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Title: Synthetic and mechanistic investigations in the formation and fission of cyclic acetals
Author: Cole, Ronald Frederick James
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1970
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The acid catalysed formation of acetals and ketals has been investigated. The synthesis of isopropylidene ketals was studied in detail by vapour phase chromatography so as to determine the reaction sequence. The ketals observed in this study have been prepared and further investigated by proton magnetic resonance and mass spectrometry. The formation of the acetals of D-glucitol and 1-deoxy-D-glucitol were studied previously and shown to exhibit kinetic and thermodynamic control. Similar control had been observed with 2-deoxy-D-glucitol and n-butyraldehyde giving the 1,3-acetal as the kinetically controlled product and the 3,4- acetal(s) as the thermodynamically controlled product. A detailed study of the mechanism of the formation of the mono-acetals of D-glucitol has been attempted. D-Glucitol is known to give the 2,3 acetal(s) as its kinetically controlled product. It would be expected that hemi-acetal formation, which must be the initial step in the reaction sequence, would occur at a primary hydroxyl and in particular at C1, so that initial cyclisation occurs with the formation of the 1,2-acetals or less probably the 1,3-acetal. Direct hemi-acetal formation has been possible with diols and triols but with hexitols alternative electrophiles have been used, chlorethers and vinylethers. These would seem to indicate hemiacetal formation is occurring at C1 hydroxyl, but that hemiscetals undergo intermolecular rearrangment to the subsequent products the 2,3 and 2,4 mono-acetals. This together with hydrolysis atudies on the 1,2;3,4;2,4;2,4;5,6 and 4,6 mono-acetals of D-glucitol, shows that it is unlikely that the 1,2 acetal or the others investigated are kinetic intermediates, since their stabilities towards hydrolysis are too high. Synthetic investigations on equi-molar solutions of n-butyraldehyde and D-gluoitol using various substrate concentrations, couple with a mathematical approach to the reaction mechanism suggest that the overall mechanism involving kinetic and thermodynamic control is goverened by both intra and an inter-molecular processes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Organic Chemistry