1,3-Dithioles, oxidative coupling

In the synthesis of a series of cyclic aromatic disulfide oligomers using oxidative coupling of dithiols with oxygen catalyzed by copper salts and an amine, an effective, easy, and rapid method for the synthesis of macrocyclic aromatic disulfide oligomer from 4,4/-oxybis(benzenethiol) by cyclodepoly-... 

C3S8, C5S7, CeSg, CeSio, and CeS. The syntheses of the sulfides involve the dithiolate complex of a transition metal ion as a precursor and are based on the oxidative coupling and electrophilic sulfiding (e.g. via S2CI2) of either the a-or anion (Figure 6) and, consequently, molecular... 

Tetrathiocanes, usually formed by the oxidative coupling of 1,2-dithiols, make up an important class of heterocycles covered in this chapter. These compounds and other polythiocanes and polythiocines are important molecules of biological interest, especially as odor and flavor components. 

Oxidative Coupling of Dithiols with Diacyl Disulfides... 

Figure 2.2 A number of small thiol-containing molecules have proven useful for modification of gold or metallic surfaces. The dithiol derivatives provide better dative bond stability and can t be displaced easily by competing thiols or oxidation. Most thiol-containing compounds used for surface modification also contain terminal functional groups or reactive groups for coupling affinity ligands.

The mixed-potential model demonstrated the importance of electrode potential in flotation systems. The mixed potential or rest potential of an electrode provides information to determine the identity of the reactions that take place at the mineral surface and the rates of these processes. One approach is to compare the measured rest potential with equilibrium potential for various processes derived from thermodynamic data. Allison et al. (1971,1972) considered that a necessary condition for the electrochemical formation of dithiolate at the mineral surface is that the measmed mixed potential arising from the reduction of oxygen and the oxidation of this collector at the surface must be anodic to the equilibrium potential for the thio ion/dithiolate couple. They correlated the rest potential of a range of sulphide minerals in different thio-collector solutions with the products extracted from the surface as shown in Table 1.2 and 1.3. It can be seen from these Tables that only those minerals exhibiting rest potential in excess of the thio ion/disulphide couple formed dithiolate as a major reaction product. Those minerals which had a rest potential below this value formed the metal collector compoimds, except covellite on which dixanthogen was formed even though the measured rest potential was below the reversible potential. Allison et al. (1972) attributed the behavior to the decomposition of cupric xanthate. 

In the past, TTF has been prepared from 1,3-dithiole-2-thione, which, by an oxidative step, was converted to a 1,3-dithiolylium salt followed by coupling with base.6 9,15 The present method uses a reductive sequence, thereby permitting milder conditions and better yields.16... 

Remarkably, although oxidation of thiols has been more intensively studied, reports on the selective coupling of dithiols are rare due to facile competitive polymerization reactions [155]. 

The oxidative polymerization has been proposed to proceed via a radical coupling that involves the coupling of neutral radicals or cation radicals. The former case corresponds to the oxidative polymerization of phenols and dithiols in which the neutral radical is formed by one-electron transfer after dissociation of a hydron from the monomer, or by the elimination of a hydron after the oxidation. The latter case takes place when the cation radical formed by one-electron oxidation exists as a stable species. The cation radicals then couple with each other, and the dimer is formed through solvent-catalyzed hydron elimination from the intermediate dication. Oxidative polymerization of pyrrole and thiophene uses this mechanism [57-62]. 

Partial oxidation of C2S4 proceeds with loss of sulfur and coupling to give the vinylidene dithiolate derivative of dmit2-. This planar dianion C4S62 is isolated as its blue-purple ELtN"1" salt (130). Treatment of this salt with metal halides affords di- and polymeric complexes, for example, [C4S6][RuCl(arene)]2 and the semiconducting [NK Seln (134) (Eq. 11). 

Coupling can also occur via a substituent, as for 1,2-dithiol-3-thiones, which are anodically oxidized to bis(dithiolyium)disulfides [48]. The related a-(l, 2 -dithioT3 -ylidene)acetophenones 16 are analogously oxidized to a di-cation (17) that de-protonates to give the uncharged dimer 18. When, however, the electrolysis was conducted in the presence of an oxidant such as DDQ, or by further oxidizing dimer 18, a new di-cation (19) was formed (Scheme 14) [49]. 

Electrochemical oxidation of l,3-dithiol-2-one and -2-thione gave behavior consistent with the formation of dimers which were subsequently oxidized to radicals of uncertain structure. Chemical oxidation of the isoelectronic dithiafulvenes 151 (R = phenyl, 4-chlorophenyl, 4-tolyl, or anisyl) led to dimeric exocyclic C—C-coupled products, indicating the intermediacy of the radical 152. 5o... 

The C,C coupling reactions of sulfur compounds are less numerous. One example is mentioned here. When 1,3-dithioles are oxidized in MeCN containing pyridine, tetrathio-fulvalenes are obtained in moderate to fair yields (13 0%) [111]. 

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