Sulfides, cyclic, polysulfides

Another preparative technique involves the ring-opening polymerization of cyclic polysulfides.56 For example, l-oxa-4,5-dithiacycloheptane polymerizes very rapidly at room temperature when treated with an aqueous sulfide (reaction (11)) ... 

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. 

These reactions can lead to the formation of numerous heterocyclics associated with meat flavor as described by Vernin and Parkanyi (57), including furans, thiophenes, pyrroles, oxazoles, imidazoles, thiaz-oles, pyrans, pyridines, pyrazines, cyclic sulfides and polysulfides. 

In straight-run gasohne a variety of sulfur compounds may be present, such as hydrogen sulfide, mercaptans, sulfides, disulfides, polysulfides, and cyclic sulfides. It is also possible that sulfonic acids and alkyl sulfates can be present because of their incomplete removal after refinery treating operations. Likewise there can be a polysulfide content as a result of doctor sweetening. Alkyl sulfates, which are hydrocarbon soluble, can form through the action of sulfuric acid upon olefins. 

A different approach to long chain fluorinated sulfides is through the reactions of fluorinated sulfenyl chlorides. Such sulfenyl chlorides are available from direct chlorination of the cyclic polysulfides described above (10). Photochemical chlorination of trithiepane 8 serves to produce bis(sulfenyl) chloride 23. Both 6 (n = 4) and 6 (n = 3) give bis(sul-fenyl chloride 24 with chlorine in an inert medium without need for photoactivation. Incomplete chlorination leads to disulfur chlorides as by-products in the latter cases. 

Fig. 12. Sulfur-based cure system designs where conventional systems are polysulfidic, EV systems are mono- to disulfidic, and semi-EV are di- to polysulfidic. A is pendent sulfide group terminated with accelerator residue, B monosulfidic cross-link, C disulfidic crosslink, D polysulfidic cross-link (x > 20), E cyclic monosulfidic cross-link, F cyclic polysulfidic cross-link, and Acc accelerator residue.

Cyclic monomers that have been polymerized via ring-opening encompass a variety of structures, such as alkanes, alkenes, compounds containing heteroatoms in the ring oxygen [ethers, acetals, esters (lactones, lactides, and carbonates), and anhydrides], sulfur (polysulfur, sulfides and polysulfides), nitrogen [amines, amides (lactames), imides, N-carboxyanhydrides and 1,3-oxaza derivatives], phosphorus (phosphates, phosphonates, phosphites, phosphines and phosphazenes), or silicon (siloxanes, silaethers, carbosilanes and silanes). For the majority of these monomers, convenient polymerization conditions have been elaborated, that result in the controlled synthesis of the corresponding polymers [1-13]. 

Vulcanization by heating with sulfur alone is a very inefficient process with approximately 40-50 sulfur atoms incorporated into the polymer per crosslink. Sulfur is wasted by the formation of long polysulfide crosslinks (i.e., high values of m in XHI), vicinal crosslinks (XIV), and intramolecular cyclic sulfide structures (XV). (Structures XIV and XV do not contribute significantly to the physical properties of the polymer.)... 

Sulfur-rich binary P-S anions of the type [S2P(p-S )2PS2] form monocyclic structures with sulfide or disulfide bridging units ( = 1, 2) (11.39). Another type of cyclic P-S anion with the general formula [(PS2) ] is formed in the reaction of white phosphorus with polysulfides in a non-aqueous medium these anions have homocyclic structures with two exocyclic sulfur atoms attached to each phosphorus atom, e.g. [P4Ss] (11.40). ... 

There is a series of analogous cyclic thiuphosphoric acids with the formula (HS2P) thal may be prepared by the oxidation of red or white phosphorus with polysulfides under a variety of conditions. For example, the reaction of white phosphorus with a mixture of sulfur and hydrogen sulfide dissolved in triethylamine (which acts as a base) and chloroform opens the phosphorus cage to form the tectamerre cyclic anion ... 

Cyclic S8 can also be copolymerized with cyclic mono- and poly sulfides such as thiiranes and trithiolanes.56 The result is a polysulfide with an augmented number of S atoms in the repeat unit. 

Alkylation of an ethanolic solution of sodium sulfide containing an equivalent amount of dissolved sulfur produces disulfides in 60-80% yields from alkyl" or o- and p-nitrophenyl halides." Cyclic disulfides are prepared by alkylation with 1,3-dihalides." Hydroxyl" and nitro" groups do not interfere. Alkylation of a solution of sodium sulfide containing 2-5 equivalents of sulfur produces polysulfides. 

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... 

These reactions are Shown on a typical cyclic voltammogram in Figure 7. The data suggest that hypersulfide is only formed chemically (Reaction 5) and not by an electrochemical reaction. In Reaction 6, it is possible that higher sulfides could be formed. However, S2" was indicated as the product because it is the most stable polysulfide. 

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