Dimethyl sulphoxide oxidation

The base catalysed autoxidation of dimethyl sulphoxide and methyl phenyl sulphoxide at 80 °C produces low quantities of methanesulphonic acid in both cases and benzenesul-phonic acid in the latter case189 (equation 71 and 72). There is no evidence of sulphone formation in either reaction. Dimethyl sulphoxide oxidation to methanesulphonic acid also occurs in the presence of trace quantities of acid and oxygen. Again the reaction would not be synthetically useful190. 

Methods of Synthesis. C-Nitrosierungen Qber Silyl-derivate [nitrosation of (trimethyl-silyl)benzene, p-(trimethylsilyl)toluene, and 4-(trimethylsilyl)pyrazole with alkyl nitrite-CFj-COaH or NaNOa-CFj COaH gives nitrosobenzene, p-nitrosotoluene, and 4-nitrosopyrazole, respectively]. Dimethyl Sulphoxide Oxidations A New Method for the Conversion of C = S and C=Se Groups into a Carbonyl Group [CFj-COaH catalyses the conversion of thio- or seleno-carbonyl groups into C=0 via reaction... 

The redox disproportionation of silver(i) sulphite complexes has been described. The species Ag(SOs) and Ag(SOa)a and higher complexes react in a rate law which is second order with respect to sulphite, the rates being greatest for the 1 1 complexes and decreasing with increasing concentrations of the higher complex ions. The silver(i) ion-assisted dimethyl sulphoxide oxidation of organic halides has been reported. ... 

Sulphide and sulphoxide complexes have been extensively studied since cis-RuC12(DMSO)4 (DMSO, dimethyl sulphoxide, (Me)2SO) was found to have anti-tumour properties and to be a precessor for radiosensitizing agents. Such complexes can act as catalysts for the oxidation of sulphides with molecular oxygen. 

Aravamudan and Venkappayya75 oxidized dimethyl sulphoxide in acetate buffer of pH 4 to 4.5 and with a reaction time of only 1 min. They then added potassium iodide and acid and titrated with thiosulphate the iodine liberated by unused reagent. They reported that cerium(IV) and Cr(VI) were much less effective oxidizing reagents for the sulphoxide. A very similar procedure was used by Rangaswama and Mahadevappa76 to determine dimethyl sulphoxide and numerous other compounds with chloramine B. 

Bohme77 employed excess monoperphthalic acid in diethyl ether to oxidize dibenzyl and benzyl ethyl sulphoxides. Reaction time was 24 h at - 15 to + 10 °C, after which he added potassium iodide and water and titrated the iodine set free with thiosulphate. Dickenson78 oxidized dimethyl sulphoxide in malt, wort or beer with Na2S2Os. In... 

Popova and colleagues47 carried out TLC of oxidation products of 4,4 -dinitrodiphenyl sulphide (the sulphoxide and sulphone) on silica gel + a fluorescent indicator, using hexane-acetone-benzene-methanol(60 36 10 l) as solvent mixture. Morris130 performed GLC and TLC of dimethyl sulphoxide. For the latter, he applied a 6% solution of the sample in methanol to silica gel and developed with methanol-ammonia solution(200 3), visualizing with 2% aqueous Co11 thiocyanate-methanol(2 1). HPLC separations of chiral mixtures of sulphoxides have been carried out. Thus Pirkle and coworkers131-132 reported separations of alkyl 2,4-dinitrophenyl sulphoxides and some others on a silica-gel (Porosil)-bonded chiral fluoroalcoholic stationary phase, with the structure ... 

Goheen and Bennett9 showed that regular nitric acid could be used, in about two molar excess, for the oxidation of dimethyl sulphoxide to dimethyl sulphone in 86% yield. The reaction temperature was 120-150°C with a reaction time of about 4 hours. The mechanism for this reaction was postulated to involve initially a protonated sulphoxide species (which has been shown to be present in other strongly acidic systems101 ) followed by nucleophilic attack by nitrate, and the loss of nitrogen dioxide as shown in equations (4) and (5). 

If acetic anhydride is employed in place of the sulphuric acid, only the sulphone is formed12,13 whilst if nitroethane or acetic acid are employed, no oxidation at sulphur occurs. A patent has been secured for the industrial oxidation of dimethyl sulphoxide to the sulphone with nitric acid14. This procedure yielded 84% of the sulphone in a continuous process which was prone to detonation at water concentrations below 14%. 

A more elegant, but expensive, approach22 has been the use of soluble iridium and rhodium catalysts which contain coordinated dimethyl sulphoxide (e.g. IrHCl2(Me2SO)3) which promote the oxidation of sulphoxides in aqueous media, equation (8). The ease of oxidation depends on the substituents and this decreases in the order Me > Ph > PhCH2. This reaction is especially useful since sulphides are not oxidized under the reaction conditions due to the formation of strong complexes with the catalyst. 

Sodium tungstate has also been used as a catalyst in the oxidation of dimethyl sulphoxide to the sulphone36. The kinetics of this reaction have been studied in great detail and it has been shown that oxygen transfer to the sulphoxide takes place via two peroxytungstic acid species (HW05 and HWOg ). 

Anions of hydroperoxides may be used to successfully obtain sulphones by the oxidation of sulphoxides in non-aqueous media, without the use of transition metal catalysts. This is in contrast to oxidations with peracids where aqueous media are invariably used. Thus, dimethyl sulphoxide was oxidized by the anion of cumene hydroperoxide in ethanol or benzene solution at room temperature in 90% yield66. The yield is very much dependent on the base used and decreases along the series ... 

Solutions of potassium superoxide-crown ether in dimethyl sulphoxide have been shown to cause oxidation of the solvent to the sulphone75 such a reaction could possibly be used synthetically. In the presence of water the reaction probably proceeds as shown ... 

The first report of the use of bromine for the oxidation of sulphoxides appeared in 1966116. Diphenyl sulphone was isolated in 0.5-1% yield when the sulphoxide was treated with bromine in aqueous acetic acid for several hours. The yield was increased to about 5% by quenching the reaction with sodium carbonate. A kinetic study117 of a similar reaction involving dimethyl sulphoxide showed no significant yield improvement but postulated that the mechanism proceeds via an equilibrium step forming a bromosulph-onium type intermediate which reacted slowly with water giving dimethyl sulphone as indicated in equation (35). 

A synthetically useful reaction has been reported between alkaline bromine water and dimethyl sulphoxide118, the product being the perbromosulphone (equation 36). A kinetic study of the oxidation of dimethyl sulphoxide by bromate ions, catalysed by ruthenium(III) salts, has also been published but no yield data are available119. 

A single report concerning the kinetics of the oxidation of dimethyl sulphoxide by tervalent manganese has been published143. This reaction proceeds by one-electron transfer forming the sulphoxide radical cation which, in the presence of a monomer such as acrylonitrile, may be used to initiate polymerization. Equation (48) has been proposed to describe the reaction. 

Dimethyl sulphoxide has also been oxidized electrochemically, using either a platinum anode or a dimensionally stable anode containing iridium and selenium in 1 M sulphuric acid solution158. The former electrode requires a potential close to that required for oxygen evolution whilst the latter needed a potential 0.5 volts lower. Thus the dimension-... 

It should also be noted in this section that studies of the metabolism of dimethyl sulphoxide in calves166, rabbits167,168, guinea pigs168, rats169 and man169-172 have shown that one metabolic pathway involves its oxidation to the sulphone. 

The photolysis of dimethyl sulphoxide (at 253.7 nm) in a wide range of solvents has been studied in detail176. Three primary reactions occur, namely (i) fragmentation into methyl radicals and methanesulphinyl radicals, equation (60), (ii) disproportionation into dimethyl sulphone and dimethyl sulphide, equation (61) and (iii) deactivation of the excited state to ground state dimethyl sulphoxide. All chemical processes occur through the singlet state. Further chemical reactions of the initial photochemical products produce species that have been oxidized relative to dimethyl sulphoxide. 

Gollnick and Stracke176 investigated the very complex mechanism involved in the photolysis of dimethyl sulphoxide and concluded that disproportionation is probably the route for the major sulphone-producing reaction. Other oxidized species such as methanesulphonic acid are also produced and are also probably formed by a series of disproportionation reactions, for example equation (62). Thus photolysis of dimethyl sulphoxide is not a synthetically useful reaction due to the large number of compounds produced. 

Dihydrodithiin sulphoxides, synthesis of 243 Dihydrothiophene dioxides, reactions of 653 /(,/( -Dihydroxyketones 619 Dimerization, photochemical 877, 884 Dimethyl sulphoxide anion of - see Dimsyl anion hydrogen bonding with alcohols and phenols 546-552 oxidation of 981, 988 photolysis of 873, 874, 988 radiolysis of 890-909, 1054, 1055 self-association of 544-546 Dimsyl anion... 

A. Nucleophilic Reactions of the P=0 Group.—Tris(trifluoromethyl)-phosphine oxide (33) reacts with hexamethyldisiloxane to give a phos-phorane, whose n.m.r. spectrum at — 140 °C shows non-equivalent trifluoromethyl groups. Although this unusual reaction clearly involves nucleophilic attack of the phosphoryl oxygen on silicon at some stage of the reaction, a full study of the mechanism has not been published. Tertiary phosphine oxides can be converted cleanly into dichlorophos-phoranes (34) by treatment with two moles of phosphorus pentachloride. Alkylation of the sodium salt of tetraphenylmethylenediphosphine dioxide (35) with alkyl halides, in dimethyl sulphoxide, has been reported to... 

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