Sulfides GEMS

Fig. 1. Global distribution of seabed mineral deposits, where x represents chromite + barite titanium, zirconium, hafnium, and thorium tin I gold, platinum, and silver 3 sand and gravel shell, calcium carbonate gems marine polymetaUic sulfides phosphorites Cl cobalt cmsts S sulfur and B...

Addition of hydrogen sulfide results in formation of monomeric gem dithiols or trimeric thioketals (511,512). The initially reported thione formation (513-515), analogous to hydration of morpholinocyclohexene... 

Homoallyl ethers or sulfides.1 gem-Methoxy(phenylthio)alkanes (2), prepared by reaction of 1 with alkyl halides, react with allyltributyltin compounds in the presence of a Lewis acid to form either homoallyl methyl ethers or homoallyl phenyl sulfides. Use of BF3 etherate results in selective cleavage of the phenylthio group to provide homoallyl ethers, whereas TiCl effects cleavage of the methoxy group with formation of homoallyl sulfides. 

The l3C chemical shifts of methyl derivatives with sulfur substituents [e.g., SH, -S, -SCH3, -SSCH3, -SSSCHj, -S(0)CH3, -S02CH3, -S(CH3)2+, -SC(0)CH3, -SC(S)CH3, and -SC(S)SCH3] (130,131) and of vicinal and gem-inal bis-sulfides (290) have been reported. Freeman and co-workers have published similar studies on thiols, sulfides, disulfides, and sulfinic and sulfonic acid derivatives (131,132,433) and Tseng and Bowler (434), on thiocarbamates, their S-oxides and S,5-dioxides [R-X-C(0)-NR 2 with X = S, SO, S02]. 

The most exotic materials in CP IDPs are particles of glass with embedded metal and sulfides, identified by the acronym GEMS (Fig. 12.8d). Although GEMS are commonly described as having chondritic bulk compositions, that description applies only for aggregates of these submicron particles. The nanometer-sized FeNi metal (kamacite) inclusions and pyrrhotite are clearly out of equilibrium with the magnesium-rich silicate... 

Other means of improving sulfide yields in the reaction of halides with thiolates are (1) the use of thiols and platinum(II) complex catalysts287, (2) the generation of thiolate anions by electrochemical means288 and (3) the use of phase-transfer conditions237. The first method has been used for the synthesis of thioketals from geminal diiodides and the third has been used for the conversion of gem-dichlorocyclopropanes into cyclopropane thioketals, which are effectively masked cyclopropane moieties. 

Long reaction times lead to the disappearance of the blue color of thione 1, related to the addition of a second molecule of hydrogen sulfide to give colorless gem-dithiols 3. Aromatic derivatives (R = Ar) are less prone to further addition of hydrogen sulfide, whereas with aliphatic derivatives (R = alkyl), gem-dithiols are generally the final reaction products and can be isolated and fully characterized.18 gem-Dithiols 3 can be converted into thioacylsilanes 1 by neutralization of the thionation solution with solid sodium hydrogen carbonate. With this procedure, enolizable acylsilanes 2 (R = R CH2) are stereoselectively transformed into Z-a-silyl enethiols 4 (vide infra). 

Figure 2.2 A GEMS particle found in an IDP, consisting of a glassy matrix with silicate-like composition and embedded nanometer-sized inclusions of iron metal and iron sulfide (dark patches). Some of them are possibly interstellar silicate dust grains. (From NASA http //stardust.jpl.nasa.gov/science/sci2.html.)...

GEMS glass with embedded metals and sulfides. 

Furthermore, the hexafluoropropene iethylamine reagent is also employed for the gem-difluorination of 1,3-dithiolanes. Formation of a-fluoro sulfides and of vinyl fluorides (see Section 1.1.7.1.) is observed. 

Under the same reaction conditions dithioacetals of aromatic aldehydes react to give gem-difluoro sulfides 12, while the dithioacetal of decanal yields the monofluoro sulfide 13. 

Figure 14 TEM image of a GEMS showing 10 nm and smaller dark beads of FeNi metal and sulfide imbedded in amorphous silicate. GEMS appear to be nonporous and usually range in size from 100 nm to 400 nm.

Figure 4 Brightfield electron micrographs of ultramictrotomed thin sections (a) CP IDP U222B42, (b) CS IDP U230A43, (c) CP IDP U222B42 with carbonaceous material, GEMS, crystalline silicates (enstatite), and sulfides (FeS), (d) CS IDP U222C29 with fibrous layer lattice silicate (saponite), pyrrhotite (FeS), and the pyroxene...

---