Of dithiols

Generally, unsaturated compounds, eg, alkenes and natural fats and their derivatives, are much more reactive toward sulfur than alkanes. Sulfur reacts with unsaturated compounds at temperatures of 120—215°C, forming products that are usually dark and often viscous cross-linked mixtures of dithiole-3-thiones (eq. 4) (2) and sulfides (Table 1) (3). 

Homolytic addition of dithiols to alkynes as a new approach to construction of dithiacyclanes and thiacrown ethers 97IZV1256. 

Irg 1076, AO-3 (CB), are used in combination with metal dithiolates, e.g., NiDEC, AO-30 (PD), due to the sensitized photoxidation of dithiolates by the oxidation products of phenols, particularly stilbenequinones (SQ, see reaction 9C) (Table 3). Hindered piperidines exhibit a complex behavior when present in combination with other antioxidants and stabilizers they have to be oxidized initially to the corresponding nitroxyl radical before becoming effective. Consequently, both CB-D and PD antioxidants, which remove alkyl peroxyl radicals and hydroperoxides, respectively, antagonise the UV stabilizing action of this class of compounds (e.g.. Table 3, NiDEC 4- Tin 770). However, since the hindered piperidines themselves are neither melt- nor heat-stabilizers for polymers, they have to be used with conventional antioxidants and stabilizers. 

Procedure. Prepare the dithiol reagent by adding 0.1 -0.2 g of dithiol to 100 mL of 0.25M sodium hydroxide solution, followed by 0.5 mL of thioglycollic acid (to inhibit oxidation of the reagent) keep at 5 °C and prepare fresh daily. 

Add to the sample solution (containing 1 -25 g of Mo) 4 mL of 1 3 sulphuric acid, 3 drops of 85 per cent phosphoric(V) acid, and 0.5 g of citric acid. Dilute with water to 20 mL and add 2 mL of dithiol solution. Allow to stand at room temperature for 2 hours. Extract the molybdenum complex with 13 mL and 10 mL portions respectively of re-distilled butyl acetate, and make up to 25.0 mL with this solvent in a graduated flask filter through glass wool if not entirely clear. Determine the absorbance of the solution at 670 nm. Prepare a calibration curve as detailed in Section 6.14. 

Rh-catalyzed reaction of hydrosilanes with thiols results in the formation of Si-S bond compounds (Scheme 5).35 37 The use of dihydrosilanes and dithiols as starting materials affords the corresponding polymers having Si-S bonds. The reaction of a trihydrosilane with 2 equivalent of dithiols in the absence of a... 

Preformed gold nanoparticles have been used as the top electrode for interrogating SAMs of dithiols diluted within an alkylthiol matrix. The alkyl tails of the alkylthiols do not coordinate to the nanoparticles, but a dithiol s second SH group, sticking above the alkyl level, can bond to the nanoparticle, which is then contacted with an Au-coated AFM probe [42]. 

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. 

Figure 5.3 Diastereoselective amplization of an alternating, meso arrangement of dithiols to create a high affinity receptor for NlCHj). ...

Henderson,). ., Feng, S., Ferrence, G.M., Bein, T. and Kubiak, C.P. (1996) Self-assembled monolayers of dithiols, diisoqfanides, and isocyanothiols on gold chemically sticky surfaces for covalent attachment of metal clusters and smdies of interfacial electron transfer. Inorg. 

If a diluted solution of dithiole 182 and sulfur monochloride in ether were mixed at low temperature, tetrathiane 183 was formed in low yield (1995JOC8056). The precipitation and purification of the final product were achieved by cooling the mixture to —78 °C (Scheme 92). 

Some miscellaneous examples of QD synthesis using surfactant systems are described below. A layer-by-layer [206] structure of dithiol self-assembled monolayers (SAM) and CdS mono- and multilayer nanoparticles were fabricated on a gold substrate covered with alkanedithiol. SAMs were formed by an alternate immersion of the substrate into ethanolic solutions of dithiol, and dispersion of CdS nanoparticles (ca. 3nm in diameter), the latter of which was prepared in A0T/H20/heptane w/o microemulsions. 

New applications of dithioles and dithiolanes include evaluation of compounds such as 69 and 70 as flavour components <98MI177>, 71 for antimycotic activity <99MIP33826>, 72 for antiviral activity <99CC1245>, 73 for antifungal and antibacterial activity <99MI6> and use of 74 in prevention and heatment of asthma complications <99EUP909758>. 

E) oxidation of NADH and NADPH in electron transport chains, and (F) oxidation of dithiols to disulfides or the reverse reaction. Three-dimensional structures are known for enzymes of each of these types. 

The oxidation products of dithiols are insoluble and removed with the clay residues by the filtration step, and the method appears particularly suitable for dithioacetals derived from dithiols as dithianes for instance. For other dithioacetals a further purification step was necessary. 

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]. 

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-... 

A novel method for synthesizing polythiaether macrocycles with Re cluster complex was proposed by Adams and coworkers [185]. This process involves catalysis by the Re complex rather than the stoichiometric displacement of dithiol or dithiolates by organic halides, and first example of a catalytic procedure for synthesis of polythiaether macrocycle using thietanes. The macro-cyclic products formed are shown in Fig. 56. 

This situation has been widely discussed [592a-c] and has not been finally resolved [592d]. At the same time, there is experimental data (reactions with halogens) in favor of the existence of dithiol structures of type 318b containing M — S bonds (M = Ni, Pd, Pt) with metal oxidation number +4 [592e,f]. 

An early nanopore study focused on an asymmetric Au-molecule-Ti junction based on thiol end-capped biphenyl 81b molecules [45], The asymmetry of the structure led to the observation of a prominent rectifying behavior with larger current when the Ti electrode was negatively biased. Recent work by Bao and coworkers [72] has shown that vapor deposition of Ti on SAMs results in penetration of the monolayer, thus destroying it. Similar observations were made using Au and A1 deposition. However, destruction of the monolayer could in this case be prevented if SAMs of dithiols were used, since the Au or A1 would react with the free thiol end. 

B. Reaction of Dithiole Derivatives with Reactive Methylene... 

Loiseau PM, Lubert P, Wolf JG (2000) Contribution of dithiol ligands to In vitro and In vivo trypanocidal activities of dithiaarsanes and investigation of ligand exchange in an aqueous solution. Antimicrob Agents Chemother 44 2954—2961... 

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