Metal deficient sulfides

XPS examination of oxidized sphalerite showed the development of a surface layer of metal-deficient sulfide (Buckley et al., 1989) whose formation in acid solution is described by... 

Later studies on the surface oxidation of galena, applying X-ray photoelectron spectroscopy, indicated that the initial product was not elemental sulfur as presented in reaction (3), but rather a metal-deficient sulfide. That is, the development of a lead xanthate phase is represented by... 

Although sufides are among the most straightforward of substrates to oxidize, the selective oxidation of sulfides to sulfoxides and to a lesser extent sulfones is often challenging for substrates other than simple dialkyl-, diaryl-, and alkylaryl-sulfides. In transition metal-catalyzed oxidations the relatively low reactivity of electron-deficient sulfides and their insolubility in polar solvents is problematic when H2O2 is employed as the terminal oxidant. 

Surface oxidation of sulfide minerals has been reviewed recently by Smart et al. [78]. Studies of the physical and chemical forms of oxidation products by SAM, XPS, STM. AFM, SEM and ToF-SIMS have revealed several different proces.ses of oxidation. The seminal work of Buckley et al. (e.g., [79,80)) was the first to identify the process of formation of oxyhydroxide products on underlying metal-deficient, sulfur-rich layers of similar forms to those described in Section 4.3. Other oxidation products have been observed directly, such as polysulfides, elemental sulfur, oxidized fine sulfide particles, colloidal hydroxide particles and flocculated aggregates, as well as continuous surface layers of... 

For the most part, adequate copper is received in diet and widespread human deficiencies do not occur, but deficiencies may arise because of antagonists. The metals Cd, Hg, Ag and Zn interfere with copper metabolism, probably by competing for copper-binding sites in proteins. Ascorbic acid depresses intestinal absorption of copper56 (in contrast to iron). Some proteins in the diet adversely affect utilization of copper. The sulfide ion is a well known inhibitor of copper absorption, since it forms copper(II) sulfide which is insoluble.56... 

Dithioacetals of aldehydes are sources of carbanions and hence may be used to form new C-C bonds in reactions in which the formerly electron-deficient character of the aldehydic carbon has been reversed. The 1,3-dithianes derived from formaldehyde or a higher aldehyde may be metallated and then alkylated (Scheme 2.27). Hydrolysis of the dithioac-etal is usually carried out in the presence of a thiophilic (sulfur seeking) metal salt such as a mercury salt. The insoluble sulfides cause the equilibrium to move in favour of the parent carbonyl compound. 

Among the oxides and sulfides, only CdO adopts the octahedral rocksalt structure found with group 2 elements, although the solid is normally very deficient in oxygen and the electrons not used in bonding give rise to metallic properties. ZnO and ZnS are prototypes of the tetrahedrally coordinated wurtzite and zinc blende (or sphalerite) structures in fact, ZnS can adopt either structure, as can CdS and CdSe. HgO and HgS have chain structures with linear two-coordination of Hg. 

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