Sulfur experimental conditions effects

The addition-elimination mechanism is also very common in the monocyclic oxygen and sulfur heterocycles (e.g. equation 20), a fact frequently cited as evidence for their low aromaticity. Pyran-2-ones can react with electrophiles at the 3- and 5-positions and pyran-4-ones at the 3-position (they also react at the carbonyl oxygen atom, but this is classified as a substituent reaction). Moreover, while the position of substitution can often be predicted on the basis of charge distribution and substituent effects, the choice of experimental conditions can also profoundly affect the outcome of the reaction, as illustrated in Schemes 2 and 3. 

One of the major results Berman et al. obtained is that the mole ratio of Ca in the absorbent to S in the flue gas has the most important effect. The experimental results for the influence of the Ca/S ratio on the sulfur-removal efficiency, jjs, at different concentrations of C02 in the flue gas are shown in Fig. 7.7. These data were obtained in a reactor with two co-axial cylinders the experimental conditions were flue gas flow rate Vo = 0.001 m3-s 1, diameter of Cylinder I in the reactor D, = 0.06 m, diameter of flue gas exit of the nozzle d = 10 mm, clearance between Cylinders I and II A2 = 5 mm. The results in Fig. 7.7 show the significant influence of C02 in flue gas on the sulfur-removal efficiency %. The reason for this is clear C02 reacts with the absorbent Ca(OH)2, too ... 

However, the sulfurization of the surface palladium has a detrimental effect on the consecutive hydrogenation (Fig. 17) the olefin yield is lower on sulfided palladium. Such a result is not in accordance with the literature cited above and this difference can be explained by differences in experimental conditions the improved consecutive selectivities were obtained with the sulfur present in the feedstock, i.e., in adsorption competition, when the detrimental effect on the consecutive hydrogenation was pointed out on partly sulfided palladium without sulfur compounds in the feedstock. The selectivity for olefin production in the hydrogenation of iso-prene is increased by the presence of sulfur in the substrate (Fig. 18). 

In this study subbituminous coals were liquefied and desulfurized effectively by hydrotreating with synthesis gas at moderate operating conditions In the presence of steam and anthracene oil used as a solvent. The data were compared when the same coals were liquefied with pure hydrogen under similar experimental conditions. Pyrltlc and organic sulfur present In these coals appear to be responsible for the formation of catalytic active form of Iron sulfide that functions as an effective hydrotreating catalyst (14). The presence of... 

The curing and dynamic properties of precipitated nano-silica on NR without and with the sulfur addition (NR with S), synthetic polyisoprene (IR), polybutadiene (BR) and SBR was investigated. Silica was treated with bis(3-triethoxysilylpropyl)tetrasulfane (TESPT) to form bonds at interfaces. Cure, Mooney viscosity, glass transition temperature, bound rubber, crosslink density and DMA were measured. The properties of silica-filled SBR and BR correlated with highest rolling resistance and SBR-silica correlated with best skid resistance. A Payne effect was observed in the loss modulus under some experimental conditions. In addition to possible filler de-agglomeration and network disruption, the nanoscale of the filler may have further contributed to the non-linear response typified by the Payne effect. ... 

Lewis et al. (1949) have discussed the three theories of browning presented by Stadtman (1948). They consider the theory that sulfur dioxide is effective because of preferential oxidation to be overruled by the fact that the sulfur dioxide was more effective under their anaerobic experimental conditions than when oxygen was present. Likewise, the theory that sulfur dioxide bleaches dark compounds during their forma-... 

The acid cleavage of the aryl— silicon bond (desilylation), which provides a measure of the reactivity of the aromatic carbon of the bond, has been applied to 2- and 3-thienyl trimethylsilane, It was found that the 2-isomer reacted only 43.5 times faster than the 3-isomer and 5000 times faster than the phenyl compound at 50,2°C in acetic acid containing aqueous sulfuric acid. The results so far are consistent with the relative reactivities of thiophene upon detritia-tion if a linear free-energy relationship between the substituent effect in detritiation and desilylation is assumed, as the p-methyl group activates about 240 (200-300) times in detritiation with aqueous sulfuric acid and about 18 times in desilylation. A direct experimental comparison of the difference between benzene and thiophene in detritiation has not been carried out, but it may be mentioned that even in 80.7% sulfuric acid, benzene is detritiated about 600 times slower than 2-tritiothiophene. The aforementioned consideration makes it probable that under similar conditions the ratio of the rates of detritiation of thiophene and benzene is larger than in the desilylation. A still larger difference in reactivity between the 2-position of thiophene and benzene has been found for acetoxymercuration which... 

Electron-accepting conjugative effects of sulfinyl and sulfonio groups may be seen in a few experimental observations. For example, it was reported twenty years ago that p-iodophenyl sulfoxide reacted readily with alkali hydroxide whereas the m-isomer did not react under the same conditions . More recent quantitative data on the electron-accepting effects of these tri- and tetra-coordinated sulfur-containing groups can be found in the quantitative data on reactivities, listed in Table 6. 

Theoretical studies have been done in order to understand this behavior difference. Semiempirical calculations (AMI, MNDO) of formation energy (of the hemithio-ketal-hemiketal interconversion) have shown that hemithioketals are less stable than the corresponding hemiketal (from 10 to 15 kcal/mol). This difference can be due to steric factors, connected to the respective sizes of sulfur and oxygen. Stereoelectronic factors can also be evoked stabilization that is brought about by the anomeric effect is a priori more important for a gem-dihydroxylated compound than for the hemi-thioketal. Moreover, at the kinetic level, displacement of the water molecule of the inhibitor (under aqueous conditions, the inhibitor is hydrated) by the thiol of the enzyme is a slow and disfavored reaction. In contrast, the same reaction is favored with the hydroxyl of a serine. Experimentally, equilibrium occurs very slowly with the enzyme as well as with model molecules. ... 

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