Tetrasulfides

A double end point, acid—base titration can be used to determine both sodium hydrosulfide and sodium sulfide content. Standardized hydrochloric acid is the titrant thymolphthalein and bromophenol blue are the indicators. Other bases having ionization constants in the ranges of the indicators used interfere with the analysis. Sodium thiosulfate and sodium thiocarbonate interfere quantitatively with the accuracy of the results. Detailed procedures to analyze sodium sulfide, sodium hydro sulfide, and sodium tetrasulfide are available (1). 

The H2S sulfanes are the subject of several reviews (129,133). Except for hydrogen sulfide these have no practical utiUty. Sodium tetrasulfide [12034-39-8] is available commercially as a 40 wt % aqueous solution and is used to dehair hides in taimeries, as an ore flotation agent, in the preparation of sulfur dyes (qv), and for metal sulfide finishes (see Leather Mineral recovery and processing). 

The initial sulfur copolymer that is formed is often high conversion and gelled. Molecular weight is reduced to the required level by cleaving some of the polysulfide Linkages, usually with tetraethylthiuram disulfide. An alkaU metal or ammonium salt (30) of the dithiocarbamate, an alkaU metal salt of mercaptobensothiasole (31), and a secondary amine (32) have all been used as catalysts. The peptization reaction results in reactive chain ends. Polymer peptized with diphenyl tetrasulfide was reported to have improved viscosity stabiUty (33). 

Thiiranes can be made from nascent sulfur , such as is obtained by the thermolysis of diethyl tetrasulfide (64HC(l9-l)59l). 

Although the polysulfur macrocycles became more interesting to the scientific community after Pedersen s report of the crown compounds (see Chap. 1), examples of such structures may be found in the literature dating back some time. The first report of a macrocyclic polysulfide appears to be that by Ray who found in 1920 that when 1,2-dimercaptoethane and 1,2-dibromoethane were heated with alcoholic potassium hydrogen sulfide as shown in Eq. (6.2), triethylene trisulfide (2) and a substance presumed to be triethylene tetrasulfide (3) could be isolated. 

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). 

DPTS-di-pentamethylene thiuram tetrasulfide TDD-thiodiazoIe derivative NC-fatty acid amide amine B-18-special curative DOTG-dior-tho-tolyl guanidine peroxide 14/40-dicumyI peroxide TAC-triallyl cyanurate. 

Poly sulfide Polymers. These polymers are made up of aliphatic hydrocarbon units connected by di-, tri- or tetrasulfide links. The synthetic rubber found useful in ordn has hydrocarbon units linked by either O or formal segments. The polymers are usually prepd by the condensation of a suitable organic dihalide, usually the chloride, with aq Na polysulfide. According to Ref 8, the most practical organic dichloride is dichlorodiethylformal viz, Bis[ 2[Pg.827]

Primary and secondary but not tertiary alkyl halides are easily converted to Bunte salts (RSSOj ) by treatment with thiosulfate ion. ° Bunte salts can be hydrolyzed with acids to give the corresponding thiols or converted to disulfides, tetrasulfides,... 

The electrochemical reduction of Sg in aprotic solvents like DMSO [87, 91, 92], DMF [92, 93], dimethylacetamide [94], acetonitrile [95], or methanol [95] yields primarily Sg ions which then equilibrate with other dianions and radical anions like 83 and others see Eqs. (4)-(8). In a second reduction step tetrasulfide ions are formed ... 

However, the actual mechanism of tetrasulfide formation may be as follows [93] ... 

The tetrasulfide radical anion will dimerize to which equilibrates with longer chains from which eventually Ss is formed by the back reaction shown in Eq. (22). 

The blue color of 83 has been observed in numerous experiments. For example, a brilliant blue color occurs if a potassium thiocyanate melt is heated to temperatures above 300 °C [132] or if eutectic melts of LiCl-KCl (containing some sulfide) are in contact with elemental sulfur [132, 133], if aqueous sodium tetrasulfide is heated to temperatures above 100 °C [134], if alkali polysulfides are dissolved in boiling ethanol or in polar aprotic solvents (see above), or if borate glasses are doped with elemental sulfur [132]. In most of these cases mixtures of much 83 and little 82 will have been present demonstrating the ubiquitous nature of these radicals [12]. 

The red tetrasulfide radical anion 84 has been proposed as a constituent of sulfur-doped alkali hahdes, of alkah polysulfide solutions in DMF [84, 86], HMPA [89] and acetone [136] and as a product of the electrochemical reduction of 8s in DM80 or DMF [12]. However, in all these cases no convincing proof for the molecular composition of the species observed by either E8R, Raman, infrared or UV-Vis spectroscopy has been provided. The problem is that the red species is formed only in sulfur-rich solutions where long-chain polysulfide dianions are present also and these are of orange to red color, too (for a description of this dilemma, see [89]). Furthermore, the presence of the orange radical anion 8e (see below) cannot be excluded in such systems. 

The more reasonable formation of the tetrasulfide radical by the reaction shown in Eq. (51)... 

The tetrasulfides R R MS4 with M=Si, Ge, Sn, or Pb bearing bulky substituents on the group 14 element were synthesized by the reaction of the corresponding divalent species R R M, which are heavier analogues of the carbenes, with elemental sulfur (see Scheme 1) [11-20]. The divalent species... 

R R M were prepared by reduction of the dibromides R R MBr2 with lithium naphthalenide (method A), by thermolysis of a disilene (method B), and the ligand exchange of divalent group 14 element species (method C). In all cases except for the synthesis of Tip2PbS4, exclusively tetrasulfides R R MS4... 

Scheme 40 Synthesis of doubly bonded compounds between group 14 elements and sulfur by the desulfurization of the corresponding tetrasulfides...

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...

Scheme 64 Reaction of tin tetrasulfide with transition metal complexes...

Figure 3. The structure of CgH 3N 3[P(S)NMe2]21P(S)(NMe2)2]2> the tetrasulfide of XIII.

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