Polysulfide ions preparation

The generated polysulfide dianions of different chain-lengths then establish a complex equilibrium mixture with all members up to the octasulfide at least see Eqs. (5) and (6). For this reason, it is not possible to separate the polysulfide dianions by ion chromatography [6]. The maximum possible chain-length can be estimated from the preparation of salts with these anions in various solvents (see above). However, since the reactions at Eqs. (22) and (23) are reversible and Sg precipitates from such solutions if the pH is lowered below a value of 6, the nonasulfide ion must be present also to generate the Sg molecules by the reverse of the reaction at Eq. (22). The latter reaction (precipitation of Sg on acidification) may be used for the gravimetric determination of polysulfides [11]. There is no evidence for the presence of monoprotonated polysulfide ions HS - in aqueous solutions [67, 72]. 

Polysulfides of several metals can be prepared by reaction of the metals with excess sulfur in liquid NH3 (group IA metals) or by heating sulfur with the molten metal sulfide. The polysulfide ion binds to metals to form coordination compounds in which it is attached to the metal by both sulfur atoms (as a so-called bidentate ligand). One example is an unusual titanium complex containing the S52-ion that is produced by the following reaction (the use of h to denote the bonding mode of the cyclo-pentadienyl ion is explained in Chapter 16) ... 

When aqueous sulfide solutions are heated with sulfur, solutions containing largely S2 and S2" are obtained. These polysulfide ions are the only ones stable in solution but a number of crystalline compounds with Sj ions from n = 3 to n = 8 can be prepared, especially by using large cations (e.g., Cs+, NH4 and enH + and R3NH+). In all those with n = 4 to 8 the S—S distances run from 2.00 to 2.11 A and the S—S—S angles are ca. 110°. Structures of some S2" ions are shown in Fig. 12-3. 

Polysulfide ions [8 ] are not prepared by deprotonation of the corresponding polysulfanes. Instead, methods of synthesis include reactions 15.18 and 15.41, and that of H2S with S suspended in NH4OH solution which yields a mixture of [NH4]2[S4] and [NH4]2[S5]. 

The dinuclear ion Mo2(S2) g (F - prepared from the reaction of molybdate and polysulfide solution (13) is a usehil starting material for the preparation of dinuclear sulfur complexes. These disulfide ligands are reactive toward replacement or reduction to give complexes containing the Mo2S " 4 core (Fig. 3f). 

Polysulfides have been prepared with many different types of cations, both monoatomic Hke alkah metal ions and polyatomic Hke ammonium or substituted ammonium or phosphonium ions. In this chapter only those salts will be discussed in detail which contain univalent main-group cations although a large number of transition metal polysulfido complexes have been prepared [7-9]. 

An interesting combination of methods is the polysulfide flux method, which can be usedforthe preparation of Ln202S (Ln trivalent rare-earth ion)-based luminescent materials (e.g. Y202S Eu or Gd202S Pr) [5.228]. In this method, the mixed oxides of the metals are mixed with excess sulfur and an alkali metal carbonate. On heating, the alkaline carbonate decomposes and reacts with sulfur to form a Uquid polysulfide flux. The oxides react with the polysulfide flux to form the oxysulfide. Flux residues can be removed by washing the reaction product in water. 

ORIGIN/INDUSTRY SOURCES/USES anthropogenic compound, not believed to occur in nature synthetic compound solvent intermediate for polysulfide rubber treatment of textiles manufacture of polymers and insecticides degreasing agents preparation of ion exchange resins... 

The reagent is prepared by warming yellow ammonium polysulfide with excess NaaSOs. Thioacetamide can also be used as a donor of S- ions. Alkali plumbites must be absent. 

Another interesting method of preparing copolymers is reported by Todorova et ai. [40-43] which involves the interaction of vinyl monomers with a polysulfide polymer. Under dispersion conditions breaking of polysulfide bonds occur forming ions, RSi w 3 RS3, oi and radicals, RS% RSS-, which then react with styrene or acrylonitrile [40] to form the copolymer ... 

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