Sulfur atom abstraction reactions

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. 

Thus, the eventual products of the two pathways (la) and (lb) by which OH reacts with DMS under atmospheric conditions have not yet been fully established. However, circumstantial evidence, namely the 70% yield of SO2 in the study of Barnes et al. (21) being roughly equal to the branching ratio for the H-atom abstraction (reaction (la)) at 298 K determined by Hynes et al. (12), indicates that S02 is a major product of the abstraction reaction and that DMSO, DMSO and MSA probably result from the primary addition of OH to the sulfur atom (reaction (lb)). 

In some cases, abstraction-recombination can lead to still larger rings. In the example illustrated, 1,8-hydrogen atom extraction leads to the formation of a seven-membered ring product (119 equation 42). The 1,7-diradical would be thermodynamically favored because of the radical-stabilizing ability of the two sulfur atoms. The reaction may not, however, proceed by direct 1,8-abstraction. A 1, S-abstraction followed by a subsequent 1,4-abstraction would give the same product and would be sterically more reasonable. 

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 ... 

Atomic chlorine reacts rapidly with DMS, with an overall rate constant of (3.3 + 0.5) X 10 1(1 cm3 molecule 1 s 1 at 298 K and 700 Torr total pressure (Stickel et al., 1992). As is the case for the OH reaction, the chlorine atom reaction proceeds by two reaction channels, one an abstraction and the other addition to the sulfur atom ... 

The reaction of OH with dimethyl disulfide proceeds primarily by addition to a sulfur atom. As discussed by Abbatt et al. (1992), although one would expect abstraction of an H atom from the CH3 group to occur as well at about the same rate as for DMS, such a channel is overwhelmed by the fast addition. 

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