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This work consists of a thermodynamic study of liquid binary mixtures of the type polar + non-polar. The polar components were chosen to be members of the n-a1kanenitrile series of compounds whereas the non-polar components are members of the n-alkane series. The experimental part of the work includes: a) the determination of upper critical solution temperatures of binary mixtures of ethanenitri1e, propanenitri1e, and n-butanenitrile with n-a1kanes in order to establish the limits of liquid-liquid miscibility; b) the measurement of the gas-liquid critical locus (pc_Tc_X) for the six mixtures ethanenitrile + n-pentane to n-decane. c) measurement of excess enthalpies of mixing at 298.15 K for propanenitrile + n-pentane to n-heptane; n-butanenitrile + n-hexane, + n_octane, + n-dodecane, and + n-tetradecane. d) and the measurement at 303.15 K of excess volumes of mixing for propanenitri1e + n-pentane to n-octane; n-butanenitrile + n-pentane, + n-hexane, +n-octane, +n-decane, + n-dodecane, +n-tetradecane; and n-hexanenitrile + n-hexane. Although the experimental results are readily related to the molecular size of the studied substances statistical theories of fluids are used for a more formal interpretation. The Scatchard - Hildebrand theory with a modification is used to predict upper critical solution temperatures. The now widely used van der Waals' one and two-fluid theories are used here to predict excess enthalpies and volumes of mixing. The gas-liquid critical properties are interpreted using a first-order theory together with the Van der Waa1s' equation of state. The predicted results show in each case satisfactory agreement with experiment, furthermore, information is obtained on the relative strength of the unlike interaction between the molecules of the mixtures studied.

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Under dry, anaerobic conditions TiO₂ photoredox catalysis has been directed away from oxidative/degradative chemistry. Instead, carboxylic acid photoredox reactions resulted in carbon-carbon bond forming processes. High yields of radical homodimers were obtained from TiO₂ treatment of carboxylic acids alone. “Benzyl-type” radicals in particular performed very well in this system. Attempts at carrying out hetero-dimerisations were unsuccessful as it is thought that the differing rates of formation of radicals at the titania surface precludes the formation of cross-coupled products. A straightforward reaction mechanism involving hole- capture by the carboxylate at the catalyst surface has been put forward and is supported by literature precedent. Intramolecular dimerisations of di-carboxylic acids have been applied to the preparation of macrocycles but with disappointing yields being recorded. Photoredox reactions employing TiO₂ and carboxylic acids, under dry anaerobic conditions, led to several types of C-C bond forming processes with electron deficient alkenes. The efficiency of alkylation varied appreciably with substituents in the carboxylic acids. The reactions of aryloxyacetic acids with maleimides resulted in a cascade process in which a pyrrolo-chromene derivative accompanied the alkylated succinimide. Selectivity for one or other of these products could be tuned to some extent by employing the photoredox catalyst in different conditions. An array of different catalyst forms was trialed for efficiency and ease of use. The proposed mechanism, involving hole capture at the TiO₂ surface by the carboxylates followed by CO₂ loss, was supported by EPR spectroscopic evidence of the intermediates. Deuterium labelling indicated the titania likely donates protons from surface hydroxyl groups as well as supplying electrons and holes thus acting as both a catalyst and a reaction partner. Suitably functionalised carboxylic acids undergo a previously unknown photoredox reaction when irradiated with UVA in the presence of maleimide. Maleimide was found to synergistically act as a radical generating photoxidant and as a radical acceptor, negating the need for a photoredox catalyst. Modest to excellent yields of the product chromenopyrroledione, thiochromenopyrroledione and pyrroloquinolinedione derivatives were obtained in thirteen preparative photolyses. In-situ NMR spectroscopy was used to study each reaction. Reactant decay and product build-up were monitored, enabling reaction profiles to be plotted. A plausible mechanism, whereby photo-excited maleimide acts as an oxidant to generate a radical ion pair, has been postulated and is supported by UV-vis. spectroscopy and DFT computations. The radical-cation reactive intermediates were also characterised in solution by EPR spectroscopy.

This thesis details the research carried out into the reaction of epoxides with various heterocumulenes, forming five-membered heterocyclic products. The catalyst systems used are numerous forms of metal salen compounds. It begins with the introduction, which summarises the body of literature outlining the reactions of epoxides with heterocumulenes. Previously developed catalytic systems are discussed along with any mechanistic studies that have taken place. A conclusion regarding the most active systems for each reaction is given, which will provide an understanding of the requirements needed to be a successful catalyst. The results and discussion section is divided into four main chapters. It begins with a study into forming novel one-component catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide. Four new catalysts are conceived and tested on this reaction, but with very limited success due to the level of steric hindrance present in the backbone of the salen ligands. The catalysts that are successfully synthesised are then examined for other reactions for which they may be suited, namely the synthesis of thiocarbonates from epoxides and carbon disulphide and asymmetric cyanohydrin synthesis. Both reactions gave mixed results. The activity exhibited for thiocarbonate synthesis ranged from 0-100 % conversion, while the asymmetric induction of the cyanohydrin products was disappointing (18-79 % ee). Both proving to be less active than previously devised salen-based systems. The next chapter describes a mechanistic exploration of previously developed monometallic and bimetallic catalyst systems for the reaction of epoxides with isocyanates. The experiments result in a proposed mechanism for this reaction which is ii distinct from those proposed for similar reactions of other heterocumulenes. This work is followed by variable temperature kinetic studies which aimed to give a comparison of the activation parameters of the reactions of epoxides with carbon dioxide, carbon disulphide and isocyanates catalysed by aluminium salen complexes to explain the relative reactivity of each heterocumulene. The results found that the reactions of isocyanates and carbon disulphide had relatively high enthalpies of activation and therefore the catalyst systems could potentially be improved by using metals with more Lewis acidic character. The last two chapters of the results and discussion cover the development of new metal salen catalyst systems for both the synthesis of oxazolidinones and thiocarbonates from epoxides by reaction with isocyanates and carbon disulphide respectively. The development of these systems was based on the results obtained from the variable temperature kinetics studies carried out in the previous chapter. The results show that new, highly active catalysts for these transformations were developed by varying the metal at the centre of the salen ligand. Use of these systems allowed catalyst loading to be decreased, in some cases by up to a factor of ten (from 5 mol% to 0.5 mol%). Kinetic studies are also included which provided the information required to propose mechanisms for the reactions. The thesis is completed with the experimental section, which provides details of all procedures (both synthetic and kinetic), along with all physical and spectral data from isolated compounds. This is then followed by an appendix of all kinetic data collected.

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