Desulfurisation

Komfeld, E. C.,J. Org. Chem., 1951, 16, 137 Raney nickel catalyst, containing appreciable amounts of the sulfide (after use to desulfurise thioamides) is rather pyrophoric. 

The pyrano[3,2-c][l]benzopyran system is available from the reaction between salicylaldehyde and 5-phenylthio-4-penten-l-ols which proceeds by an intramolecular cycloaddition of an o-quinone methide desulfurisation is facile (Scheme 29) <00TL2643>. Mild conditions have been established for the synthesis of (-)-hexahydrocannabinol 50 from the olivetol derivative 49 which also involves a quinone methide (Scheme 30) <00SC1431>. 

Studies on heterogeneous catalysts seem to invoke partial hydrogenation of thiophene prior to desulfurization [42] the catalysts are also active hydrogenation catalysts. Recently evidence for a facile and selective desulfurisation of partly hydrogenated thiophene has been reported, the reaction of 2,5-dihydrothiophene on (110) molybdenum surfaces (Figure 2.41) [43]. 

Figure 2.42. Oxidative addition of thiophene to iridium (I) followed by stoichiometric "desulfurisation" ref [39],...

A catalytic example of C-S bond breakage in benzothiophene has been reported by Bianchini [47], A catalytic desulfurisation was not yet achieved at the time as this is thermodynamically not feasible at such mild temperatures because of the relative stability of metal sulfides formed. Bianchini used a water-soluble catalyst in a two-phase system of heptane-methanol/water mixtures in which the product 2-ethylthiophenol is extracted into the basic aqueous layer containing NaOH. Figure 2.43 gives the reaction scheme and the catalyst. The 16-electron species Na(sulfos)RhH is suggested to be the catalyst. Note that a hydrodesulfurisation has not yet been achieved in this reaction because a thiol is the product. Under more forcing conditions the formation of H2S has been observed for various systems. 

This type of reagent allows a very selective and mild introduction of fluorine. Fuchigami etal. pioneered a similar approach for the desulfurisative fluorination employing hypervalent bromine (Eq. 3) and iodine (Eq. 4) reagents [45]. 

The desulfurisation of a tetrathioplumbolane Ar(Ar )PbS4 with different substituents on the lead centre unexpectedly produces the four-membered... 

Treatment of the sulfoxide prepared from p-cresol and thionyl chloride with a mixture of TFAA and KHCO3 in acetonitrile at -30°C led to formation of an orthoquinone mono(monothioketal). Desulfurisation with NiCl2(PPh3)2 gave 2-(4-methylphenoxy)-4-methylphenol in 38% overall yield. 

Units called flue gas desulfurisation (FGD) units are being fitted to some power stations throughout the world to prevent the emission of sulfur dioxide gas. Here, the sulfur dioxide gas is removed from the waste gases by passing them through calcium hydroxide slurry. This not only removes the sulfur dioxide but also creates calcium sulfate, which can be sold to produce plasterboard (Figure 11.25). The FGD units are very expensive and therefore the sale of the calcium sulfate is an important economic part of the process. 

Flue gas desulfurisation (FGD) The process by which sulfur dioxide gas is removed from the waste gases of power stations by passing them through calcium hydroxide slurry. 

Figure 5. Mass chromatogram of m/z 217 of the desulfurised polar fraction of the bitumen of an outcrop section at Naples Beach (California, U.S.A.) of the Monterey Formation.

Desulfurisation of polar fractions of relative immature oils and sediment from hypersaline palaeoenvironments yields n-alkanes with strong even-over-odd carbon number predominances (20,42 e.g., Figure 11). This phenomenon is, however, not restricted to samples from hypersaline palaeoenvironments (e.g., Jurf ed Darawish Oil Shale, Monterey Shale). 

Desulfurisation. Aliquots of polar and High-Molecular-Weight Aromatic (HMWA Figure 1) fractions were desulfurised using Raney Ni as described elsewhere (18). The mixture after desulfurisation was separated over a small (5 x 0.5 cm) alumina column using hexane/C C (9 1) to elute the saturated and aromatic hydrocarbons and CH2Cl2 to elute more polar... 

---