Sulfides thermodynamics

Electronic levels (T ) and vibrational-rotational constants of the observed states are from the optical study of Barrow et al. (J ) and the microwave work of Tiemann et al. (2). Other low-lying electronic states and their vibrational-rotational constants are estimated in isoconfIgurational groups by analogy with BaO (8) and from trends observed in the known states of the other alkaline-earth oxides and sulfides. Thermodynamic functions are calculated using first-order anharmonlc corrections to and in the partition function Q = exp(-c ej /T). Uncertainty in the energy and molecular constants for the... 

Gas-phase desulfurization using ZnO is the approach that we have pursued in past years. ZnO is an attractive adsorbent for on-board fuel processing because of its favorable sulfidation thermodynamics (<1 ppmv). The sulfidation equilibrium for ZnO (ZnO + H2S o ZnS + H2O) is a function of the temperature and the ratio of the partial pressure of H2O/H2S. To reduce the H2S concentration to <0.1 ppmv requires a temperature of 300-350°C based on the typical range of H2O concentrations present in the reformate (Carter et al. 2001). However, it has been observed that although the equilibrium becomes more favorable as the... 

The existence of reduced volatile phosphorus compounds in aquatic systems has been in question for several decades (Morton and Edwards, 2005). Similar to nitrate reduction to ammonia (dissimi-latory nitrate reduction, see Chapter 8) and sulfate reduction to sulfide, thermodynamic reduction of phosphate to phosphine is possible. Under highly anaerobic conditions, phosphate (oxidation number of +5) can be reduced by obligate anaerobes to phosphine (oxidation number of-3). 

Ma.nufa.cture. Nickel carbonyl can be prepared by the direct combination of carbon monoxide and metallic nickel (77). The presence of sulfur, the surface area, and the surface activity of the nickel affect the formation of nickel carbonyl (78). The thermodynamics of formation and reaction are documented (79). Two commercial processes are used for large-scale production (80). An atmospheric method, whereby carbon monoxide is passed over nickel sulfide and freshly reduced nickel metal, is used in the United Kingdom to produce pure nickel carbonyl (81). The second method, used in Canada, involves high pressure CO in the formation of iron and nickel carbonyls the two are separated by distillation (81). Very high pressure CO is required for the formation of cobalt carbonyl and a method has been described where the mixed carbonyls are scmbbed with ammonia or an amine and the cobalt is extracted as the ammine carbonyl (82). A discontinued commercial process in the United States involved the reaction of carbon monoxide with nickel sulfate solution. 

Physica.1 Properties. Carbonyl sulfide [463-58-1] (carbon oxysulfide), COS, is a colorless gas that is odorless when pure however, it has been described as having a foul odor. Physical constants and thermodynamic properties are Hsted ia Table 1 (17,18). The vapor pressure has been fitted to an equation, and a detailed study has been made of the phase equiUbria of the carbonyl sulfide—propane system, which is important ia the purification of propane fuel (19,20). Carbonyl sulfide can be adsorbed on molecular sieves (qv) as a means for removal from propane (21). This approach has been compared to the use of various solvents and reagents (22). 

Table 1. Physical and Thermodynamic Properties of Carbonyl Sulfide...

Chemical Properties. Although hydrogen sulfide is thermodynamically stable, it can dissociate at very high temperatures. The decomposition thermodynamics and kinetics have been reviewed and the equihbrium constant for the reaction has been deterrnined (101,102) ... 

Transition elements, for which variable valency is energetically feasible, frequently show non-stoichiometric behaviour (variable composition) in their oxides, sulfides and related binary compounds. For small deviations from stoichiometry a thermodynamic approach is instructive, but for larger deviations structural considerations supervene, and the possibility of thermodynamically unstable but kinetically isolable phases must be considered. These ideas will be expanded in the following paragraphs but more detailed treatment must be sought elsewhere. " ... 

Hydrogen sulfide is the only thermodynamically stable sulfane it occurs widely in nature as a result of volcanic or bacterial action and is, indeed, a prime source of elemental 8 (p. 647). It has been known since earliest times and its classical chemistry has been extensively studied since the seventeenth century.H28 is a foul smelling, very poisonous gas familiar to all students of chemistry. Its smell is noticeable at 0.02 ppm but the gas tends to anaesthetize the olefactory senses and the intensity of the smell is therefore a dangerously unreliable guide to its concentration. H28 causes irritation at 5 ppm, headaches and nausea at 10 ppm and immediate paralysis and death at 100 ppm it is therefore as toxic and as dangerous as HCN. 

Contrary to the expectation that a sulfur-containing substituent will be a catalyst poison, a phenylthio group serves as an effective selectivity control element in TMM cycloadditions. A single regioisomer (30) was obtained from the carbonate precursor (31) in good yield. The thermodynamically more stable sulfide (32) is readily accessible from (30) via a 1,3-sulfide shift catalyzed by PhSSPh. A wide array of synthetically useful intermediates could be prepared from the sulfides (30) and (32) with simple transformations (Scheme 2.10) [20]. 

Sulfur compounds, whether organic or inorganic in nature, cause sulfidation in susceptible materials. The sulfide film, which forms on the surface of much con-stmction materials at low temperatures, becomes friable and melts at higher temperatures. The presence of molten sulfides (especially nickel sulfide) on a metal surface promotes the rapid conversion to metal sulfides at temperatures where these sulfides are thermodynamically stable. High-alloy materials such as 25% Cr, 20% Ni alloys are widely used, but these represent a compromise between sulfidation resistance and mechanical properties. Aluminum and similar diffusion coatings can be of use. 

Carbon tetrachloride-hydrogen sulfide-water ternary system, 49, 51, 52 Carboniuin ion polymerization, 158 Carboxylic groups initiator, 174 Catalyst clathrates equilibrium, 35 Cell partition function, in calculation of thermodynamic quantities of clathrates, 26... 

Projections, linearly independent, 293 Propagation, of polymerization, 158 Propane, hydrate, 10, 33, 43, 46, 47 hydrate thermodynamic data and lattice constants, 8 + iodoform system, 99 Langmuir constant, 47 water-hydrogen sulfide ternary system, 53... 

These results indicate that the a-lithio sulfides are not configurationally stable at —78 C and thus, the high diastereoselectivity reflects the thermodynamic preference of 35 A over 35B3). 

Sulfur. It is not readily predictable from existing thermodynamic data that sulfur would be a poison of nickel catalysts. The action of sulfur is undoubtedly through the reaction of hydrogen sulfide with nickel, according to ... 

The equilibrium ratios of hydrogen-to-hydrogen sulfide for the reaction, derived (34) from available thermodynamic data (35), are plotted in Figure 10 as a function of temperature. When Ph2/Ph2s over the catalyst is less than the equilibrium value, the nickel can be sulfided and hence poisoned. Conversely, when this ratio is greater than the equi-... 

Therefore, polysulfide ions play a major role in the global geological and biological sulfur cycles [1, 2]. In addition, they are reagents in important industrial processes, e.g., in desulfurization and paper production plants. It should be pointed out however that only sulfide, elemental sulfur and sulfate are thermodynamically stable under ambient conditions in the presence of water, their particular stabihty region depending on the redox potential and the pH value [3] ... 

Aqueous polysulfide solutions are thermodynamically unstable with respect to thiosulfate and sulfide. Therefore, on heating to 150-240 °C under anaerobic conditions polysulfide ions disproportionate reversibly [72, 80, 104], e.g. ... 

K. C. Mills, Thermodynamic Data for Inorganic Sulfides, Selenides and Tellurides, Butterworths, London, 1974. 

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