Investigation into the bromination of calixarenes
| dc.contributor.advisor | Arnott, Gareth E. | en_ZA |
| dc.contributor.author | Snayer, Trégen Michael | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science | en_ZA |
| dc.date.accessioned | 2020-08-20T20:05:06Z | en_ZA |
| dc.date.accessioned | 2021-02-01T07:53:49Z | en_ZA |
| dc.date.available | 2020-08-20T20:05:06Z | en_ZA |
| dc.date.available | 2021-02-01T07:53:49Z | en_ZA |
| dc.date.issued | 2020-08 | en_ZA |
| dc.description | Thesis (MSc)--Stellenbosch University, 2022. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: Calixarenes are large bowl-shaped molecules consisting of an upper rim, lower rim, and methylene bridges. The most interesting feature of these compounds is that asymmetric modifications of these regions allows for the formation of inherent chiral calixarenes. Key to the formation of these compounds are the brominated calixarenes as the bromine group can easily be substituted via electrophilic aromatic substitution reactions. Most methods for achieving their synthesis involve debutylation of p-tertbutylcalixarene followed by careful addition of molecular bromine or N-bromosuccinimide. Recently, our group has discovered that bromination of p-tert-butylcalix[4]arene using chlorinated solvents show potential for the synthesis of ipso-brominated calix[4]arenes. This thesis reports the results of an investigation into the ipso-bromination of p-tert-butylcalix[4]arene. Initial attempts were made to synthesise mono- and dibromo calixarenes, but unfortunately efficient synthetic procedures could not be produced for these compounds. In the case of the monobromo compound, the synthesis proved challenging due the formation of spirocalixarenes when using chloroform as solvent while attempts in dichloromethane led to over-brominated products. Good conversion was achieved for the dibromo calix[4]arenes, however this always gave a mixture of distal and proximal calix[4]arenes with poor selectivity for either compound observed. Purification for all of these compounds also proved highly challenging. Successful synthesis of tri- and tetrabromo calix[4]arene was achieved with the pure compounds isolated in 60-64% and 85-90% yields respectively. Both compounds were found to be sensitive to temperature with the control of temperature key to achieving reproducibility. The role of light was carefully investigated as it was shown to heavily affect the ipso-bromination process. Reactions performed under a light source often resulted in benzylic bromination of toluene consequently hindering the ipso-bromination reaction. This led to the synthesis of these compounds being performed in the absence of light. While toluene was shown to affect the bromination process in the presence of light, it appeared to promote this process in its absence. This led to an investigation into its role, however there was no information found in literature or through experimental studies that helped to explain this phenomenon. The influence of radicals was also investigated with it being shown that their promotion negatively effects the bromination reaction due to increased bromination of toluene. Attempts at radical trapping proved unsuccessful as the trap used in this study proved to be inadequate for the trapping of bromine radicals. Importantly, the results of this study show that bromination of p-tert-butylcalix[4]arene can afford ipsobrominated product through a one-step synthesis. | en_ZA |
| dc.description.abstract | AFRIKAANS OPSOMMING: Kaliksarene is groot bak-vormige molekules wat bestaan uit 'n bo- en onder-rand met metileen brûe. Die interessantste kenmerk van hierdie verbindings is dat asimmetriese modifikasie van hierdie streke die vorming van inherente chirale kaliksarene moontlik maak. Die broom groep van gebromineerde kaliksarene word beskou as noodsaaklik vir die vorming van hierdie verbindings aangesien dit maklik deur elektrofiliese aromatiese substitusie vervang kan word. Die mees algemene sintetiese roetes behels die debutilering van p-tert-butielkaliksareen gevolg deur die noukeurige toevoeging van molekulêre broom of N-bromosuksienimied. Ons groep het onlangs ontdek dat die bromering van p-tert-butielkaliks[4]areen in gechloreerde oplosmiddels die potensiaal toon vir die sintese van ipso-gebromineerde kaliks[4]arene. Hierdie tesis berig resultate van 'n ondersoek na die ipso-bromering van p-tert-butielkaliks[4]areen. Aanvanklik is pogings aangewend om mono- en dibromo-kaliks[4]arene te sintetiseer, maar ongelukkig kon doeltreffende sintetiese prosedures vir hierdie verbindings nie teweeggebring word nie. Sintese van die enkel-gebromineerde verbinding blyk om gekompliseer te word deur die vorming van spiro-kaliksarene wanneer chloroform as oplosmiddel gebruik word, terwyl pogings in ʼn dichloormetaan oplossing tot oorgebromineerde produkte lei. Ten spyte daarvan dat goeie omskakeling vir die dibromo-kaliks[4]arene volbring is, is 'n onselektiewe mengsel van distale en proksimale kaliks[4]arene opgelewer wat die suiwering van die produkmengsel veeleisend gemaak het. Suiwer tri- en tetrabromo-kaliks[4]arene is suksesvol gesintetiseer en geïsoleer in opbrengste van 60-64% en 85-90%, onderskeidelik. Albei verbindings is temperatuurgevoelig en die bestuur van temperatuur was belangrik vir herhaalbaarheid. Die rol van lig is noukeurig ondersoek aangesien daar gevind is dat die ipsobrominering reaksie hoogs ligsensitief is. Reaksies wat onder 'n ligbron uitgevoer is het dikwels die bensielbromering van tolueen tot gevolg gehad wat die ipso-brominering van p-tert-butielkaliks[4]areen belemmer het. Reaksies is dus in die donker uitgevoer. Alhoewel dit bevind is dat tolueen die bromering reaksie negatief beïnvloed in die teenwoordigheid van lig, blyk dit dat tolueen die reaksie bevorder in die afwesigheid van lig. Hierdie verskynsel kon egter nie deur opvolg eksperimente of deur die bestudering van seldsame gevalle uit die literatuur uitgepluis word nie. Daar is verder bevind dat die teenwoordigheid van radikaal verbindings die bromering van p-tertbutielkaliks[ 4]areen kniehalter deurdat die bromering van tolueen bevorder word. Pogings van “radical trapping” was onsuksesvol aangesien dit bevind is dat vangmiddel wat in hierdie studie gebruik is onvoldoende is vir die vasvang van broom-radikale. Kortom toon hierdie studie dat ipso-gebromineerde produkte van p-tert-butielkaliks[4]areen deur middel van 'n een-stap sintese volbring kan word. | af_ZA |
| dc.description.version | Masters | en_ZA |
| dc.format.extent | xiv, 84 pages : illustrations | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/109400 | en_ZA |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Calixarenes -- Synthesis | en_ZA |
| dc.subject | Bromination -- Synthesis | en_ZA |
| dc.subject | Synthetic chemicals industry | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | Investigation into the bromination of calixarenes | en_ZA |
| dc.type | Thesis | en_ZA |
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