Sulfur polysulfide melt

The process of sulfurization is usually carried out by a sulfur bake, in which the dry organic starting material is heated with sulfur between 160 and 320°C a polysulfide bake, which includes sodium sulfide a polysulfide melt, in which aqueous sodium polysulfide and the organic starting material are heated under reflux or under pressure in a closed vessel or a solvent melt, in which butanol, CeUosolve, or dioxitol are used alone or together with water. 

Polysulfide Melt. Cl Sulfur Black 1 [1326-82-5] (Cl 53185), derived from 2,4-dinitrophenol, is the most important dye in this group which also includes the indophenol-type intermediates. The latter are appHed in the stable leuco form. The derived dyes are usually confined to violet, blue, and green shades. Other members of this group are intermediates capable of forming quinoneimine (10) or phenazone stmctures (11) that produce red-brown or Bordeaux shades ... 

Polysulfides are the key reactants in the high-density sodium-sulfur and Hthium-sulfur batteries [4] which are based on the following reversible redox reaction taking place in the polysulfide melt ... 

The understanding of the reduction process of sulfur requires the identification of the reduced forms of sulfur, that is, polysulfides or S . The phase diagrams of M2S —Sg systems (where M is an alkali-metal cation) have been reviewed [23], as also the properties of polysulfide melts [24]. Many polysulfides have been characterized in the solid state by x-ray diffraction, infrared and Raman spectroscopy [25]. The identification of polysulfides in solution is often rather difficult. The reason is that the dissolution of a M2S polysulfide leads, for most of them, to a disproportionation process of the type ... 

Sulfur dyes are a special class of dyes with regard to both preparation and application, and knowledge of their chemical constitution [1], They are made by heating aromatic or heterocyclic compounds with sulfur or species that release sulfur. Sulfur dyes are classified by method of preparation as sulfur bake, polysulfide bake, and polysulfide melt dyes. Sulfur dyes are not well-defined chemical compounds but mixtures of structurally similar compounds, most of which contain various amounts of both heterocyclic and thiophenolic sulfur. 

This class of compounds also includes phcnazone, phenothiazone, and phe-noxazone derivatives (12), and so these polysulfide melt dyes are also referred to as quinoneimine or indophenol sulfur dyes. 

The structure 15 can thus be regarded as the prototype of the polysulfide-melt dyes (quinoneimine or indophenol sulfur dyes) (Scheme 2.8). 

Polysulfide melt dyes, which are applied chiefly with dithionite and commonly show a higher degree of fastness, are called sulfur vat dyes. They include such dyes as C.I. Vat Blue 43 and C.I. Sulphur Black 11. 

The polysulfide melt process yields mainly reddish brown, violet, blue, green, and black sulfur dyes, depending on the intermediate. 

With polysulfide melt dyes (i.e., quinoneimine sulfur dyes), the reducing agent can attack not only the disulfide groups but also the quinoneimine group (as in the case of vat dyes). Dispersible pigments are used particularly for pad dyeing. 

The life-limiting increase of resistance and decrease of capacity of cycled cells is usually attributed to the deteriorating effects of corrosion of the positive current collector— the cell container in the case of sodium core cells or a rod in the case of sulfur core cells. Apart from consuming the active material, corrosion may lead to the deposition of poorly conductive layers at the current collector surface, thus interrupting the contact of the inert electrode fibers with the current collector. Corrosion products may also deposit and block both the solid electrolyte and the electrode surface. The thermodynamic instability of metals in polysulfide melts severely limits the choice of materials interfacing the sulfur electrode.A fully satisfactory solution has not yet been reported. 

The physical, chemical, and electrochemical properties of the sulfur-sodium polysulfide system influence many aspects of cell performance. For example, the 300°C operating temperature is dictated by the requirement that reaction products be liquid, and it is likewise this requirement which ultimately limits the extent of cell discharge. The phase behavior of sulfur-sodium polysulfide melts has been determined by both differen-... 

Other physical properties of the sulfur-polysulfide melt influence cell performance and have been studied. Density is perhaps foremost among these since density variation during discharge will dictate cathode void volume requirements. Furthermore since the sulfur-polysulfide melt is a two-phase system (see Figure 2) over much of the discharge range, density in conjunction with viscosity and surface tension establish the nature of the phase separation. Measurements of density (19, 23) demonstrate that the reaction proceeds at 360°C according to ... 

The sulfur-sodium polysulfide system has received the attention of electrochemists but few of the studies have been under conditions comparable to sodium-sulfur battery operating conditions. The thermodynamics of the system have been studied by means of open-circuit potentials (17,27), and dynamic measurements have been made in fused salts (28). The most pertinent studies are those of sulfur-polysulfide electrochemistry in the actual sulfur-polysulfide melts (24, 29, 35). The results of these studies seem to indicate that both the oxidation and reduction reactions are rapid, although the oxidation reaction is hindered by the formation of an insulating sulfur film. These studies also concluded that the electrode reaction sequences were quite complex because of the multitude of polysufide species. As the system becomes better characterized more quantitative descriptions are possible as evidenced by a recent work which modeled the resistive drop through an actual sulfur impregnated graphite electrode in order to correlate the spatial distribu-... 

It is not possible to review all the work concerning sulfur electrode reactions in molten salts but only to highlight the main features.Much of this work has been motivated by interests in high-temperature batteries and in the electrolytic recovery of metals from their sulfides. 8olvents such as LiCl-KCl and KCN8 have been employed, but many studies have concerned pure molten polysulfide melts (cf. the Na-8 battery). 

The blue color of 83 has been observed in numerous experiments. For example, a brilliant blue color occurs if a potassium thiocyanate melt is heated to temperatures above 300 °C [132] or if eutectic melts of LiCl-KCl (containing some sulfide) are in contact with elemental sulfur [132, 133], if aqueous sodium tetrasulfide is heated to temperatures above 100 °C [134], if alkali polysulfides are dissolved in boiling ethanol or in polar aprotic solvents (see above), or if borate glasses are doped with elemental sulfur [132]. In most of these cases mixtures of much 83 and little 82 will have been present demonstrating the ubiquitous nature of these radicals [12]. 

In this process, the reaction of the intermediates-essentially indophenols, chiefly in leuco form, or indophenol-like substances-with sulfur is effected by heating with alkali metal polysulfide in an aqueous or alcoholic medium under reflux. When monoethers of ethylene glycol or diethylene glycol (such as Carbitol) are used, the dye can be obtained in solution form after melting, without distillation and elimination of the solvent. Accordingly, these solvents are used chiefly in the preparation of ready-to-dye sulfur dye solutions. The addition of hydrotropic substances such as sodium xylenesulfonate improves the homogeneity of the melt and hinders sedimentation of the dye on storage. 

Table 3.9 Sulfur dyes made by polysulfide reflux melting in aqueous medium [3]... 

Liquid sulfur-dicyclopentadiene (DCP) solutions at 140°C undergo bulk copolymerization where the melt viscosity and surface tension of the solutions increase with time. A general melt viscosity equation rj == tj0 exp(aXH), at constant temperature, has been developed, where tj is the viscosity at time t for an S -DCP feed composition of DCP mole fraction X and rj0 (in viscosity units), a (in time 1), and b (a dimensionless number, -f- ve for X < 0.5 and —ve for X > 0.5) are empirical constants. The structure of the sul-furated products has been analyzed by NMR. Sulfur non-crystallizable copolymeric compositions have been obtained as shown by thermal analysis (DSC). Dodecyl polysulfide is a viscosity suppressor and a plasticizer for the S8-DCP system. 

Replacement of the sulfur melt by a solution of sulfur and/or its compounds offers some advantages in that the operating temperature can be lowered, the faradaic utilization of the reactant increased (i.e., the redox reactions of sulfur may involve reduction to lower polysulfide, solid at 350°C, as well as oxidation to positive valences of sulfur), the open-circuit voltage made higher, and the two-phase operation avoided. In exploratory systems which follow this route, use is made of sulfur dissolved in molten chloroalumi-... 

The electroreduction of alkenes activated by electron-withdrawing substituents, at a compact sulfur/carbon cathode in aprotic media affords thioorganic compounds.23 The electrode is prepared by melting a mixture of sulfur and graphite and serves as a source of nucleophilic polysulfides. 

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