Supramolecular chemistry considerations of fluorenyl-derived host compounds
- Authors: McFarlane, Duncan William
- Date: 2024-12
- Subjects: Supramolecular chemistry , Organic compounds , Chemistry, Organic
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/69371 , vital:77227
- Description: This work examined various supramolecular aspects of 9-fluorenone-derived host compounds, namely 4,4’-(9-fluorenylidene)diphenol (H1), 9,9-(1,4-phenylene)bis(fluoren-9-ol) (H2), 9,9- (ethyne-1,2-diyl)bis(fluoren-9-ol) (H3) and 9,9-(biphenyl-4,4-diyl)bis(fluoren-9-ol) (H4). These compounds were successfully synthesized and then screened for their host ability for, and host behaviour in, various organic compounds. At the outset, molecular modelling calculations were carried out on each of the four host compounds. Various structural parameters and the geometries of the low energy conformers that were calculated were then compared with these aspects of the guest-free host molecules obtained from single crystal X-ray diffraction (SCXRD) analysis. The host behaviour of H1 was, furthermore, assessed in the presence of four alkylnitriles, namely acetonitrile (ACE), acrylonitrile (ACRY), propionitrile (PROP) and butyronitrile (BUT). All four guests complexed with H1 with 1:1 host:guest (H:G) ratios. From SCXRD analyses, each of the complexes crystallized in the monoclinic crystal system and the centrosymmetric space group P21/n, and the host packing was isostructural in each instance. The complexes were stabilized by a plethora of short inter- and intramolecular contacts. The thermal stabilities of the four complexes were also examined together with Hirshfeld surface considerations. Finally, lattice energy calculations were carried out and the results of these compared with the relative thermal stabilities of the four complexes. The compounds H2 and H3 were examined for their selectivity behaviour in mixtures of aniline, N-methylaniline and N,N’-dimethylaniline (ANI, NMA and DMA). Both host compounds were able to form complexes with ANI and DMA with various H:G ratios, while only H3 possessed enclathration ability for NMA (H:G 1:1). SCXRD analyses showed that all of the complexes were stabilized by means of classical (host)O‒H···N(guest) hydrogen bonds in addition to other short contacts. Equimolar binary guest competition experiments with H2 revealed an extremely high host selectivity for DMA (ANI/DMA and DMA/NMA experiments furnished crystals with > 91% DMA), while the experiment with all three anilines present also resulted in a complex with an , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-12
- Authors: McFarlane, Duncan William
- Date: 2024-12
- Subjects: Supramolecular chemistry , Organic compounds , Chemistry, Organic
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/69371 , vital:77227
- Description: This work examined various supramolecular aspects of 9-fluorenone-derived host compounds, namely 4,4’-(9-fluorenylidene)diphenol (H1), 9,9-(1,4-phenylene)bis(fluoren-9-ol) (H2), 9,9- (ethyne-1,2-diyl)bis(fluoren-9-ol) (H3) and 9,9-(biphenyl-4,4-diyl)bis(fluoren-9-ol) (H4). These compounds were successfully synthesized and then screened for their host ability for, and host behaviour in, various organic compounds. At the outset, molecular modelling calculations were carried out on each of the four host compounds. Various structural parameters and the geometries of the low energy conformers that were calculated were then compared with these aspects of the guest-free host molecules obtained from single crystal X-ray diffraction (SCXRD) analysis. The host behaviour of H1 was, furthermore, assessed in the presence of four alkylnitriles, namely acetonitrile (ACE), acrylonitrile (ACRY), propionitrile (PROP) and butyronitrile (BUT). All four guests complexed with H1 with 1:1 host:guest (H:G) ratios. From SCXRD analyses, each of the complexes crystallized in the monoclinic crystal system and the centrosymmetric space group P21/n, and the host packing was isostructural in each instance. The complexes were stabilized by a plethora of short inter- and intramolecular contacts. The thermal stabilities of the four complexes were also examined together with Hirshfeld surface considerations. Finally, lattice energy calculations were carried out and the results of these compared with the relative thermal stabilities of the four complexes. The compounds H2 and H3 were examined for their selectivity behaviour in mixtures of aniline, N-methylaniline and N,N’-dimethylaniline (ANI, NMA and DMA). Both host compounds were able to form complexes with ANI and DMA with various H:G ratios, while only H3 possessed enclathration ability for NMA (H:G 1:1). SCXRD analyses showed that all of the complexes were stabilized by means of classical (host)O‒H···N(guest) hydrogen bonds in addition to other short contacts. Equimolar binary guest competition experiments with H2 revealed an extremely high host selectivity for DMA (ANI/DMA and DMA/NMA experiments furnished crystals with > 91% DMA), while the experiment with all three anilines present also resulted in a complex with an , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-12
Synthesis of two tartaric acid-derived host compounds and their behaviour in mixed pyridines and mixed heterocyclic guest compounds
- Authors: Recchia, Daniella Loridana
- Date: 2024-12
- Subjects: Compounds -- guest/host , Chemistry, Organic , Chemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/69441 , vital:77256
- Description: The host compounds (4R,5R)-bis(diphenylhydroxymethyl)-2-spiro-1’-cyclopentane-1,3-dioxolane (TADDOL5) and (4R,5R)-bis(diphenylhydroxymethyl)-2-spiro-1’-cyclohexane-1,3-dioxolane (TADDOL6) were successfully synthesized after initially reacting diethyl tartrate with either 1,1-dimethoxycyclopentane or 1,1-dimethoxycyclohexane to afford the intermediates diethyl 2-spiro-1’-cyclopentane-1,3-dioxolan-4,5-dicarboxylate or diethyl 2-spiro-1’-cyclohexane-1,3-dioxolan-4,5-dicarboxylate. These were then each subjected to a Grignard addition reaction with PhMgBr to furnish TADDOL5 and TADDOL6 in reasonably high yields (77 and 80%, respectively). Computational calculations were performed on TADDOL5 and TADDOL6 using the software programs Avogadro and ORCA. The optimised geometries of these host molecules were obtained using the MMFF94 force field in Avogadro, while ORCA was used to perform the computational modelling at the BLYP level using the 6-31G*, 6-31G**, 6-311G* and 6-311G** basis sets and, also, the B3LYP functional (with the same basis sets) to obtain the three lowest energy conformers. The final geometries of each conformer for both TADDOL5 and TADDOL6 at the B3LYP 6-311G* level were overlaid with the molecules obtained from their crystal structures. Significantly different geometries were thus noted for the calculated conformers compared with the guest-free TADDOL5 and TADDOL6 structures obtained from the SCXRD experiments. When TADDOL5 was crystallized independently from each of PYR, 2MP, 3MP and 4MP, 1:1 H:G inclusion complexes formed in each instance. This host compound was then investigated for its host separation ability of mixed pyridines through supramolecular chemistry protocols. These mixed guest experiments revealed that TADDOL5 possessed a notable selectivity towards 3MP and PYR (in the absence of 3MP) followed by 4MP and 2MP, and it was shown that TADDOL5 is a suitable host candidate for the separation of many of the mixed pyridines employed here. The results of the SCXRD analyses indicated that the only significant (host)π···π(guest) stacking interaction present was between TADDOL5 and the most favoured guest species PYR and 3MP. Furthermore, significantly shorter (host)O‒H···N(guest) hydrogen bonds were also observed in the complexes formed between this host compound and 3MP and PYR compared with these bonds involving disfavoured 4MP and 2MP. Hirshfeld surface considerations provided an explanation for the affinity of TADDOL5 for PYR (but not 3MP), while thermal analyses successfully explained this affinity: the 3MP-containing complex with the most preferred guest species was the most thermally stable one, followed by TADDOL5·PYR, as obtained through a consideration of the Ton values (the temperature at which the guest release event initiated) of the four complexes. As with TADDOL5, TADDOL6 formed 1:1 H:G inclusion compounds with each of the four pyridines. TADDOL6 was, furthermore, also assessed for its separation ability for mixed pyridines, and these guest competition experiments showed that the selectivity of TADDOL6 was for PYR and 3MP (in the absence of PYR), followed by 4MP and 2MP. (Interestingly, TADDOL5 preferred 3MP and then PYR, while both host compounds disfavoured 4MP and 2MP.) The results obtained in this work indicated that TADDOL6 may also serve as an efficient host candidate for the separation of many of these pyridyl solutions. SCXRD experiments demonstrated that the only significant (host)π···π(guest) stacking interactions were those between TADDOL6 and preferred PYR and 3MP, as was the case for TADDOL5. These experiments also revealed that the strongest (host)O‒H···N(guest) hydrogen bonds were between TADDOL6 and these favoured guest species. A consideration of Hirshfeld surfaces and quantification of the (guest)N···H(host) intermolecular interactions correlated with the host selectivity order, as did thermal analyses, where the Ton values confirmed that the thermal stabilities of these complexes decreased in the guest order PYR > 3MP > 4MP > 2MP. The behaviour of TADDOL5 was further investigated in guest compounds DIO, PYR, PIP and MOR. Each guest solvent formed 1:1 H:G inclusion complexes with the host species, with the exception of DIO, which formed a 2:1 H:G complex. Mixed guest experiments revealed a clear preference for PIP and MOR, while PYR and DIO were less favoured. The host selectivity was demonstrated to be in the order PIP > MOR > PYR > DIO. SCXRD experiments showed that TADDOL5 formed a much shorter (and more linear) (host)O‒H···N(guest) hydrogen bond with the most favoured guest, PIP, compared to those involving MOR and PYR. A (host)O‒H···O(guest) hydrogen bond was also observed in the DIO-containing inclusion complex. A consideration of the Hirshfeld surface interactions was not useful in explaining the host selectivity order for these heterocyclic guests, but thermal analyses confirmed that the most stable complex was the one with favoured PIP, followed by those with PYR, MOR and DIO. TADDOL6, on the other hand, formed 1:1 H:G inclusion compounds with all four of the heterocyclic guest solvents. Experiments in mixed guests showed that the selectivity of this host compound for these guests was in the order PYR > PIP > MOR > DIO, which differed from the TADDOL5 (which favoured PIP and then MOR). Interestingly, the strongest classical hydrogen bond was not formed with the most favoured guest PYR, but with PIP instead (this bond with TADDOL5 was also strongest with PIP, but PIP was favoured in that work). Hirshfeld surface investigations again were not useful in understanding the host selectivity behaviour. However, thermal analyses agreed with the observations made in the mixed guest experiments: the most stable complex was with PYR (favoured) and the least stable one was with DIO (least preferred). , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-12
- Authors: Recchia, Daniella Loridana
- Date: 2024-12
- Subjects: Compounds -- guest/host , Chemistry, Organic , Chemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/69441 , vital:77256
- Description: The host compounds (4R,5R)-bis(diphenylhydroxymethyl)-2-spiro-1’-cyclopentane-1,3-dioxolane (TADDOL5) and (4R,5R)-bis(diphenylhydroxymethyl)-2-spiro-1’-cyclohexane-1,3-dioxolane (TADDOL6) were successfully synthesized after initially reacting diethyl tartrate with either 1,1-dimethoxycyclopentane or 1,1-dimethoxycyclohexane to afford the intermediates diethyl 2-spiro-1’-cyclopentane-1,3-dioxolan-4,5-dicarboxylate or diethyl 2-spiro-1’-cyclohexane-1,3-dioxolan-4,5-dicarboxylate. These were then each subjected to a Grignard addition reaction with PhMgBr to furnish TADDOL5 and TADDOL6 in reasonably high yields (77 and 80%, respectively). Computational calculations were performed on TADDOL5 and TADDOL6 using the software programs Avogadro and ORCA. The optimised geometries of these host molecules were obtained using the MMFF94 force field in Avogadro, while ORCA was used to perform the computational modelling at the BLYP level using the 6-31G*, 6-31G**, 6-311G* and 6-311G** basis sets and, also, the B3LYP functional (with the same basis sets) to obtain the three lowest energy conformers. The final geometries of each conformer for both TADDOL5 and TADDOL6 at the B3LYP 6-311G* level were overlaid with the molecules obtained from their crystal structures. Significantly different geometries were thus noted for the calculated conformers compared with the guest-free TADDOL5 and TADDOL6 structures obtained from the SCXRD experiments. When TADDOL5 was crystallized independently from each of PYR, 2MP, 3MP and 4MP, 1:1 H:G inclusion complexes formed in each instance. This host compound was then investigated for its host separation ability of mixed pyridines through supramolecular chemistry protocols. These mixed guest experiments revealed that TADDOL5 possessed a notable selectivity towards 3MP and PYR (in the absence of 3MP) followed by 4MP and 2MP, and it was shown that TADDOL5 is a suitable host candidate for the separation of many of the mixed pyridines employed here. The results of the SCXRD analyses indicated that the only significant (host)π···π(guest) stacking interaction present was between TADDOL5 and the most favoured guest species PYR and 3MP. Furthermore, significantly shorter (host)O‒H···N(guest) hydrogen bonds were also observed in the complexes formed between this host compound and 3MP and PYR compared with these bonds involving disfavoured 4MP and 2MP. Hirshfeld surface considerations provided an explanation for the affinity of TADDOL5 for PYR (but not 3MP), while thermal analyses successfully explained this affinity: the 3MP-containing complex with the most preferred guest species was the most thermally stable one, followed by TADDOL5·PYR, as obtained through a consideration of the Ton values (the temperature at which the guest release event initiated) of the four complexes. As with TADDOL5, TADDOL6 formed 1:1 H:G inclusion compounds with each of the four pyridines. TADDOL6 was, furthermore, also assessed for its separation ability for mixed pyridines, and these guest competition experiments showed that the selectivity of TADDOL6 was for PYR and 3MP (in the absence of PYR), followed by 4MP and 2MP. (Interestingly, TADDOL5 preferred 3MP and then PYR, while both host compounds disfavoured 4MP and 2MP.) The results obtained in this work indicated that TADDOL6 may also serve as an efficient host candidate for the separation of many of these pyridyl solutions. SCXRD experiments demonstrated that the only significant (host)π···π(guest) stacking interactions were those between TADDOL6 and preferred PYR and 3MP, as was the case for TADDOL5. These experiments also revealed that the strongest (host)O‒H···N(guest) hydrogen bonds were between TADDOL6 and these favoured guest species. A consideration of Hirshfeld surfaces and quantification of the (guest)N···H(host) intermolecular interactions correlated with the host selectivity order, as did thermal analyses, where the Ton values confirmed that the thermal stabilities of these complexes decreased in the guest order PYR > 3MP > 4MP > 2MP. The behaviour of TADDOL5 was further investigated in guest compounds DIO, PYR, PIP and MOR. Each guest solvent formed 1:1 H:G inclusion complexes with the host species, with the exception of DIO, which formed a 2:1 H:G complex. Mixed guest experiments revealed a clear preference for PIP and MOR, while PYR and DIO were less favoured. The host selectivity was demonstrated to be in the order PIP > MOR > PYR > DIO. SCXRD experiments showed that TADDOL5 formed a much shorter (and more linear) (host)O‒H···N(guest) hydrogen bond with the most favoured guest, PIP, compared to those involving MOR and PYR. A (host)O‒H···O(guest) hydrogen bond was also observed in the DIO-containing inclusion complex. A consideration of the Hirshfeld surface interactions was not useful in explaining the host selectivity order for these heterocyclic guests, but thermal analyses confirmed that the most stable complex was the one with favoured PIP, followed by those with PYR, MOR and DIO. TADDOL6, on the other hand, formed 1:1 H:G inclusion compounds with all four of the heterocyclic guest solvents. Experiments in mixed guests showed that the selectivity of this host compound for these guests was in the order PYR > PIP > MOR > DIO, which differed from the TADDOL5 (which favoured PIP and then MOR). Interestingly, the strongest classical hydrogen bond was not formed with the most favoured guest PYR, but with PIP instead (this bond with TADDOL5 was also strongest with PIP, but PIP was favoured in that work). Hirshfeld surface investigations again were not useful in understanding the host selectivity behaviour. However, thermal analyses agreed with the observations made in the mixed guest experiments: the most stable complex was with PYR (favoured) and the least stable one was with DIO (least preferred). , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-12
Investigation of the host potential of compounds derived from tartaric acid, succinic acid and 1,4-cyclohexanedioic acid
- Authors: Adam, Muhammad Ameen
- Date: 2024-04
- Subjects: Chemical reactions , Chemistry, Organic , Bacteriology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63617 , vital:73562
- Description: The present investigation considered the host behaviour of three compounds, namely (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (H1), 1,1,4,4-tetraphenyl-1,4-butanediol (H2) and cyclohexane-1,4-diylbis(diphenylmethanol) (H3) in various guest mixtures. These host compounds were readily synthesized by means of Grignard addition reactions on the diesters of tartaric acid, succinic acid and 1,4-cyclohexanedioic acid. The guest mixtures included cyclopentanone, cyclohexanone, cycloheptanone and cyclooctanone, γ-butyrolactone, 2-pyrrolidone, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, and pyridine, 2-methylpyridine, 3-methylpyridine and 4-methylpyridine. Crystals of (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (H1) were grown from cyclopentanone (5-ONE), cyclohexanone (6-ONE), cycloheptanone (7-ONE) and cyclooctanone (8-ONE,) producing 1:1 host:guest complexes in each instance. Thermal analysis showed the thermal stabilities of these complexes to be in the order 6-ONE > 7-ONE > 8-ONE > 5-ONE which correlated exactly with results from binary guest/guest competition experiments, where 6-ONE was always preferred by H1, while 5-ONE was consistently disfavoured. Single crystal X-ray diffraction (SCXRD) analyses demonstrated that each guest compound was retained in the crystals by means of a hydrogen bond with an alcohol moiety of the host compound. Furthermore, preferred guests 6- and 7-ONE produced crystals with greater densities than guests less favoured (5- and 8-ONE). A conformational analysis of the guest geometries in the four complexes with H1 revealed that the low energy guest conformers were present. The host selectivity for 6- and 7-ONE was proposed to be due to the improved molecular packing in the crystals of the complexes containing these two guest compounds, observed from their higher crystal densities. Hirshfeld surface analyses were not useful in explaining the preference of H1 for 6-ONE relative to 7-ONE (these types of analyses were not possible for the 5-ONE and 8-ONE-containing inclusion compounds due to the nature and degree of disorder present in the guest molecules). H1 was also crystallized from γ-butyrolactone (GBL), 2-pyrrolidone (NP), N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP), and 1H-NMR spectroscopy revealed that all but GBL were included. The host compound was also presented with these guest solvents in various mixtures, and it was observed that NMP was an extremely favoured guest solvent, followed by NEP and NP, with GBL being consistently disfavoured in every experiment. It was therefore shown that in certain instances, H1 may serve as an alternative tool for separating some of these mixtures through host-guest chemistry strategies. The hydrogen bonding motifs present in each of the successfully formed complexes were extensively investigated through SCXRD analysis, as was the thermal behaviour of these complexes. In the latter instance, the peak temperature of the endotherm (from the DSC trace) representing the guest release was greater for the inclusion compound with favoured NMP (145.5 °C) relative to the complexes with NP (139.8 °C) and NEP (120.5 °C). Host compounds H2 and H3 were revealed to have the ability to include each of pyridine (PYR), 2-methylpyridine (2MP), 3-methylpyridine (3MP) and 4-methylpyridine (4MP). H2 displayed selective behaviour for 3MP and 4MP when presented with mixtures of these guest compounds, whilst H3 preferred PYR. In the latter case, this PYR-containing inclusion compound was also the more stable one (the guest release onset temperature was highest, Ton 66.0 °C). It was demonstrated that H2 has the ability to separate very many binary mixtures of these pyridines on a practical platform, since K (the selectivity coefficient) values were 10 or greater in many instances. However, unfortunately, the more difficult-to-separate mixtures containing 3MP and 4MP cannot be purified or separated by employing H2 and supramolecular chemistry strategies. H3 was also shown to be a likely candidate for binary guest separations in very many of the guest solutions considered here, where K was also 10 or greater, and even infinity in many cases. SCXRD demonstrated that 2MP, 3MP and 4MP were retained in the crystals of their complexes by means of classical hydrogen bonds with the host compound. Satisfyingly, this hydrogen bond between 2MP and H2 (3.0213(18) Å) was significantly longer than that between this host compound and both disorder components of 3MP (2.875(2) and 2.825(9) Å) and that between H2 and 4MP (2.8458(13) Å). This observation explains the affinity of H2 for both 3MP and 4MP, and why 2MP was disfavoured. The results of thermal experiments did not wholly concur with observations from the guest/guest competition experiments. Hirshfeld surface analyses were also conducted but were not entirely conclusive with respect to explaining the host selectivity behaviour. In the case of H3, SCXRD analyses revealed that favoured PYR experienced a classical hydrogen bond with the host compound that was statistically significantly shorter (2.795(2) Å, 165°) than those between the other guest compounds and H3. Additionally, this guest compound was the only one to be involved in a (host)C−H···π(guest) interaction (2.91 Å, 139°) and also a non-classical hydrogen bond with the host compound ((host)C−H···N−C(guest), 2.77 Å (144°)). Finally, Hirshfeld surface analyses showed also that preferred PYR experienced a greater percentage of C···H/H···C (33.1%) and H···N/N···H (11.1%) interactions compared with the complexes with 2MP, 3MP and 4MP. However, it is not clear whether these Hirshfeld observations explain the affinity of H3 for PYR. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Adam, Muhammad Ameen
- Date: 2024-04
- Subjects: Chemical reactions , Chemistry, Organic , Bacteriology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63617 , vital:73562
- Description: The present investigation considered the host behaviour of three compounds, namely (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (H1), 1,1,4,4-tetraphenyl-1,4-butanediol (H2) and cyclohexane-1,4-diylbis(diphenylmethanol) (H3) in various guest mixtures. These host compounds were readily synthesized by means of Grignard addition reactions on the diesters of tartaric acid, succinic acid and 1,4-cyclohexanedioic acid. The guest mixtures included cyclopentanone, cyclohexanone, cycloheptanone and cyclooctanone, γ-butyrolactone, 2-pyrrolidone, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, and pyridine, 2-methylpyridine, 3-methylpyridine and 4-methylpyridine. Crystals of (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (H1) were grown from cyclopentanone (5-ONE), cyclohexanone (6-ONE), cycloheptanone (7-ONE) and cyclooctanone (8-ONE,) producing 1:1 host:guest complexes in each instance. Thermal analysis showed the thermal stabilities of these complexes to be in the order 6-ONE > 7-ONE > 8-ONE > 5-ONE which correlated exactly with results from binary guest/guest competition experiments, where 6-ONE was always preferred by H1, while 5-ONE was consistently disfavoured. Single crystal X-ray diffraction (SCXRD) analyses demonstrated that each guest compound was retained in the crystals by means of a hydrogen bond with an alcohol moiety of the host compound. Furthermore, preferred guests 6- and 7-ONE produced crystals with greater densities than guests less favoured (5- and 8-ONE). A conformational analysis of the guest geometries in the four complexes with H1 revealed that the low energy guest conformers were present. The host selectivity for 6- and 7-ONE was proposed to be due to the improved molecular packing in the crystals of the complexes containing these two guest compounds, observed from their higher crystal densities. Hirshfeld surface analyses were not useful in explaining the preference of H1 for 6-ONE relative to 7-ONE (these types of analyses were not possible for the 5-ONE and 8-ONE-containing inclusion compounds due to the nature and degree of disorder present in the guest molecules). H1 was also crystallized from γ-butyrolactone (GBL), 2-pyrrolidone (NP), N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP), and 1H-NMR spectroscopy revealed that all but GBL were included. The host compound was also presented with these guest solvents in various mixtures, and it was observed that NMP was an extremely favoured guest solvent, followed by NEP and NP, with GBL being consistently disfavoured in every experiment. It was therefore shown that in certain instances, H1 may serve as an alternative tool for separating some of these mixtures through host-guest chemistry strategies. The hydrogen bonding motifs present in each of the successfully formed complexes were extensively investigated through SCXRD analysis, as was the thermal behaviour of these complexes. In the latter instance, the peak temperature of the endotherm (from the DSC trace) representing the guest release was greater for the inclusion compound with favoured NMP (145.5 °C) relative to the complexes with NP (139.8 °C) and NEP (120.5 °C). Host compounds H2 and H3 were revealed to have the ability to include each of pyridine (PYR), 2-methylpyridine (2MP), 3-methylpyridine (3MP) and 4-methylpyridine (4MP). H2 displayed selective behaviour for 3MP and 4MP when presented with mixtures of these guest compounds, whilst H3 preferred PYR. In the latter case, this PYR-containing inclusion compound was also the more stable one (the guest release onset temperature was highest, Ton 66.0 °C). It was demonstrated that H2 has the ability to separate very many binary mixtures of these pyridines on a practical platform, since K (the selectivity coefficient) values were 10 or greater in many instances. However, unfortunately, the more difficult-to-separate mixtures containing 3MP and 4MP cannot be purified or separated by employing H2 and supramolecular chemistry strategies. H3 was also shown to be a likely candidate for binary guest separations in very many of the guest solutions considered here, where K was also 10 or greater, and even infinity in many cases. SCXRD demonstrated that 2MP, 3MP and 4MP were retained in the crystals of their complexes by means of classical hydrogen bonds with the host compound. Satisfyingly, this hydrogen bond between 2MP and H2 (3.0213(18) Å) was significantly longer than that between this host compound and both disorder components of 3MP (2.875(2) and 2.825(9) Å) and that between H2 and 4MP (2.8458(13) Å). This observation explains the affinity of H2 for both 3MP and 4MP, and why 2MP was disfavoured. The results of thermal experiments did not wholly concur with observations from the guest/guest competition experiments. Hirshfeld surface analyses were also conducted but were not entirely conclusive with respect to explaining the host selectivity behaviour. In the case of H3, SCXRD analyses revealed that favoured PYR experienced a classical hydrogen bond with the host compound that was statistically significantly shorter (2.795(2) Å, 165°) than those between the other guest compounds and H3. Additionally, this guest compound was the only one to be involved in a (host)C−H···π(guest) interaction (2.91 Å, 139°) and also a non-classical hydrogen bond with the host compound ((host)C−H···N−C(guest), 2.77 Å (144°)). Finally, Hirshfeld surface analyses showed also that preferred PYR experienced a greater percentage of C···H/H···C (33.1%) and H···N/N···H (11.1%) interactions compared with the complexes with 2MP, 3MP and 4MP. However, it is not clear whether these Hirshfeld observations explain the affinity of H3 for PYR. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
The on-demand continuous flow generation, separation, and utilization of monosilane gas, a feedstock for solar-grade silicon
- Authors: Mathe, Francis Matota
- Date: 2024-04
- Subjects: Chemistry, Organic , Chemistry , Silicon -- Synthesis
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/64179 , vital:73660
- Description: This research is dedicated to the development of a continuous flow process for the production and utilization of monosilane gas. The utilization of continuous flow techniques was instrumental in addressing the challenges and conditions associated with the handling of monosilane gas. Furthermore, the integration of Process Analytical Technologies (PAT) facilitated in-process monitoring and analysis. Chapter one of this research provides an extensive background and literature review encompassing the purification methods of silicon, the latest advancements in the direct synthesis of alkoxysilanes, current synthesis methods for monosilane, the various applications of monosilane, as well as the utilization of continuous flow technology and process analytical technologies. In chapter two, a detailed account of the experimental procedures employed in this research is presented. Chapter three delves into the results derived from each section of the research. The first section discusses an attempt to upscale the continuous flow synthesis of triethoxysilane, based on previous group research. Process Analytical Technologies (PAT), specifically thermocouples, were utilized in this endeavor. The study revealed temperature inconsistencies along the packed bed reactor, which had a notable impact on the reaction capabilities. The subsequent section explores the continuous flow synthesis of monosilane from triethoxysilane. A Design of Experiment (DoE) approach was employed to identify the optimal reaction conditions and compare the effectiveness of two catalysts. The study determined that Amberlyst-A26 emerged as the superior catalyst, offering stability and reasonable conversions over a 24-hour period. In a residence time of 6 minutes and at a temperature of 55 °C, the maximum triethoxysilane conversion of 100% was achieved. PAT, particularly inline FT-IR, was instrumental in monitoring catalyst activity, while continuous flow gas separation techniques facilitated the separation of monosilane. The research also demonstrated further applications of continuous flow techniques in the synthesis of monosilane from tetraethoxysilane and magnesium silicide. The former aimed to , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Mathe, Francis Matota
- Date: 2024-04
- Subjects: Chemistry, Organic , Chemistry , Silicon -- Synthesis
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/64179 , vital:73660
- Description: This research is dedicated to the development of a continuous flow process for the production and utilization of monosilane gas. The utilization of continuous flow techniques was instrumental in addressing the challenges and conditions associated with the handling of monosilane gas. Furthermore, the integration of Process Analytical Technologies (PAT) facilitated in-process monitoring and analysis. Chapter one of this research provides an extensive background and literature review encompassing the purification methods of silicon, the latest advancements in the direct synthesis of alkoxysilanes, current synthesis methods for monosilane, the various applications of monosilane, as well as the utilization of continuous flow technology and process analytical technologies. In chapter two, a detailed account of the experimental procedures employed in this research is presented. Chapter three delves into the results derived from each section of the research. The first section discusses an attempt to upscale the continuous flow synthesis of triethoxysilane, based on previous group research. Process Analytical Technologies (PAT), specifically thermocouples, were utilized in this endeavor. The study revealed temperature inconsistencies along the packed bed reactor, which had a notable impact on the reaction capabilities. The subsequent section explores the continuous flow synthesis of monosilane from triethoxysilane. A Design of Experiment (DoE) approach was employed to identify the optimal reaction conditions and compare the effectiveness of two catalysts. The study determined that Amberlyst-A26 emerged as the superior catalyst, offering stability and reasonable conversions over a 24-hour period. In a residence time of 6 minutes and at a temperature of 55 °C, the maximum triethoxysilane conversion of 100% was achieved. PAT, particularly inline FT-IR, was instrumental in monitoring catalyst activity, while continuous flow gas separation techniques facilitated the separation of monosilane. The research also demonstrated further applications of continuous flow techniques in the synthesis of monosilane from tetraethoxysilane and magnesium silicide. The former aimed to , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
The synthesis and assessment of thioxanthone- and xanthone- derived compounds as hosts for application in host-guest chemistry
- Authors: Greyling, Lizé
- Date: 2019
- Subjects: Chemistry, Organic , Biochemistry
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/42525 , vital:36665
- Description: In this work, the host capabilities of two structurally related compounds, N,N’-bis(9-phenyl-9- thioxanthenyl)ethylenediamine (H1) and N,N’-bis(9-phenyl-9-xanthenyl)ethylenediamine (H2) were compared in the presence of a wide variety of guest species. Additionally, the selectivity displayed by these host compounds were examined when exposed to mixtures of guests in order to ascertain whether it would be feasible to employ them in alternative separation strategies for the purification of industrially relevant chemicals. H1 and H2 were synthesized by reacting thioxanthone and xanthone with phenylmagnesium bromide. The resultant alcohol was then treated with perchloric acid and, finally, two of these molecules were effectively linked by utilizing ethylenediamine to afford the two host compounds. Initially, H1 and H2 were investigated for their inclusion abilities by recrystallizing each from a number of potential isomeric and non-isomeric guest compounds such as the xylenes and ethylbenzene, methylanisoles and anisole, methylpyridines and pyridine, methylcyclohexanones and cyclohexanone, heterocyclic five- and six- membered ring compounds, alkylsubstituted benzenes, anilines, and dihaloalkanes. H1 displayed excellent inclusion ability when presented with the above-mentioned compounds, and a 1:1 H:G ratio was consistently preferred in each case. H2 also proved to be successful in this regard but did not include the methylcyclohexanones and cyclohexanone nor the heterocyclic five-membered ring solvents. Furthermore, varying host:guest ratios were observed for the complexes formed with H2. Mixed competition experiments were carried out in the presence of either isomeric or related but non-isomeric guest species. When H1 and H2 were independently recrystallized from mixtures of the former, selectivity orders correlated for both hosts, but it was observed that H2 exhibited an enhanced selectivity for the preferred guests in each case, compared with H1. Interestingly, in mixtures of the latter, host behaviours were distinctly opposing (with the exception of the dihaloalkanes). H1, and even more so H2, demonstrated very high selectivities for p-xylene, aniline and N,Ndimethylaniline from the xylene and aniline guest series, respectively, where selectivities were found to be ~90% or higher for host recrystallization experiments from respective mixtures of these guests. Single crystal X-ray diffraction, Hirshfeld surface and thermal analyses were employed in order to elucidate the reasons for any selectivity observations. The inclusion of these guests was, in most cases, found to be as a result of interactions between host and guest species, which included π∙∙∙π stacking, C‒H∙∙∙π, hydrogen bonding and various other short contact types. Guest compounds were accommodated in either cavities or channels and this was dependent on the nature of the guest. The host molecule conformations showed H1 to adopt a bent tricyclic fused ring system with the N atoms of the linker in a synclinal arrangement, while in complexes with H2, the fused ring system was near-planar and the N atoms adopted an antiperiplanar geometry. These key differences resulted in a very ordered host‒host packing for H2 as a direct result of the more planar O-containing ring and linear linker; for H1, on the other hand, the buckled S-containing ring and gauche-orientated N atoms resulted in a less ordered packing, which ultimately related to the differences in the behaviour of the two host species. Hirshfeld surface analyses, in general, did not provide much information to explain the host selectivities, with the exception of complexes containing the five-membered ring guest heterocyclics. Thermal analyses were completed on all suitable host-guest complexes and, in most cases but not all, the onset and peak temperatures (terms Ton and Tp, respectively) were related to the thermal stability of the complexes, which were used to rationalize the selectivities of these host compounds.
- Full Text:
- Date Issued: 2019
- Authors: Greyling, Lizé
- Date: 2019
- Subjects: Chemistry, Organic , Biochemistry
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/42525 , vital:36665
- Description: In this work, the host capabilities of two structurally related compounds, N,N’-bis(9-phenyl-9- thioxanthenyl)ethylenediamine (H1) and N,N’-bis(9-phenyl-9-xanthenyl)ethylenediamine (H2) were compared in the presence of a wide variety of guest species. Additionally, the selectivity displayed by these host compounds were examined when exposed to mixtures of guests in order to ascertain whether it would be feasible to employ them in alternative separation strategies for the purification of industrially relevant chemicals. H1 and H2 were synthesized by reacting thioxanthone and xanthone with phenylmagnesium bromide. The resultant alcohol was then treated with perchloric acid and, finally, two of these molecules were effectively linked by utilizing ethylenediamine to afford the two host compounds. Initially, H1 and H2 were investigated for their inclusion abilities by recrystallizing each from a number of potential isomeric and non-isomeric guest compounds such as the xylenes and ethylbenzene, methylanisoles and anisole, methylpyridines and pyridine, methylcyclohexanones and cyclohexanone, heterocyclic five- and six- membered ring compounds, alkylsubstituted benzenes, anilines, and dihaloalkanes. H1 displayed excellent inclusion ability when presented with the above-mentioned compounds, and a 1:1 H:G ratio was consistently preferred in each case. H2 also proved to be successful in this regard but did not include the methylcyclohexanones and cyclohexanone nor the heterocyclic five-membered ring solvents. Furthermore, varying host:guest ratios were observed for the complexes formed with H2. Mixed competition experiments were carried out in the presence of either isomeric or related but non-isomeric guest species. When H1 and H2 were independently recrystallized from mixtures of the former, selectivity orders correlated for both hosts, but it was observed that H2 exhibited an enhanced selectivity for the preferred guests in each case, compared with H1. Interestingly, in mixtures of the latter, host behaviours were distinctly opposing (with the exception of the dihaloalkanes). H1, and even more so H2, demonstrated very high selectivities for p-xylene, aniline and N,Ndimethylaniline from the xylene and aniline guest series, respectively, where selectivities were found to be ~90% or higher for host recrystallization experiments from respective mixtures of these guests. Single crystal X-ray diffraction, Hirshfeld surface and thermal analyses were employed in order to elucidate the reasons for any selectivity observations. The inclusion of these guests was, in most cases, found to be as a result of interactions between host and guest species, which included π∙∙∙π stacking, C‒H∙∙∙π, hydrogen bonding and various other short contact types. Guest compounds were accommodated in either cavities or channels and this was dependent on the nature of the guest. The host molecule conformations showed H1 to adopt a bent tricyclic fused ring system with the N atoms of the linker in a synclinal arrangement, while in complexes with H2, the fused ring system was near-planar and the N atoms adopted an antiperiplanar geometry. These key differences resulted in a very ordered host‒host packing for H2 as a direct result of the more planar O-containing ring and linear linker; for H1, on the other hand, the buckled S-containing ring and gauche-orientated N atoms resulted in a less ordered packing, which ultimately related to the differences in the behaviour of the two host species. Hirshfeld surface analyses, in general, did not provide much information to explain the host selectivities, with the exception of complexes containing the five-membered ring guest heterocyclics. Thermal analyses were completed on all suitable host-guest complexes and, in most cases but not all, the onset and peak temperatures (terms Ton and Tp, respectively) were related to the thermal stability of the complexes, which were used to rationalize the selectivities of these host compounds.
- Full Text:
- Date Issued: 2019
Assessment of the host potential of TETROL [(+)-(2R,3R)-1,1,4,4- tetraphenylbutane-1,2,3,4-TETROL] for the separation of isomers and related compounds
- Authors: Dorfling, Sasha-Lee
- Date: 2018
- Subjects: Chemistry, Organic , Thermal analysis Hydrogen bonding
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/22060 , vital:29817
- Description: In this study, we investigated the potential of a host compound, (+)-(2R,3R)-1,1,4,4- tetraphenylbutane-1,2,3,4-tetrol (TETROL), for use in the separation of isomers and related compounds using host-guest chemistry. The synthesis of this host was carried out using a standard Grignard procedure, reacting naturally-occurring optically active tartaric acid with phenylmagnesium bromide. The feasibility of this host for separating isomers and structurally-related compounds was investigated by recrystallizing it from various potential cyclic, aromatic and aliphatic guest compounds. The extent of host inclusion and guest separation were determined using 1H-NMR spectroscopy and GCMS analyses. Competition studies were conducted to establish the selectivity of TETROL for the various guest species and whether this host would be able to discriminate between them. In this instance, the host was recrystallized from equimolar amounts of binary, ternary, quaternary or quinary mixtures of the guests present in each target study. Subsequent binary or ternary competitions were conducted where the molar ratios of the guest species were varied beyond equimolar, and the guest selectivity of TETROL thus evaluated by means of selectivity profiles. Further analyses included single crystal X-ray diffraction (SCXRD), thermal analysis and Hirshfeld surface analysis. Any crystalline inclusion complex formed between host and guest, with suitable crystal quality, was analysed using SCXRD in order to determine the nature of any significant host–guest interactions present. Thermogravimetric and differential scanning calorimetry experiments provided further insight into complex stability by analysing the thermal events experienced by the complexes as they were heated at 10 °C/min. The data obtained from Hirshfeld surface analyses were used to determine whether host selectivity and/or thermal stability of the complexes were related to the number and types of interactions, observed from SCXRD, between host and guest. The ability of TETROL to discriminate between related compounds was favourable. This host proved to have selective preference for aniline over its methylated derivatives, N-methylaniline and N,N-dimethylaniline. It was also selective for cyclohexylamine over cyclohexanol and cyclohexanone, and discriminated against the pyridine, piperidine and dioxane heterocyclics in favour of morpholine. Furthermore, this host was successful in the selective separation of isomers; for example, it selectively showed discrimination between the three toluidine isomers (p-toluidine > m-toluidine > o-toluidine) and the cresols (p-cresol > m-cresol > o-cresol). Each guest mixture was selected based on data from experiments using either the industrial significance of its separation or because the mixture would add to the knowledge base of the host compound’s preferences and selectivities. In a separate study, TETROL and its derivative, (–)-(2R,3R)-2,3-dimethoxy-1,1,4,4- tetraphenylbutane-1,4-diol (DMT), were also allowed to compete for the inclusion of the guest cyclohexanone, where TETROL demonstrated superior ability. This host, in addition, showed potential for the separation of cis- and trans- 2-methylcyclohexanol.
- Full Text:
- Date Issued: 2018
- Authors: Dorfling, Sasha-Lee
- Date: 2018
- Subjects: Chemistry, Organic , Thermal analysis Hydrogen bonding
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/22060 , vital:29817
- Description: In this study, we investigated the potential of a host compound, (+)-(2R,3R)-1,1,4,4- tetraphenylbutane-1,2,3,4-tetrol (TETROL), for use in the separation of isomers and related compounds using host-guest chemistry. The synthesis of this host was carried out using a standard Grignard procedure, reacting naturally-occurring optically active tartaric acid with phenylmagnesium bromide. The feasibility of this host for separating isomers and structurally-related compounds was investigated by recrystallizing it from various potential cyclic, aromatic and aliphatic guest compounds. The extent of host inclusion and guest separation were determined using 1H-NMR spectroscopy and GCMS analyses. Competition studies were conducted to establish the selectivity of TETROL for the various guest species and whether this host would be able to discriminate between them. In this instance, the host was recrystallized from equimolar amounts of binary, ternary, quaternary or quinary mixtures of the guests present in each target study. Subsequent binary or ternary competitions were conducted where the molar ratios of the guest species were varied beyond equimolar, and the guest selectivity of TETROL thus evaluated by means of selectivity profiles. Further analyses included single crystal X-ray diffraction (SCXRD), thermal analysis and Hirshfeld surface analysis. Any crystalline inclusion complex formed between host and guest, with suitable crystal quality, was analysed using SCXRD in order to determine the nature of any significant host–guest interactions present. Thermogravimetric and differential scanning calorimetry experiments provided further insight into complex stability by analysing the thermal events experienced by the complexes as they were heated at 10 °C/min. The data obtained from Hirshfeld surface analyses were used to determine whether host selectivity and/or thermal stability of the complexes were related to the number and types of interactions, observed from SCXRD, between host and guest. The ability of TETROL to discriminate between related compounds was favourable. This host proved to have selective preference for aniline over its methylated derivatives, N-methylaniline and N,N-dimethylaniline. It was also selective for cyclohexylamine over cyclohexanol and cyclohexanone, and discriminated against the pyridine, piperidine and dioxane heterocyclics in favour of morpholine. Furthermore, this host was successful in the selective separation of isomers; for example, it selectively showed discrimination between the three toluidine isomers (p-toluidine > m-toluidine > o-toluidine) and the cresols (p-cresol > m-cresol > o-cresol). Each guest mixture was selected based on data from experiments using either the industrial significance of its separation or because the mixture would add to the knowledge base of the host compound’s preferences and selectivities. In a separate study, TETROL and its derivative, (–)-(2R,3R)-2,3-dimethoxy-1,1,4,4- tetraphenylbutane-1,4-diol (DMT), were also allowed to compete for the inclusion of the guest cyclohexanone, where TETROL demonstrated superior ability. This host, in addition, showed potential for the separation of cis- and trans- 2-methylcyclohexanol.
- Full Text:
- Date Issued: 2018
Investigation of the potential separation of isomers and related compounds using host compound (2R,3R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol
- Authors: Pohl, Pieter Lourens
- Date: 2018
- Subjects: Chemistry, Organic , Clathrate compounds Thermal analysis
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23131 , vital:30432
- Description: In this study, we investigated the potential of a host compound, (2R,3R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT), for use in the separation of isomers and related compounds using host-guest chemistry. The title molecule, DMT, is composed of a butane chain bearing hydroxyl moieties on the terminal carbons and methoxy moieties on the two internal, chiral carbon atoms. In addition, there are two phenyl rings on each of the terminal carbons. The synthesis of DMT was carried out by subjecting the diester of naturally-occurring optically active tartaric acid to a Grignard reaction employing phenylmagnesium bromide. Subsequent methylation of the secondary hydroxy groups with dimethyl sulfate afforded DMT. The resulting host molecule was investigated for its inclusion abilities by crystallizing with a number of potential aromatic, aliphatic and alicyclic guests such as toluene, aniline, nitrobenzene, anisole, cyclohexane, ethyl acetate and ethanol. Host:guest ratios were determined by means of 1H-NMR spectroscopy. Of the hosts investigated, DMT favoured a host:guest ratio of 2:1 for all included guests investigated. It complexed with most non-polycyclic aromatic guests as well as cyclohexane, cyclohexene and cyclohexanone. It was not able to include short chain or branched alcohols such as methanol, ethanol or 2-propanol, or other hetero-aliphatic or hetero- cyclic compounds such as diethyl ether, acetonitrile, morpholine or dioxane. Competition inclusion experiments were performed in which DMT was crystallized from equimolar and non-equimolar binary, ternary and quaternary mixtures of appropriate guests. The mother liquor mixtures and resultant crystals were subjected to GC-MS analysis in order to determine whether DMT showed discriminatory behaviour towards the guests from a mixture. It was observed that DMT was able to differentiate between related compounds, for example, the host preferred to include N,N-dimethylaniline compared with N-methylaniline and aniline. The host also discriminated against isomers, for example, p-xylene was preferentially included over o-xylene and m-xylene, while o-cresol was included in preference to p-cresol and m-cresol. Single crystal X-ray analysis was used to investigate the host–guest interactions responsible for guest inclusion, as well as to discern reasons for the host’s selective behaviour. X-ray data for the inclusion complexes indicated that each complex was isostructural, crystallizing in the monoclinic C2 crystal system. A pair of 1,3- and 2,4- intramolecular hydrogen bonds, as well as intramolecular non-classic hydrogen bonds between adjacent ortho-aromatic hydrogens and hydroxy moieties was a significant stabilizing factor for the geometry of the host. Guests were held within discrete cavities in the crystal lattice, and experienced only π–π stacking, CH–π interactions and other short contacts. Thermal analyses were used to determine the relative thermal stabilities of the complexes, and these data compared to the selectivity preference of DMT, obtained from the competition experiments, in order to assess the reasons for any discriminatory behaviour. Finally, Hirshfeld surface analysis data was used to determine if the thermal stability of the complexes was related to the number and type of interactions between host and guest.
- Full Text:
- Date Issued: 2018
- Authors: Pohl, Pieter Lourens
- Date: 2018
- Subjects: Chemistry, Organic , Clathrate compounds Thermal analysis
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23131 , vital:30432
- Description: In this study, we investigated the potential of a host compound, (2R,3R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT), for use in the separation of isomers and related compounds using host-guest chemistry. The title molecule, DMT, is composed of a butane chain bearing hydroxyl moieties on the terminal carbons and methoxy moieties on the two internal, chiral carbon atoms. In addition, there are two phenyl rings on each of the terminal carbons. The synthesis of DMT was carried out by subjecting the diester of naturally-occurring optically active tartaric acid to a Grignard reaction employing phenylmagnesium bromide. Subsequent methylation of the secondary hydroxy groups with dimethyl sulfate afforded DMT. The resulting host molecule was investigated for its inclusion abilities by crystallizing with a number of potential aromatic, aliphatic and alicyclic guests such as toluene, aniline, nitrobenzene, anisole, cyclohexane, ethyl acetate and ethanol. Host:guest ratios were determined by means of 1H-NMR spectroscopy. Of the hosts investigated, DMT favoured a host:guest ratio of 2:1 for all included guests investigated. It complexed with most non-polycyclic aromatic guests as well as cyclohexane, cyclohexene and cyclohexanone. It was not able to include short chain or branched alcohols such as methanol, ethanol or 2-propanol, or other hetero-aliphatic or hetero- cyclic compounds such as diethyl ether, acetonitrile, morpholine or dioxane. Competition inclusion experiments were performed in which DMT was crystallized from equimolar and non-equimolar binary, ternary and quaternary mixtures of appropriate guests. The mother liquor mixtures and resultant crystals were subjected to GC-MS analysis in order to determine whether DMT showed discriminatory behaviour towards the guests from a mixture. It was observed that DMT was able to differentiate between related compounds, for example, the host preferred to include N,N-dimethylaniline compared with N-methylaniline and aniline. The host also discriminated against isomers, for example, p-xylene was preferentially included over o-xylene and m-xylene, while o-cresol was included in preference to p-cresol and m-cresol. Single crystal X-ray analysis was used to investigate the host–guest interactions responsible for guest inclusion, as well as to discern reasons for the host’s selective behaviour. X-ray data for the inclusion complexes indicated that each complex was isostructural, crystallizing in the monoclinic C2 crystal system. A pair of 1,3- and 2,4- intramolecular hydrogen bonds, as well as intramolecular non-classic hydrogen bonds between adjacent ortho-aromatic hydrogens and hydroxy moieties was a significant stabilizing factor for the geometry of the host. Guests were held within discrete cavities in the crystal lattice, and experienced only π–π stacking, CH–π interactions and other short contacts. Thermal analyses were used to determine the relative thermal stabilities of the complexes, and these data compared to the selectivity preference of DMT, obtained from the competition experiments, in order to assess the reasons for any discriminatory behaviour. Finally, Hirshfeld surface analysis data was used to determine if the thermal stability of the complexes was related to the number and type of interactions between host and guest.
- Full Text:
- Date Issued: 2018
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