Chemistry of hexafluorobut-2-yne
This thesis is concerned with the preparation and reactions of hexafluorobut-2-yne (H.F.B.). Attempts to improve the somewhat unsatisfactory literature method for preparing this acetylene were unsuccessful. However, the pyrolysis of perfluorocyclobutene over fluoride ion, a reaction first reported by a previous worker in this laboratory, has been developed to provide a new high yield route to H.F.B. Free radical additions to H.F.B. have been investigated and a series of novel adducts was obtained. The behaviour of H.F.B. was found to differ considerably from that of fluoroalkenes, which have been studied previously. A number of reactions of H.F.B. involving the use of caesium fluoride as an initiator have been studied. Copolymers of various compositions were obtained from reactions with acetylenic esters and several interesting co-oligomers were prepared from fluoroalkenes. The additions of a variety of nucleophiles to H.F.B. were investigated with a view to obtaining cyclic products. Most of these experiments gave polyhexafluorobut-2-yne as the only product but a reaction with sulphur did give a thiophene derivative. A reaction with dimethyl sulphoxide gave an interesting sulphonium ylid of surprisingly high thermal and chemical stability. A series of reactions was carried out in order to investigate some of the factors which influence the stereochemistry of nucleophilic addition to H.F.B. These experiments showed that both catalysed and uncatalysed additions of alcohols give mainly anti addition products. Only in the case of uncatalysed reactions employing an inert aprotic solvent does eyn addition predominate.