Thiols metal sulfides

Metal Ion-Promoted Reactions of Thiols. Metal ion-promoted reactions of thiols have been reviewed (53). The bulk of the coverage concerns metal ion promoted aspects of sulfur chemistry. The main topics of interest are the formation of sulfenamides, sulfides, and disulfides using metal-mediated reactions. 

Woods, R. Chemisorption of Thiols on Metals and Metal Sulfides 29... 

In a series of papers, metal sulfide cluster anions of first-row transition metals, principally copper, have been reacted with a variety of reagents including thiols, sulfur, phosphorus, and phosphines (99, 145, 256, 257). 

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. 

The sulfur analogue of the Wittig rearrangement is an isomerization of a-metalated sulfides to skeletally rearranged metal thiolates, which yield thiols (equation 80). 

In organo-fluorine compounds fluorine atoms can be eliminated by nucleophilic sulfur species to form C —S bonds. In principle, the fluorine to be eliminated can be bonded to aliphatic or araliphatic compounds, as well as to aromatic or heterocyclic compounds however, the replacement proceeds more efficiently the more the fluorine is activated. Therefore, the synthetic usefulness of these reactions is the broadest with fluoroaromatic compounds, including heteroaromatics, with which the reactions often proceed smoothly under mild conditions. The nucleophilic sulfur compound to be reacted is. in most cases, an aliphatic or aromatic thiol or a metal sulfide, but reactions with, for example, thiourea or ammonium thiocyanate have also been described. The sulfur introduced this way can be either oxidized or removed by reduction, opening additional possibilities for modifications of the original fluoro compounds. 

Be(Pc) and Mg(Pc) are obtained by the condensation reaction of phthalonitrile in the presence of metallic Be and Mg respectively.197,198 They form very stable complexes with water. Mg(Pc)(OH2) is square pyramidal and the magnesium atom is displaced out of the N4 plane by 0.5 A with an Mg—distance of 2.04 A. They lose the water on sublimation. Amines, alcohols, ketones, thiols and sulfides also coordinate to Mg(Pc). Ca(Pc) and Ba(Pc) are obtained from phthalonitrile and the metal oxide.197,199... 

Based on the analyses of the trace contaminants conducted on the wheat millfeed-derived products, numerous potential problem components were identified, relative to catalyst activity (3). These components (shown in Table 1) include sulfate (potential for metal sulfide formation) calcium, magnesium, and phosphate (potential for catalyst pore plugging by insoluble salt precipitation) sodium or potassium (alkali attack on the catalyst support) organic nitrogen components, such as amino acids (thiol... 

Lone-pair nucleophiles contain atoms with lone pairs. The lone pair is used to make anew bond to an electrophilic atom. Alcohols (ROH), alkoxides (RO ), amines (R3N), metal amides (R2N ), halides (X ), thiols (RSH), sulfides (R2S), and phosphines (R3P) are all examples of lone-pair nucleophiles, as are the O atoms of car-... 

This cubane cluster can be converted back to the original one by reaction with CO (30 atm) to form COS, thus completing a cyclic reaction. Although this pair of reactions indicates the possibility of constructing a catalytic cycle for the HDS of thiophene, the presence of free CO unfortunately inhibits the forward desulfurization reaction and therefore the process cannot be rendered catalytic [68]. The exact mechanism of thiophene HDS by use of these clusters in not clearly understood, mainly because the reaction is fast and no intermediates have been isolated or identified. Nevertheless, Curtis has reported extensive related mechanistic studies on the desulfurization of a variety of thiols and sulfides using the same metal cluster Cp 2Mo2Co2S3(CO)4 and as a result of that, the main reaction pathways for desulfurization of these simpler substrates are now well understood [69],... 

The best preparative method for mercaptopyrimidines varies from position to position from thioureas and their equivalents. Thiones in any of the electrophilic positions are prepared by thiolysis of halo-pyrimidines, or commonly by thiation of pyrimidinones using phosphorus pentasulfide or, more recently, the superior Lawesson reagent 2,4-bis-/ -methoxyphenyl-l,3,2,4-dithiadiphosphetane 2,4-disulfide. Thiolysis in the 5-position requires a metal sulfide and a 5-bromide under vigorous conditions. Alternatively, pyrimidines substituted with strongly electron-donating substituents may be sulfonated, for example, by chlorosulfonic acid, in the 5-position with subsequent reduction to thiol. 

Eyring and Wadsworth (50) and Little (51) present spectroscopic evidence that thiols bond to ZnO surfaces and xanthates bond to PbS surfaces by way of hydroxyl-exchange reactions in which metal-sulfide bonds are formed, and metal-hydroxyl bonds are broken during adsorption. We expect that trends exhibited in the relative stabilities of amino acid and hydroxo complexes of various dissolved cations should parallel trends in the relative reactivities and adsorption free energies, should this type of bonding control adsorption. 

The majorify of sulfur compounds (thioles and sulfides) have been successfully removed from liquid fuel using a hydrodesulfurization process where high temperature and high pressure are required [7-9, 159]. As mentioned in section 2.5 some sulfur species are very resistant to hydrodesulfurization and those include thiophenic compounds, especially dibenzothiophene and 4,6 dimethyldibenzothiophene [148]. Various methods based on extraction and adsorption have been proposed to remove these compounds [7, 8, 13,145, 147-149, 151-158]. In the extraction route, sulfiir species are first oxidized and then extracted using organic solvents as, for instance acetonitrille [13, 149]. On the other hand, an adsorption process is usually tailored to enhance either adsorption forces, selectivity, or to impose a chemical reaction. So fer the enhancement in the removal of thiophenic compounds was reported on materials where n-complexation can occur as on Cu-Y zeolites [151, 153], or on alumina with highly dispersed sodium [147]. In the latter case, mono- and disodium thiophene metallates are formed. Another desulfurization methods use formation and subsequent precipitation of S-alkylsulfonium salts [148]. 

Aromatic organosulfur compounds such as thiophenes, benzothiophenes and dibenzothiophenes are frequently contained in fossil oil and their sulfur atoms are generally difficult to remove in HDS process [106], In the industrial HDS process, Mo/Co/S or Ni/Mo/S heterogeneous catalysts supported on alumina are widely employed. In order to obtain ideas to develop more efficient catalysts as well as to shed some light on their mechanisms at a molecular level, transition metal complex-mediated cleavages of C-S bond are extensively studied. On the other hand, thiiranes and thietanes are frequently employed for preparation of transition metal sulfides, in which their C-S bonds are smoothly cleaved. In this section, the C-S bond cleavages of thiophene derivatives, thiiranes, thietanes, vinylic sulfides, allylic sulfides, thiols and dithioacetals are overviewed. 

Hydrodesulfurization [HDS, Eq. (1)] is the process by which sulfur is removed from fossil materials upon treatment with a high pressure of H2 (3.5-17 MPa) at high temperature (300-425 °C) in the presence of heterogenexius catalysts, generally transition metal sulfides (Mo, W, Co, Ni) supported on alumina [1]. About 90% of the sulfur in fossil materials is contained in thiophenic molecules, which comprise an enormous variety of substituted thiophenes, and benzo[b]thiophenes, di-benzo[b,d]thiophenes as well as other fused-ring thiophenes, most of which are generally less easily desulfurized over heterogeneous catalysts than any other sulfur compound in petroleum feedstocks (e.g., thiols, sulfide, and disulfides). 

When the solution contains thiols (RSH) in addition to other requisite metal salts and is irradiated with ionizing radiation, solvated electrons react with the thiol group (Equation 23.7) yielding HS", which reacts with metal ions producing metal sulfide (Equation 23.8) followed by nanoclusters ... 

Thus, the reaction mechanism is influenced by the nature of the alkyl group, R , since mercaptides of secondary and thertiary thiols and thiophenols cannot provide nucleophilic substitution (SN2). Thiophenol thermolysis usually results in a metal sulfide with diphenyl molecule formation as a by-product. However, these ionic compounds melt and decompose at high temperatures and therefore are not adequate for nanocomposite synthesis. 

Thyolysis reaction Analogous to hydrolysis, thiolysis involves reaction of H2S, in lieu of H2O, to form metal thiols, which subsequently condense to form metal sulfides TMB Trimethylbenzene TMCS Trimethylchlorosilane... 

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