Epoxidation of unsaturated esters
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Eight isomeric 9,12-diunsaturated c₁₈ methyl esters and seven isomers from two series of positionally isomeric methyl octadecacis, cis-dienoates, ie. 18:2 (5c12c - 8c12c) and (6c9c - 6c11c) were epoxidised to furnish monounsaturated monoepoxy esters and diepoxy esters. The monoepoxides and diepoxides were separated in pure form by column and thin layer chromatography, A comparative study was made of the chromatographic (TLC and GLC) behaviour and the NMR spectra of the unsaturated epoxy esters. TLC gave some indication of the position and geometry of the epoxy group and the nature of the unsaturated centre. The geometry of the epoxy group and the olefinic or acetylenic nature of the unsaturated centre were also revealed by GLC. 220 MHz NMR spectra, recorded for all unsaturated epoxy esters and diepoxy esters, exhibited up to nine more or less resolved signals which showed the long range deshielding influences of the ester group, the unsaturated centre, and the epoxy group. These influences were noticeable even when five methylene groups separated the deshielding group and the proton under consideration. Even though the NMR spectra did not give a complete structural analysis of the epoxy esters, they nevertheless revealed the geometry of the epoxy group as well as the nature of the unsaturated centre. The epoxides were convened to vicinal diether derivatives the mass spectrometric examination of which allowed the unambiguous location of the epoxy group and therefore also of the original double bond. Melting points of the vicinal dihydroxy acids, derived from all the twenty-six unsaturated epoxy esters by acetolysis and hydrolysis, were determined. The melting point differences between the various Isomers reflected such structural features as the geometry and position of the alpha-diol group and of the accompanying unsaturated centre. Two diepoxy esters, methyl cis-6,7, cis-9,10-diepoxystearate and methyl cis-8,9, cis-12,13 diepoxystearate, were reacted with boron trifluoride etherate. Instead of the expected dioxo derivatives, various cyclic ethers were obtained. A minor study was concerned with the hydroboration of various unsaturated long chain esters. The intermediate organoboranes were subjected to oxida.tion, protonolysis and coupling reactions to give in good yields hydroxy, oxo and hydroperoxy esters as well as hydrogenated and coupled products.
Thesis, PhD Doctor of Philosophy
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