Abstract
This thesis is concerned with the remediation of acid herbicides by the use of calix[4]arene based receptors attached to silica. Following a review on the chemistry and uses of herbicides, main aspects of Supramolecular Chemistry (with particular emphasis on calixarene receptors) and previous work in the area, the main objectives of the thesis are outlined. Thermodynamic parameters of solution of 5,11,17,23-tetra-rer/-butyl-25,27-bis(ethylamine)ethoxy-26,28-dihydroxy calix[4]arene (receptor) are reported. Several techniques were used to investigate the interaction of this macrocycle with the acid herbicides. Thus from 1H-NMR studies on 5,11,17,23-tetra-tert-butyl-25,27-bis(ethylamine)ethoxy-26,28-dihydroxy calix[4]arene and several acid herbicides in CD3CN and CD3OD at 298 K, it is concluded that the tertiary amino groups on the pendant arms of the ligand provide the active sites of interaction with these acids. Conductometric measurements were performed with the aim of determining i) the composition of the ligand-herbicide interaction and to gain information regarding the strength of interaction of the ligand with acid herbicides in acetonitrile, methanol and N,N-dimethylformamide at 298.15 K. ii) the degree of association of these acids in the non-aqueous media. Conductance data were used to calculate the equilibrium constants (proton transfer, association and overall constant) resulting from the interaction process between the calix[4]arene amino derivative and the herbicides. In doing so, the mathematical treatment developed by Danil de Namor and co-workers to derive equilibria data for a 1:1 process was extended for processes involving interactions between one unit of macrocycle and two units of herbicide. Lower rim calix[4]arene amino derivatives (partially and fully substituted) were attached onto a silica-based solid support. Following the characterisation of modified silicas, the ability of these materials to remove acid herbicides from water was tested. The enthalpy associated with the extraction process was calorimetrically determined. Final conclusions and suggestions for further research in this area are given.