Reactions sulfanes

Azaferrocene reacts with aromatic hydrocarbons in the presence of aluminium chloride, giving rise to the cationic complexes of the type (Ti -arene)(Ti -cyclopenta-dienyl)iron(l+) isolated as BF4 salts [87JOM(333)71]. The complex 28 is obtained by reaction of the sulfane compound [Cp(SMc2)3Fe]BF4 with pentamethyl-pyrrole [88AG(E)579 88AG(E)1468 90ICA(170)155]. The metallic site in this center reveals expressed Lewis acidity (89CB1891). 

Since the chain-lengths of the molecules present in crude sulfane oil is different from the chain-length of the anions in the original sodium polysulfide solution one has to conclude that in addition to the reaction at Eq. (4) the reactions at Eqs. (5) and (6) also take place during the preparation by protonation of the polysulfide anions. 

There are a number of other methods to prepare crude sulfane oils, e.g., from hquid H2S and elemental chlorine or bromine [10] or by reaction of H2S with sulfur fluorides [10] or sulfur chlorides [20] but these processes are of httle practical importance. 

The higher sulfanes H2S with n>3 are usually prepared by condensation reactions since their volatihty is low and vacuum distillation is difficult if not impossible. The starting products are the lower sulfanes and certain dichlorosulfanes SmCl2 which provide all members up to octasulfane by reactions of the following types ... 

The liquid components are mixed at -78 °C. To suppress side reactions the sulfane component is applied in a large excess (>10 1). The unreacted starting sulfane and hydrogen chloride are distilled off after the reaction has... 

Hahn and Altenbach designed a method to prepare specific sulfanes with 2 to 5 sulfur atoms in small quantities in solution by the following reactions (RjSi = MePh2Si) [29] ... 

Reactions at Eqs. (12) and (13) are carried out in toluene solution. The yellow crystalline products are purified by recrystallization from pentane and stored in a dry atmosphere at —20 °C. Reaction at Eq. (14) takes place slowly at 20 °C in benzene. The sulfane product H2S is separated from the silylester side product by distillation together with the benzene solvent (in the case of n=2-4) or by phase separation (for n=4, 5). For certain preparative purposes the ester and the solvent may not interfere. If deuterated triflu-oroacetic acid is used in the reaction at Eq. (14) the fully deuterated sulfane is obtained [29]. 

MeO)2S [36]. These evidently originated from the reaction of the dichloro-sulfanes with the methanol solvent used in the preparation of the sulfanes by mixing sodium polysulfide with dichlorosulfanes. 

By ab initio MO and density functional theoretical (DPT) calculations it has been shown that the branched isomers of the sulfanes are local minima on the particular potential energy hypersurface. In the case of disulfane the thiosulfoxide isomer H2S=S of Cg symmetry is by 138 kj mol less stable than the chain-like molecule of C2 symmetry at the QCISD(T)/6-31+G // MP2/6-31G level of theory at 0 K [49]. At the MP2/6-311G //MP2/6-3110 level the energy difference is 143 kJ mol" and the activation energy for the isomerization is 210 kJ mol at 0 K [50]. Somewhat smaller values (117/195 kJ mor ) have been calculated with the more elaborate CCSD(T)/ ANO-L method [50]. The high barrier of ca. 80 kJ mol" for the isomerization of the pyramidal H2S=S back to the screw-like disulfane structure means that the thiosulfoxide, once it has been formed, will not decompose in an unimolecular reaction at low temperature, e.g., in a matrix-isolation experiment. The transition state structure is characterized by a hydrogen atom bridging the two sulfur atoms. 

Older Raman data obtained using a mercury lamp are available for the sul-fanes H2S (n=5-8) and for crude sulfane oil. However, there is some suspicion that the lines observed near 150 and 217 cm result from Ss as a byproduct of the preparation reactions or as a photochemical decomposition... 

In the literature tetrathiosulfuranes have been discussed as possible intermediates in the thermal decomposition of sulfanes and other polysulfur compounds. High-level ab initio MO calculations have in fact revealed that such species are local minima on the potential energy hypersurface [34]. However, recent results show that both the Gibbs reaction energies as well as the activation enthalpies for reactions of the type... 

As the reaction proceeds higher sulfanes and finally Ss are formed. The reaction is autocatalytic which makes any kinetic analysis difficult. The authors discussed a number of reaction mechanisms which are, however, obsolete by today s standards. Also, the reported Arrhenius activation energy of 107 17 kJ mol is questionable since it was derived from the study of the decomposition of a mixture of disulfane and higher sulfanes. Nevertheless, the observed autocatalytic behavior may be explained by the easier ho-molytic SS bond dissociation of the higher sulfanes formed as intermediate products compared to the SS bond of disulfane (see above). The free radicals formed may then attack the disulfane molecule with formation of H2S on the one hand and higher and higher sulfanes on the other hand from which eventually an Ss molecule is split off. 

In the gas phase all sulfane molecules are relatively strong Bronsted acids. Their acidity is defined by the enthalpy or, alternatively, by the Gibbs energy of the following deprotonation reaction ... 

The reaction of organic sulfenyl chlorides RSCl or chlorodisulfanes RSSCl with sulfanes provides organic polysulfanes in preparative quantities [2] ... 

However, some interconversion reactions take place simultaneously and therefore the composition of the sulfane mixtime is not a mirror image of the composition of the polysulfide solution [103]. The sulfane mixture forms a yellow oily hydrophobic liquid which precipitates from the aqueous phase. At 20 °C it decomposes more or less rapidly to H2S and Sg. 

Sulfanes decompose to produce H2S and sulfur in a thermodynamically favored reaction. 

The reaction of S2C12 with sulfanes produces the chlorosulfanes. 

Cyanide is metabolized in the body by two metabolic pathways that have been identified (Ansell and Lewis 1970). The first and major metabolic pathway involves the transfer of sulfane sulfurs from a donor to cyanide to yield thiocyanate (see Section 2.3). The reaction employs the enzyme rhodanese as a... 

Although these equations held true for some strains of bacteria under some growth conditions, they did not help explain the commonly observed quantitative conversion of both sulfur atoms of thiosulfate to sulfate, rather than the liberation of the sulfane-sulfur mainly as elemental sulfur. During the 1960s, cyclic reactions of polythionates and other polysulfur compounds continued to be postulated as mechanisms for thiosulfate and polythionate metabolism (Trudinger 1967), but none of these was supported at the time by strong biochemical evidence. The time was opportune for a new approach to the problem of thiosulfate oxidation in thiobacilli. 

Wilhelm and Schmidt prepared lightly yellow-green solids, containing Sjo rings by reactions of various matching combinations of sulfanes and chlorosulfanes 94,125), e.g.,... 

Schmidt synthesized S20 from sulfanes and chlorosulfanes (98) by using carefully designed mixtures of compounds and catalyzing the reaction with HCl. 

According to Davis the reaction mechanism includes the intermediate formation of unstable chain-like sulfane-monosulfonic acids ... 

In order to obtain heterodimers a cysteine residue of one peptide has to be specifically activated for subsequent reaction with the cysteine residue of the second peptide. Thiols are activated by introducing an electron-withdrawing substituent that increases the responsiveness of the sulfur to nucleophilic substitution. This topic has been reviewed 41311 Of the various older methods known in sulfur chemistry for the preparation of unsymmetrical disulfides, i.e. thiosulfates,11321 S-alkylthiosulfonates,11331 5-alkylthiosulfinates,11341 sulfanyl-amines,11351 sulfanylimides,11361 sulfanyl thiocyanates and sulfenyl chlorides,1137,1381 sulfan-... 

The hydroxy group is far more reactive to (dialkylamino)trifluoro-A4-sulfanes than most other functional groups. Thus, at low temperatures a hydroxy group can be selectively fluorinated in the presence of another functional group. This, coupled with the inertness of (dialkylamino)-trifluoro-A4-sulfanes towards most protection groups, and the mild reaction conditions required has enabled a vast array of functionalized fluorinated compounds to be synthesized, for example, carbohydrates,24-29,31 nucleosides,30 and steroids32 35 (see Table 3). 

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