Sulfide catalysis

Sulfided catalysis are used to minimize reduciion of the carbonyl to an alcohol. 

Compensation-type behavior is quite general and has been extensively studied, especially in transition-metal catalysis [8a], sulfide catalysis [8b], and zeolite catalysis [7]. 

Bagreev, A., Katikaneni, S., Parab, S., and Bandosz, T.J. Desulfurization of digester gas Prediction of activated carbon bed performance at low concentrations of hydrogen sulfide. Catalysis Today, 2005, 99, 329. 

MONTANO ET AL. Iron Sulfide Catalysis in Coal Liquefaction... 

Recent studies by Moreau et al. (1988, 1991) have established the effectiveness of sulfided catalysis in the synthesis of organic intermediates and small-volume chemicals. An example is the hydroprocessing of chloronitrobenzenes over a sulfided industrial catalyst HR 306 (3% CoO, 14% M0O3 on 7-alumina) at T = 50-250 °C and P = 2Q atm. 

Often surface reconstruction occurs at higher adsorbate surface concentrations within the overlayer. Reconstruction can lead to more reactive surface phases. As we will see in Chapter 3, the kinetic implication is that mean-field theory does not always apply since the reactions now predominantly occur at the boundaries of the different overlayer phases present on the catalyst. Similarly Chapter 5 treats, in detail, examples from oxide and sulfide catalysis which show the importance of surface phase changes in relation to catalytic activity. 

The conclusion from these studies is that under practical sulfide catalysis conditions, both the Mo edge and the S edge contain coordinatively saturated Mo atoms. The bright rim of white spots in the STM picture (Fig. 5.25) near the sulfide particle edge is indicative... 

The thioboration of terminal alkynes with 9-(alkylthio)-9-borabicyclo[3.3.1]-nonanes (9-RS-9-BBN) proceeds regio- and stereoselectively by catalysis of Pd(Ph,P)4 to produce the 9-[(Z)-2-(alkylthio)-l-alkeny)]-9-BBN derivative 667 in high yields. The protonation of the product 667 with MeOH affords the Markownikov adduct 668 of thiol to 1-alkyne. One-pot synthesis of alkenyl sulfide derivatives 669 via the Pd-catalyzed thioboration-cross-coupling sequence is also possible. Another preparative method for alkenyl sulfides is the Pd-catalyzed cross-coupling of 9-alkyl-9-BBN with l-bromo-l-phe-nylthioethene or 2-bromo-l-phenylthio-l-alkene[534]. 

Aryl sulfides are prepared by the reaction of aryl halides with thiols and thiophenol in DMSO[675,676] or by the use of phase-transfer catalysis[677]. The alkenyl sulfide 803 is obtained by the reaction of lithium phenyl sulfide (802) with an alkenyl bromide[678]. 

Sulfides (172) in which Rj = alkyl can be obtained also by direct alkylation of the 2-mercaptothiazoles either in alcaline medium (156, 597) or by phase-transfer catalysis in better yield (824). 

The hberated iodine, as the complex triiodide ion, may be titrated with standard thiosulfate solution. A general iodometric assay method for organic peroxides has been pubUshed (253). Some peroxyesters may be determined by ferric ion-catalyzed iodometric analysis or by cupric ion catalysis. The latter has become an ASTM Standard procedure (254). Other reducing agents are ferrous, titanous, chromous, staimous, and arsenite ions triphenylphosphine diphenyl sulfide and triphenjiarsine (255,256). 

Hydrogen Sulfide andMercaptans. Hydrogen sulfide and propylene oxide react to produce l-mercapto-2-propanol and bis(2-hydroxypropyl) sulfide (69,70). Reaction of the epoxide with mercaptans yields 1-aLkylthio- or l-arylthio-2-propanol when basic catalysis is used (71). Acid catalysts produce a mixture of primary and secondary hydroxy products, but ia low yield (72). Suitable catalysts iaclude sodium hydroxide, sodium salts of the mercaptan, tetraaLkylammonium hydroxide, acidic 2eohtes, and sodium salts of an alkoxylated alcohol or mercaptan (26,69,70,73,74). 

Catalysis by Metal Sulfides. Metal sulfides such as M0S2, WS2, and many others catalyze numerous reactions that are catalyzed by metals (98). The metal sulfides are typically several orders of magnitude less active than the metals, but they have the unique advantage of not being poisoned by sulfur compounds. They are thus good catalysts for appHcations with sulfur-containing feeds, including many fossil fuels. 

The most intensively studied oxidizing system is that developed by Pfitzner and Moflatt in which the oxidation is carried out at room temperature in the presence of dicyclohexylcarbodiimide (DCC) and a weak acid such as pyridinium trifluoroacetate or phosphoric acid. The DCC activates the DMSO which in turn reacts with the carbinol to give an oxysulfonium intermediate. This breaks down under mild base catalysis to give the desired ketone and dimethyl sulfide. 

The performance of VASP for alloys and compounds has been illustrated at three examples The calculation of the properties of cobalt dislicide demonstrates that even for a transition-metal compound perfect agreement with all-electron calculations may be achieved at much lower computational effort, and that elastic and dynamic properties may be predicted accurately even for metallic systems with rather long-range interactions. Applications to surface-problems have been described at the example of the. 3C-SiC(100) surface. Surface physics and catalysis will be a. particularly important field for the application of VASP, recent work extends to processes as complex as the adsorption of thiopene molecules on the surface of transition-metal sulfides[55]. Finally, the efficiciency of VASP for studying complex melts has been illustrate for crystalline and molten Zintl-phases of alkali-group V alloys. 

Nucleophilic catalysis is also observed with iodide ions. Fluoride ion does not form nitrosyl fluoride under diazotization conditions, as is to be expected from Pearson s hard and soft acids and bases principle which was discussed briefly in Section 3.2. More recently, nucleophilic catalysis has also been shown to occur with thiocyanate ion (SCN ), thiosulfate ion (HS2Of), dimethyl sulfide, and thiourea (H2NCSNH2) or its alkyl derivatives (see below). 

The selection of the thirty procedures clearly reflects the current interest of synthetic organic chemistry. Thus seven of them illustrate uses of T1(I), T1 (III), Cu(I), and Li(I), and three examples elaborate on the process now termed phase-transfer catalysis. In addition, newly developed methods involving fragmentation, sulfide contraction, and synthetically useful free radical cyclization arc covered in five procedures. Inclusion of preparations and uses of five theoretically interesting compounds demonstrates the rapid expansion of this particular area in recent years and will render these compounds more readily and consistently available. 

ALKYL-l-ALKYNES, 58, 1 ALKYL ARYL SULFIDES, 58,143 Alkyl aryl thioethers, 58,145 Alkylation, enolates, 56, 52 C-ALKYLATION, phase transfer catalysis... 

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