Sulfides solid support

This work is a contribution to the understanding of the effect of spillover hydrogen in a type of catalyst of considerable industrial importance, namely that composed of transition metal sulfides and amorphous acidic solids. This is typically the case of sulfided CoMo supported on silica-alumina used for mild hydrocracking. 

A solid-phase sulfur oxidation catalyst has been described in which the chiral ligand is structurally related to Schiff-base type compounds (see also below). A 72% ee was found using Ti(OPr-i)4, aqueous H2O2 and solid-supported hgand 91 . More recently, a heterogeneous catalytic system based on WO3, 30% H2O2 and cinchona alkaloids has been reported for the asymmetric oxidation of sulfides to sulfoxides and kinetic resolution of racemic sulfoxides. In this latter case 90% ee was obtained in the presence of 92 as chiral mediator. ... 

Recently, Kerr introduced a promoter anchored to a solid support to facilitate workup after the reaction. For example, the PKR proceeds to completion by use of the amine A-oxide anchored on solid support 14, and then the polymeric amine is recovered by simple filtration. The recovered polymer is cleaned by washing with a THF-aqueous 2 M HGl mixture (2 1 mixture), followed by washing of hydrochloride salt with a 10% solution of Pr2NEt in DMF. The resultant resin is oxidized again and then used without loss of activities.Kerr and Pauson also successfully employed sulfide promoters anchored on the solid support 15 for this cycloaddition (Figure 1). ... 

The synthesis uses Evans chemistry to introduce enantioselectively an azide group, which is then reduced to the a-amino group (Scheme 16). Note that in all cases, the phosphinyl group is protected as its sulfide during the synthesis to avoid complication (oxidation) observed with the phosphine. The phosphine sulfide is compatible with Fmoc- and Boc-peptide synthesis conditions. The free phosphine can later be regenerated by treating the sulfide with Raney nickel in MeOH (as shown in Scheme 15) or by methylation followed by treatment with HMPTJ50 This reduction was even applied successfully to sulfide-protected phosphine peptides still attached to the solid support.151 ... 

Many of the catalysts for the hydrodesulfurization process are produced by combining (Table 5-5) a transition metal (or its salt) with a solid support. The metal constituent is the active catalyst. The most commonly used materials for supports are alumina, silica, silica-alumina, kieselguhr, magnesia (and other metal oxides), as well as the zeolites. The support can be manufactured in a variety of shapes or may even be crushed to particles of the desired size. The metal constituent can then be added by contact of the support with an aqueous solution of the metal salt. The whole is then subjected to further treatment that will dictate the final form of the metal on the support (i.e., the metal oxide, the metal sulfide, or even the metal itself). 

A few benzisoselenazol-3(2//)-oncs were covalently immobilized to the solid support, either silica [165] or polymer [246] (147-150) (Fig. 8). They exhibited appreciable catalytic activity similar to the activity of ebselen. The most interesting prospective oxygen-transfer catalyst is benzisoselenazolone covalently bound to a silica support (147) named HALICAT. It has been applied to hydrogen peroxide oxidation of the sulfides and TBHP oxidation of the aromatic aldehydes and alky-larenes. The catalyst can be easily filtered off from the mixture after the reaction and reused several times [165],... 

Catalysts were some of the first nanostructured materials applied in industry, and many of the most important catalysts used today are nanomaterials. These are usually dispersed on the surfaces of supports (carriers), which are often nearly inert platforms for the catalytically active structures. These structures include metal complexes as well as clusters, particles, or layers of metal, metal oxide, or metal sulfide. The solid supports usually incorporate nanopores and a large number of catalytic nanoparticles per unit volume on a high-area internal surface (typically hundreds of square meters per cubic centimeter). A benefit of the high dispersion of a catalyst is that it is used effectively, because a large part of it is at a surface and accessible to reactants. There are other potential benefits of high dispersion as well— nanostructured catalysts have properties different from those of the bulk material, possibly including unique catalytic activities and selectivities. 

Procedural variations of the oxidation of sulfides with Phl=0 include micellar medium containing a quaternary ammonium salt, and dispersion on a solid support. While the former reaction gives sulfoxides, the latter can lead to C-S bond cleavage. 

MW protocols for oxidation-reduction reactions using immobilized reagents on solid supports have been extensively explored. The oxidation of sulfides to sulfoxides and sulfones was also developed under MW irradiation with good... 

To the fully derivatized product on the solid support was then added TFA/ H20/dimethyl sulfide (15 mL 95 5 10) and the mixture was stirred for 12 h. The cleavage solution was removed by filtration through a caimula, and the resin was rinsed wfith an appropriate solvent (e. g., MeOH/CH2Cl2). Concentration of the combined filtrates then provided the crude product 6. The products could be purified by chromatography on siHca gel with hexane/ EtOAc (50-0/0.5-100%) as eluent to give the purified products in yields of 52-82%. 

Alternative to High Dilution Techniques. The macrocyclization of terminal dibromoalkanes with sodium sulfide was performed onto alumina (Na2S/ AI2O3). In this case, the use of a solid support for intramolecular cyclization represents a viable alternative procedure to the more traditional high dilution technique in solution [Eq. (9)] [16,17]. 

Solid-Supported Surface Catalysis by Metal Complexes. Hong et al. (1987a, b, in press) have prepared a variety of hybrid catalysts between Co(II) phthalocyanine complexes and the surfaces of silica gel, polystyrene-divinylben-zene, and Ti02 and tested these hybrids for catalytic activity with respect to the autoxidation of hydrogen sulfide, sulfur dioxide, 2-mercaptoethanol, cysteine, and hydrazine ... 

To the solid support and the finely ground oxidant (SPC or SPB as appropriate) was added the appropriate sulfide. The mixture was heated in a screw-cap sealed reaction vessel in an aluminum block at the temperature and for the time indicated. The reaction mixture was allowed to cool to room temperature. The products were isolated by extraction with methanol (60 mL). Solvent and unreacted reagent were removed in vacuo and the residue was weighed and analyzed by H-NMR spectroscopy. 

Sucholeiki [152] has recently suggested the use of benzyl sulfide photocleavage for detachment from a solid support. His results are consistent with Fleming s work. The pam-phenyl-substituted benzyl sulfide, 108 R = Ph, has enhanced benzylic cleavage compared to benzyl sulfide, 108 R = H. The increase in benzyl cleavage precludes the competitive Norrish type n reaction pathway which is shown in Eq. (40). However, the wavelength of excitation was... 

Anodic a-methoxylation of phenyl 2,2,2-trifluoroethyl sulfide was carried out using various solid-supported bases as shown in Equation 12.6. Polystyrene and silica -gel are suitable as the solid support for an organic base such as piperidine. It is noteworthy that anodic methoxylation was successfully carried out even after 10 recycles of the solid-supported base. The method has also been successfully applied to electrochemical acetoxylation in acetic add/acetonitrile. 

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