Diego-Castro, Michael John; (1999) Micellar Media and Catalysis of the Diels-Alder Reaction. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis is divided into eight chapters. Initially the Diels-Alder reaction is described from its mechanism using Frontier Molecular Orbital theory to rate enhancements of the reaction using Lewis acid catalysis, together with the use of chiral auxiliaries and the selectivity rules for the Diels-Alder reaction. Finally some solvent effects on the Diels-Alder reaction are reviewed. Surfactant and micelle solutions are then discussed, describing their physical properties and known effects of micellar solutions on selected organic reactions, as well as the study of micellar systems using light scattering and surface tension experiments. The first section of the results and discussion describes the study of Diels-Alder reactions of the acrylates and cyclopentadiene using solvents of varying polarity, highlighting the different yields and selectivities observed together with a rationalisation of the results. Rate acceleration was observed with the Diels-Alder reaction when performed in aqueous media, more so in the presence of surfactants at their critical micelle concentration (cmc). The rate acceleration was accompanied with higher endo/exo ratio when compared to organically mediated Diels-Alder reactions. Hydroquinone derivatives were shown to acts as dienophiles, participating in the Diels-Alder reactions in an aqueous media but not in organic solvents. The synthesis of surfactants derived from amino acids, together with measurements of some physical properties is given, including the determination of their cmc using methyl orange dye and surface tension experiments. Brief calculations are given to determine their aggregation number and micelle size of the phenylalanine-derived (86) (aggregation number: 23; micelle size: 43.6 Å2) and leucine-derived (89) surfactants (aggregation number: 19; micelle size: 54.6 Å2). Finally, the use of chiral surfactant in water as a reaction medium for the Diels-Alder reaction is described, including analysis of results, enantioselectivity observed, and determination of the direction of selectivity. The phenylalanine-derived (86) surfactant gave an enantiomeric excess (e.e.) of 16-18% in the exo isomer (74b), whilst the leucine-derived (89) surfactant gave a 15% e. e. with the endo isomer (74a) in the Diels-Alder reaction between nonyl acrylate and cyclopentadiene. A conclusion, summarising the key results to date and future work is outlined. A detailed description of the experimental procedures and summary of spectroscopic data are given in the experimental chapter. This includes a brief description of the physical chemistry studies on the synthetic chiral surfactants and the results obtained.

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