Polysulfide modification

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. 

The Kindler modification dodges heating in closed vessels under pressure by using, instead of aqueous ammonium polysulfide, a mixture of sulfur and morpholine. After being refluxed for 6-12 h, the ketone is converted into the thiomorpholide of the carboxylic acid. Subsequent alkaline hydrolysis yields the carboxylic acid as the final product [501, 503, 504, 1170]. 

A useful procedure for the isolation of humic substances from groundwater is that of Thurman and Malcolm (1981) with the following modifications. Hydrochloric acid should be added immediately to the water sample to prevent the precipitation of iron hydroxide, and the sample should be evacuated with a vacuum pump to remove hydrogen sulfide. If the sulfide is not removed, it can react to form both elemental sulfur and polysulfides that adsorb onto and clog the XAD resin (Leenheer and Noyes, in press Thurman, 1979). 

A modification of the preceding process involves the use of an organic solvent, which is immiscible with water, for the m-dinitrobenzene. Accordingly, 100 parts of technical dinitrobenzene, 90 per cent purity, and 160 parts of either solvent naphtha or toluene are put into the reducer, and the mixture is warmed to 60 C to effect solution. Then, 4,000 parts of hot water is added, and the m-dinitrobenzene solution is stirred and heated to 95°C. A hot polysulfide (NaSz) solution— made by heating 720 parts of 7 per cent NaS with 40 parts of flowers of sulfur—is then added rather rapidly. The reaction of the polysulfide is distinctly exothermic, and the charge boils vigorously, but overheating is avoided because of the vaporization of the solvent. Reduction of the dinitrobenzene to m-nitroaniline is found to take place very quickly under such conditions. 

Swaab and Sutker [24] reported a modification of the foregoing procedure in which a solid, particulate, polysulfide polymer mixture is formed that is free flowing, insensitive to moisture, and redispersible in water to form a stable latex. The process involves the reaction of a Bimte salt (reaction product of sodium thiosulfate and bis(chloroethyl) ether with calcium sulfide in the presence of 5-30% of a dispersing agent [Mg(OH)2 or the sodium salt of a polyalkyl-naphthalenesulfonic acid]. 

The original Willgerodt Reaction conditions required high temperature and pressure, with use of ammonium polysulfide (NH4)2S and H2O to give either an amide or the ammonium salt of the corresponding acid. Kindler s modification, shown above, eliminated these problems and substituted Sg and a dry amine, most commonly morpholine. 

Recent advances have resulted in chemical modification of conventional liquid polysulfide polymers in a one-step reaction with dithiol, as follows ... 

Bis(i) -cyclopentadienyl)titanium pentasulflde was prepared first Samuel and Schmidt from TiCpjClj (Cp = cyclopentadienyl) and polysulfide salts. It can also be prepared from the reaction of TiCp2(CO)2 or TiCp2(CH2R)2 with elemental sulfur. The method presented here is a modification of Kopf s procedure and is equally applicable to the Cp, MeCp, and i-PrCp (i-Pr = isopropyl) derivatives. This reaction has been successfully conducted at 40 times... 

It has been shown that modification of the distribution of species in aqueous polysulfide solution can be correlated to variations in transparency, conductivity, activity, and cadmium chalcogenide photoelectrochemistry. Specifically, the separate effects of hydroxide and pH modification [42], sulfur [43] and sulfide [44], and cation [45, 46] were investigated in terms of spedation and photoelectrochemical phenomena. Previously cadmium chalcogenide polysulfide PECs had generally employed electrolytes composed 1 molar in sodium sulfide, sulfur and sodium hydroxide and resulted in solar conversion efficiencies of approximately 7% [31-33]. However, added hydroxide is to be minimized in these cells, cesium is the... 

TOF-SIMS data for Armco iron point on the highest degree of sulfur modification being the result of friction against ebonite, SBR vulcanizate and cured polysulfide rubber. The spectra represent the highest amount of species containing sulfur. 

Tribological characteristics confirm the influence of sulfur modification of metal counter face on lowering fiiction for the metal-polymer couples studied. In the case of ebonite, the coefficient of friction reduced significantly for the whole experimental mn, whereas application of SBR vulcanizate or polysulfide rubber was effective only during the first period of experimental cycles. Any improvement of tribiological characteristics was not assigned for polysulphone. The polymer was observed to worn the surface of iron counterface, what resulted in increase of the coefficient of friction in this case. 

---