Tetrasulfane

Natrium-trithio-dihydrido-borat Alkohol, Disulfan, Tetrasulfan 26... 

Natrium-tri thio-dihydrido-borat reduziert Aldehyde und Ketone in THF bei 20° in guten Ausbeuten zu Alkoholen, wahrend bei Siedetemperatur aus Aldehyden undof-fenkettigen Ketonen auch Disulfane, aus cyclischen Ketonen auch Tetrasulfane gebil-det werden3 z.B. ... 

The structures, energies, torsional barriers and vibrational spectra of three rotamers of tetrasulfane, H2S4, have been examined by Drozdova, Miaskiewicz and Steudel at the MP2/6-311G level [34]. Surprisingly, the cis-trans conformation (motif -l-H— symmetry Ci) is found to be most stable, followed by the all-cfs form (h—t symmetry C2), while the helical all-... 

The S-S bond dissociation energies of H2S2, H2S3 and H2S4 have been studied by Steudel et al. at the GCSD(T)//6-311 G(2df,p) level [42]. The calculated enthalpies AH° for the dissociation at the central bonds at 298 K are 247, 201 and 159 kJ mol respectively. The lower stability of the tri- and tetrasulfanes towards homolytic S-S cleavage is attributed to the stability of the generated HSS radical which is stabilized by the formation of a three-electron n bond. 

Fig. 2 Three conformational isomers of the tetrasulfane molecule H2S4 differing by the signs of the torsional angles at the three SS bonds (after [47])...

Very similar values were calculated at the MP2(full)/6-31G level [48] and at the MP2/6-311++G level [34]. No experimental structure determination has been reported for tetrasulfane. 

The symmetrical thiosulfoxide isomer of tetrasulfane (HS)2S=S is also of Cs symmetry and by 123 kJ mol" less stable than the chain-like ground state of C2 symmetry (at the MP2/6-31GV/HF/4-31G level of theory) [51]. However, at the much higher G3(MP2) level the energy difference is only 93 kJ mol [52]. Similarly, the two hexasulfane isomers (HSS)2S=S (Cs symmetry) and (HS)(HSSS)S=S (Q symmetry) have recently been calculated at the G3X(MP2) level to be by 53 and 54 kJ mol respectively, less stable than the helical chain of C2 symmetry [52]. The decreasing energy difference be-... 

Table 7 Vibrational spectra of tetrasulfane (after [58] wavenumbers in cm" )...

The decomposition of tri- and tetrasulfane in CCI4 solution (0.2 mol 1 ) at 70 °C and in the absence of oxygen has been studied by H NMR spectroscopy [64]. Initially, tetrasulfane decomposes to a mixture of tri- and pentasul-fane but slowly and after an induction period hydrogen sulfide and disulfane are formed in addition. These results have been interpreted in terms of a radical-chain reaction. The initial step is assumed to be the homolytic cleavage of the central SS bond which has by far the lowest dissociation enthalpy of the molecule ... 

The initial products in the trisulfane decomposition are H2S4 and approximately equal amounts of H2S and H2S2. This reaction is much faster than the tetrasulfane decomposition despite the higher dissociation enthalpy. Therefore, it was assumed that the radicals formed in the initial step are more reactive [64] ... 

For example, trichloromethyl sulfenylchloride yields the corresponding tri- and tetrasulfanes on reaction with disulfane [87] ... 

A number of metal complexes with disulfurmonoxide as a ligand have been prepared either by oxidation of precursor complexes containing the 2 hgand or by trapping S2O formally produced in situ from a suitable precursor by heating [52]. Such molecules are cyclic di-, tri-, or tetrasulfane monoxides or dioxides such as the one shown in Scheme 1. 

Figure 8.4 The use of bis(3-trimethoxysilyl)tetrasulfane) modified silica in the vulcanization of elastomers (idealized a+b=4, l3Ax3A8) taken from ref (55).

Analog entsteht mit Dichlordisulfan das Bis-[chlor-phenyl-thiophosphonyl]-tetrasulfan und mit Thionylchlorid das l,3-Bis-[chlor-phenyl-thiophosphonyl]-trisulfan-2-oxid. 

However, since only SCI2 and S2CI2 are easily available, equations (1) and (2) are primarily used to make tri- and tetrasulfanes. Sulfur-rich dichlorosulfanes Sj Cl2 x > 2) may be synthesized in analogous reactions from H2S, H2S2, or H2S3 and excess SCI2 or S2CI2 (equation 4). 

Bis(alkoxycarbonyl)polysulfanes (n = 3, 4) have been prepared from the sulfenyl chlorides R0C(0)8C1 with H28 (x = 1, 2) " or Na28x (v = 1, 2). " It is, however, usually observed that equation (18) does not proceed in a clean way to give the tri- or tetrasulfane in high yield but, owing to secondary interconversion reactions catalyzed by 8H compounds or sulfide ions (see 8ection 5.3), results in complex mixtures of polysulfanes R2 8 , which can be detected by L " or HPL " " (see 8ection 4). 

When organochlorodisulfanes are used, RS2CI (dissolved in dichloromethane), the product should be the corresponding tetrasulfane, but owing to secondary interconversion reactions (see Section 5), possibly catalyzed by iodine, a mixture of polysulfanes is observed (HPLC analysis see Section 4) (equations 21 and 22). " ... 

Therefore, depending on the reaction conditions, either the trisulfane or the tetrasulfane is isolated as the main product. " The aqueous solution of Nal and Na2S406 may also be used for halogen exchange reactions of the type shown in equation (19)." " ... 

AUcyl chlorides, -bromides, and -iodides can be converted to tri- or tetrasulfanes by treatment with elemental sulfur at 20 °C in the presence of KOH and traces of water methyl-, ethyl-, isopropyl-, and allylpolysulfanes have been prepared in this manner. Sometimes hydrazine is added to rednce Sg to polysulfide anions. ... 

AUcyltri- and -tetrasulfanes may be conveniently prepared from thiols and elemental sulfur in the presence of catalytic amounts of n-butylamine at 25-63 °C (equation 30 with Y = H2S). The products formed are determined by the molar ratio RSHiSg, the polarity of the solvent (CFI2CI2, MeOH), the reaction time, and the temperature -, i-, and t-alkyl thiols as well as cycloalkyl thiols have also been applied. ... 

Sulfur may react with alkenes either by addition to the C=C double bond or by substitution of H by S with the elimination of H2S. In both cases polysulfanes are formed. Octafluoroisobutene, (CF3)2C=CF2, reacts at 60-70 °C in dimethylformamide (DMF) and in the presence of cesium fluoride with elemental sulfur to give the thioketene dimer (5) and the trisulfane (6) (yield 21 % and 3 5% based on the alkene). Use of KF instead of CsF also produced some tetrasulfane analogous to (6). ... 

Aliphatic ketones and aldehydes react with H2S under pressure to give a mixture of geminal dithiols and tri- and tetrasulfanes according to equations (67-69). ... 

Primary and secondary aUcyltetrasulfanes may be prepared from ketones via hydrazones by reaction with H2S (equations 70 and 71). The mechanism and stoichiometry of equation (71) are unknown, but MeC02H and 2NH4+ are probably formed as by-products, in which case four equivalents of H2S are needed, resulting in a tetrasulfane. 

Various aliphatic and aromatic dichlorides and -bromides have been used to synthesize tri- and tetrasulfanes by reaction with aqueous or alcoholic sodium poly sulfide. For instance, the benzotrithiepin (8) was obtained from... 

Similarly, bifimctional tosylates yield cyclic di-, tri-, and tetrasulfanes on treatment with sodium polysulfide (equation 84). ... 

The highly reactive S2 molecule can be prepared by various routes in solution. Its intermediate presence has been deduced from trapping reactions with alkenes, which are turned into disulfanes, however, tri- and tetrasulfanes are sometimes also formed only the latter reactions will be reported here. 

A mixture of Sg and phosphorus(V) sulfide may also be used to sulfurize organic compounds certain epidisulfanes are transformed to epitrisulfanes. The reaction of SCI2 with 1,4-diethoxybenzene, catalyzed by A CI, in CS2 or CHCI3, yields a bis-tetrasulfane in which two S4 units bridge the two benzene rings. ... 

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