Olav Foss

IONIC SCISSION OF THE SULFUR-SULFUR BOND

Abstract A survey is made of nucleophilic substitutions at divalent sulfur involving ionic scission of a sulfur-sulfur bond. Such reactions are quite numerous; those which have been studied kinetically are of second order and thus of the SN2 type. The kinds of reactions discussed are: Desulfurations of disulfides and polysulfides, thiol-disulfide exchanges, reactions of elemental sulfur, and reactions of thiolsulfonates and thiosulfates. It is pointed out that the oxidation of a mercaptide ion or thio ion to the disulfide by another disulfide probably proceeds in two steps, each an ionic displacement, and that there is a close correspondence between the ease with which a thio ion is oxidized to the disulfide, and the nucleophilic reactivity of the thio ion toward divalent sulfur.

Crystal structures and rotameric forms of some diarylsulphonyl-mono-, -di-, and -tri-selanes and their sulphur analogues

The crystal structures of the compounds S2(SO2Ph)2(1), Se2(SO2Ph)2·½C6H6(2), S2(SO2C6H4Me-p)2(3), Se2(SO2C6H4Me-p)2(4), S(SO2C6H4Me-p)2(5), Se(SO2C6H4Me-p)2(6), S3(SO2C6H4Me-p)2(7), and Se3(SO2C6H4Me-p)2(8) have been determined by X-ray methods and refined to R 0.033–0.045 for 1 384–3 058 observed reflections. Crystals of (3) and (4) are isomorphous, as are those of (5) and (6), and (7) and (8). In (5)–(8) the molecules lie across crystallographic two-fold axes. In the disulphonyl-sulphane or -selane chains, the lengths of the terminal bonds are S–S 2.101(1)–2.141(1) and S–Se 2.242(1)–2.286(1)A, and the lengths of the central bonds, between bivalent atoms, are S–S 1.987(1)–2.037 (1) and Se–Se 2.246(1)–2.304(1)A. The rotameric forms, and reasons for variations in the lengths of bonds of the same type, are discussed. With three exceptions, the YXSC torsion angles (X,Y = S or Se) of 12 independent sulphonyl groups lie in the range 70–89, average 80°. In the S–SO2R groups of the disulphonylsulphanes the S–S bond lengths correlate with the triple angle averages around the bonds.

STEREOCHEMISTRY OF DISULFIDES AND POLYSULFIDES

Abstract Physicochemical measurements and structure determinations by electron and X-ray diffraction methods have shown that in disulfides and polysulfides the sulfur chains are unbranched. The non-planarity of the chains gives rise to rotational-isomeric forms, namely to two enantiomorphs of a disulfide, two forms of a trisulfide of which one is a pair of enantiomorphs, and to three pairs of enantiomorphs of a tetrasulfide. In six- and five-membered cyclic disulfides the disulfide group is more planar than in non-cyclic disulfides; a dihedral angle of 60° has been observed in racem-1,2-dithiane-3,6-dicarboxylic acid, 27° in l,2-dithiolane-4-carboxylic acid, and 0° in thiuret hydroiodide.

ASPECTS OF THE STRUCTURAL CHEMISTRY OF POLYTHIONATES

Topics discussed are: some chemical characteristics of the tetra-, penta-, and hexathionate ions; structures of the tetra-, penta-, and hexathionate ions and the seleno- and telluropentathionate ions; reactions of the penta-, selenopenta-, and telluropentathionate ions with methylxanthate ions, and structures of reaction products; the prevalence of unbranched sulphur chains.