D.Sc. (Chemistry) / Two different projects with the central theme of oxidation are discussed, namely the ozonation of saturated hydrocarbons and the total synthesis of an unusual steroid glycoside. The oxidation of saturated hydrocarbons by ozone with the so-called dry ozonation technique was investigated. This study led to the development of improved procedures in which the rate, yield and selectivity of the reaction between ozone and various saturated substrates could be controlled. Subsequently the dry ozonation of a broadspectrum of long straight chain saturated hydrocarbons, including waxes, was investigated. Reaction with these highly unreactive compounds gave almost exclusively ketones as products in high yields. The average amount of keto functionalities in the products is dependent on the reaction conditions as well as the chain length of the substrate. Therefore, a reliable method has been developed for the selective oxidation of straight chain saturated hydrocarbons, a process that is of great chemical, industrial as well as commercial importance. The dry ozonation of various straight chain monoketo compounds was also studied. Poliketo compounds are mainly formed in these reactions. This investigation showed that keto functionalities in the substrates exert a deactivating effect on neighbouring methylene groups, so that oxidations do not take place at these positions. Therefore, it was possible to predict the product distribution formed during the dry ozonation of shorter chain length monoketo compounds (Cg) . An effective synthesis of an unusual steroid glycoside similar to orbicusides A-C, compounds that contain extraordinary carbohydrate and A-ring moieties, was developed. Oxidation reactions played a prominent role in this reaction sequence. A substantial effort was also directed towards obtaining the correct stereochemistry at the various stereocentres of the carbohydrate moiety. This facilitated ring closure to a final product that contained carbohydrate and A-ring moieties similar to orbicusides A-C. As a result of this work, a method was developed for the introduction of a vicinal cis-diol on the sterically hindered face of an alkene. This method is especially suited for substrates where acid labile functional groups are present.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:4330 |
| Date | 13 March 2014 |
| Creators | Dixon, John Thomas |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Johannesburg |
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