REDUCTIVE DEHALOGENATION VERSUS SUBSTITUTION IN THE POLYETHERIFICATION OF 4,4'-DIHALODIPHENYL SULFONES WITH BISPHENOLATES

A competition between reductive dehalogenation and substitution in the polyetherification of 4,4'-dihalodiphenyl sulfones with bisphenolates is described. The polycondensations of 4,4'-dihalodiphenyl sulfones w ith tert-butylhydroquinone, 4,4'-isopropylidenediphenol (Bisphenol A), and 4,4'-oxydiphenol in the presence of excess K2CO3 in N,N-dimethyla cetamide (DMAc), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP) at 160-degrees-C were investigated. The polycondensations of 4, 4'-difluorodiphenyl sulfone, 4,4'-dichlorodiphenyl sulfone, and 4,4'-d ibromodiphenyl sulfone with tert-butylhydroquinone result in high mole cular weight polymers, whereas the polycondensation of 4,4'-diiododiph enyl sulfone with tert-butylhydroquinone affords a low molecular weigh t polymer which contains diphenyl sulfone chain ends. The polycondensa tions of 4,4'-diiododiphenyl sulfone with 4,4'-isopropylidenediphenol and 4,4'-oxydiphenol result in high molecular weight polymers. Only in the polyetherification of 4,4'-diiododiphenyl sulfone with tert-butyl hydroquinone is reductive dehalogenation observed. The reductive elimi nation of iodide from the 4-iododiphenyl sulfone moiety to form a poly mer containing diphenyl sulfone chain ends is proposed to occur by a s ingle electron transfer (SET) mechanism, whereas the substitution of t he halide by the phenolate occurs by a polar mechanism. The electronic and spatial properties of the 4,4'-dihalodiphenyl sulfone and bisphen olate govern the course of the reaction. These results suggest that th e phenolate may act as both the nucleophile and the electron donor and can be rationalized in terms of two scenarios which describe the natu re of the polar and SET pathways and their relationship to each other. One scenario views the polar and SET pathways as separate and distinc t pathways with no common intermediates. The other scenario views the polar reaction as the concerted occurrence of single electron transfer and bond formation rather than a two-electron process, and consequent ly, the polar and SET pathways are very similar.