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Title: Some studies of the mechanisms of substitution and elimination reactions
Author: Parish, J. H.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1964
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Previous work has covered some displacement reactions, eliminations and olefine-rearrangements in the systems n-octane1, t-butylyclohexane2, and decalin3. In order to facilitate product-analyses in the last-named system, by the author and by future workers, two analytical problems were examined. The first problem was to devise a gas-liquid chromatographic method of separating the six alcohols (1-6) shown below. These alcohols are related to the possible substitution-products to be obtained form the solvolyses of trans-decalyl sulphonate esters. Out of a survey of three possible stationary phases, 1,1-oxydiglycerol was selected as the successful one. The second problem was the separation of the following olefines (7-12). Although only four of these olefines (7,8,9 and 11) are likely products from solvolyses of trans-decalyl compounds, the complete analysis of the octalins would be useful in the study of their equilibration. Previous work has involved the use of more than one partial analysis. In this instance a successful phase proved to be 1,2-bis(2'-cyanoethoxy)ethane. It was chosen from a survey of ten phases. An analytical method was devised whereby mixtures of decalyl acetates (after conversion to the corresponding alcohols via treatment with lithium aluminium hydride) or of octalins could be reliably analysed as percentages of products formed during a reaction in solution in acetic acid. It was found that a number of precautions were needed if the former method was to be reliable. Otherwise equilibration (presumably via an Oppenauer-Ponndorf mechanism) leads to the more stable (equatorial) epimer. The first application of the above methods was the analysis of products from the acetolysis of toluene-p-sulphonates of axial (5) and equatorial (6) trans-β-decalols. These compounds react more slowly than the corresponding compounds in the 4-t-butycyclohexyl system3g. The products from these latter reactions have recently been analysed2b. Comparison with these results indicated that the higher rate in the 4-t-butylcyclohexyl system is parelled by a higher olefine-yield in the equatorial case (but not in the axial one). A possible explanation of the slower rate of reaction of the decalyl compounds is that the hybridisation-change (sp3 to sp2) involved in these reactions of trans-decalin. Another factor contributing to the rate- and product- differences may be that non-chair forms are significant reacting conformations; possible non-chair forms are different for the two systems. A more detailed comparison of the products shows a much higher ratio of retention/inversion from the decalyl compounds. This is probably due to material rearranged to the other β-position. this ambiguity could be solved by repeating the work with resolved material. The effect of different cations (included as acetates to neutralise toluene-p-sulphonic acid formed during the reaction) on the reaction was found to be very small. The effects of the nature of leaving group and the temperature were small and in the same sense as was observed in other systems 1c, 2b. Streitwieser obtained kinetic evidence for sulphonate-exchange during the acetolysis of 2-actyl sulphonates4. Evidence was obtained that decalyl naphthalene-β-sulphonates are formed during the acetolyses of trans-β-decalyl tolune-p-sulphonates in the presence of potassium naphthalene-β-sulphonates. The extent was such that any effect on products would be negligibly small. Products were analysed from the acetolyses of the tolune-p-sulphonates of the trans-α-decalols (3 and 4). Kinetics3g and product-analysis from the axial epimer (3) suggest hydrogen-participation leading to the tertiary carbonium ion. the equatorial epimer is slow o react and the products contain material derived from a rearranged β-carbonium ion-pair, apparently similar to the one formed during the acetolysis of the tolune-p-sulphonate of the β-axial alcohol (5). A preliminary study of the reaction of trans-β-octalin (11) with solutions of toluene-p-sulphonic acid in acetic acid showed the reaction to be reduced in rate by tetrahydrofuran. An analysis of such acetylated material as was formed from this reduced reaction showed it to be largely axial. Nuclear magnetic resonance spectra of some decalyl compounds were recorded. Differences in chemical shifts for the proton marked (13) in pairs of epimers were in moderately good agreement with the value based on calculations of long-range shielding5.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available