Sulfur monoclinic

Sulfuration. Hydiocaibons, such as cyclohexane and / -pentane have been converted to dicyclohexyl and dipentyl sulfides by monoclinic sulfur... 

Sulfur crystallizes in at least two distinct systems the rhombic and the monoclinic forms. Rhombic sulfur, Sa, is stable at atmospheric pressures up to 95.5°C, at which transition to monoclinic sulfur, SP, takes place. Monoclinic sulfur is then stable up to its natural melting point of 114.5°C. The basic molecular unit of both of these crystalline forms of sulfur is the octatomic sulfur ring Other forms of sohd sulfur include hexatomic sulfur as well as... 

At about 95.3 " a-Sg becomes unstable with respeci to -monoclinic sulfur in which the packing of the Sg molecules is altered and their... 

Figure 15.4 Various representations of the molecule cycloSf fouud iu tr-orthorhombic, -monoclinic, and y-monoclinic sulfur.

Sulfur has about 20 different allotropes. The most common are rhombic sulfur (file stable form at 25°C and 1 atm) and monoclinic sulfur. They differ in their crystal structures. Given... 

E6.7 Bronsted measured the solubility of solid orthorhombic and monoclinic sulfur at 298.15 K in various solvents (benzene, diethyl ether and ethanol). He found that the solubility of monoclinic sulfur is always 1.28 times that of orthorhombic sulfur. That is, the concentration of sulfur in the solution in equilibrium with monoclinic sulfur is always 1.28 times the concentration of sulfur in the solution in equilibrium with orthorhombic sulfur. Sulfur exists in these solvents exclusively in the form of Sg molecules. 

E8.2 Solid monoclinic sulfur spontaneously converts to solid rhombic sulfur at 298.15 K and 0.101 MPa pressure. For the conversion process ... 

Elemental sulfur exists in several forms, with rhombic-sulfur the most stable under normal conditions and monoclinic sulfur slightly less stable. The standard enthalpies of combustion of the two forms (to sulfur dioxide) are —296.83 kj-mol 1 and —297.16 kj-mol, respectively. Calculate the enthalpy of the rhombic —> monoclinic transition. 

Sei.f-Tf.ST 8.4B From the phase diagram for sulfur (Fig. 8.8), predict which phase is more dense, liquid sulfur or monoclinic sulfur. Explain your conclusion. 

In Fig. 8.8, we see that sulfur can exist in any of four phases two solid phases (rhombic and monoclinic sulfur), one liquid phase, and one vapor phase. There are three triple points in the diagram, where various combinations of these phases, such as monoclinic solid, liquid, and vapor or monoclinic solid, rhombic solid, and liquid, coexist. However, four phases in mutual equilibrium (such as the vapor, liquid, and rhombic and monoclinic solid forms of sulfur, all in mutual equilibrium) in a one-component system has never been observed, and thermodynamics can be used to prove that such a quadruple point cannot exist. 

FIGURE 15.12 One of the two most common forms of sulfur is the blocklike rhombic form (a). It differs from the needlelike monoclinic sulfur tb) in the manner in which the S8 rings are stacked together. 

Elemental sulfur is a yellow, tasteless, almost odorless, insoluble, nonmetallic molecular solid of crownlike S8 rings (9). The two common crystal forms of sulfur are monoclinic sulfur and rhombic sulfur. The more stable form under normal conditions is rhombic sulfur, which forms beautiful yellow crystals (Fig. 15.12). At low temperatures, sulfur vapor consists mainly of S8 molecules. At temperatures above 720°C, the vapor has a blue tint from the S, molecules that form. The latter are paramagnetic, like O,. 

B The positive slope of the solid-liquid boundary shows that monoclinic sulfur is more dense than liquid sulfur over the temperature range in which monoclinic sulfur is stable the solid is more stable at high pressure. 

Williams and Rastetter also accomplished an elegant synthesis of ( )-hyalodendrin (83) in 1980 [39]. Beginning with the sarcosine anhydride-derived enolic aldehyde 78, silyl protection of the enal enabled alkylation of the glycine center with benzyl bromide and thiolation using LDA and monoclinic sulfur a la Schmidt. After protection of the thiol with methylsulfenyl chloride and deprotection of the silyl ether, the enol was sulfenylated with triphenylmethyl chlorodisulfide to afford bis(disulfide) 82 as a 2 1 mixture of diastereomers favoring the anti isomer. Reduction of the disulfides with sodium borohydride and oxidation with KI3 in pyridine afforded ( )-hyalodendrin (83) in 29 % yield (Scheme 9.4). 

Figure 1.6 Heat capacity of rhombic and monoclinic sulfur [4,5] and the derived entropy of transition between the two polymorphs.

The third law of thermodynamics can be verified experimentally. The stable rhombic low-temperature modification of sulfur transforms to monoclinic sulfur at 368.5 K (p = 1 bar). At that temperature, Ttrs, the two polymorphs are in equilibrium and the standard molar Gibbs energies of the two modifications are equal. We therefore have... 

Monoclinic crystal system, 8 114t Monoclinic parallelepiped lattice, 8 114t Monoclinic sulfur, 23 565 Monoclinic symmetry, 8 114t Monoclonal antibodies, 3 847 72 150, 475 cell culture technologies used for,... 

Rhombic sulfur is the stable form at room temperature, and monoclinic sulfur is the metastable form. The transition temperature is 95.5°C. The melting point of monoclinic sulfur is 120°C. How would you evaluate a report that 77°C is the melting point of rhombic sulfur Answer in terms of a diagram of Gibbs function versus temperature for this system. 

OK can be computed from heat capacity measurements [8] for each crystalline form from near 0 K to the transition temperature (368.6 K) and the heat of transition. The result is zero within experimental error. Hence, both rhombic and monoclinic sulfur ate assigned zero entropy at 0 K. 

The solubility of monoclinic sulfur in CS2 is 22-molal. What is the solubility of rhombic sulfur in the same solvent Assume that the activity coefficient for both forms of dissolved sulfur is 1. 

The first structure determination of j3-monoclinic sulfur, which forms from j8-orthorhombic by phase transition at 94.2°C, was performed by Trillat and Forestier (113). Burwell (13) and Sands (85) refined the structure ... 

Irradiation of sulfur by various means yields discoloration of elemental sulfur, but it is doubtful that these forms will ever lead to pure allotropes. Above 92°C, a-sulfur converts into monoclinic sulfur. The kinetics of the transformation depend on various factors. Thermal analysis of single crystals of a-sulfur shows that the conversion is so slow that a-sulfur can be heated to 112°C, where it melts, before j8-sulfur is formed (19). 

Both rhombic and monoclinic sulfur contain eight sulfur atoms per cyclic molecule in a crown (distorted octagon) configuration. 

Elemental sulfur exhibits complicated allotropy, that is, it exists in many modifications.4 The stable, prismatic crystal form at room temperature, a-S or orthorhombic sulfur, is built up of stacks of Ss rings (Section 3.4). If heated quickly, it melts at 112.8 °C. If it is heated slowly, however, it changes to needlelike crystals of /3-S or monoclinic sulfur, which is the stable form above 95.5 °C and which melts at 119 °C. Both 0-S and the yellow mobile melt (below 160 °C) are composed exclusively of Ss rings. Solids containing S7, Sg, S10, S12, and other rings are known, but all slowly revert to Sg below 160 °C. 

The enthalpy of combustion of rhombic sulfur is -70.96 kcal/mole. The enthalpy of combustion of monoclinic sulfur is -70.88 kcal/mole. Calculate the standard enthalpy and entropy of transition from rhombic to monoclinic sulfur. 

Sulfur with two forms, alpha-rhombic sulfur with a density of 2.07 and a mp of I I2.8°C. and bela-monoclinic sulfur with a density of 1.96 and a mp of I I9 C. The beta form changes to the alpha form below WC. 

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