Sulfides, alkyl aryl desulfurization

Li, Na and K in hydrocarbons, ethereal solvents, HMPA or DMA have been used to desulfurize sul-fides, but applications are limited to simple sulEdes, and particularly to aryl alkyl sulfides. Since these desulfurizations were performed without protic solvent, the organometallics formed may react further and particularly with the solvent. Thus low temperatures were recommended. Potassium graphite (CgK) in excess in ether was also proposed for the desulfurization of allyl or vinyl sulfones, but this reagent is not free of disadvantages. ... 

In the special case of aryl alkyl sulfides, desulfurization may be performed by 5n2 reactions with nucleophiles such as RS , RSe , and sometimes RO or RiR2N-43b.43c,s9 i,2-Eliminations, where the thioaryl group is the leaving group, have also been used. ... 

Aryl and alkyl hydroxylations, epoxide formation, oxidative dealkylation of heteroatoms, reduction, dehalogenation, desulfuration, deamination, aryl N-oxygenation, oxidation of sulfur Oxidation of nucleophilic nitrogen and sulfur, oxidative desulfurization Oxidation of aromatic hydrocarbons, phenols, amines, and sulfides oxidative dealkylation, reduction of N-oxides Alcohol oxidation reduction of ketones Oxidative deamination... 

The types of organosulfur compounds found in petroleum feedstocks are shown in Table Of them, the alkyl and aryl thiols (RSH), sulfides (RSR ), and disulfides (RSSR ) are the most rapidly desulfurized (equation 1). It is the broad class of thiophenes, stabilized by their aromatic character, that are most difficult to desulfurize and require relatively severe temperatures ( 400 °C) and H2 pressures ( 100 atm). Thus, it is the HDS of thiophenes that has been of greatest interest to inorganic and organometallic chemists. There are fewer model studies of the HDS of thiols, sulfides, and disulfides. Organometallic aspects of HDS and HDN have been summarized most comprehensively in a recent book by Sanchez-Delgado. A briefer overview has also been published. More specific reviews are cited in later sections of this chapter. 

Benzothiazolyl alkyl sulfides, prepared from the corresponding alcohols, are easily desulfurized (87-99%) by TBTH-AIBN. This reaction constitutes a good indirect deoxygenation of alcohols. Desulfurization of dithioketals may be controlled. Thus 1,3-dithiolanes with 1 mol equiv. of TBTH lead to 3-alkyl (or 3-aryl) thiols (64-82%), while 4 mol equiv. of TBTH leads to the completely desulfurized derivative. Desulfurization of heterocyclic thiones is also performed with this reagent. In passing, it should be noted that generation of radicals from C—S bonds and tin hydrides in the presence of radical initiators is of large synthetic interest. ... 

The aryl sulfide linker system shown in Scheme 16.22 was reported by Janda et al. in 1996 [87, 88]. After attachment of alkyl bromides to the benzenethiol linker to give resin 93, cleavage was achieved by desulfurization under quite harsh conditions with Raney-nickel, yielding the new hydrocarbon product 95. Alternatively, the linker can be oxidized with mCPBA or KHSOs to the corresponding sulfone 94 (Table 16.2) subsequent treatment with 5% sodium/mercury furnishes the parent hydrocarbon in high yields [89]. 

---