m-sulfonphenyl)-phosphine} [Rh(CO)(OH2)(TPPTS)2]OTf were synthesized as catalyst precursors and anchored onto the mesoporous MCM-41 and SBA-15 framework structure via an electrostatic method to form immobilized (heterogenized) catalysts. The support and catalyst were characterized using a range of solid-state techniques. Results showed that the structural integrity of the catalyst supports was maintained after immobilization. Results also revealed a strong interaction between rhodium complex species and the inner walls of the ordered mesoporous materials, thus leading to the formation of stable heterogenized catalysts. In addition, immobilized catalysts constrained the pores, thus leading to a confinement effect, which enhanced activity and regioselectivity in the hydroformylation process. Selected immobilized catalysts were...
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Nitrogen-based nickel and palladium complexes as catalysts for olefin oligomerization, Heck and Suzuki coupling reactions
- Authors: Nelana, Simphiwe Maurice
- Date: 2009-03-31T09:40:18Z
- Subjects: Nickel compounds , Nickel catalysts , Palladium compounds , Palladium catalysts , Alkenes , Transition metal compounds synthesis
- Type: Thesis
- Identifier: uj:8272 , http://hdl.handle.net/10210/2381
- Description: Ph.D. , This thesis deals with the synthesis of nitrogen-donor compounds and their reaction with metal ions. The first type of nitrogen-donor compounds are the unconjugated diimines (N,N´-bis(diphenylmethylene)ethylenediamine (L1) and (N,N´-bis(diphenylmethylene)propylenediamine (L2). Compounds L1 and L2 were reacted with [NiBr2(DME)] or [NiCl2·6H2O] to form complexes (2.1a), (2.2a), (2.3a) and (2.4a). These nickel complexes were characterized by IR spectroscopy, elemental analysis and mass spectrometry. When the complexes were left in chloroform for prolonged periods, hydrolysis of the diimine ligand took place, leading to the formation of nickel complexes 2.1b, 2.2b, 2.3b and 2.4b. The identity of the hydrolysed nickel complexes 2.1b and 2.2b was confirmed by single crystal X-ray crystallography. Complex 2.1b crystallised in the P21/n space group, whilst 2.2b crystallised in the P-1 space group. Compounds L1 and L2 were also reacted with [PdClMe(MeCN)2] to form the palladium complexes (3.1) and (3.2). The palladium complexes were characterized by NMR spectroscopy, elemental analysis and single crystal X-ray crystallography. Attempts to recrystallize 3.1 from a dichloromethane solution led to the formation of 3.1a. Both complexes 3.1a and 3.2 crystallised in the P21/n space group. Complexes 3.1 and 3.2 were tested as catalysts for the Heck coupling reaction of iodobenzene with methyl acrylate or butyl acrylate at 80 C. The products from the coupling reactions were characterized by GC and NMR spectroscopy. These complexes were found to be highly active with 100% conversions observed in some instances. The second type of ligands that were prepared are the benzoylpyrazolyl compounds, (3,5-dimethylpyrazol-1-yl)phenylmethanone (C1), (3,5-ditertiarybutylpyrazol-1-yl)phenylmethanone (C2), (3,5-dimethylpyrazol-1-yl)-o-toluoylmethanone (C3), (3,5-ditertiarybutylpyrazol-1-yl)-o-toluoylmethanone (C4), (2-chlorophenyl)-(3,5-dimethylpyrazol-1-yl)methanone (C5), (2-chlorophenyl)-(3,5-ditertiarybutylpyrazol-1-yl)methanone (C6), (2-flourophenyl)-(3,5-dimethylpyrazol-1-yl)methanone (C7), (2-flourophenyl)-(3,5-ditertiarybutylpyrazol-1-yl)methanone (C8). These compounds were fully characterized using NMR spectroscopy, IR spectroscopy and elemental analysis. Compounds C1, C3, C5 and C7 were reacted with [NiBr2(DME)] to form nickel complexes (4.31-4.34). These nickel complexes were found to be insoluble in all common organic solvents and hence were characterized only by IR spectroscopy and elemental analysis. Compounds C1-C8 were also reacted with [PdCl2(MeCN)2] to form palladium complexes (4.35-4.42). Complexes 4.35-4.42 were characterized using NMR spectroscopy, IR spectroscopy, elemental analysis and in selected cases single crystal X-ray crystallography. Complex 4.39 crystallised in the C2/n space group and complex 4.42 crystallised in the P21/n space group. Attempts to recrystallize 4.37a led to the formation of 4.37b, which contains both 3,5-dimethylpyrazol-1-yl)-o-toluoylmethanone and 3,5-dimethylpyrazole as ligands. Complex 4.37b was confirmed by NMR spectroscopy and single crystal X-ray crystallography. Complex 4.37b crystallised in the Pbca space group. The formation of 4.37b is attributed to hydrolysis of 3,5-dimethylpyrazol-1-yl)-o-toluoylmethanone ligand in 4.37a due to the presence of adventitious water in the solvent. The palladium complexes (4.35-4.42) were tested as catalysts for the Heck coupling reaction of iodobenzene with butyl acrylate and also for the Suzuki coupling reaction of iodobenzene with phenylboronic acid or 4-chlorophenylboronic acid. In these reactions, complexes 4.35-4.42 were found to be highly active at 120 C. The pyrazolyl nickel and palladium complexes were further tested as catalysts in ethylene oligomerization reactions using EtAlCl2 as the co-catalyst. The nickel complexes were found to be the most active reaching TONs of 10.8105 g mol-1 h-1. The palladium analogues only gave TONs of up to 3.9105 g mol-1 h-1. The oligomers were characterized by GC and NMR spectroscopy and were found to be in the C10-C16 range, with C16 the most abundant olefin.
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- Authors: Nelana, Simphiwe Maurice
- Date: 2009-03-31T09:40:18Z
- Subjects: Nickel compounds , Nickel catalysts , Palladium compounds , Palladium catalysts , Alkenes , Transition metal compounds synthesis
- Type: Thesis
- Identifier: uj:8272 , http://hdl.handle.net/10210/2381
- Description: Ph.D. , This thesis deals with the synthesis of nitrogen-donor compounds and their reaction with metal ions. The first type of nitrogen-donor compounds are the unconjugated diimines (N,N´-bis(diphenylmethylene)ethylenediamine (L1) and (N,N´-bis(diphenylmethylene)propylenediamine (L2). Compounds L1 and L2 were reacted with [NiBr2(DME)] or [NiCl2·6H2O] to form complexes (2.1a), (2.2a), (2.3a) and (2.4a). These nickel complexes were characterized by IR spectroscopy, elemental analysis and mass spectrometry. When the complexes were left in chloroform for prolonged periods, hydrolysis of the diimine ligand took place, leading to the formation of nickel complexes 2.1b, 2.2b, 2.3b and 2.4b. The identity of the hydrolysed nickel complexes 2.1b and 2.2b was confirmed by single crystal X-ray crystallography. Complex 2.1b crystallised in the P21/n space group, whilst 2.2b crystallised in the P-1 space group. Compounds L1 and L2 were also reacted with [PdClMe(MeCN)2] to form the palladium complexes (3.1) and (3.2). The palladium complexes were characterized by NMR spectroscopy, elemental analysis and single crystal X-ray crystallography. Attempts to recrystallize 3.1 from a dichloromethane solution led to the formation of 3.1a. Both complexes 3.1a and 3.2 crystallised in the P21/n space group. Complexes 3.1 and 3.2 were tested as catalysts for the Heck coupling reaction of iodobenzene with methyl acrylate or butyl acrylate at 80 C. The products from the coupling reactions were characterized by GC and NMR spectroscopy. These complexes were found to be highly active with 100% conversions observed in some instances. The second type of ligands that were prepared are the benzoylpyrazolyl compounds, (3,5-dimethylpyrazol-1-yl)phenylmethanone (C1), (3,5-ditertiarybutylpyrazol-1-yl)phenylmethanone (C2), (3,5-dimethylpyrazol-1-yl)-o-toluoylmethanone (C3), (3,5-ditertiarybutylpyrazol-1-yl)-o-toluoylmethanone (C4), (2-chlorophenyl)-(3,5-dimethylpyrazol-1-yl)methanone (C5), (2-chlorophenyl)-(3,5-ditertiarybutylpyrazol-1-yl)methanone (C6), (2-flourophenyl)-(3,5-dimethylpyrazol-1-yl)methanone (C7), (2-flourophenyl)-(3,5-ditertiarybutylpyrazol-1-yl)methanone (C8). These compounds were fully characterized using NMR spectroscopy, IR spectroscopy and elemental analysis. Compounds C1, C3, C5 and C7 were reacted with [NiBr2(DME)] to form nickel complexes (4.31-4.34). These nickel complexes were found to be insoluble in all common organic solvents and hence were characterized only by IR spectroscopy and elemental analysis. Compounds C1-C8 were also reacted with [PdCl2(MeCN)2] to form palladium complexes (4.35-4.42). Complexes 4.35-4.42 were characterized using NMR spectroscopy, IR spectroscopy, elemental analysis and in selected cases single crystal X-ray crystallography. Complex 4.39 crystallised in the C2/n space group and complex 4.42 crystallised in the P21/n space group. Attempts to recrystallize 4.37a led to the formation of 4.37b, which contains both 3,5-dimethylpyrazol-1-yl)-o-toluoylmethanone and 3,5-dimethylpyrazole as ligands. Complex 4.37b was confirmed by NMR spectroscopy and single crystal X-ray crystallography. Complex 4.37b crystallised in the Pbca space group. The formation of 4.37b is attributed to hydrolysis of 3,5-dimethylpyrazol-1-yl)-o-toluoylmethanone ligand in 4.37a due to the presence of adventitious water in the solvent. The palladium complexes (4.35-4.42) were tested as catalysts for the Heck coupling reaction of iodobenzene with butyl acrylate and also for the Suzuki coupling reaction of iodobenzene with phenylboronic acid or 4-chlorophenylboronic acid. In these reactions, complexes 4.35-4.42 were found to be highly active at 120 C. The pyrazolyl nickel and palladium complexes were further tested as catalysts in ethylene oligomerization reactions using EtAlCl2 as the co-catalyst. The nickel complexes were found to be the most active reaching TONs of 10.8105 g mol-1 h-1. The palladium analogues only gave TONs of up to 3.9105 g mol-1 h-1. The oligomers were characterized by GC and NMR spectroscopy and were found to be in the C10-C16 range, with C16 the most abundant olefin.
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Nitrogen-donor nickel and palladium complexes as olefin transformation catalysts
- Authors: Ojwach, Stephen Otieno
- Date: 2009-04-30T10:05:35Z
- Subjects: Alkenes , Transition metal catalysts , Transition metal compounds , Nickel compounds , Palladium compounds , Complex compounds synthesis
- Type: Thesis
- Identifier: uj:8340 , http://hdl.handle.net/10210/2466
- Description: Ph.D. , Compounds, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (L2) were prepared by phase transfer alkylation of 2,6-bis(bromomethyl)pyridine with two mole equivalents of the appropriate pyrazole. Ligands L1 and L2 reacted with either [PdCl2(NCMe)2] or [PdClMe(COD)] to form mononuclear palladium complexes [(PdCl2(L1)] (1), [(PdClMe(L1)] (2), [(PdCl2(L2)] (3), [(PdClMe(L2)] (4). All new compounds prepared were characterised by a combination of 1H NMR, 13C NMR spectroscopy and microanalyses. The coordination of L2 in a bidentate fashion through the pyridine nitrogen atom and one pyrazolyl nitrogen atom has been confirmed by single crystal X-ray crystallography of complex 3. Reactions of 1, 2 and 3 with the halide abstractor NaBAr4 (Ar = 3,5-(CF3)2C6H3) led to the formation of the stable tridentate cationic species [(PdCl(L1)]BAr4 (5), [(PdMe(L1)]BAr4 (6) and [(PdCl(L2)]BAr4 (7) respectively. Tridentate coordination of L1 and L2 in the cationic complexes has also been confirmed by single X-ray crystallography of complexes 5 and 6. The analogous carbonyl linker cationic species, [Pd{(3,5-Me2pz-CO)2-py}Cl]+ (9) and [Pd{(3,5-tBu2pz-CO)2-py}Cl]+ (10), prepared by halide abstraction from [Pd{(3,5-Me2pz-CO)2-py}Cl2] and [Pd{(3,5-tBu2pz-CO)2-py}Cl2] with NaBAr4, were however less stable. While cationic complexes 5-7 showed indefinite stability in solution, 9 and 10 had t1/2 of 14 and 2 days respectively. Attempts to crystallise 1 and 3 from the mother liquor resulted in the isolation of the salts [PdCl(L1)]2[Pd2Cl6] (11) and [PdCl(L2)]2[Pd2Cl6] (12). Although when complexes 1-4 xviii were reacted with modified methylaluminoxane (MMAO) or NaBAr4, no active catalysts for ethylene oligomerisation or polymerisation were formed, activation with silver triflate (AgOTf) produced active catalysts that oligomerised and polymerised phenylacetylene to a mixture of cis-transoidal and trans-cisoidal polyphenylacetylene. Compounds 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L3) and 2-(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L4) were prepared by phase transfer alkylation of 2-picolylchloride hydrochloride with one mole equivalent of the appropriate pyrazole. Compounds 2-(3,5-bis-trifluoromethyl-pyrazol-1-ylmethyl)-6-(3,5-dimethyl-pyrazol-1-ylmethyl)-pyridine (L5) and 2-(3,5-dimethyl-pyrazol-1-ylmethyl)-6-phenoxymethyl-pyridine (L6) were isolated in good yields by reacting (2-chloromethyl-6-3,5-dimethylpyrazol-1-ylmethyl)pyridine with an equivalent amount of potassium salt of 3,5-bis(trifluoromethyl)pyrazolate and potassium phenolate respectively. L3-L6 react with either [Pd(NCMe)2Cl2] or [PdClMe(COD)] to give mononuclear palladium complexes 13-18 of the general formulae [PdCl2(L)] or [PdClMe(L)] where L = is the bidentate ligands L3, L4, L5 and L6 respectively. Single crystal X-ray crystallography of complexes 13, 15 and 16 has been used to confirm the solid state geometry of the complexes. In attempts to generate active olefin oligomerisation catalysts, the chloromethyl Pd(II) complexes 14 and 16 were reacted with the halide abstractor NaBAr4 in the presence of stabilising solvents (i.e Et2O or NCMe) but no catalytic activities were observed. Decomposition was evident as observed from the deposition of palladium black in experiments using Et2O. In experiments where NCMe was used as the stabilising solvent, the formation of cationic species stabilised by NCMe was evident from 1H NMR analyses. Reaction of complex 14 with NaBAr4 on a preparative scale in a mixture of CH2Cl2 and NCMe solvent gave the cationic complex [[PdMeNCMe(L3)]BAr4 (19) in good yields. Complex 17 reacted with NABAr4 to give tridentate cationic species [[PdMe(L5)]BAr4 (20) which is inactive towards ethylene oligomerisation or polymerisation reactions. The tridentate coordination of L5 in 20 has also been established by single crystal X-ray structure of 20. Catalysts generated from 18 and 19 catalysed ethylene polymerisation at high pressures to branched polyethylene; albeit with very low activity. The Choromethyl palladium complex 14 reacted with sulfur dioxide to form complex 21. The nature of the product has been established by 1H NMR, 13C NMR and mass spectrometry to be an insertion product of SO2 into the Pd-Me bond of 14. Compounds L1-L4 reacted with the nickel salts NiCl2 or NiBr2 in a 1:1 mole ratio to give the nickel complexes [NiCl2(L1)] (22), [NiBr2(L1)] (23), [NiCl2(L2)] (24), and [NiBr2(L2)] (25), [Ni2(μ2-Cl)2Cl2(L3)2] (26), [Ni2(μ2-Br)2Br2(L3)2] (27), [NiCl2(L4)] (29) and [NiBr2(L4)] (30) in good yields. Reaction of L3 with NiBr2 in a 2:1 mole gave the octahedral complex [NiBr2(L4)2] (28) in good yields. Complexes 22-30 were characterised by a combination micro-analyses, mass spectrometry and single crystal X-ray analyses for 27 and 30. No NMR data were acquired because of the paramagnetic nature of the complexes. When complexes 22-30 were activated with EtAlCl2, highly active olefin oligomerisation catalysts were formed. In the ethylene oligomeristion reactions, three oligomers: C11, C14 xx and C16 were identified as the major products. Selectivityof 40% towards α-olefins were generally obtained. In general catalysts that contain the bidentate ligands L3 and L4 were more active than those that contain the tridentate ligands L1 and L2. Dichloride complexes exhibited relatively higher catalytic activities than their dibromide analogues. Turn over numbers (TON) for oligomer formation showed high dependence on ethylene concentration. A Lineweaver-Burk analysis of reactions catalysed by 22 and 26 showed TON saturation of 28 393 kg oligomer/mol Ni.h and 19 000 kg oligomer/mol Ni.h respectively. Catalysts generated from complexes 22-30 also catalysed oligomerisation of the higher olefins, 1-pentene, 1-hexene and 1-heptene and displayed good catalytic activities. Only two products C12 and C15 were obtained in the 1-pentene oligomerisation reactions. The 1-hexene reactions also gave two products, C12 and C18, while 1-heptene oligomerisation reactions gave predominantly C14 oligomers. Five benzoazoles were used to prepare a series of palladium complexes that were invesitigated as Heck coupling catalysts. The compounds 2-pyridin-2-yl-1H-benzoimidazole (L7) and 2-pyridin-2-yl-benzothiazole (L8) were prepared following literature procedures. The new ligands 2-(4-tert-butylpyridin-2-yl)-benzooxazole (L9) and 2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L10) were prepared by ring closure of aminophenol and aminothiophenol with tert-butyl picolinic acid respectively. The ligand 6-tert-Butyl-2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L11) was prepared by intramolecular cyclisation under basic conditions is described. Reactions of L7-L11 with either [Pd(NCMe)2Cl2] or [Pd(COD)MeCl] afforded the corresponding mononuclear palladium complexes [PdClMe(L7)] (31), [PdClMe(L8)] (32), [PdCl2(L9)] (33), [PdMeCl(L9)] (34), [PdCl2(L10)] (5), [PdMeCl(L10)] (36) and [PdMeCl(L11)] (37) as xxi confirmed by mass spectrometry and micro-analyses. The palladium complexes 31-37 were efficient Heck coupling catalysts for the reaction of iodobenzene with butylacrylate under mild conditions and showed good stability.
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- Authors: Ojwach, Stephen Otieno
- Date: 2009-04-30T10:05:35Z
- Subjects: Alkenes , Transition metal catalysts , Transition metal compounds , Nickel compounds , Palladium compounds , Complex compounds synthesis
- Type: Thesis
- Identifier: uj:8340 , http://hdl.handle.net/10210/2466
- Description: Ph.D. , Compounds, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (L2) were prepared by phase transfer alkylation of 2,6-bis(bromomethyl)pyridine with two mole equivalents of the appropriate pyrazole. Ligands L1 and L2 reacted with either [PdCl2(NCMe)2] or [PdClMe(COD)] to form mononuclear palladium complexes [(PdCl2(L1)] (1), [(PdClMe(L1)] (2), [(PdCl2(L2)] (3), [(PdClMe(L2)] (4). All new compounds prepared were characterised by a combination of 1H NMR, 13C NMR spectroscopy and microanalyses. The coordination of L2 in a bidentate fashion through the pyridine nitrogen atom and one pyrazolyl nitrogen atom has been confirmed by single crystal X-ray crystallography of complex 3. Reactions of 1, 2 and 3 with the halide abstractor NaBAr4 (Ar = 3,5-(CF3)2C6H3) led to the formation of the stable tridentate cationic species [(PdCl(L1)]BAr4 (5), [(PdMe(L1)]BAr4 (6) and [(PdCl(L2)]BAr4 (7) respectively. Tridentate coordination of L1 and L2 in the cationic complexes has also been confirmed by single X-ray crystallography of complexes 5 and 6. The analogous carbonyl linker cationic species, [Pd{(3,5-Me2pz-CO)2-py}Cl]+ (9) and [Pd{(3,5-tBu2pz-CO)2-py}Cl]+ (10), prepared by halide abstraction from [Pd{(3,5-Me2pz-CO)2-py}Cl2] and [Pd{(3,5-tBu2pz-CO)2-py}Cl2] with NaBAr4, were however less stable. While cationic complexes 5-7 showed indefinite stability in solution, 9 and 10 had t1/2 of 14 and 2 days respectively. Attempts to crystallise 1 and 3 from the mother liquor resulted in the isolation of the salts [PdCl(L1)]2[Pd2Cl6] (11) and [PdCl(L2)]2[Pd2Cl6] (12). Although when complexes 1-4 xviii were reacted with modified methylaluminoxane (MMAO) or NaBAr4, no active catalysts for ethylene oligomerisation or polymerisation were formed, activation with silver triflate (AgOTf) produced active catalysts that oligomerised and polymerised phenylacetylene to a mixture of cis-transoidal and trans-cisoidal polyphenylacetylene. Compounds 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L3) and 2-(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L4) were prepared by phase transfer alkylation of 2-picolylchloride hydrochloride with one mole equivalent of the appropriate pyrazole. Compounds 2-(3,5-bis-trifluoromethyl-pyrazol-1-ylmethyl)-6-(3,5-dimethyl-pyrazol-1-ylmethyl)-pyridine (L5) and 2-(3,5-dimethyl-pyrazol-1-ylmethyl)-6-phenoxymethyl-pyridine (L6) were isolated in good yields by reacting (2-chloromethyl-6-3,5-dimethylpyrazol-1-ylmethyl)pyridine with an equivalent amount of potassium salt of 3,5-bis(trifluoromethyl)pyrazolate and potassium phenolate respectively. L3-L6 react with either [Pd(NCMe)2Cl2] or [PdClMe(COD)] to give mononuclear palladium complexes 13-18 of the general formulae [PdCl2(L)] or [PdClMe(L)] where L = is the bidentate ligands L3, L4, L5 and L6 respectively. Single crystal X-ray crystallography of complexes 13, 15 and 16 has been used to confirm the solid state geometry of the complexes. In attempts to generate active olefin oligomerisation catalysts, the chloromethyl Pd(II) complexes 14 and 16 were reacted with the halide abstractor NaBAr4 in the presence of stabilising solvents (i.e Et2O or NCMe) but no catalytic activities were observed. Decomposition was evident as observed from the deposition of palladium black in experiments using Et2O. In experiments where NCMe was used as the stabilising solvent, the formation of cationic species stabilised by NCMe was evident from 1H NMR analyses. Reaction of complex 14 with NaBAr4 on a preparative scale in a mixture of CH2Cl2 and NCMe solvent gave the cationic complex [[PdMeNCMe(L3)]BAr4 (19) in good yields. Complex 17 reacted with NABAr4 to give tridentate cationic species [[PdMe(L5)]BAr4 (20) which is inactive towards ethylene oligomerisation or polymerisation reactions. The tridentate coordination of L5 in 20 has also been established by single crystal X-ray structure of 20. Catalysts generated from 18 and 19 catalysed ethylene polymerisation at high pressures to branched polyethylene; albeit with very low activity. The Choromethyl palladium complex 14 reacted with sulfur dioxide to form complex 21. The nature of the product has been established by 1H NMR, 13C NMR and mass spectrometry to be an insertion product of SO2 into the Pd-Me bond of 14. Compounds L1-L4 reacted with the nickel salts NiCl2 or NiBr2 in a 1:1 mole ratio to give the nickel complexes [NiCl2(L1)] (22), [NiBr2(L1)] (23), [NiCl2(L2)] (24), and [NiBr2(L2)] (25), [Ni2(μ2-Cl)2Cl2(L3)2] (26), [Ni2(μ2-Br)2Br2(L3)2] (27), [NiCl2(L4)] (29) and [NiBr2(L4)] (30) in good yields. Reaction of L3 with NiBr2 in a 2:1 mole gave the octahedral complex [NiBr2(L4)2] (28) in good yields. Complexes 22-30 were characterised by a combination micro-analyses, mass spectrometry and single crystal X-ray analyses for 27 and 30. No NMR data were acquired because of the paramagnetic nature of the complexes. When complexes 22-30 were activated with EtAlCl2, highly active olefin oligomerisation catalysts were formed. In the ethylene oligomeristion reactions, three oligomers: C11, C14 xx and C16 were identified as the major products. Selectivityof 40% towards α-olefins were generally obtained. In general catalysts that contain the bidentate ligands L3 and L4 were more active than those that contain the tridentate ligands L1 and L2. Dichloride complexes exhibited relatively higher catalytic activities than their dibromide analogues. Turn over numbers (TON) for oligomer formation showed high dependence on ethylene concentration. A Lineweaver-Burk analysis of reactions catalysed by 22 and 26 showed TON saturation of 28 393 kg oligomer/mol Ni.h and 19 000 kg oligomer/mol Ni.h respectively. Catalysts generated from complexes 22-30 also catalysed oligomerisation of the higher olefins, 1-pentene, 1-hexene and 1-heptene and displayed good catalytic activities. Only two products C12 and C15 were obtained in the 1-pentene oligomerisation reactions. The 1-hexene reactions also gave two products, C12 and C18, while 1-heptene oligomerisation reactions gave predominantly C14 oligomers. Five benzoazoles were used to prepare a series of palladium complexes that were invesitigated as Heck coupling catalysts. The compounds 2-pyridin-2-yl-1H-benzoimidazole (L7) and 2-pyridin-2-yl-benzothiazole (L8) were prepared following literature procedures. The new ligands 2-(4-tert-butylpyridin-2-yl)-benzooxazole (L9) and 2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L10) were prepared by ring closure of aminophenol and aminothiophenol with tert-butyl picolinic acid respectively. The ligand 6-tert-Butyl-2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L11) was prepared by intramolecular cyclisation under basic conditions is described. Reactions of L7-L11 with either [Pd(NCMe)2Cl2] or [Pd(COD)MeCl] afforded the corresponding mononuclear palladium complexes [PdClMe(L7)] (31), [PdClMe(L8)] (32), [PdCl2(L9)] (33), [PdMeCl(L9)] (34), [PdCl2(L10)] (5), [PdMeCl(L10)] (36) and [PdMeCl(L11)] (37) as xxi confirmed by mass spectrometry and micro-analyses. The palladium complexes 31-37 were efficient Heck coupling catalysts for the reaction of iodobenzene with butylacrylate under mild conditions and showed good stability.
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Pd(II) catalysed oxidative acetoxylation of selected alkene substrates
- Authors: Mdakane, Bongani Patrick
- Date: 2010-04-08T08:43:02Z
- Subjects: Palladium catalysts , Palladium oxidation , Alkenes , Cyclohexane
- Type: Thesis
- Identifier: uj:6762 , http://hdl.handle.net/10210/3169
- Description: M.Sc. , The main objective of this study was to identify and optimise the homogeneous catalytic systems for Pd(II) catalysed alkene acetoxylation in acetic acid to directly yield allyl or vinyl acetates as opposed to the usual aldehydes or ketones. Part of the intention of this study was to investigate potentially suitable re-oxidants and reaction conditions suitable for industrial application. The synthesis of butenyl acetate (via 1-butene acetoxylation) in particular is regarded as a potential value-adding opportunity for solvents producers. For safety considerations the study was performed with liquid alkenes (cyclohexene, cyclopentene, cycloheptene, cyclooctene and 1-hexene). Cyclohexene was used for the bulk of these studies. One of the most important and pioneering reactions in this field is the similar system for the oxidation of alkenes to ketones (the Wacker process). The related reaction, oxidative acetoxylation, is the result of the discovery of the Wacker process. The problems associated with both these reactions is the difficulty in re-oxidising the catalyst Pd once it has been reduced in the catalytic process from Pd(II) to Pd(0). Various reaction systems have been developed to improve these processes. Some of the systems that have been developed in the acetoxylation of alkenes were investigated. From the studies it has become obvious that for ease of Pd(0) re-oxidation a co-catalyst, benzoquinone, is essential for the catalytic process. This system employing a co-catalyst required another oxygen efficient re-oxidant to oxidize hydroquinone once reduced from benzoquinone in the oxidation of Pd(0). The re-oxidant would in turn be oxidized by oxygen. Various types of re-oxidants such as Cu(II) salts, heteropolyacids and metal macrocycles (e.g. Schiff base complexes and phthalocyanine metal complexes) were investigated in the multi-step electron transfer process. The most promising of the systems was the Pd(OAc)2/ benzoquinone/ heteropolyacid (H5PMo10V2O40 .34H2O)/ O2 system. From the studies it was apparent that the type of the re-oxidant can influence the yield of the product. Various other parameters were found to influence the reaction outcome. The type of Pd(II) salt was found to be influential in the reaction, for instance Pd(OAc)2 was found to be a better catalyst than Pd(CF3CO2)2. The catalyst loading was found to improve the yield iv when increased whilst this was not trivial since Pd is expensive the system needed to have as low catalyst loading as possible. The type of alkene used dictated the rate of the reaction and the product distribution. It was found that the conditions used for cyclohexene were not transferable to other alkenes without changing certain parameters to suit the alkene in question. Cycloalkenes acetoxylation was found to proceed without the addition of the strong nucleophile additive NaOAc, whilst for 1-hexene acetoxylation the reaction did not proceed without the additive. The product distribution was found to also differ between cycloalkenes and 1-hexene. For cyclohexene the by-products observed were the disproportionation products cyclohexane and benzene. In the case of 1-hexene the by-products were 2-hexanone (the Wacker reaction) and 2-hexenes (isomerisation). The operating temperature also played a role in the reaction outcome. In some instances the increase in reaction temperature negatively affected the reaction whilst in other cases it improved the reaction. Oxygen pressure also influenced the reaction to a lesser extent, with an increase in pressure favouring the reaction.
- Full Text:
- Authors: Mdakane, Bongani Patrick
- Date: 2010-04-08T08:43:02Z
- Subjects: Palladium catalysts , Palladium oxidation , Alkenes , Cyclohexane
- Type: Thesis
- Identifier: uj:6762 , http://hdl.handle.net/10210/3169
- Description: M.Sc. , The main objective of this study was to identify and optimise the homogeneous catalytic systems for Pd(II) catalysed alkene acetoxylation in acetic acid to directly yield allyl or vinyl acetates as opposed to the usual aldehydes or ketones. Part of the intention of this study was to investigate potentially suitable re-oxidants and reaction conditions suitable for industrial application. The synthesis of butenyl acetate (via 1-butene acetoxylation) in particular is regarded as a potential value-adding opportunity for solvents producers. For safety considerations the study was performed with liquid alkenes (cyclohexene, cyclopentene, cycloheptene, cyclooctene and 1-hexene). Cyclohexene was used for the bulk of these studies. One of the most important and pioneering reactions in this field is the similar system for the oxidation of alkenes to ketones (the Wacker process). The related reaction, oxidative acetoxylation, is the result of the discovery of the Wacker process. The problems associated with both these reactions is the difficulty in re-oxidising the catalyst Pd once it has been reduced in the catalytic process from Pd(II) to Pd(0). Various reaction systems have been developed to improve these processes. Some of the systems that have been developed in the acetoxylation of alkenes were investigated. From the studies it has become obvious that for ease of Pd(0) re-oxidation a co-catalyst, benzoquinone, is essential for the catalytic process. This system employing a co-catalyst required another oxygen efficient re-oxidant to oxidize hydroquinone once reduced from benzoquinone in the oxidation of Pd(0). The re-oxidant would in turn be oxidized by oxygen. Various types of re-oxidants such as Cu(II) salts, heteropolyacids and metal macrocycles (e.g. Schiff base complexes and phthalocyanine metal complexes) were investigated in the multi-step electron transfer process. The most promising of the systems was the Pd(OAc)2/ benzoquinone/ heteropolyacid (H5PMo10V2O40 .34H2O)/ O2 system. From the studies it was apparent that the type of the re-oxidant can influence the yield of the product. Various other parameters were found to influence the reaction outcome. The type of Pd(II) salt was found to be influential in the reaction, for instance Pd(OAc)2 was found to be a better catalyst than Pd(CF3CO2)2. The catalyst loading was found to improve the yield iv when increased whilst this was not trivial since Pd is expensive the system needed to have as low catalyst loading as possible. The type of alkene used dictated the rate of the reaction and the product distribution. It was found that the conditions used for cyclohexene were not transferable to other alkenes without changing certain parameters to suit the alkene in question. Cycloalkenes acetoxylation was found to proceed without the addition of the strong nucleophile additive NaOAc, whilst for 1-hexene acetoxylation the reaction did not proceed without the additive. The product distribution was found to also differ between cycloalkenes and 1-hexene. For cyclohexene the by-products observed were the disproportionation products cyclohexane and benzene. In the case of 1-hexene the by-products were 2-hexanone (the Wacker reaction) and 2-hexenes (isomerisation). The operating temperature also played a role in the reaction outcome. In some instances the increase in reaction temperature negatively affected the reaction whilst in other cases it improved the reaction. Oxygen pressure also influenced the reaction to a lesser extent, with an increase in pressure favouring the reaction.
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Pd-catalysed methoxycarbonylation reactions of alkynes
- Authors: Makume, Boitumelo Francinah
- Date: 2013-09-11
- Subjects: Alkynes , Palladium catalysts , Carbonyl compounds , Hydrocarbons , Alkenes
- Type: Thesis
- Identifier: uj:7733 , http://hdl.handle.net/10210/8602
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
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- Authors: Makume, Boitumelo Francinah
- Date: 2013-09-11
- Subjects: Alkynes , Palladium catalysts , Carbonyl compounds , Hydrocarbons , Alkenes
- Type: Thesis
- Identifier: uj:7733 , http://hdl.handle.net/10210/8602
- Description: M.Sc. (Chemistry) , Please refer to full text to view abstract
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Preparation of higher alpha olefin oligomers
- Authors: Crause, Chantelle
- Date: 2012-08-20
- Subjects: Oligomers , Alkenes
- Type: Thesis
- Identifier: uj:2796 , http://hdl.handle.net/10210/6234
- Description: M.Sc. , The economic growth of a country can be stimulated by value-adding to basic resources e.g., chemical intermediates. Alpha olefins are products of the Sasol Fischer-Tropsch process and oligomerization is one of the most significant beneficiation processes available for these alpha olefins. Alpha olefin oligomers obtained from the cationic oligomerization with BF3/ROH, have been used mainly as base stocks in synthetic lubricants. These oligomers consist of a mixture of isomeric products that complicates the investigation and rational modification of this and other closely related oligomerization processes. A comparison of these isomeric mixtures to alkane standards could assist in the study of these processes, but almost no standards are available. This project was aimed, in part, at establishing a methodology for the synthesis of 1-pentene model oligomers. A model branched 1-pentene dimer and trimer as well as a precursor to the analogous tetramer were prepared. The syntheses of other model oligomers in conjunction with the comparison of the properties of model oligomers with different branching patterns will certainly be of value. Some of the main classes of catalysts were evaluated for the oligomerization of higher alpha olefins and especially of 1-pentene. The BF3/n-BuOH cationic oligomerization of 1-pentene yielded dimers, trimer, tetramers and pentamers consisting of a large number of isomers and the product distribution peaked at the trimer. This is in agreement with previous results for other monomers. Radical oligomerization of 1-pentene with organic peroxide initiators proceeded in low yield. Dimers and trimers consisting of a mixture of isomers were mainly formed. Metallocene catalysts offer a convenient route to single component, structurally well characterized alpha olefin oligomers. A variety of functional group transformations and consequent applications are possible for these oligomers. The general nature of the oligomerization of 1-pentene, 1-hexene and 1-octene with allocene/methylaluminoxane catalysts was investigated. The influence of different metals, the number of cyclopentadienyl groups and substitution on the cyclopentadienyl groups in the metallocene moiety, the reaction temperature and the purity of the monomer were studied. By employing the appropriate metallocene in combination with methylaluminoxane, higher alpha olefin dimers and trimers could be formed in high yield at ambient temperatures. Cp2ZrC12 was the most active of the metallocene catalysts and single isomers were formed with high selectivity. The etallocene-based oligomerization of higher alpha olefins offers great scope for further research and promises a new era in olefin oligomerization.
- Full Text:
- Authors: Crause, Chantelle
- Date: 2012-08-20
- Subjects: Oligomers , Alkenes
- Type: Thesis
- Identifier: uj:2796 , http://hdl.handle.net/10210/6234
- Description: M.Sc. , The economic growth of a country can be stimulated by value-adding to basic resources e.g., chemical intermediates. Alpha olefins are products of the Sasol Fischer-Tropsch process and oligomerization is one of the most significant beneficiation processes available for these alpha olefins. Alpha olefin oligomers obtained from the cationic oligomerization with BF3/ROH, have been used mainly as base stocks in synthetic lubricants. These oligomers consist of a mixture of isomeric products that complicates the investigation and rational modification of this and other closely related oligomerization processes. A comparison of these isomeric mixtures to alkane standards could assist in the study of these processes, but almost no standards are available. This project was aimed, in part, at establishing a methodology for the synthesis of 1-pentene model oligomers. A model branched 1-pentene dimer and trimer as well as a precursor to the analogous tetramer were prepared. The syntheses of other model oligomers in conjunction with the comparison of the properties of model oligomers with different branching patterns will certainly be of value. Some of the main classes of catalysts were evaluated for the oligomerization of higher alpha olefins and especially of 1-pentene. The BF3/n-BuOH cationic oligomerization of 1-pentene yielded dimers, trimer, tetramers and pentamers consisting of a large number of isomers and the product distribution peaked at the trimer. This is in agreement with previous results for other monomers. Radical oligomerization of 1-pentene with organic peroxide initiators proceeded in low yield. Dimers and trimers consisting of a mixture of isomers were mainly formed. Metallocene catalysts offer a convenient route to single component, structurally well characterized alpha olefin oligomers. A variety of functional group transformations and consequent applications are possible for these oligomers. The general nature of the oligomerization of 1-pentene, 1-hexene and 1-octene with allocene/methylaluminoxane catalysts was investigated. The influence of different metals, the number of cyclopentadienyl groups and substitution on the cyclopentadienyl groups in the metallocene moiety, the reaction temperature and the purity of the monomer were studied. By employing the appropriate metallocene in combination with methylaluminoxane, higher alpha olefin dimers and trimers could be formed in high yield at ambient temperatures. Cp2ZrC12 was the most active of the metallocene catalysts and single isomers were formed with high selectivity. The etallocene-based oligomerization of higher alpha olefins offers great scope for further research and promises a new era in olefin oligomerization.
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Pyrazole and pyrazolylethylamine nickel(II) and palladium(II) complexes as catalysts for olefin oligomerization and Friedel-Crafts reactions
- Authors: Moeti, Lerato Petunia
- Date: 2015-06-29
- Subjects: Palladium catalysts , Pyrazoles , Palladium compounds - Synthesis , Nickel catalysts , Alkenes , Nickel compounds - Synthesis
- Type: Thesis
- Identifier: uj:13650 , http://hdl.handle.net/10210/13834
- Description: M.Sc. (Chemistry) , This study deals with the synthesis of nitrogen-donor pyrazole- and pyrazolylethylamine compounds, their reactions with palladium(II) and nickel(II) precursors to form complexes and the applications of theses palladium(II) and nickel(II) complexes as catalysts for ethylene oligomerization reactions and reactions of higher α-olefins in Friedel-Crafts alkylation of aromatic solvents. A series of ligands, 3,5-di-tert-butyl-1H-pyrazole (L3), 3,5-diphenyl-1H-pyrazole (L4), 5-phenyl-3-(trifluoromethyl)-1H-pyrazole (L5) were synthesized using appropriate amounts of diketones and hydrazine hydrate; while ligands, 2-(1H-pyrazol-1-yl)ethylamine (L6), 2-(3,5-dimethyl-1H-pyrazol-1-yl)-ethylamine (L7), 2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)-ethylamine (L8), 2-(3,5-diphenyl-1H-pyrazol-1-yl)-ethylamine (L9) and 2-(5-phenyl-3-(trifluoromethyl)-1H-pyrazol-1-yl)ethylamine (L10) were prepared via the N sp3 alkylation of the corresponding pyrazoles with bromoethylamine Reactions of L1-L5 with [PdCl2(CNMe)2] formed five complexes of general formula [PdCl2 (L)2] {L = L1 (2.1), L2 (2.2), L3 (2.3), L4 (2.4) and L5 (2.5)}. Similarly [NiBr2(DME)] formed five complexes of general formula [NiBr2(L)2] {L = L1(2.6), L2 (2.7), L3 (2.8), L4 (2.9) and L5 (2.10)}. Complexes 2.1-2.10 were synthesized in a 2:1 mole ratio of ligand and metal precursor. Reactions of L6-L10 with [PdCl2(MeCN)2] yielded complexes 3.1-3.5 respectively. Ligands L6-L10 were also complexed with NiCl2.6H2O to give complex 3.6 while [NiCl2(DME)] and [NiBr2(DME)] gave complexes 3.7-3.8 and 3.9-3.13 respectively...
- Full Text:
- Authors: Moeti, Lerato Petunia
- Date: 2015-06-29
- Subjects: Palladium catalysts , Pyrazoles , Palladium compounds - Synthesis , Nickel catalysts , Alkenes , Nickel compounds - Synthesis
- Type: Thesis
- Identifier: uj:13650 , http://hdl.handle.net/10210/13834
- Description: M.Sc. (Chemistry) , This study deals with the synthesis of nitrogen-donor pyrazole- and pyrazolylethylamine compounds, their reactions with palladium(II) and nickel(II) precursors to form complexes and the applications of theses palladium(II) and nickel(II) complexes as catalysts for ethylene oligomerization reactions and reactions of higher α-olefins in Friedel-Crafts alkylation of aromatic solvents. A series of ligands, 3,5-di-tert-butyl-1H-pyrazole (L3), 3,5-diphenyl-1H-pyrazole (L4), 5-phenyl-3-(trifluoromethyl)-1H-pyrazole (L5) were synthesized using appropriate amounts of diketones and hydrazine hydrate; while ligands, 2-(1H-pyrazol-1-yl)ethylamine (L6), 2-(3,5-dimethyl-1H-pyrazol-1-yl)-ethylamine (L7), 2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)-ethylamine (L8), 2-(3,5-diphenyl-1H-pyrazol-1-yl)-ethylamine (L9) and 2-(5-phenyl-3-(trifluoromethyl)-1H-pyrazol-1-yl)ethylamine (L10) were prepared via the N sp3 alkylation of the corresponding pyrazoles with bromoethylamine Reactions of L1-L5 with [PdCl2(CNMe)2] formed five complexes of general formula [PdCl2 (L)2] {L = L1 (2.1), L2 (2.2), L3 (2.3), L4 (2.4) and L5 (2.5)}. Similarly [NiBr2(DME)] formed five complexes of general formula [NiBr2(L)2] {L = L1(2.6), L2 (2.7), L3 (2.8), L4 (2.9) and L5 (2.10)}. Complexes 2.1-2.10 were synthesized in a 2:1 mole ratio of ligand and metal precursor. Reactions of L6-L10 with [PdCl2(MeCN)2] yielded complexes 3.1-3.5 respectively. Ligands L6-L10 were also complexed with NiCl2.6H2O to give complex 3.6 while [NiCl2(DME)] and [NiBr2(DME)] gave complexes 3.7-3.8 and 3.9-3.13 respectively...
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