Polysulfides, generation

Similar reducing effects are obtained from alkali sulfides, hydrosulfides and polysulfides [241]. A peculiar reaction believed to be due to sodium polysulfide formed in situ by refluxing sulfur in aqueous-ethanolic sodium hydroxide is a conversion of p-nitrotoluene to p-aminobenzaldehyde [242]. Oxidation of the methyl group by the polysulfide generates hydrogen sulfide which then reduces the nitro group to the amino group. 

Earlier accounts of the reaction of halogenated products with potassiiun sulfide did not report useful polymeric products [10]. Patrick and Mnookin [11] were the first to report useful polysulfide products that were to become the early basis of the Thiokol Chemical Corp. business. Polysulfides generated interest before and after World War II because natural rubber was difficult to obtain at times and was also high in price [12]. 

Dobson, H. A. (2001). The mixing sensitivity of polysulfide generation, M.A.Sc. thesis. University of British Columbia, Vancouver, British Columbia, Canada. 

PolysuWde Process. One modification to the kraft process being appHed commercially is the polysulfide process (38). Under alkaline conditions and relatively low temperature (100—120°C), polysulfides oxidize the active end group of the polysaccharide polymer to an alkaH-stable aldonic acid. This reaction, known for many years (39), was not produced on a commercial scale until the development of an efficient method for in situ generation of the polysulfide in kraft white Hquor. 

Tendering Effects. CeUulosic materials dyed with sulfur black have been known to suffer degradation by acid tendering when stored under moist warm conditions. This effect may result from the Hberation of small quantities of sulfuric acid which occurs when some of the polysulfide links of the sulfur dye are mptured. A buffer, such as sodium acetate, or a dilute alkaH in the final rinse, especially after oxidation in acidic conditions, may prevent this occurrence. Copper salts should never be used with sulfur black dyes because they cataly2e sulfuric acid generation. Few instances of tendering with sulfur dyes other than black occur and the problem is largely confined to cotton. 

Both sodium sulfide and the bisulfide are used in the flotation process for copper minerals and as a depilatory for animal liides (see Copper Copper ALLOYS Leather). Also, sodium polysulfide can be produced from Na2S, and elemental sulfur can be produced if H2S is generated as an intemiediate. 

The generated polysulfide dianions of different chain-lengths then establish a complex equilibrium mixture with all members up to the octasulfide at least see Eqs. (5) and (6). For this reason, it is not possible to separate the polysulfide dianions by ion chromatography [6]. The maximum possible chain-length can be estimated from the preparation of salts with these anions in various solvents (see above). However, since the reactions at Eqs. (22) and (23) are reversible and Sg precipitates from such solutions if the pH is lowered below a value of 6, the nonasulfide ion must be present also to generate the Sg molecules by the reverse of the reaction at Eq. (22). The latter reaction (precipitation of Sg on acidification) may be used for the gravimetric determination of polysulfides [11]. There is no evidence for the presence of monoprotonated polysulfide ions HS - in aqueous solutions [67, 72]. 

More recently, 84 may have been identified by ESR spectroscopy of solutions of Li2S ( >6) in DMF at 303 K. The lithium polysulfide was prepared from the elements in liquid ammonia. These polysulfide solutions also contain the trisulfide radical anion ( 2.0290) but at high sulfur contents a second radical at g=2.031 (Lorentzian lineshape) was formed which was assumed to be 84 generated by dissociation of octasulfide dianions see Eq. (32) [137],... 

The photoelectrochemical behavior of ZnSe-coated CdSe thin Aims (both deposited by vacuum evaporation on Ti) in polysulflde solution has been described by Russak and Reichman [112] and was reported to be similar to MIS-type devices. Specifically, Auger depth profiling showed the ZnSe component of the (ZnSe)CdSe heterostructures to convert to ZnO after heat treatment in air, thus forming a (ZnO)CdSe structure, while the ZnO surface layer was further converted to a ZnS layer by cycling the electrode in polysulfide electrolyte. This electrochemically generated ZnS layer provided an enhanced open-circuit potential compared to CdSe alone. Efficiencies as high as 5.4% under simulated AM2 conditions were recorded for these electrodes. 

Cathodic generation of Sx species in the presence of alkylhalogenides provides polysulfides Alk-5jc-Alk (x =... 

The decomposition generates amine and MBTS. Small quantities of MBT and benzothiazyl (Bt) polysulfides form just before the onset of cross-linking. Sulfur disappears and large quantities of MBT are formed during the main cross-linking reaction. The development of cross-links is shown as the rheometer line (curve C) in Figure 3. 

Alkali metal polysulfides are prepared by the direct reaction of an alkali metal with cyclo-Sg. Alternatively, n-butyllithium may be used to generate... 

Ammonia is generated by the reaction of diphenylguanidine and magnesium oxide with ammonium perchlorate. The cure rate of polysulfide propellant formulations can be a function, of the amount of ammonia removed during the mix cycle. Frequently, a vacuum is placed on uncured propellant to remove entrapped air. Too long a vacuum mix cycle, with polysulfide propellants, can remove excess ammonia changing the reaction condition during cure. 

If a volatile component is present in the cured propellant, another effect must be considered. In polysulfide formulations a molecule of water is generated each time a polysulfide bond is formed. The vapor pressure of the ammonium perchlorate propellant formulation becomes that of an ammonia-ammonium perchlorate saturated solution. Ammonia and water can be driven from the formulation, and the water condenses on cold surfaces. If the condensate returns to the propellant surface, perchlorate is leached from the surface of the propellant. This perchlorate may later recrystallize on the surface. A surface void of perchlorate is very difficult to ignite, while a perchlorate-rich surface produces the... 

Sodium polysulfide and sodium hydrosulfide are other agents that are used. They do not produce excess sludge, but can generate highly toxic hydrogen sulfide gas. Good ventilation and pH control are needed in any system employing these chemicals. 

These new synthetic rubbers were accessible from potentially low cost raw materials and generated considerable woddwide interest. For a time, it was hoped that the polysulfide rubbers could substitute for natural mbber in automobile tires. Unfortunately, these original polymers were difficult to process, evolved irritating fumes during compounding, and properties such as compression set, extension, and abrasion characteristics were not suitable for this application. 

The formation of 1,2,3-benzotrithiole with very low yield (1.3%) was detected by gas chromatography-mass spectrometry (GC/MS) in a mixture of other polysulfides produced by the reaction of elemental sulfur with benzyne generated either by treatment of o-(X>(, 111 with BuLi in Et20 at —60 °C, or by decomposition of benzenediazonium-... 

Epoxy-polysulfide systems do not generate significant amounts of exotherm, and their cure rate does not rely on the exothermic reaction. Thus, epoxy-polysulfide compositions have a cure rate that is relatively insensitive to temperature, and they can cure at very low temperatures (below room temperature). 

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