Hydrogen peroxide-Dimethyl sulfoxide

The oxidation of thioamides 63 with a wide variety of oxidizing agents is a well-employed method for the synthesis of 3,5-disubstituted-l,2,4-thiadiazoles 64 <1982AHC285>. However, this method is limited mainly to arylthioamides. The most common oxidizing agents tend to be halogens, hydrogen peroxide, dimethyl sulfoxide (DMSO), and nitrous acid. Yields from these reactions are variable and depend on the thioamide, oxidant, and conditions used (Equation 19). By-products such as nitriles and isothiocyanates are usually formed. 

Hydrogen peroxide-Dimethyl sulfoxide. Hydration of nitriles. This conversioi... 

A number of chemiluminescent reactions may proceed through unstable dioxetane intermediates (12,43). For example, the classical chemiluminescent reactions of lophine [484-47-9] (18), lucigenin [2315-97-7] (20), and transannular peroxide decomposition. Classical chemiluminescence from lophine (18), where R = CgH, is derived from its reaction with oxygen in aqueous alkaline dimethyl sulfoxide or by reaction with hydrogen peroxide and a cooxidant such as sodium hypochlorite or potassium ferricyanide (44). The hydroperoxide (19) has been isolated and independentiy emits light in basic ethanol (45). 

Reaction takes place ia aqueous solution with hydrogen peroxide and catalysts such as Cu(II), Cr(III), Co(II), ferricyanide, hernia, or peroxidase. Chemiluminescent reaction also takes place with oxygen and a strong base ia a dipolar aprotic solvent such as dimethyl sulfoxide. Under both conditions Qcis about 1% (light emission, 375—500 am) (105,107). 

Mercapto-l,2,4-thiadiazoles exist as an equilibrium of tautomers with the equilibrium favoring the thione tautomer. They are acidic with a pA a of around 5. A variety of methylating agents (e.g., diazomethane, dimethyl sulfate and methyl iodide) give S-methylated products and no N-methylation has been observed. They are readily oxidized to sulfoxides and sulfones with either z-chloroperbenzoic acid or hydrogen peroxide in acetic acid <1996CHEC-II(4)307>. There have been no new publications on S-linked substituents since the publication of CHEC-II(1996). 

Copper(II) sulfate Cumene hydroperoxide Cyanides Cyclohexanol Cyclohexanone Decaborane-14 Diazomethane 1,1-Dichloroethylene Dimethylformamide Hydroxylamine, magnesium Acids (inorganic or organic) Acids, water or steam, fluorine, magnesium, nitric acid and nitrates, nitrites Oxidants Hydrogen peroxide, nitric acid Dimethyl sulfoxide, ethers, halocarbons Alkali metals, calcium sulfate Air, chlorotrifluoroethylene, ozone, perchloryl fluoride Halocarbons, inorganic and organic nitrates, bromine, chromium(VI) oxide, aluminum trimethyl, phosphorus trioxide... 

Solvents Water (purified water or water-for-injection grade) toluene, methanol, ethanol, ether, acetate, dimethyl sulfoxide, tetrahydrofuran, hexane, cyclohexane, dichloromethane, acetonitrile, acetone Oxidizing Agents Hydrogen peroxide, chromic acid, potassium permanganate, manganese dioxide, ozone... 

It is evident that some leeway is available in the substituents tolerable in the m-position. The bronchodilator sulfonterol (28) is descended from this observation. Chloromethylanisole (29) is reacted with methylmereaptan to give 30, and the newly introduced group is oxidized to the methyl-sulfonyl moiety of 31 with hydrogen peroxide. Ether cleavage, acetylation and Fries rearrangement of the phenolic acetate produces 32, which is next brominated with pyrrolidinone hydrobromide tribromide and then oxidized to the glyoxal (33) with dimethyl sulfoxide. 

Pentadienone (divinyl ketone) was epoxidized55 by means of hydrogen peroxide in alkaline solution, to give a mixture of DL- and me.so-l,2 4,5-dianhydro-3-pentanones in the ratio of 13 7. Reduction of the ketone group in the DL-diepoxide with sodium horohvdride, followed by alkaline hydrolysis in dimethyl sulfoxide, was fully stereo-specific, and afforded DL-arabinitol. The same reaction-sequence performed on the meso-diepoxide led to a mixture of ribitol and xylitol. 

Oxidation of the sulfur- or selenium-bridged azepines (171 X=S or Se) with mercury(II) oxide in methanol yields ultimately the 4f/-azepine (68JCS(C)23ll) with hydrogen peroxide as oxidant, the sulfur compound furnishes the sulfoxide (171 X=SO). Selenium dioxide oxidation of 7,8-dimethyl-lf/-l-benzazepin-2-one affords the 2,3-dioxo derivative (173) that displays no evidence of enol tautomers or heteroaromaticity (7ici(L)1439). 

Enzyme substrates- A variety of different substrates for both alkaline phosphatase and peroxidase are available. In this chapter, only the alkaline phosphatase substrate nitroblue tetrazolium/bromochloroindolylphosphatase (NBT/BCIP) and the peroxidase substrate 3-amino-9-ethyl carbazole (AEC) are described. Other substrates can be found in textbooks of histochemistry (see also Chapter 24) a NBT/BCIP is made in advance, and stored at -20°C. After equilibration of 30 mL of alkaline phosphatase substrate buffer at 37°C, 10 mg of NBT are dissolved m 200 pL of dimethylformamide (DMF), and added to I mL of the prewarmed substrate buffer. The mixture is added dropwise to the remaining substrate buffer BCIP (5 mg), dissolved in 200 pL of DMF, is then added slowly, and the whole preparation stored m 4-mL aliquots at—20°C b AEC is prepared fresh daily by dissolving 2 mg of AEC in 1 2 mL of dimethyl-sulfoxide in a glass tube. The mixture is added to 10 mL of 20 mM acetate buffer, pH 5 0-5.2. Immediately prior to use, 1 pL of 30% (v/v) hydrogen peroxide is added The final mix may require filtration prior to use... 

Actually the irradiation chemistry of even simple amino acids and peptides is much more complex than these equations imply, and many other radiochemical products have been reported (13, 14, 49). These include glyoxylic acid, formaldehyde, hydrogen peroxide, carbon dioxide, succinic acid, aspartic acid, diaminosuccinic acid, methylamine, methane, dimethyl mercaptan, a-aminobutyric acid, methionine sulfoxide, methinonine sul-fone, methionine sulfoxime, homocysteic acid, and several unidentified nitrogen compounds (46, 51). 

Methanesulfonic acid, dimethyl sulfoxide and dimethyl sulfone are potential intermediates in the gas phase oxidation of dimethylsulfide in the atmosphere. We nave measured the rate of reaction of MSA with OH in aqueous solution using laser flash photolysis of dilute hydrogen peroxide solutions as a source of hydroxyl radicals, and using competition kinetics with thiocyanate as the reference solute. The rate of the reaction k (OH + SCN ) was remeasured to be 9.60 1.12 x 109 M 1 s 1, in reasonable agreement with recent literature determinations. The rates of reaction of the hydroxyl radical with the organosulfur compounds were found to decrease in the order DMSO (k = 5.4 0.3 x 109 M-i s 1) > MSA (k = 4.7 0.9 x 107 M l S 1) > DMS02 (k = 2.7 . 15 x 107 M 1 s ). The implications of the rate constant for the fate of MSA in atmospheric water are discussed. 

Analytical grade potassium thiocyanate (Fisher), hydrogen peroxide (Mallinckrodt), dimethyl sulfoxide, (Fluka), dimethyl sulfone (Sigma) were used... 

As a unique reaction with the Fenton system, the alkylation of heteroaromatics with alkyl iodide, hydrogen peroxide, and dimethyl sulfoxide in the presence of FeS04 can be carried out. This reaction comprises of the initial formation of reactive HO by the reaction of FeS04 and hydrogen peroxide, reaction of HO on the sulfur atom of dimethyl sulfoxide to form CH 3 and methanesulfinic acid (SH2 reaction), reaction of CH3 on the iodine atom of alkyl iodide via SH2 pathway to form more stable R and methyl iodide, and then addition of R to the a-position of y-picoline (1) to form an addition-intermediate radical which is rearomatized under oxidative conditions to 2-alkyl-4-methylpyridine (2) [15, 16]. 

Mildly basic conditions can be provided using quaternary ammonium fluorides with aqueous hydrogen peroxide in dimethyl sulfoxide solution. For example, carvone gives 82% epoxide in six hours at room temperature. The method is particularly suited to base-sensitive substrates such as cinnamalde-hyde.65... 

Radical nucleophile oxidation based on one-electron oxidation, known as the Minisci reaction, is employed for the functionalization of /V-heterocycles with acidic hydrogen peroxide in the presence of iron(II) salts (Figure 3.112).472 A range of A-heterocycles (pyridines, pyrazines, quinolines, etc.) which are activated towards attack by nucleophilic radicals when protonated are suited to this chemistry. The Minisci reaction is suitable for the preparation of carboxylic amides (from formamide), carboxylic esters (from pyruvic esters via a hydroxyhydroperoxide), aldehydes (from 1,3,5-trioxane) and alkylated pyridines (either from carboxylic acids or from alkyl iodides in dimethyl sulfoxide).473 The latter reaction uses dimethyl sulfoxide as the source of methyl radical (Figure 3.112). 

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