Dialkyl sulphide

Alkene complexes Alkynyl complexes Ammine complexes Aqueous chemistry Arsine complexes Auranofin Auride ion Aurophilicity Binary compounds Bond lengths acetylacetonate complex alkyls and aryls ammine complexes carboxylates cyanide complexes dialkyl sulphide complexes dithiocarbamates to gold... 

It was reported earlier that even dialkyl sulphides are efficiently oxidized to sulphoxides without a concomitant C—S bond cleavage by NBS or N-chlorosuccinimide (NCS) when the reaction is performed in anhydrous methanol at low temperature103. iV-Chloro-Nylon-6,6 in methanol-water or dioxane-water104 and iV-bromo- -caprolactam in water or alcohols105 were also used successfully for oxidation of sulphides. 

Photochemical synthesis of sulphoxides was reported for the first time by Foote and Peters111 in 1971. They found that dialkyl sulphides undergo smoothly dye-photosensitized oxidation to give sulphoxides (equation 32). This oxidation reaction has been postulated to proceed through an intermediate adduct 63, which could be a zwitterionic peroxide, a diradical or cyclic peroxide, which then reacts with a second molecule of sulphide to give the sulphoxide (equation 33). 

Esters which are unstable and/or too reactive, such as those of CF3S03H, require a negative modifier (donor), e.g., a dialkyl sulphide, to give living systems such modifiers form a D-A complex with an acceptor centre, e.g., the acidic protons, at the growing end. 

The S-alkyl-O-methyl dithiocarbonate, prepared by procedure 4.1.14 from MeOCS2K (48.26 g, 0.33 mol), is extracted from the reaction mixture with Et20 (3 x 25 ml). The ethereal extracts are washed with H20 (3 x 100 ml) and evaporated under reduced pressure at 40°C. Aqueous Na2C03 (2%, 300 ml) is added and the aqueous mixture is stirred at 50°C for ca. 3 h. The mixture is then extracted with EtjO (3 x 50 ml) and the dried (Na2S04) extracts are evaporated under reduced pressure at 70 °C. The temperature of the residue is maintained at 70°C for 30 min and the 5,5-dialkyl ester, which is contaminated with the 0,5-dialkyl ester, the dialkyl sulphide and the disulphide, is isolated by chromatography from silica. 

An alternative route to sulphones utilizes the reaction of the appropriate activated halide with sodium dithionite or sodium hydroxymethanesulphinite [6], This procedure is limited to the preparation of symmetrical dialkyl sulphones and, although as a one-step reaction from the alkyl halide it is superior to the two-step oxidative route from the dialkyl sulphides, the overall yields tend to be moderately low (the best yield of 62% for dibenzyl sulphoxide using sodium dithionite is obtained after 20 hours at 120°C). The mechanism proposed for the reaction of sodium hydroxymethanesulphinite is shown in Scheme 4.20. The reaction is promoted by the addition of base and the best yield is obtained using Aliquat in the presence of potassium carbonate. It is noteworthy, however, that a comparable yield can be obtained in the absence of the catalyst. The reaction of phenacyl halides with sodium hydroxy-methane sulphinite leads to reductive dehalogenation [7]. 

Although there are other more cost effective and efficient procedures, the periodate oxidation of dialkyl sulphides to the sulphoxides has been shown to proceed in high yield [24, 25, 29] thiols are oxidized to disulphides (95-100%) [29]. The potency of the quaternary ammonium periodate for the oxidation of sulphides is improved by the addition of wieso-tetraphenylporphinatoironflll) chloride [TPPFe(III)Cl] [27]. In contrast with the oxidation conducted in the absence of TPPFe(III)Cl [24,25], aryl sulphides are oxidized more rapidly than alkyl sulphides. 

Tetra-n-propylammonium perruthenate also oxidizes sulphides to sulphones [45]. Yields are generally high for dialkyl sulphides and alkyl aryl sulphides, but lower for diaryl sulphides. 

HNO, (10%, 16 ml, 25 mmol) and TBA-AuCl4 or TBA-AuBr4 (0.25 mmol) are added to the dialkyl sulphide (5 mmol) in nitromethane (8 ml). The initially colourless solution is stirred until a yellow colour persists. Aqueous Na2S20, (sat. soln. 10 ml) is then added (for basic substrates, Na,CO, is also added to make the mixture alkaline). The mixture is extracted with CH2Cl2 (2 x 25 ml) and the dried (Na2S04) extracts are evaporated to yield the sulphoxides. 

Desulphurization of thiols has been accomplished in high yield under phase-transfer conditions using tri-iron dodecacarbonyl (or dicobalt octacarbonyl). The mechanism proposed for the formation of the alkanes and the dialkyl sulphide byproducts involves a one electron transfer to the thiol from the initially formed quaternary ammonium hydridoiron polycarbonyl ion pair [14], Similar one electron transfers have been postulated for the key step in the cobalt carbonyl promoted reactions, which tend to give slightly higher yields of the alkanes (Table 11.18). 

Related three-electron bond radical-cations 1 are formed from dialkyl sulphides by oxidation with hydroxyl radicals generated using pulse radiolysis [2]. An isoe-lectronic three-electron bond between two nitrogen atoms in 2 is formed by reduc-... 

Retrosynthetic C—S disconnection reveals two possible routes to dialkyl sulphides. 

Dialkyl sulphides are converted into trialkylsulphonium salts by treatment with an alkyl halide (the bromide or iodide is usually the reactant of choice). An important example of this group is trimethylsulphonium iodide, which is used as a methylene transfer reagent by virtue of its being converted in the presence of base into a sulphur ylide, which is a nucleophilic carbene equivalent. 

Dialkyl sulphides may be oxidised to the sulphoxides (4) (alkylsulphinylal-kanes), and thence to the sulphones (5) (alkylsulphonylalkanes). 

The reactions of [WF6] with binary fluorides may be explained by the disproportionation of this ion to WF6 and WF4 followed, in some instances, by the complex-ing of the WF4 with the fluoroanion.431" WC16 or WC15 react with an excess of a dialkyl sulphide, R2S (R = Me or Et), via an S-dealkylation sequence to produce (R3S)2[WC16] 4316 Synthetic procedures suitable for the preparation of WOX2 (X = Cl or Br) have been described432 and thermochemical data have been obtained for WSF2.352... 

Electrochemical fluorination of dialkyl sulphides leads to sulphur(VI) derivatives (see Chapter 2, Section III), and oxidation of sulphur also occurs [246] in cobalt fluoride or direct fluorination reactions (Figure 8.89). 

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