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.
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- Date Issued: 2018
Novel camphor derivatives as potential asymmetric alkylation auxiliaries
- Authors: Skiti-Mama, Neliswa
- Date: 2008
- Subjects: Alkylation , Chemistry, Organic
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10372 , http://hdl.handle.net/10948/1077 , Alkylation , Chemistry, Organic
- Description: The investigation has been focussed on the synthesis and characterisation of camphor-derived chiral auxiliaries that incorporate two camphor skeletons and an evaluation of their stereodirecting potential in ester α-benzylation reactions. Two regioisomeric camphorquinone-derived monoketals were synthesised and identified by 1D- and 2D-NMR, and X-ray crystallography. The stereo-directing potential of the alcohols that resulted from reduction of these ketones as chiral auxiliaries in the alkylation of carboxylate ester derivatives has been studied. The diastereoselectivities shown by NMR spectroscopy range from 14- 30 % d.e. for (1R,2 S, 3R) -2 ,2-[ (1R, 2 S, 3R) -bornane-2,3-dioxy] - bornan-3-ol and 68-74 % d.e. for (1R, 2S ,3R) -3 ,3-[ (1R, 2S ,3R) - bornane-2, 3 -dioxy]bornan-2-ol with selectivities that correlate with the size of the alkyl group in the ester moiety. Trapping of the enolates generated from (1R, 2S ,3R)-2, 2 -[(1R,2 S, 3R) -bornane- 2,3-dioxy]bornan-3-yl propanoate afforded both E- and Z-silyl ketene acetal derivatives in the ratio of 64:36 confirming the formation of both possible enolate structures during enolization. Chiral auxiliaries containing a hemiaminal ether blocking group as well as two chiral alcohols containing monothio-ketal blocking groups have also been synthesised. α-Benzylation of their corresponding propanoate esters afforded the alkylated product with disappointingly low diastereos electivities. Asymmetric reduction of α-keto esters attached to (1R, 2 S, 3R) - 2,2- [ (1R,2 S, 3R) -bornane-2, 3 -dioxy]bornan-3-ol and (1R, 2S ,3R) - 3,3- [ (1R,2 S, 3R) -bornane-2, 3 -dioxy]bornan-2-ol with metal hydrides proceeded with selectivities of up to 30 % d.e. Modelling of the keto ester derivatives at DFT levels provided useful insights into possible conformations adopted by the two α-keto esters and hence the preferred face of attack by metal hydride during reduction.
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- Date Issued: 2008
Synthesis, properties and reactions of Novel Quinone Methides
- Authors: Taljaard, Jana Heloïse
- Date: 2007
- Subjects: Quinone , Chemistry, Organic
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10408 , http://hdl.handle.net/10948/616 , Quinone , Chemistry, Organic
- Description: Novel p-quinone methides have been synthesized by the dealkylation of 5-(p-alkyloxyaryl)- 10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-ols and related compounds. Aspects of the dealkylation reaction were investigated using computational methods in order to identify possible intermediates and postulate reasons for the observed reactivity patterns. This included studying the effect of varying the size of the central B-ring, changing the alkyloxy group, and altering the substitution pattern on the parent alcohols. We have assessed the relative energies of reaction intermediates and have also evaluated the influence of factors such as charge delocalisation, LUMO properties of the carbocations and thermodynamic factors on the dealkylation reaction. The use of different dealkylating reagents was also briefly investigated. Demethylation of 1,3- dimethyl-11-(4-methoxyphenyl)-6,11-dihydrodibenzo[b,e]oxepin-11-ol with pyridine hydrochloride led to acid-catalyzed ring-contraction of the parent alcohol to form a novel substituted anthraquinone, 9-(4-hydroxyphenyl)-1,3-dimethyl-anthracen-10-(9H)-one, in good yield. The general reactivity of the p-quinone methides of interest to us was explored by subjecting these compounds to reaction with a range of nucleophiles (bases, Grignard reagents and alcohols). A range of aryl Grignard reagents were reacted with the p-quinone methides, with the main product isolated in almost all cases being the aryl-coupled 1,2-addition product. The nucleophilic addition reactions of alcohols were supported by a computational study and a probable reaction mechanism has been postulated. A base-catalyzed rearrangement is proposed to account for the formation of products in which dehydrogenation of the ethane bridge was observed. These studies showed that in these p-quinone methides, chemical reactivity is strongly influenced by steric crowding, resulting in reversal of the normal 1,2- vs. 1,6- selectivities expected for nucleophilic addition. The ketalization process was explored further using diols and thiols. Products analogous to those obtained with the monohydric alcohols resulted from the diols, along with a series of novel bis-ethers. A range of miscellaneous reactions of 4-(dibenzo[a,d]cycloheptan-5-ylidene)cyclohexa-2,5,- dienone and related systems were investigated. Functionalization by epoxidation, dichlorocarbenation and Diels-Alder reactions, photochemical and [2+2] cycloaddition were attempted and reduction and oxidation reactions were also explored. Photochemical demethylation of an ortho-methoxyl substituent on the p-quinone methide system was observed to occur in good yield. The p-quinone methides underwent reductive coupling in the presence of Zn/AlCl3. The electronic spectra of highly conjugated carbocations were obtained and their potential as novel dyes evaluated. A low-temperature Grignard exchange reaction followed by spontaneous cyclization upon workup, was successful in synthesizing the lactone, spiro[10,11- dihydro-5H-dibenzo[a,d]cyclohepten-(3’,4’H)-phenyl-5,2’(5’H)-furan-5’-one], in one step from the starting ketone. A novel seven-membered Malachite Green dye analogue, 11-(4- dimethylamino-phenyl)-3-morpholin-4-yl-6,11-dihydro-dibenzo[b,e]oxepin-11-ol, was also synthesized and its electronic spectra compared to that of the unannulated Malachite Green dye series. All novel compounds synthesized were characterized using NMR, IR and HRMS-analysis.
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- Date Issued: 2007
Intersolid pyrotechnic reactions of silicon
- Authors: Rugunanan, Rajan Anil
- Date: 1992
- Subjects: Thermochemistry , Thermal analysis , Chemistry, Analytic , Chemistry, Organic , Silicon
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4527 , http://hdl.handle.net/10962/d1015571
- Description: A study of the role of different oxidants with silicon as the fuel in simple binary pyrotechnic compositions is reported. Several oxidants were examined, but only three (Sb₂0₃, Fe₂0₃ and Sn0₂) satisfied the restrictions that the combustion temperatures should be below the melting point of platinum/rhodium thermocouples (1760°C), that burning rates should not exceed the response of the thermocouples, and that burning should occur without significant mass-transport. A fourth oxidant, KN0₃, was selected on account of its low melting point and general importance as a pyrotechnic oxidant. The oxidation of silicon in the presence of either Sb₂0₃ or KN0₃ could be identified from thermal analysis curves. No thermal events were noted when Si/Sn0₂ and SiFe₂0₃ compositions were heated under similar conditions. The oxidation of Si powder in oxygen was also studied. All four binary systems sustained burning over a reasonably wide range of compositions. The range of burning rates measured (2 to 35 mm s⁻¹) depended on the oxidant used. Fe₂0₃ and Sb₂0₃ gave slow burning mixtures compared to Sn0₂ and to KN0₃ compositions with a high Si content. Burning rates generally increased with increasing specific surface area of silicon, but decreased in the presence of inert diluents and moisture. The burning rates of the Si/Fe₂0₃ and Si/Sn0₂ systems increased with increasing compaction of the samples. Kinetic parameters derived from the temperature proftles recorded during combustion were generally low (6 to 37 kJ mol⁻¹). This is in keeping with proposals that burning is diffusion controlled. The values of kinetic parameters derived from thermal analysis curves were considerably greater ( > 250 kJ mol⁻¹). Two other fuels, FeSi₇ and CaSi₂, gave similar thermal analysis curves when used instead of silicon. There were considerable differences in the burning rates for binary mixtures of these fuels compared to silicon. Ternary systems with two fuels or two oxidants showed that only limited interaction occurs during thermal analysis. The use of a second fuel or oxidant did, however, modify the burning behaviour considerably. Other techniques used in this study to probe the details of the reaction processes included bomb calorimetry, measurement of thermal conductivities, infrared spectroscopy, X-ray diffraction and scanning electron micoscropy.
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- Date Issued: 1992