Hydrogen polysulfide formation

The presence of the liquid sulfur phase in the Richard process may favor the formation of the product liquid sulfur by aiding the formation of the intermediate hydrogen polysulfide building block. The success of a 5LTD demonstration plant may well determine whether future sulfur recovery from H2S feed continues to be by... 

The reaction at Eq. (12) allows the preparation of Na2S4 and K2S5 from the alkali metals, hydrogen sulfide and sulfur in anhydrous ethanol (ROH). First the metal is dissolved in the alcohol with formation of ethanolate (MOR) and hydrogen. Bubbling of H2S into this solution produces the hydrogen sulfide (MHS). To obtain the polysulfide the solution is refluxed with the calculated amount of elemental sulfur. After partial evaporation of the solvent and subsequent cooling the product precipitates. 

Many desirable meat flavor volatiles are synthesized by heating water-soluble precursors such as amino acids and carbohydrates. These latter constituents interact to form intermediates which are converted to meat flavor compounds by oxidation, decarboxylation, condensation and cyclization. 0-, N-, and S-heterocyclics including furans, furanones, pyrazines, thiophenes, thiazoles, thiazolines and cyclic polysulfides contribute significantly to the overall desirable aroma impression of meat. The Maillard reaction, including formation of Strecker aldehydes, hydrogen sulfide and ammonia, is important in the mechanism of formation of these compounds. 

Figure 4. Formation of important meat aroma polysulfide heterocyclics by heating acetaldehyde and hydrogen sulfide. (Reprinted from ref. 39. Copyright 1976 American Chemical Society.)...

The formation of sulfur intermediates is both chemically and biologically mediated. Oxidation of hydrogen sulfide with oxygen and Fe(Mn) oxyhy-droxides and sulfate reduction are the main processes responsible for sulfur intermediates formation in the euxinic water columns, except for elemental sulfur, which is formed only during hydrogen sulfide oxidation. Chemically mediated reactions of thiosulfate formation are elemental sulfur(polysulfides)... 

Polymers of = 1600—6500 with polydispersity 1.2—2.8 were prepared by addition of diolefins with dithiols and the following two-phase oxidation of the resulting polydisulfides. The effective oxidation (up to 92% of sulfoxide units) of polysulfides was conducted by using aqueous hydrogen peroxide in chloroform with or without heating. The formation of polysulfoxides was strongly supported by spectroscopic analysis. Poly(hexamethylene sulfoxide) obtained in this way was subject to Swern oxidation of primary or secondary alcohols, in which 1-octanol [111-87-5] and 6-undecanol [23708-56-7] were oxidized to give 1-octanal [124-13-0] and 6-undecanone [927-49-1], respectively, in quantitative yields (18). 

Summarized from all findings reported in the literature, the mechanism of accelerated sulfur vulcanization probably involves initial formation of an accelerator polysulfide [126,135-142], 2,2 -dithiobenzothiazole 16 taken for example. The accelerator polysulfide 17 reacts with a poly(butadiene) chain segment at the allylic hydrogen [118] to form a rubber polysulfide pendent group with one accelerator fragment at the polysulfide group 18. 

Conversion of Hydrogen Sulfide to Elemental Su ur. The form of sulfur that is thermodynamically stable at ambient conditions is the rhombic form, Sg. One of the most plausible sulfur precipitation mechanisms involves the formation of polysulfides (S,, where x = 2-S) along with elemental sulfur. The 84 and Ss polysulfide species are likely to predominate at the pH and HS concentration typical of the Stretford liquor (Giggenbach, 1972). 

Liquid polysulfides can also be prepared directly with thiol end groups by reacting a mixture of aliphatic di- and polyhalides with a mixture of sodium disulfide and sodium hydrogen sulfide [77]. Reaction polymeric disulfides with polymercaptans also leads to the formation of liquid polysulfides [37]. LP polymers with M in the range of 600 to 8000 are generally f eferred. The uncured LP polymers are soluble in toluene, benzene and chlorinated hydrocarbons such as ethylene chloride [17, 78]. LP polym like LP-31, LP-2, LP-32, LP-12, LP-3, LP-33, LP-5, LP-8, based on range of viscosities, molecular weights and functionalities, are available [17]. 

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