Oxidation with DMSO mechanism

This oxidation of DMSO is catalyzed by Ag+ cations. Kinetic and infrared spec-trometric evidence fits a mechanism where DMSO coordinates rapidly with Ag+ through its oxygen atom. The oxidation of this complex by Ce4 + then constitutes the slow step. The Ag2+ adduct would then undergo an intramolecular electron transfer in a fast step resulting in the oxidation of DMSO. 

The direct oxidative conversion of primary halides and sulfonates to aldehydes can be carried out by reaction with DMSO under alkaline conditions. Formulate a mechanism for this reaction. 

Certain Schiff bases, i.e. 122, were synthesized as model compounds for Latia luciferin. This compound exhibits strong blue chemiluminescence ( max 385 nm) on oxidation with oxygen in DMSO/potassium t.-butylate, the main products being acetone and 2-formamido pyridine 124. The mechanism suggested by Me Capra and Wrigglesworth includes the concerted bond cleavage of a dioxetane derivative 123. 

Very recently, interesting macrocyclic diureido derivatives 39a,b lower rim bridged by a spacer unit were reported [50]. Their oxidation with (CF3COO)3Tl led to the corresponding quinones 39c,d, potentially useful as electrochemical anion receptors. A similar upper rim bridged system 40 was shown to exhibit good shape-selective recognition abilities towards various aromatic dicarbox-ylates in DMSO [51]. The molecular mechanics force field calculations indicate... 

The role of the acid catalyst during the oxidation of epoxides with DMSO has been explored by DFT studies of three acids, namely H30+, Li+, and Mg2+. Stationary points have been obtained at the B3LYP/6-31+- -G(d,p) level of theory and the reaction barriers have been evaluated through tree-energy calculations. The mechanism proceeds in two steps, namely ring opening followed by an intramolecular proton transfer that leads to an a-hydroxy carbonyl compound.88 The epoxidation... 

A mechanism suggested for Swern-Moffatt oxidation with TFAA is shown in Scheme 8.6. In the first step, DMSO reacts with TFAA to form cationic reactive species I, which is known to be stable only below —At higher temperatures, rearrangement of I takes place to give species II. The reaction of II with an alcohol IQ upon treatment with a base leads to formation of a major by-product, trifluoroacetic acid (TFA) ester VII. Therefore, the first step should be carried out below —50 °C. In the second step, reactive species I is allowed to react with an alcohol HI at or below —50°C to obtain intermediate IV. IV may also undergo the Pummerer rearrangement to give a methyl thiomethyl (MTM) ether VI upon treatment with a base. In the third step, IV is treated with a base (usually triethylamine) to obtain the desired carbonyl compound V and dimethyl sulfide. 

Dimethyl sulfoxide-Acetic anhydride [1, 305, after citation of ref. 43J. Albright and Goldman433 have reported further on the oxidation of secondary alcohols to ketones with DMSO-Ac20 at room temperature. In the case of yohimbine and the steroid secondary alcohols studied, oxidation apparently was faster than acetylation. The method is particularly useful for sterically hindered alcohols. The following mechanism is proposed ... 

Sulfoxides (essentially DMSO) can be used for oxidation of alcohols to carbonyl compounds as in the Moffatt, Swern and related oxidations [237, 238]. These mild and useful processes proceed through an oxosulfonium salt. In the Pfitzner-Moffatt procedure the alcohol is treated with DMSO, DCC and anhydrous phosphoric acid. The proposed mechanism involves an alkylsulfonium ylide as an intermediate. 

An overall mechanism for the DMS-OH reaction is shown in Figure 6.19. Many of the details of this mechanism are still uncertain. The principal stable products of the oxidation are DMSO, DMS02, MSA, S02, and H2S04. The ratio of MSA to SO4- is indicative of the path that is followed subsequent to formation of CH3S in the abstraction branch. This ratio is measured in the marine atmosphere as the ratio of MSA to nonseasalt sulfate (nss-S04). (Nonseasalt sulfate, the amount of sulfate present in particles in excess of that expected from seasalt particles, is a direct measure of the sulfuric acid formed.) Measurements as a function of latitude indicate that this ratio is quite temperature-dependent, with the ratio varying from about 0.1 near the equator to close to 0.4 in Antarctic waters. Thus the colder the temperature, the more favored the path to MSA formation as opposed to that to S02 and eventually to sulfuric acid. This behavior is consistent with a competition between a radical decomposition step, with a fairly large activation energy, namely... 

With [Eu(dpm)3], 3,3-dimethylthietane 1 -oxide and DMSO gave 1 1 adducts, which had near perfect wedged octahedral structures, the Lewis bases occupying one of four equivalent positions of lowest symmetry. The species [M(dpm)3] (M = La, Pr, Eu, Er, Ho, or Lu) were monomeric in dry CCI4, and 1 1 adducts were formed with pyridine, borneol, and neopentanol. However, lanthanide shift reagents (L) could react with substrates (S) by a two-step mechanism, viz. 

Isolable transition metal complexes containing hydride and terminal oxo ligands are rare however, Tp Re( = 0)(H)X (X = Cl, H or OTf) and TpRe( = 0)(H)Cl have been synthesized, isolated and characterized. Reactions of Tp Re( = 0)(H) OTf (12) with unsaturated substrates (e.g., ethene, propene or acetaldehyde) result in insertion of C = C or C = 0 bonds into the Re-H bond to yield Tp Re( = 0)(R) (OTf) (R = ethyl or propyl) or Tp Re( = 0)(0Et)(0Tf) (Scheme 6). Oxidation of 12 with pyridine-iV-oxide or DMSO produces Tp Re( = 0)3, acid and free pyridine or dimethylsulfide, respectively. A likely mechanism involves initial oxidation of 12 to produce [Tp Re( = 0)2H][0Tf] (13) followed by the formation of Tp Re( = 0) (OH)(OTf) (14) via a 1,2-migration of the hydride to an oxo ligand (Scheme 6). Reaction of 14 with a second equivalent of oxidant in the presence of base yields Tp Re( = 0)3 (15). Direct deprotonation of 13 is noted as less likely than the pathway shown in Scheme 6 due to the lack of precedent for acidity of related rhenium hydride systems. 

Oxidation of methyl 2,3,6-tri-O-benzoyl-a-D-galactopyranoside with DMSO-acetic anhydride yielded mainly the enolone (336 R = OBz), owing to the tendency of the initially formed hexopyranosid-4-ulose to eliminate benzoic acid. The enolone (336 R = OBz) yielded the hydroxymaltol derivative (337) or (338) when treated with acetic acid-sodium acetate or with trifluoroacetic acid, respectively. Mechanisms for the conversions (336) - (337) and (338) were proposed on the... 

The alkaline oxidations of etamsylate (ETM) and salbutamol (SBL) , and the acidic oxidations of phenylephrine (PHE) and butacaine sulfate (BCS) " with N-chlorobenzenesulfonamide (CAB) in MeOH have some common features. The rates in each case increase with decreasing dielectric constant of the solvent. The reactions are of fractional order in ETM, SBL, PHE, and BCS. A fractional order in OH and H" " ions is noted in the reaction of ETM and PHE, respectively. However, a negative fractional order in OH ions and rate retardation with benzenesulfonamide (BSE) is observed in the oxidation of SBL. The observed Michaelis-Menten kinetics provide the basis of the proposed mechanism in each case. The Ir(IIl)-catalysed A-chlorobenzenesulfonamide (CAB) oxidation of DMSO in acidic solution has an order less than one in Ir(III) and the rate decreased with increase in H" " ions. A suitable mechanism involving formation of an intermediate is proposed. ... 

The use of crown polyethers to solubilize potassium permanganate in benzene has been reported. In a study of the oxidation of alkyl toluene-/ -sulphonates with DMSO-sodium bicarbonate, the elements of carbon dioxide are retained in the product (86) as a cyclic carbonate (Scheme 170), inferring that, for this substrate, bicarbonate ion is a more effective nucleophile than DMSO this leads to a revision of the mechanism of such oxidations to that shown in Scheme 170. 

The rates of hydrolysis of monomeric ruthenium(n) chloride complexes which are generated electrochemically have been reported and are much more rapid than those observed for the corresponding ruthenium(m) species. It is suggested that Ru chloride complexes may exist as unstable intermediates when the ruthenium(iii) species are reduced. Ruthenium(n) dimethyl sulphoxide complexes have been shown to be the products of refluxing the hydrated ruthenium(iii) chloride with DMSO. The use of ruthenium tetroxide as an oxidant has also been described. In the oxidation of tetrahydrofuran in aqueous perchloric acid, an inverse hydrogen-ion dependence is observed, the proposed mechanism involving hydride abstraction with recombination to yield an ester. A scheme consistent with isotope-labelling data may be represented as... 

The oxidation of 3-substituted indole to oxindoles can also be done with a mixture of DMSO and cone, hydrochloric acid[6-9]. This reaction probably involves a mechanism similar to the halogenation with a protonated DMSO molecule serving as the electrophile[10]. 

DMSO, molybdenum peroxide, benzene, reflux, 7-20 h, 60% yield. This method was used to m onoprotect 1,2-diols. The method is not general because oxidation to a-hydroxy ketones and diketones occurs with some substrates. On the basis of the mechanism and the results it would app>ear that overoxidation has a strong conformational dependence. 

Ce4+ is a versatile one-electron oxidizing agent (E° = - 1.71 eV in HC10466 capable of oxidizing sulfoxides. Rao and coworkers66 have described the oxidation of dimethyl sulfoxide to dimethyl sulfone by Ce4+ cation in perchloric acid and proposed a SET mechanism. In the first step DMSO rapidly replaces a molecule of water in the coordination sphere of the metal (Ce v has a coordination number of 8). An intramolecular electron transfer leads to the production of a cation which is subsequently converted into sulfone by reaction with water. The formation of radicals was confirmed by polymerization of acrylonitrile added to the medium. We have written a plausible mechanism for the process (Scheme 8), but there is no compelling experimental data concerning the inner versus outer sphere character of the reaction between HzO and the radical cation of DMSO. 

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