Sulfur 54 2+ cation

Previously, the same author [52] reported that compounds containing the tricoordinated sulfur cation, such as the triphenylsulfonium salt, worked as effective initiators in the free radical polymerization of MMA and styrene [52]. Because of the structural similarity of sulfonium salt and ylide, diphenyloxosulfonium bis-(me-thoxycarbonyl) methylide (POSY) (Scheme 28), which contains a tetracoordinated sulfur cation, was used as a photoinitiator by Kondo et al. [63] for the polymerization of MMA and styrene. The photopolymerization was carried out with a high-pressure mercury lamp the orders of reaction with respect to [POSY] and [MMA] were 0.5 and 1.0, respectively, as expected for radical polymerization. 

Under special conditions sulfur cations with up to 56 atoms have been observed [209]. Evaporation of liquid sulfur and cooling the vapor in an atmosphere of a cold buffer gas (He) at low pressures followed by adiabatic expansion into the vacuum of a mass spectrometer and El ionization produced mass spectra of clusters of sulfur molecules with m/e ratios up to ca. 1800. The intensity pattern shows that the species (Ss)h are most abundant n = 1-7) followed by (Sy)(S8)n-i clusters and (S6)(Ss)h-i clusters. The latter have the same mass as (Sy)2(S8) -2 clusters see Fig. 34. Thus, the composition of the clusters reflects the composition of hquid sulfur near the melting point which contains Sg, Sy and Se molecules as the majority species [34, 210]. 

See the Review on Homocychc Sulfur Cations by 1. Krossing, Top. Curr. Chem. 2003, 230, in print... 

Kreiter R, KleiJ AW, Klein Gebbink RJM, van Koten G (2001) Dendritic Catalysts. 217 163-199 Krossing I (2003) Homoatomic Sulfur Cations. 230 135-152... 

Only molecular S7 and Se7 are firmly known, yet only the former has been characterized by X-ray analysis. However, Re complexes of Se7 are known55,56 and the neutral Se7 homocycle cocrystallized with salts of polyselenides.57,58 S7+ is thought to be present in S02 solutions of sulfur cations however, this is an unproven but likely hypothesis. Other than that, only the structures of Sig2+ and Se172+ contain E7 homocycles (see there). 

Elemental sulfur Sulfur cations Sulfur oxides Sulfur halide cations... 

This review has shown the complexity of the chemistry and the electrochemistry of sulfur, polysulflde ions, and sulfur cations. This complexity originates from the ability of sulfur to form catenated species, which leads to disproportionation and dissociation equilibria. 

The structures of S4 qei. jua, Og I iei. JUU auu oi9 depicted in Figure 12.10 they are the only homoatomic sulfur cations that have been characterised in the solid state. The cyclo-S4 cation forms an undistorted... 

The intermediate contains a tricoordinate sulfur cation or sulfonium salt. The chloride ion now attacks the other sulfur atom of this intermediate and two molecules of RSC1 result. Each atom of the original disulfide has formed an S-Cl bond. One sulfur atom was a nucleophile towards chlorine and the other an electrophile. 

The deeply colored solutions of sulfur in oleum have been known for a long time (39), but it was not until the identification of the sulfur cations Sg , and that the nature of these solutions became clear (66). In 95-100% H2SO4 sulfur forms a colloidal solution but after 12 hr at 75° the element dissolves as Sg molecules. In 5% oleum, oxidation is observed and Sig + is formed. In 10% and 157 oleum, sulfur is oxidized first rather rapidly to a mixture of S g and Sg " and then very slowly to SOg. In 30% oleum, Sjg and Sg produced initially are further oxidized to 84 + and finally to SOg. In more concentrated oleums (45 and 65%), Sg " and 84 are the initial products, and as 84 " appears to be rather stable in these solvents further oxidation to 8O2 is very slow. Changes in concentration of the various species with time and with 8O3 concentration are complicated by disproportionation reactions. Thus, 8g disproportionates to 8O2 and 8ig in oleum containing less than 15% 80g, and 84 + disproportionates to 8g + and SO2 in oleum conteining less than 407, SO3. 

Solutions of sulfur in oleum give rise to ESR spectra, but the interpretation of these spectra has been the subject of some controversy in the literature (62, 76, 77). No progress was made in the interpretation of these spectra until it had been established that the main species present under various conditions are the sulfur cations 84 +, S8 , andSi0 . It was then shown that solutions of in HSO3F... 

The structure of See in Seg(AlCl4)2 (36, 87) is similar to that of Sg except that the cross-ring distance Scg-Se is relatively shorter than that found in the sulfur cation, and the other cross-ring distances,... 

The intermediate contains a tricoordinate sulfur cation or sulfonium salt. The chloride ion now... 

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