Sulfur Atom Abstraction

Two p-thio compounds are noteworthy, MeRe(NAr)2 2(p-S)2, 20, and MeRe(NAr)2 2(p-S), 21. For comparison purposes reference is also made to 22, the p-oxo analogue of 21. 

Compounds 21 and 22 are not isostructural 22 has a syn,syn arrangement, whereas 21 exists as the syn,anti form with Cs symmetry. There was no indication that 21 rearranges over time at 243-323 K. Even at 263 K, 21 shows the two C/f3 resonances merged into one, but two resonances for the Me2CZf proton of the isopropyl groups were observed. In contrast, one CHS and one Me2CHresonance were observed for 22. 

With mono- and di-phosphines the rate laws take different forms, 

This poses a complication for the mechanism, because a direct study of the kinetics shows that 21 reacts with PR3 much more slowly than 20 

To explore the origin of the term in Eq. (32) with the [PR3]2 dependence, experiments were carried out with added pyridine. The rate law now includes a second term 

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Process (3.8) is a total 2e per cadmium atom and indicates that CdS formation occurs via a sulfur atom abstraction from 8203 . This reaction was called for in order to suggest that the reduction of Cd " is the only electrochemical step, whereby charge is consumed, followed by a subsequent chemical step comprising sulfur association to reduced cadmium. Sulfur is generated by the decomposition of thiosulfate. On the other hand, reaction (3.9) corresponds to an overall 4e /Cd process where reduction of S2O3 itself must occur as well as that of Cd ", the former comprising actually the rate-determining step. This route becomes more favorable as pH decreases for it requires additional protons. 

The salts of alkyl xanthates, A/,A/ -di-substituted dithio-carbamates and dialkyidithiophosphates [26] are effective peroxide decomposers. Since no active hydrogen is present in these compounds, an electron-transfer mechanism was suggested. The peroxide radical is capable of abstracting an electron from the electron-rich sulfur atom and is converted into a peroxy anion as illustrated below for zinc dialkyl dithiocarbamate [27] ... 

The isolation, separation, and chemistry of dithio- and perthioaryl-carboxylate complexes of Ni(II), Pd(II), and Pt(II) were reported in two complementary reports (381, 415). The perthiocarboxylate complexes have also been obtained by oxidative addition of sulfur to the dithiocar-boxylic acid complexes. The abstraction of the sulfur atom adjacent to carbon by PPha was again observed, and rationalized as follows. 

Abstract Inorganic polysulfide anions and the related radical anions S play an important role in the redox reactions of elemental sulfur and therefore also in the geobio chemical sulfur cycle. This chapter describes the preparation of the solid polysulfides with up to eight sulfur atoms and univalent cations, as well as their solid state structures, vibrational spectra and their behavior in aqueous and non-aqueous solutions. In addition, the highly colored and reactive radical anions S with n = 2, 3, and 6 are discussed, some of which exist in equilibrium with the corresponding diamagnetic dianions. 

Due to the high rate of reaction observed by Meissner and coworkers it is unlikely that the reaction of OH with DMSO is a direct abstraction of a hydrogen atom. Gilbert and colleagues proposed a sequence of four reactions (equations 20-23) to explain the formation of both CH3 and CH3S02 radicals in the reaction of OH radicals with aqueous DMSO. The reaction mechanism started with addition of OH radical to the sulfur atom [they revised the rate constant of Meissner and coworkers to 7 X 10 M s according to a revision in the hexacyanoferrate(II) standard]. The S atom in sulfoxides is known to be at the center of a pyramidal structure with the free electron pair pointing toward one of the corners which provides an easy access for the electrophilic OH radical. 

Nozaki reported the reaction of trialkylboranes with styryl sulfoxides and sulfones. Alkyl radicals generated from trialkylboranes add at the -position of /3-styryl sulfoxides and sulfones (a- to the sulfur atom). The resulting radicals fragment and deliver the -styryl adducts [108]. Interestingly, the sulfoxides eliminate very rapidly leading to partially stereospecific substitution (Scheme 44). The radical nature of the process is demonstrated by the presence of a side product derived from the solvent (THF) by hydrogen atom abstraction. 

The principal products in the oxidation of the sulfides are sulfur dioxide and aldehydes. The low-temperature initiating step is similar to reaction (8.138), except that the hydrogen abstraction is from the carbon atom next to the sulfur atom that is,... 

The addition of trisubstituted silanes to carbonyl sulfide has been applied to the synthesis of the corresponding silanethiol derivatives (Reaction 5.40) [78]. In Scheme 5.12 the mechanism is depicted, starting from the silyl radical attack to the sulfur atom of 0=C=S and ejection of carbon monoxide. The resulting silanethiyl radical abstracts hydrogen from the starting silane, to give the silanethiol and to generate fresh silyl radical (see Section 3.4). 

Reaction (7.63) shows an example of C—S bond formation [73,74]. In fact, the aryl radical formed by iodine abstraction by (TMS)3Si radical rearranged by substitution to the sulfur atom, with expulsion of the acyl radical and concomitant formation of dihydrobenzothiophene (60). This procedure... 

The strongly distorted M0484 cube of the latter species is produced by abstraction of a sulfur atom from each of the four type III ligands. A reasonable mechanism for the reaction of the two type lib ligands would... 

The reaction of OH with DMS is believed to proceed by two channels, abstraction of a hydrogen from a methyl group and addition of OH to the sulfur atom ... 

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