Sulphur Atom

Figure Bl.8.4. Two of the crystal structures first solved by W L Bragg. On the left is the stnicture of zincblende, ZnS. Each sulphur atom (large grey spheres) is surrounded by four zinc atoms (small black spheres) at the vertices of a regular tetrahedron, and each zinc atom is surrounded by four sulphur atoms. On the right is tire stnicture of sodium chloride. Each chlorine atom (grey spheres) is sunounded by six sodium atoms (black spheres) at the vertices of a regular octahedron, and each sodium atom is sunounded by six chlorine atoms.

The first crystal structure to be detennined that had an adjustable position parameter was that of pyrite, FeS2 In this structure the iron atoms are at the comers and the face centres, but the sulphur atoms are further away than in zincblende along a different tln-eefold synnnetry axis for each of the four iron atoms, which makes the unit cell primitive. 

Figure B3.3.12. Sulphur atoms in liquid iron at the Earth s core conditions, simnlated by first-principle Car-Parrinello molecular dynamics, (a) Initial conditions, showing a mannally-prepared initial cluster of snlphur atoms, (b) A short tune later, indicating spontaneous dispersal of the snlphur atoms, which mingle with the surroundmg iron atoms. Thanks are dne to D Alfe and M J Gillan for this figure. For fiirtlier details see [210. 211].

There is a controversy about tire bonding state of tire sulphur. Most evidence suggests tliat it is bound in tire fonn of a tliiolate [122], while x-ray diffraction suggests tliat tire sulphur atoms may dimerize [147]. Flowever, not all of tire observed overstmctures can be explained witli tliis latter assumption. 

However, the sulphide ion can attach to itself further atoms of sulphur to give polysulphide ions, for example Sj , Sj , and so these are found in solution also. Further, the sulphite ion can add on a sulphur atom to give the thiosulphate ion, S203 which is also found in the reaction mixture. 

In the sulphate ion, the four oxygen atoms are tetrahedrally arranged round the sulphur atom, at equal distances hence all the S—O bonds are identical, and their short length suggests that they are double bonds (as in SOj, SO3, and SO3") ... 

In addition to the simple acids discussed above, sulphur forms two peroxosulphuric acids containing the —O—O— linkage and a number of thionic acids containing more than one sulphur atom. 

Diselenium dichloride acts as a solvent for selenium. Similarly disulphur dichloride is a solvent for sulphur and also many other covalent compounds, such as iodine. S Clj attacks rubber in such a way that sulphur atoms are introduced into the polymer chains of the rubber, so hardening it. This product is known as vulcanised rubber. The structure of these dichlorides is given below ... 

In some situations the nitro group behaves as if it exerted its influence mainly by the inductive process, but in nitration its behaviour seems to place it with this group of —I —M substituents. The precise way in which a sulphone group is described depends on how much weight is given to the ability of the sulphur atom to expand its octet the positive... 

The main symmetry elements in SFg can be shown, as in Figure 4.12(b), by considering the sulphur atom at the centre of a cube and a fluorine atom at the centre of each face. The three C4 axes are the three F-S-F directions, the four C3 axes are the body diagonals of the cube, the six C2 axes join the mid-points of diagonally opposite edges, the three df, planes are each halfway between opposite faces, and the six d planes join diagonally opposite edges of the cube. 

Also shown in Figure 8.15 is the line due to removal of a 2p electron from the sulphur atom in thiophene. Spin-orbit coupling is sufficient to split the resulting core term, as it is called, into 3/2 and 1/2 states, the multiplet being inverted. 

An extreme example of hybidization is the structure proposed for sulphur hexafluoride, SFe. The six S-F bonds are dhected to the apices of a regular octahedron. An aiTangement which would satisfy this number of covalent bonds is sp d hybridization. The ground state of the sulphur atom is s p° and... 

Polymer chains with sulphur atoms, improving breakdown of polychloroprene during mastication, increasing tear resistance and dynamic behaviour. 

Shatenshtein et al.5 5 5- 591 have also measured rate coefficients for dedeuteration of thiophen derivatives by lithium or potassium l-butoxides in dimethyl sulphoxide or l-butyl alcohol (70 vol. %) in diglyme (Table 178). Interestingly, the 2 position is more reactive than the 3 position and this was reasonably attributed to the —I effect of the hetero sulphur atom. The methyl substituent lowers the reactivity of the 2 position from each position in accord with its +1 effect and consequently the effect was greatest from the 3 position. However, the deactivation from the 5 position was greater than from the 4 position, and this was incorrectly attributed to the +M effect of methyl group operating from the 5 position since... 

Sulphur atoms as ligands in metal complexes. H. Vahrcnkamp, Angew. Chem., Int. Ed. Engl., 1975,14,322-329 (121). 

FIGURE 20. The free surface on the sulphur atom, S, (A2), as a function of ring strain for sulphide, sulphoxide and sulphone molecules. 

Exchange of organic substituents at the sulphinyl sulphur atom. . 361... 

A rapid and clean oxidation of sulphides to sulphoxides can also be carried out using the titanium(III) trichloride/hydrogen peroxide reagent35. On a milimole scale, the oxidation takes place in a time shorter than 20 min upon addition of a solution of hydrogen peroxide to a solution of the sulphide and titanium(III) trichloride in methanol at room temperature. It was suggested that the formation of a sulphoxide in this reaction resulted from a direct coupling of the hydroxy radical with cation radical 20 formed at the sulphur atom of the sulphide (equation 6). 

Based on detailed kinetic investigations, a tentative mechanism for this asymmetric oxidation was proposed (Scheme 2) according to which optically active sulphoxides may be formed by two pathways external attack on the sulphur atom by the chiral titanium hydroperoxide (path A) or coordination of sulphur to titanium prior to the oxidation step (path B). Although paths A and B could not be distinguished experimentally, the temperature effect was tentatively ascribed to a change of the mechanism, path A being predominant above — 20 °C and path B becoming competitive at lower temperatures (or vice versa). 

Asymmetric oxidation of this sulphide was also catalyzed by two isocytochromes P 450 purified from phenobarbital induced rat liver309. Both P 450 isocytochromes, termed PB-1 and PB-4, when reconstituted with purified rat liver NADPH-cytochrome P 450 reductase and cytochrome b5 afforded ethyl p-tolyl sulphoxide with S-configuration at the sulphur atom. In the case of PB-1 optical purity of this sulphoxide was 58% whereas with PB-4 it was 78%. 

Sulphoxides and sulphones form hydrogen bonds with proton donors and association complexes with metallic salts by using either the oxygen atom or the sulphur atom in their S—O linkages. The capability for the formation of hydrogen bonds or complexes depends... 

The sites for complex formation in DMSO with inorganic salts depend remarkably on the nature of the metals involved in the salts. The alkali or alkali earth metallic salts form a complex with the oxygen atom in DMSO while Pd(II) or Pt(II) associates strongly at the sulphur atom. The IR frequency of the S—O bond of DMSO shifts to even lower wave numbers when associated with such metal cations as Li+, Na+ or Ca+ +34. On the other hand, in the case of Pd(II) or Pt(II), the S—O frequency appears at higher wave numbers, at around llOO-llAOcm 135. These different shifts for the S—O frequency afford a convenient diagnosis to determine whether the cation associates with the oxygen or the sulphur atom in DMSO. 

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