Polysulfide, linear

The reaction of suitable aliphatic dihalogen compounds with alkali or alkaline earth polysulfides results in the formation of linear, rubbery or resinous, po-ly(alkylene sulfide)s ... 

The linear polysulfide obtained by this reaction may be oxidized, the sulfur atoms being removed from the chain either one at a time to form sulfite or two at a time to form thiosulfate.322 3223 Thiosulfate is oxidized by all species, the major pathway beginning with cleavage to S° and S032 (Eq. 18-21, step a). At high thiosulfate concentrations some may be oxidized to tetrathionate (step b), which is hydrolyzed to sulfate (step c). 

This reaction also plays a role in the degradation of polysulfides. A back-biting mechanism as shown in equation 6 results in formation of the cyclic disulfide (5). Steam distillation of polysulfides results in continuous gradual collection of (5). There is an equilibrium between the linear polysulfide polymer and the cyclic disulfide. Although the linear polymer is favored and only small amounts of the cyclic compound are normally present, conditions such as steam distillation, which remove (5), drive the equilibrium process toward depolymerization. 

From the reaction of Au with alkali metal polysulfide liquids, LiAuS and NaAuS were discovered. Both compounds contain infinite one-dimensional (AuS) chains, featuring alternating sulfide anions and linear coordinated Au centers. In LiAu8, the chains are zigzag and fully extended and they pack in mutually perpendicular sets. In NaAuS, the same chains coil in an unusual fashion so that they become interwoven to form layers reminiscent of chicken-wire (Figure 17). This novel coiling mode allows Au Au contacts to form, which help to stabilize the structure. 

Thus the Eh-E22- relation should be linear when in the presence of sulfide and polysulfide ions. The term [Eh - E 2-] can be estimated from the thermodynamic data on S0, Ag, Ag2S. For the... 

In most non-crystalline linear polymers described to date, the relaxation mechanism (in the absence of such extraneous factors as degradation) is the simple molecular flow, or the a mechanism. Exceptions have been found, for instance in the case of the polysulfides (4,54,56,57) or pol5mrethanes (57) in which far above the gla transition temperature a ixmd interchange mechanism was observed. For a number of reasons (which will be described below), it is of interest to study viscoelasticity of polymers which are subject to both mechanisms, i. e., a and (as bond-interchange will be called due to the intrinsically chemical nature of the reaction), particularly if both mechanisms occur with comparable relaxation times. Among the benefits of such a study, particularly in the case of the ionic inorganic polymers would be ... 

The electroreduction of sulfur in nonaqueous solvents (DMF, DMSO etc.) has been studied by several authors for the past 35 years [47-60]. Experimentally, a solution of sulfur is yellow (pale) and the reduced solutions are intensely colored. Electrochemically, the response of the electroreduction of sulfur in classical organic solvent (DMF, DMA, DMSO, CH3CN etc.) is similar. The reduced forms, that is, polysulfides S 2 or S , have characteristic absorption bands in the visible range. Structurally, sulfur is a ring and polysul-fldes are expected to be linear chains. To understand the electrochemical behavior of sulfur, it was necessary to take into account these structural aspects. This was done only in 1997 [60]. 

Various polarographic techniques have been successfully used to measure elemental sulfur, S , and sulfide (H2S and HS ) concentrations in laboratory solutions [116], salt water [117], saline lake [118], freshwater [119], lake porewaters [120], salt marsh sediments [109,120], and marine porewaters [121], Using stripping square wave voltammetry, researchers have been able to measure sulfide species at nanomolar concentrations [118-120, 122,123], Recently, cyclic and linear sweep voltammetries have been used to quantify elemental sulfur S , hydrogenosulfide (HS ) and polysulfides (S ) with fast scan rates (IV s ) [124] for example, in estuarine sediments (from Rehoboth Bay, an inland bay located in Delaware), the sulfur speciation was found to change throughout a core profile, with dominant in the top layers (0-6 cm), dominant... 

Data have been published dealing with successful applications of HAS in stabilization of other polymers than PO elastomers, styrenic polymers, polyamides, polycarbonates, polyacetals, polyurethanes, linear polyesters, thermoplastic polyester elastomers, polyacrylates, epoxy resins, poly(phenylene oxide) or polysulfide [12]. In spite of their basicity, HAS may also be used for stabilization of PVC. This application includes less basic derivatives of piperidine and 1,4-dihydropyridine [12,13,145,146]. 

Before we present the results of these calculations, it is useful to consider the expected results. Sulfur rings are isovalent to cycloalkanes (CH2)n and might be expected to have large gaps between the top filled and lowest empty orbitals. The sulfanes HSnH, formerly called polysulfides, would be expected also to have large gaps between the top filled and lowest empty orbitals in analogy to the isovalent linear alkanes. On the other hand, the open chain S allotropes are isovalent to alkane diradicals and would be expected to be colored. We considered also the possibility of branched chain allotropes, whose properties we could not predict in advance. The extended Hiickel calculation was used to see whether the expected properties were supported by the simplest model orbital calculation, to determine the dependence on number of sulfur atoms, and to see if branched chain structures are reasonable. Moreover,... 

In the presence of metallic lithium the reaction of 8 with 1,4-dichlorobenzene yields a linear poly(l,4-phenylene polysulfide) in which the sulfur content could be 3 sulfur atoms per phenylene unit (M as high as 12,000) [Ilia]. 

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