Tetrasulfides, cyclic

Dithiatopazine 73 serves as a sulfur-transfer reagent under thermal conditions. Tlius, heating 73 and diene 130 in toluene at 100°C formed a cyclic disulfide 131 (25%) and a tetrasulfide 132 (28%) with the formation of the alkene 118 (90%). Under similar conditions, the highly strained acetylene 133 was converted to the 1,2-dithiete 134 (65%) and the congested thiophene 135 (12%) (90JA3029). 

Reactions of cyclic tetrasulfides containing a heavier group 14 element, Tbt(Ar)MS4 (M=Ge, Ar=Mes or Tip M=Sn, Ar=Tip), with diphenyl diazomethane gives l,2,3,5-tetrathia-4-metallacyclohexanes, l,2,4,5-tetrathia-3-metallacyclohexanes, and l,2,4-trithia-3-metallacyclopentanes (Scheme 54) [52, 118-120],... 

Scheme 54 Reaction of cyclic tetrasulfides containing a heavier group 14 element with diphenyl diazomethane...

Cyclic aromatic disulfides, polymerization reactions of, 23 706 Cyclic (arylene) disulfides, 23 712 Cyclic batch adsorption processes, 1-613 Cyclic bis(arylene tetrasulfide)s, 23 712 Cyclic carbon, polymer materials with, 15 177... 

The most widely used dihalide is 1,2-dichloroethane. The use of polyhalides (e.g., 2% 1,2,3-trichloropropane) results in the formation of branched or crosslinked products. Sodium tetrasulfide (Na2S4) is generally used as the polysulfide since it contains scarcely any of the monosulfide which reacts with dihalides to form cyclic by-products with unpleasant odors. 

Only a few examples are known of polymerizations to cyclic species that have more than three consecutive S atoms in the repeat unit. One example is poly(tetrafluo-roethylene tetrasulfide), which can be prepared in a manner similar to that shown in reaction (15).56... 

Dithietane intermediate 145 (Scheme 18, path a) either directly transfers its two sulfur atoms to a diene trap 143 to form 147 (Scheme 18, path aj) or undergoes a cycloreversion to cyclohexene and 1S2, which is then trapped by diene 143 (Scheme 18, path a2). Conversely, intermediate 144 could fragment (Scheme 18, path b) directly to deliver 1S2, which is then trapped (Scheme 18, path a2) by the diene 143 to form cyclic 147. A second capture of a two-sulfur unit apparently takes place resulting in cyclic tetrasulfide 149 as the major product. It was also found that cyclic tetrasulfide 149 can be converted quantitatively to disulfide adduct 147 by an in situ treatment with triphenylphosphine 148. As a result, this methodology serves to transfer a two-sulfur unit to a diene in high yield < 1998JOC8654>. 

Formation of Cyclic Di- and Symmetrical Tetrasulfides by Oxidation of Dithiols 788... 

Several cyclic bis(arylene tetrasulfides) have been synthesized within the last few years. These ring compounds can be polymerized thermally in much the same way as sulfur itself. However, whereas polymeric sulfur depolymerizes on standing at room temperature, the poly(arylene polysulfides) considered here are stable polymers under ordinary conditions. The mechanism by which the cyclic bis-(arylene tetrasulfides) polymerize has been established by ESR as a free-radical process. The maximum number-average molecular weights are from 15,000 to 16,000. 

The work described here deals with a new approach to preparing poly(arylene polysulfide). This approach involves a free-radical mechanism—namely, the thermal polymerization of cyclic bis(arylene tetrasulfides ) ... 

These cyclic bis(arylene tetrasulfides) were originally synthesized by Z. S. Ariyan and R. L. Martin (13, 14, 15) by the reaction of the appropriate aromatic moiety with sulfur monochloride in the presence of a mineral acid-clay catalyst. 

Several sulfur-containing nine-membered rings have been isolated from natural sources. The hexasulfide (417) was tentatively identified as a component of the Shiitake mushroom on the basis of GC-MS <86MI 927-02). A mixture of cyclic tri- and tetrasulfides, typified by structures (418) and (419), and isolated from Azadirachta indica leaves, were identified by GC-MS <85MI 927-01). 

A similar mechanism applies to the diphenyldithianes, i.e., the cyclic styrene polysulfide dimers. However, in this case the most thermally stable compound is not the simplest cyclic dimer (m/z 272), but a thiophene derivative produced by thermal induced loss of H2S and sulfur (Scheme 5.3). As a consequence, 3,4-diphenylthiophene can be generated from head-to-tail poly(styrene tetrasulfide) units and 2,4-diphenylthiophene from tail-to-tail units. The formation of thiophene derivatives from 1,4-dithiadiene rings, by thermal loss of sulfur, is well-known in the literature. ... 

Pyridine Cyclic tetrasulfides from cyclic disulfides C,H,N Q... 

Figure 5.15 Separation of accelerators by thin-layer chromatography. Solvent benzene - ethylacetate - acetone (100 5 1) development distance 15 cm indicators (a) 4 N hydrochloric acid (b) 0.5% ninhydrin in ethanol containing 10% acetic acid and 0.5% cadmium acetate. 1 = tetramethylthiuram monosulfide 2 = tetrabutylthiuram monosulfide 3 = tetramethylthiuram disulfide 4 = tetraethylthiuram disulfide 5 = dipentamethylenethiuram tetrasulfide 6 = cyclic thiuram 7 = piperidinium pentamethylene dithiocarbamate 8 = zinc dimethyldithiocarbamate 9 = zinc diethyldithiocarbamate 10 =...

Earlier attempts of ROP without adding any catalyst were performed on some cyclic his(arylene tetrasulfide)s upon heating (78) and 1,2,3-trithiane [3325-33-5] upon standing at room temperature (77). Some cyclic (arylene) disulfides were already prepared earlier by using iodine or DMSO as oxidizing agent, mainly to study their structural geometry and their potential for complexation (79-84). 

The occurrence of cyclic structures also depends on the sulfur content of initial polysulfides the lower the sulfur content is, the more cyclic structures are formed. For this reason, to yield polysulfide polymers, the use of sodium tetrasulfide is preferred to sodium disulfide. More than 100 different monomers have been used [8-15], and based on experimental data, an attempt was made to establish reactivity-structure correlation. For halide derivatives, the most reactive are allylic and benzylic halide derivatives the primary derivatives are more active than the secondary or tertiary derivatives. As far as industrial monomers are concerned, 1,2-dichloroethane is more active than 2,2-dichloroethane or 2,2-dichlorodiethyl formal. 

Refluxing a reservoir of sulfur (445 °Q and passing the tetrafluoroethylene directly into the hot sulfur vapor gives three monomers namely tetrafluoro-1,2,3,4-tetrathiane (cyclfc tetrasulfide), tetrafluoro-l,2,3-trithiolane (cyclic trisulfide) and tetrafluorothirane (cyclic sulfide) respectively [140] ... 

Synthesis of the polymeric disulfide was achieved by heating an equimolar mixture of cyclic tetrasulfide with tetrafluoroethylene at 200 °C. The cyclic tetrasulhde probably undergoes homolysis at the isolated or 2,3 sulfur-sulfur bond giving relatively stable thiyl radicals which then interact with tetrafluoroethylene, possibly forming an eight-membered ring intermediate, to yield the polymer ... 

Monomeric cyclic tetrasulfide distills off along with other compounds and sulfur from the tetrasulfide polymer at 250 C. But when pyrolyzed under pressure at 300 °C, octafluoro-l,4-dithaine and sulfur are formed ... 

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