Polysulfide Hydrogenation Catalyst

of ice, and 130 ml. of concentrated sulfuric acid. The reaction mixture is held at 0° during this operation. Stirring at 0° is continued for 2 hours after addition of the zinc, and then the mixture is carefully heated to reflux. The crystalline precipitate is filtered off and suspended in a boiling mixture of 720 ml. of water and 130 ml. of concentrated sulfuric acid. Another 120 g. of zinc dust is added to the refluxing mixture in small portions. The mixture is steam-distilled, and 35 g. (70%) of p-chlorothiophenol is separated from the distillate. The product melts at 51-53.5°. 

Fifty grams (0.38 mole) of freshly distilled cinnamaldehyde is added to 85 g. of phosphorus pentachloride with agitation and exclusion of moisture from the apparatus. The mixture is stirred and heated on a water bath for 2-3 hours. The excess phosphorus pentachloride and the phosphorus oxychloride are distilled off under vacuum, and the residue is subjected to further vacuum distillation. The product is collected at 121-122°/14 mm., and the solid obtained is recrystallized from petroleum ether (b.p. 40-60°). Cinnamal chloride is obtained in 82-85% yield, and the product melts at 58.5-59°. 

Farlow, Hunt, Langkammerer, Lazier, Peppel, and Signaigo, J. Am. Chem. Soc., 70, 1393 (1948). 

A mixture of 1.5 1. of water, 240 g. (1.0 mole) of sodium sulfide nonahydrate, and 64 g. (2.0 gram atoms) of sulfur is stirred until the sulfur dissolves. After filtration the solution is added (10-15 minutes) with stirring to a solution of 242 g. (1.02 moles) of cobalt chloride hexahydrate in 1.7 1. of water. Stirring is continued for an additional 

30 minutes the solid is removed by suction filtration and washed with water until the filtrate is colorless. The remaining hard paste weighs 750 g. to 1 kg. and contains about 150 g. of cobalt trisulfide (15-20% solid). It should be stored out of contact with air. 

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Hydrogen cyanide (HCN) and aliphatic nittiles (RCN) can be used to form imidazolines. For example, EDA and HCN form 2-imidazoline (38). In the presence of sulfur or polysulfides as catalysts, 2-aIkyl-2-imidazolines can be prepared from ahphatic nitriles and EDA (39,40). 

Catalytic hydrogenation of thiophene poses a problem since noble metal catalysts are poisoned, and Raney nickel causes desulfurization. Best catalysts proved to be cobalt polysulfide [425], dicobalt octacarbonyl [426], rhenium heptasulfide [5i] and rhenium heptaselenide [54]. The last two require high temperatures (230-260°, 250°) and high pressures (140, 322 atm) and give 70% and 100% of tetrahydrothiophene (thiophane, thiolene), respectively. 

Among the sulfides of molybdenum, cobalt, nickel, iron, rhodium, rhenium, osmium, and ruthenium, only the polysulfide of cobalt153 and the sulfide of ruthenium showed good selectivities. Optimum conditions over cobalt polysulfide included temperatures of 85-120°C, hydrogen pressures of 2.8-6.9 MPa, substrate concentrations of up to 25%, and substrate catalyst ratios of 50-80 1 (g of feed/g of Co). A typical run is shown in eq. 9.64. The hydrogenation over ruthenium disulfide was successful... 

The nse of polysnlfide complexes in catalysis has been discnssed. Two major classes of reactions are apparent (1) hydrogen activation and (2) electron transfers. For example, [CpMo(S)(SH)]2 catalyzes the conversion of nitrobenzene to aniline at room temperature, while (CpMo(S))2S2CH2 catalyzes a number of reactions snch as the conversion of bromoethylbenzene to ethylbenzene and the rednction of acetyl chloride, as well as the rednction of alkynes to the corresponding cw-alkenes. Electron transfer reactions see Electron Transfer in Coordination Compounds) have been studied because of their relevance to biological processes (in, for example, ferrodoxins), and these cluster compounds are dealt with in Iron-Sulfur Proteins. Other studies include the use of metal polysulfide complexes as catalysts for the photolytic reduction of water by THF and copper compounds for the hydration of acetylene to acetaldehyde. ... 

The selective hydrogenation of an aryl nitro group has been accomplished even in the presence of an easily hydrogenated acetylene group. Cobalt polysulfide and ruthenium sulfide have been reported to be effective for the selective hydrogenation of the nitro group in m-nitrophenyl acetylenes giving the amino-acetylenes in 75-85% yields (Eqn. 19.2). Ruthenium catalysts were also effective for this reaction but since the order of reactivity over these catalysts was found to be ... 

Saturated elastomers are often cured by peroxide, often aided by catalysts. These include chlorinated polyethylene, fluorocarbon, acrylic ester, epichlorohydrin, polysulfide, polyurethane, and silicone. The peroxide radical abstracts an unstable hydrogen from the polymer, leaving a polymer radical, and then polymer radicals couple to produce C-C cross-links. 

Improved pre-sulfurised eatalysts eontaining polysulfides or metal oxysul-fides were later developed to overcome these problems. Polysulfides still react rapidly with hydrogen during eonversion of the eobalt, nickel, and molybdenum oxides to sulfides and prodnee a temperature rise in the catalyst bed. On the other hand, metal oxysulfides react slowly over a much wider temperature range and do not produce an exotherm. 

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