Sulfur-rich

In fine wool such as that obtained from merino sheep, the cuticle is normally one cell thick (20 x 30 x 0.5 mm, approximate dimensions) and usually constitutes about 10% by weight of the total fiber. Sections of cuticle cells show an internal series of laminations (Figs. 1 and 2) comprising outer sulfur-rich bands known as the exocuticle and inner regions of lower sulfur content called the endocuticle (13). On the exposed surface of cuticle cells, a membrane-like proteinaceous band (epicuticle) and a unique hpid component form a hydrophobic resistant barrier (14). These hpid and protein components are the functional moieties of the fiber surface and are important in fiber protection and textile processing (15). 

Chloroethyldisulfides are obtained by electrophilic attack on the sulfur atom of thiiranes by sulfenyl halides (Scheme 39). Sulfur dichloride and disulfur dichloride react similarly to give more sulfur-rich derivatives di- and tri-sulfenyl halides, and tri- and tetra-sulfides (Scheme 42). A 1 1 ratio of sulfur halide to thiirane gives the di- or tri-sulfenyl halide a 2 1 ratio the tri- or tetra-sulfide. Thiirane 1-oxides are cleaved by sulfenyl halides to thiolsulfinates (Scheme 43) (74JAP7440461). 

Sulfuric acid (H1SO4) and ammonium bisulfate (NH4HSO4) contribute importantly to ambient acid aerosols, particularly in geographic locations where sulfur-rich coal is used for power plant fuel, such as the eastern United States.Studies on animals and human subjects have shown that H2SO4 and NH4HSO4 alter mucociliary transport in a dose-dependent fashion and... 

The simplest chain compounds of the type RS NyR are the sulfur diimides RNSNR (Section 10.4) The other known thiazyl chains are summarized in Table 14.1. They can be conveniently classified as sulfur-rich, nitrogen-rich or even-chain species. 

The sulfur-rich analogue TI3B3S10 was likewise prepared as yellow plates from the appropriate stoichiometric mixture of (3TI28 -b 6B -b 178) at... 

It was proposed that the formation of the sulfur-rich species M(R2dtc>3S takes place via the activated complex... 

The chemistry of the dithiocarboxylate complexes of nickel (II) has been investigated extensively. Interest in recent years has been mainly in the further investigation of the "sulfur-rich species, the perthiocarboxylates, and the unusual structures discovered in the dithiocarboxylate complexes (359). The violet complex formed by reaction of [Ni(C H5CS2)2] with sulfur or polysulfide, [Ni(CgHsCS2)2]2, origi-... 

Many of the sulfur-rich compounds considered in this chapter are unstable reactive species so that important properties such as geometrical structures, vibrational spectra and reaction energies are difficult to obtain experimentally and remain uncertain. In these cases, theory is particularly suited to provide the necessary complementary information to understand and interpret the experimental observations for these systems. 

Quantum-Chemical Calculations of Sulfur-Rich Compounds... 

In this review, we consider the application of quantum-chemical calculations to a range of sulfur-rich compounds. The empirical, semiempirical and ab initio MO calculations published before 1980 are considered rather inadequate. Therefore, theoretical calculations before 1980 will not be mentioned in detail here. 

Extensive quantum chemical calculations have been reported for sulfur-rich compounds in the past two decades. These calculations were used to investigate molecular structures and spectroscopic properties, as well as to understand the nature chemical bonding and reaction mechanism. Many high-level ab initio calculations were used for interpretation of experimental data and for providing accurate predictions of molecular structures and thermochemical data where no reliable experimental values are available. In recent years, density functional calculations have been extensively tested and used on many first- and second-row compounds. These proven DFT methods look promising for larger systems because for their computational efficiency. 

Similarly, the thermal sensitivity of sulfur allotropes makes mass spectrometry of elemental sulfur and sulfur-rich compounds difficult especially with the conventional electron impact ionization. Nevertheless, valuable information has been obtained by this technique also. 

Since hydrogen sulfide and elemental sulfur occur together in hot underground deposits of natural gas (so-called sour gas ) the formation of sulfur-rich polysulfanes under these high-pressure conditions is very likely. If the gas is produced and in this context the pressure and temperature lowered, the decomposition reaction (Eq. 1) takes place and the precipitated sol-... 

Certain older reports [14] on the existence of extremely sulfur-rich sulfanes in mixtures of high sulfur content obtained from sodium thiosulfate and hydrochloric acid are in error since elemental sulfur was shown to be the main component besides traces of H2S [15]. 

In the Introduction it has already been mentioned that sulfanes are likely to occur in underground sulfur-rich deposits of sour natural gas. This gas is freed from H2S by washing with an alkaline solvent from which the hydrogen sulfide is later expelled by heating. The Claus process is then applied to convert H2S into elemental sulfur ... 

Sulfur-Rich Polysulfides with Complex Univalent Cations. 132... 

Inorganic polysulfides are ionic substances containing chain-like dianions Sn - 8uch ions are formed in numerous reactions, e.g., by oxidation of monosulfide ions H8 in water or other polar solvents as well as by reaction of aqueous monosulfide with sulfur-rich compounds including elemental sulfur ... 

Many of the polysulfides described above have been investigated by X-ray diffraction on either powders or single crystals. In all cases the more sulfur-rich anions (n>3) form unbranched chains the symmetry of which varies between Ci, C2, and Cs. According to Fig. 1 the symmetry C2 results if all torsion angles have the same sign (right-handed helix + + +... left-handed helix ----...). If the different torsion angles of the anion vary between + and... 

Table 2 Structure data of sulfur-rich polysulfides with univalent cations (for abbreviations, see text)... 

The chemistry of elemental sulfur and sulfur-rich molecules including polysulfides in liquid ammonia [82] and in primary as well as secondary amines [83] is complex because of the possible formation of sulfur-nitrogen compounds. Therefore, polysulfide solutions in these solvents will not be discussed here. Inert solvents which have often been used are dimethylfor-mamide (DMF) [84-86], tetrahydrofuran (THF) [87], dimethylsulfoxide (DMSO) [87], and hexamethylphosphoric triamide (HMPA) [86, 88]. 

The addition of elemental sulfur to systems containing 82 or 83 results in the formation of more sulfur-rich species [89] ... 

The red tetrasulfide radical anion 84 has been proposed as a constituent of sulfur-doped alkali hahdes, of alkah polysulfide solutions in DMF [84, 86], HMPA [89] and acetone [136] and as a product of the electrochemical reduction of 8s in DM80 or DMF [12]. However, in all these cases no convincing proof for the molecular composition of the species observed by either E8R, Raman, infrared or UV-Vis spectroscopy has been provided. The problem is that the red species is formed only in sulfur-rich solutions where long-chain polysulfide dianions are present also and these are of orange to red color, too (for a description of this dilemma, see [89]). Furthermore, the presence of the orange radical anion 8e (see below) cannot be excluded in such systems. 

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