Homolytic and Heterolytic Reactions of Organic Peroxides and Organic Sulphides and their Application to the Structural Characterisation of Polymer Networks

Abstract

Very few techniques exist to study complex chemical structures in which polymer chains are joined by peroxide and sulphur bridges. One of the more successful techniques viz.the use of chemical probes, has its limitations, consequently the objective in this thesis is to investigate the reactions of nucleophiles with organic peroxides and disulphides with a view towards extending the range of nucleophiles suitable for use as chemical probes. Triphenylphosphine and sodium dialkyl phosphites react in a well established manner with disulphides and in view of the similar chemical behaviour of oxygen and sulphur analogues, these two nucleophiles were initially selected for development as chemical probes for the structural elucidation of oxidised polymer networks. A study of the reactions of cyclic phosphoramidites with alkenyl disulphides has been carried out with the aim of replacing triphenylphosphine by a nucleophile requiring shorter reaction times. Finally, the reactions of Grignard reagents with disulphides and peroxides were observed since it was expected that this group of nucleophiles would be very effective in cleaving 0-0 and S-S bonds. It has been found that reaction of triphenylphosphine with cyclic allylic peroxides involves a SNi ’ rearrangement similar to that involved in the corresponding reactions of alkenyl disulphides; reaction of triphenylphosphine with acyclic allylic peroxides is complex and an allylic rearrangement does not appear to be involved. In the absence of steric hindrance, sodium dialkyl phosphites cleave peroxides to form a phosphate and sodium alkoxide. Grignard reagents cleave peroxides by two simultaneous reactions; disulphides are, however, more resistant to attack and only one reaction pathway is involved. Desulphuration of alkenyl disulphides by cyclic phosphoramidites involves an SNi' rearrangement but reaction does not yield the allylically rearranged monosulphide quantitatively.