OLIGOMERIZATION AND CYCLIZATION OF 1,2-ETHANEDITHIOL (EDT), HSCH2CH2SH, BY SELENIUM DIOXIDE AND IODINE

The reaction of 1,2 ethanedithiol (EDT) with selenous acid in water or alcohol leads to selenopolysulfide chains or cycles, (C2H4SSeSC2H4SS) (n), with randomly distributed -SSeS-and -SS-moieties. The reaction in water produces incompletely reacted material, which on recrystallizat ion, gives an oligomer corresponding to 5 EDT units (pentamer) as conf irmed by molecular mass determination, Se analysis, H-1-and Se-77-NMR spectroscopy. In both the pentamer and cyclic forms the incidence of n eighboring -SSeS-moieties is higher than that expected statistically. The mechanism for the reaction of thiols with selenous acid provides s ome rationalization for this observation in as much as neighboring -SS eS-groups, or groups that will lead rapidly to neighboring -SSeS-group s are formed in general before -SS-links can be formed. The Raman spec trum of these products show typical strong SS, SeS, and CS stretching bands at 510, 370, and 730 cm(-1). The high frequency of upsilon(cs) i s attributed to a preferred gauche conformation at the CS bonds. For c omparison, polydisulfides were also prepared from EDT and iodine in me thanol. These products consist of at least seven cyclic polymers rangi ng from the four-membered 1,2-dithietane to higher members. Heating ab ove 100 degrees C in chloroform for several hours gives a solution con taining the four lowest molecular mass rings, which on standing for 24 h, precipitate highly insoluble material, which is probably chain or large-ring polymer. Molecular mass determination in camphor indicates that, like yellow sulphur, chain polymers are formed at the melting po int of camphor (170 degrees C). (C) 1998 John Wiley & Sons, Inc.