Solvent-free synthesis of bisferrocenylimines and their coordination to rhodium (I)
- Authors: Kleyi, Phumelele Eldridge
- Date: 2009
- Subjects: Organic compounds -- Synthesis , Organic solvents , Solution (Chemistry) , Chemistry, Organic , Coordination compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10393 , http://hdl.handle.net/10948/1053 , Organic compounds -- Synthesis , Organic solvents , Solution (Chemistry) , Chemistry, Organic , Coordination compounds
- Description: Solvent-free reactions possess advantages compared to the solvent route, such as shorter reaction times, less use of energy, better yields, etc. Herein, the synthesis and characterization of bisferrocenylimines and arylbisamines are described. Reduction of the above compounds with LAH resulted in the formation of bisferrocenylamines and arylbisamines, respectively. The coordination chemistry of all the above compounds to rhodium(I) is also discussed in the prepared complexes [Rh(COD)(NN)]ClO4, where NN = bisferrocenylimines, and [Rh(COD)(NN)]BF4, where NN = bisferrocenylamines and arylbisamines. X-ray crystal structures of the complexes [Rh(COD)(NN)]ClO4 ([3.2] and [3.3]) have been obtained. Complexes of the type [Rh(COD)(NN)]BF4 were characterized with IR and UV-vis spectroscopy, cyclic voltammetry and conductometry. The catalytic activity of the complexes was also investigated: [Rh(COD)(NN)]ClO4 for the polymerization of phenylacetylene and [Rh(COD)(NN)]BF4 for the hydroformylation of styrene.
- Full Text:
- Date Issued: 2009
- Authors: Kleyi, Phumelele Eldridge
- Date: 2009
- Subjects: Organic compounds -- Synthesis , Organic solvents , Solution (Chemistry) , Chemistry, Organic , Coordination compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10393 , http://hdl.handle.net/10948/1053 , Organic compounds -- Synthesis , Organic solvents , Solution (Chemistry) , Chemistry, Organic , Coordination compounds
- Description: Solvent-free reactions possess advantages compared to the solvent route, such as shorter reaction times, less use of energy, better yields, etc. Herein, the synthesis and characterization of bisferrocenylimines and arylbisamines are described. Reduction of the above compounds with LAH resulted in the formation of bisferrocenylamines and arylbisamines, respectively. The coordination chemistry of all the above compounds to rhodium(I) is also discussed in the prepared complexes [Rh(COD)(NN)]ClO4, where NN = bisferrocenylimines, and [Rh(COD)(NN)]BF4, where NN = bisferrocenylamines and arylbisamines. X-ray crystal structures of the complexes [Rh(COD)(NN)]ClO4 ([3.2] and [3.3]) have been obtained. Complexes of the type [Rh(COD)(NN)]BF4 were characterized with IR and UV-vis spectroscopy, cyclic voltammetry and conductometry. The catalytic activity of the complexes was also investigated: [Rh(COD)(NN)]ClO4 for the polymerization of phenylacetylene and [Rh(COD)(NN)]BF4 for the hydroformylation of styrene.
- Full Text:
- Date Issued: 2009
Reactions towards the synthesis of the uncommon P57 cymarose moiety
- Authors: Mahanjana, Lungelwa
- Date: 2013
- Subjects: Chemistry, Organic , Organic compounds -- Synthesis
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/6711 , vital:21136
- Description: The work described in this study aims to investigate methods that will improve a lengthy synthetic pathway in the synthesis of the P57 cymarose moiety, and to examine the conformational structure of certain glycosides in order to shed light on the problematic stereochemical issues surrounding the formation of the cymarose glycosyl donor. The cymarose moiety forms part of the trisaccharide derivative present in P57, an appetite suppressant molecule. Modification of reaction steps in the conversion of the stereochemistry at C-3 of a previously reported synthesis of the P57 cymarose moiety was carried out. The first step was the selective oxidation of D-glucal using Pd/C in the presence of acetonitrile. These reaction conditions are more appropriate for the oxidation step to avoid decomposition of the formed molecules. Successive protection of the free OH groups was followed by NaBH4 reduction under stereo-controlled conditions, influenced by CeCl3•7H2O. However, the reduced product could not be isolated from the starting material and this led to ambiguous results when attempting to confirm whether the conversion of the stereochemistry at C-3 had occurred or not. The effect of reaction conditions, such as change in reaction temperature, during the preparation of the cymarose glycosyl donor was studied in order to find suitable reaction conditions to produce α,β-allo derivatives with high stereoselectivity. Compared to the reported synthetic method, this set-up gave improved yields with, unfortunately, similar or slightly lower selectivity to the formation of α-altro:α,β-allo derivative. Examination of the conformational structure of the allal derivative, in order to understand the mechanism at work during the placement of the directing group at C-2, was carried out using molecular modelling. The mechanistic implications of this very short study are discussed and it provides some insights into the likely pathway of the iodination reaction and its selectivity in particular, to the D-allose system.
- Full Text:
- Date Issued: 2013
- Authors: Mahanjana, Lungelwa
- Date: 2013
- Subjects: Chemistry, Organic , Organic compounds -- Synthesis
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/6711 , vital:21136
- Description: The work described in this study aims to investigate methods that will improve a lengthy synthetic pathway in the synthesis of the P57 cymarose moiety, and to examine the conformational structure of certain glycosides in order to shed light on the problematic stereochemical issues surrounding the formation of the cymarose glycosyl donor. The cymarose moiety forms part of the trisaccharide derivative present in P57, an appetite suppressant molecule. Modification of reaction steps in the conversion of the stereochemistry at C-3 of a previously reported synthesis of the P57 cymarose moiety was carried out. The first step was the selective oxidation of D-glucal using Pd/C in the presence of acetonitrile. These reaction conditions are more appropriate for the oxidation step to avoid decomposition of the formed molecules. Successive protection of the free OH groups was followed by NaBH4 reduction under stereo-controlled conditions, influenced by CeCl3•7H2O. However, the reduced product could not be isolated from the starting material and this led to ambiguous results when attempting to confirm whether the conversion of the stereochemistry at C-3 had occurred or not. The effect of reaction conditions, such as change in reaction temperature, during the preparation of the cymarose glycosyl donor was studied in order to find suitable reaction conditions to produce α,β-allo derivatives with high stereoselectivity. Compared to the reported synthetic method, this set-up gave improved yields with, unfortunately, similar or slightly lower selectivity to the formation of α-altro:α,β-allo derivative. Examination of the conformational structure of the allal derivative, in order to understand the mechanism at work during the placement of the directing group at C-2, was carried out using molecular modelling. The mechanistic implications of this very short study are discussed and it provides some insights into the likely pathway of the iodination reaction and its selectivity in particular, to the D-allose system.
- Full Text:
- Date Issued: 2013
Development of a small production platform for citronellal processing
- Mafu, Lubabalo Rowan, Zeelie, Ben
- Authors: Mafu, Lubabalo Rowan , Zeelie, Ben
- Date: 2016
- Subjects: Organic compounds -- Synthesis , Plasticizers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/8488 , vital:26370
- Description: The aim of the project was to develop a small production platform for citronellal processing. The objective of the study was to develop a single continuous flow reactor system for the synthesis of novel derivatives of citronellal and isopulegol. The first step was to develop a continuous flow reactor system for the isopulegol synthesis. The stainless steel tubular fixed-bed reactor equipped with a reaction column (I.D: 9.53 mm and length: 120 mm) was used for the study. The reactor column was packed with H-ZMS-5 zeolite extrusion catalyst. The solvent-free cyclisation reaction of citronellal was investigated and at optimum conditions, 100% of citronellal conversion and almost 100% selectivity towards isopulegol was achieved. A good catalytic performance was observed from the H-ZSM-5 catalyst and proved to be stable for a prolonged reaction time. The second reaction step was to develop a continuous flow reactor system for the synthesis of isopulegyl-ether derivatives. A UniQsis FlowSyn reactor system equipped with a stainless steel reactor column was used for the study. The reactor column was packed with amberlyst-15 dry catalyst. Wherein, n-propanol was employed as a model etherifying agent and as a reaction solvent. At optimum reaction condition, only 30% selectivity of isopulegyl propoxy-ether was achieved. The reaction was found to depend highly on temperature and residence time. The increase of these parameters was found to increase the side reactions and reduced the selectivity of the desired product. Other heterogeneous catalysts such as H-beta zeolite, aluminium pillared clay, Aluminium oxide and H-ZSM-5 were also evaluated in the reaction. Among these catalysts, a catalytic activity was observed with H-beta zeolite (19%) and aluminium pillared clay (5%). Based on these results, none of the evaluated catalysts provided the desired selectivity (greater than 70%) towards the isopulegyl propoxy-ether, therefore the process was not investigated further. In light of this, the isopulegol etherification synthetic route was terminated. Consequently, another analogue of citronellal was used as an alternative intermediate in place of isopulegol, namely para-menthane-3,8-diol (PMD). The initial studies for the synthesis of the novel PMD di-esters from isopulegol were performed in the batch-scale reactor. In a solvent-free reaction, acetic anhydride was initially used as a model acetylating agent. The reaction was performed using polymer-bound scandium triflate (PS-Sc(OTf)3) catalyst. The effect of reaction parameters such as temperature, molar ratio, and reaction time were studied towards the PMD conversion and di-esters selectivity. At optimum reaction conditions, PMD conversion of 70% and di-acetate selectivity of 67% were observed. The reaction was found to follow the zeroth-order kinetics with respect to PMD conversion and obeyed the Arrhenius equation. Other types of di-ester derivatives were synthesized from PMD by varying the carbon chain length of the acetylating agent. The prepared compounds were separated from the product mixtures by vacuum distillation, purified on a column chromatography and characterised by FT-IR, GC-MS, and 1H-NMR, 13C-NMR. The developed methodology was optimised in flow by using an ArrheniumOne microwave-assisted continuous-flow fixed-bed reactor system. A detailed experimental design was used to carry-out the reactions. The reaction parameters such as temperature and flow-rate were studied towards the PMD conversion and di-ester selectivity. From the experimental design analysis, the di-ester selectivity was found to depend highly on the residence time (flow-rate) and significantly on temperature. The PMD conversion and di-ester selectivity were found to increase with decrease in the flow-rate. The conversion and selectivity achieved in the continuous flow process were significantly higher than the achieved in the batch-scale process with respect to the residence time.
- Full Text:
- Date Issued: 2016
- Authors: Mafu, Lubabalo Rowan , Zeelie, Ben
- Date: 2016
- Subjects: Organic compounds -- Synthesis , Plasticizers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/8488 , vital:26370
- Description: The aim of the project was to develop a small production platform for citronellal processing. The objective of the study was to develop a single continuous flow reactor system for the synthesis of novel derivatives of citronellal and isopulegol. The first step was to develop a continuous flow reactor system for the isopulegol synthesis. The stainless steel tubular fixed-bed reactor equipped with a reaction column (I.D: 9.53 mm and length: 120 mm) was used for the study. The reactor column was packed with H-ZMS-5 zeolite extrusion catalyst. The solvent-free cyclisation reaction of citronellal was investigated and at optimum conditions, 100% of citronellal conversion and almost 100% selectivity towards isopulegol was achieved. A good catalytic performance was observed from the H-ZSM-5 catalyst and proved to be stable for a prolonged reaction time. The second reaction step was to develop a continuous flow reactor system for the synthesis of isopulegyl-ether derivatives. A UniQsis FlowSyn reactor system equipped with a stainless steel reactor column was used for the study. The reactor column was packed with amberlyst-15 dry catalyst. Wherein, n-propanol was employed as a model etherifying agent and as a reaction solvent. At optimum reaction condition, only 30% selectivity of isopulegyl propoxy-ether was achieved. The reaction was found to depend highly on temperature and residence time. The increase of these parameters was found to increase the side reactions and reduced the selectivity of the desired product. Other heterogeneous catalysts such as H-beta zeolite, aluminium pillared clay, Aluminium oxide and H-ZSM-5 were also evaluated in the reaction. Among these catalysts, a catalytic activity was observed with H-beta zeolite (19%) and aluminium pillared clay (5%). Based on these results, none of the evaluated catalysts provided the desired selectivity (greater than 70%) towards the isopulegyl propoxy-ether, therefore the process was not investigated further. In light of this, the isopulegol etherification synthetic route was terminated. Consequently, another analogue of citronellal was used as an alternative intermediate in place of isopulegol, namely para-menthane-3,8-diol (PMD). The initial studies for the synthesis of the novel PMD di-esters from isopulegol were performed in the batch-scale reactor. In a solvent-free reaction, acetic anhydride was initially used as a model acetylating agent. The reaction was performed using polymer-bound scandium triflate (PS-Sc(OTf)3) catalyst. The effect of reaction parameters such as temperature, molar ratio, and reaction time were studied towards the PMD conversion and di-esters selectivity. At optimum reaction conditions, PMD conversion of 70% and di-acetate selectivity of 67% were observed. The reaction was found to follow the zeroth-order kinetics with respect to PMD conversion and obeyed the Arrhenius equation. Other types of di-ester derivatives were synthesized from PMD by varying the carbon chain length of the acetylating agent. The prepared compounds were separated from the product mixtures by vacuum distillation, purified on a column chromatography and characterised by FT-IR, GC-MS, and 1H-NMR, 13C-NMR. The developed methodology was optimised in flow by using an ArrheniumOne microwave-assisted continuous-flow fixed-bed reactor system. A detailed experimental design was used to carry-out the reactions. The reaction parameters such as temperature and flow-rate were studied towards the PMD conversion and di-ester selectivity. From the experimental design analysis, the di-ester selectivity was found to depend highly on the residence time (flow-rate) and significantly on temperature. The PMD conversion and di-ester selectivity were found to increase with decrease in the flow-rate. The conversion and selectivity achieved in the continuous flow process were significantly higher than the achieved in the batch-scale process with respect to the residence time.
- Full Text:
- Date Issued: 2016
Synthesis of L-menthyl glyoxylate, an important intermediate in the manufacture of ARVS, using flow chemistry technology
- Authors: Moyo, McQuillan
- Date: 2017
- Subjects: Chemistry , Pharmaceutical chemistry , Organic compounds -- Synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12019 , vital:27018
- Description: Herein an alternative approach to the conventional batch synthesis of L-menthyl glyoxylate hydrate (MGH), an important intermediate in the synthesis of drugs of importance is reported, through flow chemistry technology. MGH was initially synthesized in batch and various reaction parameters optimized. It was found to proceed to completion after 6 hours of esterifying glyoxylic acid with excess alcohol (L-menthol) in the presence of a catalyst, ideally amberlyst-15 (an ion exchange resin) at 105 °C giving a yield of 72 %. The batch reaction conditions were adopted in a continuous flow synthesis setup, using the Labtrix Start system, in which reaction conditions were optimized. The optimization of glyoxylic acid conversion (92 %) in the Labtrix Start system gave reaction conditions that resulted in low MGH selectivity (25 %) whereas the optimization for MGH selectivity (100 %) gave a conversion a poor glyoxylic acid conversion (15 %). The FlowSyn system fitted with a column reactor gave the best results, in which the optimum conditions were an excess of L-menthol (1.5 M, 6.0 equiv.), temperature (80 °C) and a residence time of 2.5 minutes with a high selectivity (77 %) and average conversion (50 %). The optimized reaction conditions for conversion and selectivity on the different flow systems did not vary significantly and similar trends were observed for the systems. It was shown that an increase in temperature, mole equivalents and residence time led to an increase in MGH conversion in all flow systems. The scale up of the esterification reaction from the Labtrix Start system (19 μL microreactor) to the FlowSyn system fitted with a 2 mL reactor chip, showed that the reaction proceeds with a slight drop in selectivity from 100 % to 92 % while conversion dropped from 15 to 12 %. On the contrary, a significant drop in conversion and selectivity were observed when the FlowSyn column reactor was up-scaled to the Elite-tubular furnace, owing to the poor mixing in the larger channel size reactor.
- Full Text:
- Date Issued: 2017
- Authors: Moyo, McQuillan
- Date: 2017
- Subjects: Chemistry , Pharmaceutical chemistry , Organic compounds -- Synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12019 , vital:27018
- Description: Herein an alternative approach to the conventional batch synthesis of L-menthyl glyoxylate hydrate (MGH), an important intermediate in the synthesis of drugs of importance is reported, through flow chemistry technology. MGH was initially synthesized in batch and various reaction parameters optimized. It was found to proceed to completion after 6 hours of esterifying glyoxylic acid with excess alcohol (L-menthol) in the presence of a catalyst, ideally amberlyst-15 (an ion exchange resin) at 105 °C giving a yield of 72 %. The batch reaction conditions were adopted in a continuous flow synthesis setup, using the Labtrix Start system, in which reaction conditions were optimized. The optimization of glyoxylic acid conversion (92 %) in the Labtrix Start system gave reaction conditions that resulted in low MGH selectivity (25 %) whereas the optimization for MGH selectivity (100 %) gave a conversion a poor glyoxylic acid conversion (15 %). The FlowSyn system fitted with a column reactor gave the best results, in which the optimum conditions were an excess of L-menthol (1.5 M, 6.0 equiv.), temperature (80 °C) and a residence time of 2.5 minutes with a high selectivity (77 %) and average conversion (50 %). The optimized reaction conditions for conversion and selectivity on the different flow systems did not vary significantly and similar trends were observed for the systems. It was shown that an increase in temperature, mole equivalents and residence time led to an increase in MGH conversion in all flow systems. The scale up of the esterification reaction from the Labtrix Start system (19 μL microreactor) to the FlowSyn system fitted with a 2 mL reactor chip, showed that the reaction proceeds with a slight drop in selectivity from 100 % to 92 % while conversion dropped from 15 to 12 %. On the contrary, a significant drop in conversion and selectivity were observed when the FlowSyn column reactor was up-scaled to the Elite-tubular furnace, owing to the poor mixing in the larger channel size reactor.
- Full Text:
- Date Issued: 2017
The characterization and application of novel xanthenyland thioxanthenyl-derived compounds as hosts in the presence of various applicable guest mixtures
- Authors: Jooste, Daniel Victor
- Date: 2020
- Subjects: Organic compounds -- Synthesis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/49104 , vital:41601
- Description: In this work, the host potential of four novel, structurally-related compounds, trans- N,N’-bis(9-phenyl-9-xanthenyl)cyclohexane-1,2-diamine (1,2-DAX), trans-N,N’-bis(9- phenyl-9-thioxanthenyl)cyclohexane-1,2-diamine (1,2-DAT), trans-N,N’-bis(9-phenyl- 9-xanthenyl)cyclohexane-1,4-diamine (1,4-DAX), and trans-N,N’-bis(9-phenyl-9- thioxanthenyl)cyclohexane-1,4-diamine (1,4-DAT), were investigated for their possible employment in the separation of isomers and other related compounds using host– guest chemistry. These hosts were synthesized following a Grignard reaction with phenylmagnesium bromide on either xanthone or thioxanthone. The resultant alcohol was treated with perchloric acid, before finally being linked with either trans-1,2- or trans-1,4-diaminocyclohexane to afford the four title host compounds. Initially, the feasibility of these hosts for separating isomers and related compounds was investigated by recrystallizing each one independently from various guest compounds including the methylpyridines and pyridine, xylenes and ethylbenzene, heterocyclic six-membered ring compounds, aniline, N-methylaniline and N,Ndimethylaniline, and also the alkylbenzenes toluene, cumene and ethylbenzene. 1HNMR spectroscopy was used to ascertain if inclusion of the guest species had occurred in this manner and, if so, the host:guest ratio of the complex. Guest–guest competitions were subsequently conducted in order to establish the selectivity of the hosts when presented with a mixture of guests, and if the host would be able to discriminate between them. Gas chromatography-mass spectrometry (GC-MS) was the analytical method of choice here if 1H-NMR spectroscopy was not suitable owing to guest–guest signal overlap. Here, the host was recrystallized from binary, ternary and quaternary mixed guests, where each was present in equimolar amounts. Additionally, binary competition experiments were conducted in mixed guest solvents where the molar ratios of the guests were varied, and host selectivity for these guests evaluated visually by means of selectivity profiles. Single crystal X-ray diffraction (SC-XRD) and thermal analysis were performed on any complexes that afforded crystals of suitable quality in order to relate inherent host–guest interactions and thermal stability to the observed host selectivity from the competition experiments. The more prevalent interactions that were evident in these inclusion complexes between host and guest species were, more usually, and interactions, as well as other short contacts. Hydrogen bonding interactions were observed in only a few of the complexes. Guest accommodation type was also investigated, and these species resided in either discrete cavities or channels within the host crystal, depending on the guest. For the most part, traces obtained from thermal analyses were highly convoluted and difficult to interpret. As a result, guest release onset temperatures could not be determined for all of the inclusion complexes. In some cases, however, this temperature was successfully measured and correlated directly with the observed selectivity order of the host suggested by the competition experiments. Both enhanced and contrasting results were obtained for the four host compounds. In all cases, 1,2-DAX and 1,2-DAT successfully formed complexes with each of the guest species from each series. Interestingly, the 1,4-derived hosts, however, were more selective in that 1,4-DAX did not complex with only one of the guest solvents, while 1,4-DAT did not enclathrate as many as ten of these solvents. The competition investigations showed that, in most of these experiments, the host compounds displayed selectivity for one of the guests present in the mixture, and in some cases, this selectivity was pronounced, alluding to the feasibility of separating related guests from one another through host–guest chemistry principles. Computational calculations were, additionally, conducted on each of the host molecules in order to gain a better understanding of their geometries, and to compare these with the apohost crystal structures. Significant geometry differences were noted between the calculated and crystal structures.
- Full Text:
- Date Issued: 2020
- Authors: Jooste, Daniel Victor
- Date: 2020
- Subjects: Organic compounds -- Synthesis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/49104 , vital:41601
- Description: In this work, the host potential of four novel, structurally-related compounds, trans- N,N’-bis(9-phenyl-9-xanthenyl)cyclohexane-1,2-diamine (1,2-DAX), trans-N,N’-bis(9- phenyl-9-thioxanthenyl)cyclohexane-1,2-diamine (1,2-DAT), trans-N,N’-bis(9-phenyl- 9-xanthenyl)cyclohexane-1,4-diamine (1,4-DAX), and trans-N,N’-bis(9-phenyl-9- thioxanthenyl)cyclohexane-1,4-diamine (1,4-DAT), were investigated for their possible employment in the separation of isomers and other related compounds using host– guest chemistry. These hosts were synthesized following a Grignard reaction with phenylmagnesium bromide on either xanthone or thioxanthone. The resultant alcohol was treated with perchloric acid, before finally being linked with either trans-1,2- or trans-1,4-diaminocyclohexane to afford the four title host compounds. Initially, the feasibility of these hosts for separating isomers and related compounds was investigated by recrystallizing each one independently from various guest compounds including the methylpyridines and pyridine, xylenes and ethylbenzene, heterocyclic six-membered ring compounds, aniline, N-methylaniline and N,Ndimethylaniline, and also the alkylbenzenes toluene, cumene and ethylbenzene. 1HNMR spectroscopy was used to ascertain if inclusion of the guest species had occurred in this manner and, if so, the host:guest ratio of the complex. Guest–guest competitions were subsequently conducted in order to establish the selectivity of the hosts when presented with a mixture of guests, and if the host would be able to discriminate between them. Gas chromatography-mass spectrometry (GC-MS) was the analytical method of choice here if 1H-NMR spectroscopy was not suitable owing to guest–guest signal overlap. Here, the host was recrystallized from binary, ternary and quaternary mixed guests, where each was present in equimolar amounts. Additionally, binary competition experiments were conducted in mixed guest solvents where the molar ratios of the guests were varied, and host selectivity for these guests evaluated visually by means of selectivity profiles. Single crystal X-ray diffraction (SC-XRD) and thermal analysis were performed on any complexes that afforded crystals of suitable quality in order to relate inherent host–guest interactions and thermal stability to the observed host selectivity from the competition experiments. The more prevalent interactions that were evident in these inclusion complexes between host and guest species were, more usually, and interactions, as well as other short contacts. Hydrogen bonding interactions were observed in only a few of the complexes. Guest accommodation type was also investigated, and these species resided in either discrete cavities or channels within the host crystal, depending on the guest. For the most part, traces obtained from thermal analyses were highly convoluted and difficult to interpret. As a result, guest release onset temperatures could not be determined for all of the inclusion complexes. In some cases, however, this temperature was successfully measured and correlated directly with the observed selectivity order of the host suggested by the competition experiments. Both enhanced and contrasting results were obtained for the four host compounds. In all cases, 1,2-DAX and 1,2-DAT successfully formed complexes with each of the guest species from each series. Interestingly, the 1,4-derived hosts, however, were more selective in that 1,4-DAX did not complex with only one of the guest solvents, while 1,4-DAT did not enclathrate as many as ten of these solvents. The competition investigations showed that, in most of these experiments, the host compounds displayed selectivity for one of the guests present in the mixture, and in some cases, this selectivity was pronounced, alluding to the feasibility of separating related guests from one another through host–guest chemistry principles. Computational calculations were, additionally, conducted on each of the host molecules in order to gain a better understanding of their geometries, and to compare these with the apohost crystal structures. Significant geometry differences were noted between the calculated and crystal structures.
- Full Text:
- Date Issued: 2020
A Combined Experimental and Computational Study of Hydridospirophosphorane Ligand Systems Featuring Halogenated Mandelic Acids
- Authors: Maritz, Marius Johann
- Date: 2023-12
- Subjects: Organic compounds -- Synthesis , Heterocyclic compounds , catalysis -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62096 , vital:71911
- Description: The search for new stereoselective catalysts remains important for the isolation of enantiomeric products from racemic mixtures. The need exists for these catalysts to be more efficient, to be more cost effective as well as be stable over time without undergoing changes in molecular structure and selectivity. The purpose of this research project was to experimentally synthesise and characterise asymmetric catalysts for the use in enantioselective synthesis. The catalysts consisted of the main group element phosphorous as central atom, with the phenyl rings of mandelic acid ligands monosubstituted with halogen atoms fluorine, chlorine and bromine in different configurations. Ligand binding resulted in the formation of hydridospirophosphorane structures, from which the molecular properties and binding geometry of these molecules could be explained by the theory of apicophilicity. Characterization was performed by NMR and IR spectroscopy as well as diffraction studies that provided the experimental crystal structures. The structural, energetic and spectroscopy results were compared to the theoretically obtained molecular properties using DFT analysis. Various interand intramolecular interactions that existed between molecules found in crystal packing environments were discussed. Additional properties that were investigated included modelling solvation effects, molecular orbital analysis, Hirshfeld surfaces, orbital and atomic energy and population analysis as well as ESP energy calculations with the optimized crystal structures as input. Molecular overlay comparisons were also performed between the experimental and optimized structures where the effectiveness of various DFT functionals and basis sets could be determined. The method with the best overall cost-to-accuracy ratio was found to be the triple-zeta def2-tzvp basis set with B3LYP functional theory and the addition of Grimme’s dispersion correction. Results indicated differences in crystal packing depending largely on the given halogen atoms present in the substituted phenyl rings, with differences observed in electronegativity and steric effects. One of the crystal systems showed additional interactions with solvent molecules, giving the impression that obtaining crystal void formation was possible. Alterations in the transition state activation energies between the isomers of each molecule were found to be present and supported the theory behind the mechanism of stereochemical induction. The studied compounds were therefore effective in isolating different enantiomeric ligands by means of energy differences between conformers and displayed unique catalytic properties resulting from the phosphorous main group element. The hydridospirophosphoranes conformers responsible for the lowest theoretically calculated activation energy induced crystallization as was seen by diffraction results for all compounds. Even as an intriguing observation, crystallization will largely depend on solubility rather than a specific conformer’s amount in solution. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Maritz, Marius Johann
- Date: 2023-12
- Subjects: Organic compounds -- Synthesis , Heterocyclic compounds , catalysis -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62096 , vital:71911
- Description: The search for new stereoselective catalysts remains important for the isolation of enantiomeric products from racemic mixtures. The need exists for these catalysts to be more efficient, to be more cost effective as well as be stable over time without undergoing changes in molecular structure and selectivity. The purpose of this research project was to experimentally synthesise and characterise asymmetric catalysts for the use in enantioselective synthesis. The catalysts consisted of the main group element phosphorous as central atom, with the phenyl rings of mandelic acid ligands monosubstituted with halogen atoms fluorine, chlorine and bromine in different configurations. Ligand binding resulted in the formation of hydridospirophosphorane structures, from which the molecular properties and binding geometry of these molecules could be explained by the theory of apicophilicity. Characterization was performed by NMR and IR spectroscopy as well as diffraction studies that provided the experimental crystal structures. The structural, energetic and spectroscopy results were compared to the theoretically obtained molecular properties using DFT analysis. Various interand intramolecular interactions that existed between molecules found in crystal packing environments were discussed. Additional properties that were investigated included modelling solvation effects, molecular orbital analysis, Hirshfeld surfaces, orbital and atomic energy and population analysis as well as ESP energy calculations with the optimized crystal structures as input. Molecular overlay comparisons were also performed between the experimental and optimized structures where the effectiveness of various DFT functionals and basis sets could be determined. The method with the best overall cost-to-accuracy ratio was found to be the triple-zeta def2-tzvp basis set with B3LYP functional theory and the addition of Grimme’s dispersion correction. Results indicated differences in crystal packing depending largely on the given halogen atoms present in the substituted phenyl rings, with differences observed in electronegativity and steric effects. One of the crystal systems showed additional interactions with solvent molecules, giving the impression that obtaining crystal void formation was possible. Alterations in the transition state activation energies between the isomers of each molecule were found to be present and supported the theory behind the mechanism of stereochemical induction. The studied compounds were therefore effective in isolating different enantiomeric ligands by means of energy differences between conformers and displayed unique catalytic properties resulting from the phosphorous main group element. The hydridospirophosphoranes conformers responsible for the lowest theoretically calculated activation energy induced crystallization as was seen by diffraction results for all compounds. Even as an intriguing observation, crystallization will largely depend on solubility rather than a specific conformer’s amount in solution. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
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