Polysulfides synthesis

The effect of pH and the piC of the thiol has been discussed. This reaction is not of great synthetic interest, primarily because it yields a mixture of products, but it is of commercial consequence. It is also appHcable ia polysulfide synthesis, where the presence of small amounts of thiols can cause significant problems for the stabiUty of the polysulfide (51). A similar reaction between thiols and sulfides has also been described (52). In this instance, the process is heterogenous and acid-cataly2ed. 

Polysulfide synthesis based on the reaction of malononitrile, carbon disulfide, and cx,a -dichloro-p-xylene [95]. 

Although sodium sulfide is commonly used in inorganic polysulfide synthesis, other alkali ammonium and alkaline earth polysulfides can also be used provided they are sufficiently soluble [31]. Sodium polysulfide solutions are prepared by reacting aqueous NaOH solution with sulfur, their ratio determining the sulfur rank ... 

Recently, the above mentioned model reaction has been extended to polycondensation reactions for synthesis of polyethers and polysulfides [7,81]. In recent reports crown ether catalysts have mostly been used in the reaction of a bifunctional nucleophile with a bifunctional electrophile, as well as in the monomer species carrying both types of functional groups [7]. Table 5 describes the syntheses of aromatic polyethers by the nucleophilic displacement polymerization using PTC. 

Some compounds with network structures are synthesized by high-temperature reactions of metals with elemental sulfur [2, 8]. Rauchfuss et al. exploited the low-temperature synthesis of metal polysulfides by the reaction of metals with elemental sulfur in strong donor solvents. The reaction of copper powder with Ss in pyridine gives a copper polysulfide cluster Cu4(S5)2(-py)4 as orange crystals (Scheme 10) [45]. Furthermore, zinc powder reacts... 

Reactions of metal halides with polysulfide dianions are useful methods for the synthesis of polysulfido complexes of main group elements and transition metals. In most of these reactions, similarly to other methods, the chain lengths and coordination types of the polysulfide ligands depend on the other ligands coordinated to the metal, on the ratio between the metal and sulfur, on the reaction temperature, and other parameters. 

Scheme 20 Synthesis of group 13 polysulfido complexes by the reaction of the corresponding metal halides with polysulfide dianions...

The solvothermal reaction between metal halides and polysulfide anions is also a useful method for the synthesis of metal-polysulfide clusters. Hydrothermal reaction of K2PtCl4 with K2S4 (5 eq) at 130 °C in a sealed tube... 

Polymerizations are classified as either step (condensation) or chain (addition) polymerizations. The two differ in the time-scale of various reaction events, specifically in the length of time required for the growth of large-sized molecules. The synthesis of polysulfides (Eq. 1) and polyurethanes (Eq. 2) are... 

The synthesis of polysulfide elastomers involves the use of a small amount of trichloroalkane in addition to dichloroalkane and sodium sulfide in order to form a branched polymer. The prepolymer is treated with a mixture of sodium hydrosulfide and sodium sulfite followed by acidification to convert all end-groups to thiol groups. Further polymerization and crosslinking is achieved by oxidative coupling of the thiol end-groups by treatment with lead dioxide, p-quinone dioxime, or other oxidizing agent... 

The technically most important polysulfide is poly thiophenylene or poly(p-phe-nylene sulfide), PPS. It is obtained by reacting sodium sulfide and p-dichlo-robenzene in a polar solvent, for example, l-methyl-2-pyrrolidone at about 280 °C under pressure. The mechanism of the reaction is very complex and cannot be described by a simple aromatic substitution. This synthesis requires special autoclaves and is therefore not suitable for a laboratory course (for an experimental procedure see Table 2.3). 

NQR, 22 216 olefin complexes of, 4 85 in organogermanium compounds, 27 141,143 oxyfluoride, properties of, 11 29 pentacarbonyl dimets of sulfur oxydifluoride imide, 19 203-205 pentafluoride, structure, 27 102 peroxides, 6 325-326 phthalocyanine, 7 54 physical properties of, 11 18 polysulfide complexes, 31 100, 102 envelope conformation, 31 115 synthesis, 31 103-104 [Pt[15]aneS5) f, 35 75, 77 reaction with fluorinated peroxides, 16 120 salts, lattice energy and thermochemistry, 22 52-56... 

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