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Title: Cyclic organo-boron compounds
Author: Pearn, Elizabeth Joy
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1963
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The new boron heterocycle, 2-chloro-1,3,2-dioxaborinan has been prepared and characterised. Nucleophilic substitution of the reactive halogen in this compound resulted a series of new compounds with the dioxaborinan skeleton. The stability of 2-chloro-1,3,2-dioxaborinan at 100°C has been studied and the catalytic effect of traces of Lewis acid on the stability has been noted. The cyclic compound is shown to have greater thermal stability than the corresponding acyclic compounds. The mechanism for the pyrolysis has been established. Replacement of the reactive halogen in the compound by alkoxyl groups gave a series of cyclic esters. The disproportionation of these esters has been shown to be related to the volatility of the corresponding trialkyl borate. The reaction of 2-chloro-1,3,2-dioxaborinan with amines has been studied. Pyridine has been shown to give a molecular complex but reaction with triethylamine gave a novel reaction. It is noted that the 2-chloro-1,3,2-dioxaborinan and related compounds are not associated in dilute benzene solution whereas the dioxaborolans are highly associated. The effect of the degree of association on the thermal stability of dioxaborolans has been examined. The analogous sulphur compounds, 2-chloro-1,3,2-dithioborolan and 2-chloro-1,3,2-dithioborinan have been synthesized and shown to be monomeric in benzene solution. The stability of these compounds at 100°C has been investigated. The infra-red spectra of these new organo-boron heterocycles have been recorded and a qualitative analysis of these spectra has been attempted. A linear relationship between the asymmetric and symmetric B-0 vibrations in the dioxaborinan series has been found. The high frequencies assigned to the B-0 vibrations suggest that the dioxaborinans are internally stabilized by back co-ordination of the oxygen to boron. The position of the B-Cl stretching vibration is discussed with reference to that located for 2-chloro-1,3,2-dioxa-borolan and the effect of association on the B-0 and B-Cl vibrations in this compound is discussed. A survey has been made of the possibility of synthesizing a molecule containing a B-B link using a Wurtz-type reaction. Wherever possible a general comparison between acyclic and cyclic compounds has been made. The relative stabilityof five-and six-membered rings in both the oxygen and sulphur heterocycles is also discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Organic Chemistry