Browsing by Author "Snayer, Trégen Michael"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Investigation into the bromination of calixarenes
    (Stellenbosch : Stellenbosch University, 2020-08) Snayer, Trégen Michael; Arnott, Gareth E.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science
    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.