抄録 Reaction of< I> S,< I> S-diphenyl-< I> S-fluorothiazyne with< I> N- unsubstituted< I> S,< I> S-diphenylsulfilimine afforded the corresponding< I> S- sulfiliminothiazyne. Measurement of the pKa value of< I> S-sulfiliminothiazyne and its reactivity were examined. The molecular structure of the sulfonediiminosulfonium salt was determined by the X-ray crystallographic analysis.