Oxygen Sulfide Research Articles

Effect of added donor ligands on the selective oxygenation of organic sulfides by oxo(salen)chromium(V) complexes

Abstract Oxo(salen)chromium(V) complexes, [(salen)Cr V O] + , oxidize organic sulfides selectively to sulfoxides in high yield. This oxygenation reaction is catalyzed by ligand oxides (LO's), pyridine N -oxide, 4-picoline N -oxide, 4-phenyl pyridine N -oxide and triphenylphosphine oxide. The rate is accelerated by 10–20 times with an increase in yield of sulfoxide in less reaction time. This catalytic activity is highly sensitive to the nature of the substituent in the phenyl ring of ArSMe and in the 3- and 5-position of the salen ligand. The reaction constant ( ρ ) value obtained with the ligand oxide catalyzed reaction is low compared to the value in the absence of LO. The strong binding and catalytic activity of ligand oxides on the oxo(salen)chromium(V) ion oxygenation is explained in terms of binding constants and a mechanism involving the electrophilic attack of [(salen)Cr V O] + –LO adduct on the sulfur centre of phenyl methyl sulfide.

New complexes and materials for O 2-based oxidations

Key experiments in three developing dioxygen activation and oxo transfer projects are described. First, the Pt–oxo complex, K 7Na 9Pt IV(O)(OH 2)(PW 9O 34) 2 (KNa 1) is further addressed and its first reactivity is noted (oxo transfer under Ar at ambient temperature to PPh 3 forming O PPh 3 with nearly quantitative selectivity). Second, an unusually reactive catalyst for aerobic oxygenation of sulfides to sulfoxides (TBANO 3 in the presence of TBA 4Fe(H 2O)PW 11O 39 in acetonitrile solvent) is reported and its stoichiometry is established to be the desired atom-efficient dioxygenase one (RSR + (1/2)O 2 → RS(O)R). Third, a crystalline microporous solid (metal organic framework material) capable of catalyzing air-based oxidations is described. Reaction of the bis(triesterified)hexavanadate unit terminating in two carboxylate functions, [( n-C 4H 9) 4N] 2[V 6O 13{(CH 2O) 3CNHCH 2(4-C 6H 4COOH)} 2] reacts with Co(NO 3) 2·6H 2O and 4,4′-bipyridine to form a ladder-like microporous polymer, characterized by X-ray crystallography, that catalyzes the air-based oxidation of a representative thiol, n-PrSH, cleanly to the corresponding disulfide, PrSSPr. The esterified hexavanadate units are the catalysts, and there is no reaction in the absence of the microporous material.

Sulfide oxygenation by tert-butyl hydroperoxide with mononuclear (Me 3TACN)Mn catalysts

Mononuclear (Me 3TACN)MnX 3 compounds, where X is Cl −, Br −, or N 3 −, and Me 3TACN is 1,4,7- N, N′, N″-trimethyl-1,4,7-triazacyclononane, have been tested for catalyzing both sulfide oxygenation and styrene epoxidation by tert-butyl hydroperoxide (TBHP) and display turnover frequencies (TOF) up to 200 h −1 at room temperature. Sulfoxides or sulfones may be produced selectively by varying reaction conditions. Product distribution from the oxygenation reactions of ethyl phenyl sulfide, 2-chloroethyl phenyl sulfide, and styrene is consistent with a mechanism involving an early single-electron transfer (SET) step.

Oxygenation of sulfides by bis(μ-oxo)dicopper(III) complexes. A theoretical study

The First computational study on the oxygenation of organic sulfides by bis(μ-oxo)dicopper(III) complexes was carried out at PWP91/LACV3P**+//PWP91/LACVP* level of theory. Two reaction paths have been explored. One is the precoordination of sulfur with copper atom followed by oxygen transfer. Another is the precoordination with oxygen. In both cases the precoordination was found to be very weak to give a detectable intermediate. The oxygen atom transfer shows activation energies of less than 10 kcal mol both in the solution and in the gas phase suggesting validity of the proposed mechanism. Dissociation of the intermediate formed after oxygen atom transfer gives free sulfoxide. Solvation plays an important role favoring the reaction and facilitating dissociation of the final complex. The ground state of all studied dicopper intermediates are open-shell singlets. Complexes 4a, b and 5 have significant contribution from biradical structure to the ground state with antiferromagnetic coupling between copper atoms.

Photosensitized Oxygenation of Sulfides within an Amphiphilic Dendrimer Containing a Benzophenone Core

Photosensitized oxygenation of sulfides within amphiphilic dendrimers, Gn [n(generation) = 1-3], consisting of a benzophenone (BZP) sensitizing core, apolar interior based on n-undecane spacer, and polar dendron exterior based on 2,2-bis(hydroxymethyl)propionic acid, has been investigated in O(2)-saturated methanol. Sulfoxide formation occurring via reaction of O(2) with triplet excited-state sulfide ((3)sulfide), which is formed by a triplet energy transfer (TET) from photoformed (3)BZP to sulfide, was accelerated by the dendric sensitizers, where G2 showed the highest yields of alkylaryl and dialkyl sulfoxides. Laser photolysis studies revealed that enhanced access of sulfide to the (3)BZP core inside the apolar microenvironment accelerates the TET to sulfide, whereas prompt migration of polar sulfoxide to the polar outer shell of the dendrimer suppresses a competitive TET to sulfoxide, thus resulting in effective (3)sulfide formation. Another notable feature of the dendric sensitizer appears in oxygenation of diaryl sulfide, which is promoted by a persulfoxide intermediate formed by photooxygenation of dialkyl sulfide; photoirradiation of a mixture of diethyl sulfide (1a) and diphenyl sulfide (4a) with G2 gave 17-fold higher diphenyl sulfoxide (4b) yield than that obtained with unmodified BZP. The apolar microenvironment within the dendric sensitizer encapsulates a large quantity of 4a, which is oxidized effectively by the persulfoxide of 1a, thus resulting in high 4b yield. The BZP core within the dendric sensitizer is stable even by photoexcitation in protic solvent, suggesting potential utilities of this dendric system for effective and selective photosensitized oxygenation of sulfides.

Highly efficient utilization of H 2O 2 for oxygenation of organic sulfides catalyzed by [γ-SiW 10O 34(H 2O) 2] 4−

Remarkable efficiency of hydrogen peroxide utilization is reported for oxygenation of four organic sulfides catalyzed by a divacant lacunary silicotungstate, (Bu 4N) 4[γ-SiW 10O 34(H 2O) 2] ( 1 ), under mild conditions. The addition of imidazole, phosphate, or carboxylates significantly enhances the rate of organic sulfide oxygenation. Most notably, use of 1 and imidazole, both at 1% molar concentration, resulted in the quantitative conversion of phenylsulfide to sulfoxide with 1 equiv of H 2O 2 in 3 h, and to sulfone with 2 equiv of H 2O 2 in 6 h.

Facile oxygenation of organic sulfides with H2O2 catalyzed by Mn?Me3TACN compounds

Facile oxygenation of organic sulfides with H2O2 catalyzed by Mn?Me3TACN compounds

Facile oxygenation of organic sulfides with H2O2 catalyzed by Mn–Me3TACN compounds

Two binuclear Mn–Me3TACN (Me3TACN is 1,4,7-N,N′,N″-trimethyl-1,4,7-triazacyclononane) compounds catalyze the oxygenation of organic sulfides utilizing H2O2 under ambient conditions. Both phenyl sulfide and ethyl phenyl sulfide were converted to the corresponding sulfones and chloroethyl phenyl sulfide proceeds to its elimination product of phenyl vinyl sulfone.

Photosensitized oxidation of phenyl and tert-butyl sulfides.

The photosensitized oxygenation of diphenyl (1), di-tert-butyl (2) and phenyl tert-butyl sulfide (3) was studied. Bimolecular rate constants of singlet oxygen quenching are low (1 to 5 x 10(4) M(-1)s(-1)) since the sulfides are poor nucleophiles due to sterical hindrance (2, 3) or the HOMO on the sulfur atom being a less accessible p(z) orbital (1). The quenching is mainly physical, but chemical reaction leading to sulfoxides also takes place in methanol and, to a lower degree, in acetonitrile. Catalysis by carboxylic acids considerably enhances the rate of sulfoxidation. Inefficiency in the chemical reaction is again due to the poor nucleophilicity of the sulfides, which limits oxygen transfer by electrophilic intermediates such as the protonated persulfoxide.

Biphenyl derived Schiff-base vanadium(V) complexes with pendant OH-groups--structure, characterization and hydrogen peroxide mediated sulfide oxygenation.

A series of mononuclear oxovanadium(v) complexes of tridentate Schiff bases HL(1)-HL(4) and H(2)L(5)-H(2)L(8) derived from 6-phenylsalicylaldehyde and 6-(2-hydroxyphenyl)salicylaldehyde and four different amines was synthesized. The systematically selected ligands contain aliphatic or aromatic nitrogen, or alkoxy- and phenoxy-oxygen as third donor atom. The complexes were characterised by spectroscopic methods in solution and the solid state. Single-crystal X-ray analyses were performed with VO(2)L(1)(), VO(2)L(3)x1/2EtOH (), VO(2)L(4)(), VO(OiPr)L(7)xiPrOH, VO(OiPr)L(8) and H(2)L(8). For all compounds the vanadium(v) cores contain distorted tetragonal pyramidal geometry around the dioxo- and oxovanadium site at which the N(2)O- and NO(2)-donor ligands bind equatorially. Complexes and display intramolecular hydrogen bonding of the pendant hydroxyphenyl group to a coordinated oxygen trans to a nitrogen atom and therefore serve as suitable models for the native site of vanadium dependent haloperoxidases. Variable-temperature (1)H NMR spectra revealed significant hydrogen bond interaction in acetonitrile solution. In situ prepared catalysts are active for hydrogen peroxide mediated oxygenation of ethyl phenyl sulfide and showed complete conversion of the substrate to ethyl phenyl sulfoxide, together with small amounts of the corresponding sulfone, as detected by GC/MS after 10 min. The complex of H(2)L(7) turned out to be most efficient while HL(1) and HL(2) were completely inactive. Catalysis is supported by the pendant OH group in the complex of HL(3), the catalyst is twice as active as the complex of HL(4).

Electronic and steric effects on the oxygenation of organic sulfides and sulfoxides with oxo(salen)chromium(V) complexes.

The kinetics of oxygenation of several para-substituted phenyl methyl sulfides and sulfoxides with a series of 5-substituted and sterically hindered oxo(salen)chromium(V) complexes have been studied by a spectrophotometric technique. Though the reaction of sulfides follows simple second-order kinetics, sulfoxides bind strongly with the metal center of the oxidant and the oxygen atom is transferred from the oxidant-sulfoxide adduct to the substrate. The reduction potentials, E(red), of eight Cr(V) complexes correlate well with the Hammett sigma constants, and the reactivity of the metal complexes is in accordance with the E(red) values. The metal complexes carrying bulky tert-butyl groups entail steric effects. Organic sulfides follow a simple electrophilic oxidation mechanism, and the nonligated sulfoxides undergo electrophilic oxidation to sulfones using the oxidant-sulfoxide adduct as the oxidant. Sulfoxides catalyze the Cr(V)-salen complexes' oxygenation of organic sulfides, and the catalytic activity of sulfoxides is comparable to pyridine N-oxide and triphenylphosphine oxide. The rate constants obtained for the oxidation of sulfides and sulfoxides clearly indicate the operation of a pronounced electronic and steric effect in the oxygenation reaction with oxo(salen)chromium(V) complexes.

Kinetics and mechanism of oxygenation of aromatic sulfides and arylmercaptoacetic acids by peroxomonophosphoric acid

The oxygenation of aryl methyl sulfides and diaryl sulfides by peroxomonophosphoric acid in acetonitrile–water mixture follows an overall second-order kinetics, first-order in each reactant. The study of the influence of [H +] on the oxidation of phenyl methyl and diphenyl sulfides reveals that H 2PO 5 − and HPO 5 2− are the oxidising species in the oxidation process. In substituted phenyl methyl sulfides and diphenyl sulfides, the rate of oxygenation is accelerated by electron-donating substituents and retarded by electron-withdrawing groups, indicating the nucleophilic displacement by the sulfide sulfur on the peroxide oxygen. The negative ρ value obtained in the correlation analysis of rate constants with σ constants also shows the formation of a more positively charged sulfur species in the rate-limiting step. Studies with different alkyl phenyl sulfides (C 6H 5SR; R=Me, Et, Pr i or Bu t ) indicate that the rate is retarded by bulky R groups. Similar kinetic results are also obtained in the peroxomonophosphoric acid oxidation of sodium phenylmercaptoacetate. On the basis of the kinetic studies, a common mechanism has been proposed.

Oxo-transfer reaction from a bis(mu-oxo)dicopper(III) complex to sulfides.

Oxygenation of sulfides to the corresponding sulfoxides by a distinct bis(mu-oxo)dicopper(III) complex has been accomplished for the first time using 2-(2-pyridyl)ethylamine derivative L(Py1Bz) (N-ethyl-N-[2-(2-pyridyl)ethyl]-alpha,alpha-dideuteriobenzylamine) as the supporting ligand. Detailed kinetic analysis has indicated that the reaction consists of two distinct steps, where the first quick process is association of the substrate to the bis(mu-oxo)dicopper(III) complex (k(1)) and the second slow process is intramolecular oxygen atom transfer from the copper-oxo species to the substrate in the associated complex (k(2)). The rate constant k(2) of the second process is rather insensitive to the oxidation potential of the substrates, suggesting that the oxo-transfer reaction proceeds via a mechanism involving direct oxygen atom transfer rather than a mechanism involving electron transfer.

Hydrogen peroxide oxidation of mustard-model sulfides catalyzed by iron and manganese tetraarylporphyrines. Oxygen transfer to sulfides versus H(2)O(2) dismutation and catalyst breakdown.

Fe(III)- and Mn(III)-meso-tetraarylporphyrin catalysis of H(2)O(2) oxidation of dibenzyl and phenyl-2-chloroethyl sulfides, 1, is investigated in ethanol with the aim of designing catalytic systems for mustard decontamination. The sulfide conversion, the sulfoxide and sulfone yields, the oxygen transfer from H(2)O(2) to the sulfide, and the catalyst stability depend markedly on the metal, on the substituents of its ligand, and on the presence or the absence of a cocatalyst, imidazole or ammonium acetate. With Fe, sulfones, the only oxidation products, are readily obtained whatever the ligand (TPP, F(20)TPP, or TDCPP) and the cocatalyst; the oxygen transfer is fairly good, up to 95% when the catalyst concentration is small ([1]/[Cat] = 420); the catalyst breakdown is insignificant only in the absence of any cocatalyst. With Mn, the sulfide conversion is achieved completely when the ligand is TDCPP or TSO(3)PP, but not F(20)TPP or TPP; a mixture of sulfoxide, 2, and sulfone, 3, is always obtained with [2]/[3] = 3.5-0.85 depending on the ligand and the cocatalyst (electron withdrawing substituents favor 3 and NH(4)OAc, 2). The catalyst stability is very good, but the oxygen transfer is poor whatever the ligand and the cocatalyst. These results are discussed in terms of a scheme in which sulfide oxygenation, H(2)O(2) dismutation, and oxidative ligand breaking compete. It is shown that the efficiency of the oxygen transfer is related not only to the rate constant of the dismutation route but also to the concentration of the active metal-oxo intermediate, most likely a perferryl or permanganyl species, i.e., to the rate of its formation.

Oxidations by the system “hydrogen peroxide–manganese(IV) complex–carboxylic acid”: Part 3. Oxygenation of ethane, higher alkanes, alcohols, olefins and sulfides

The manganese(IV) complex salt [L2Mn2O3](PF6)2 (L=1,4,7-trimethyl-1,4,7-triazacyclononane) (compound 1, see Scheme 1 ) very efficiently catalyzes the hydroperoxidation of saturated hydrocarbons, including ethane by H2O2 in acetontitrile or nitromethane solution at low (room or lower) temperature, provided a carboxylic (typically acetic) acid is present. The hydroperoxidation of tertiary positions in disubstituted cyclohexanes proceeds with partial retention of configuration in nitromethane or acetonitrile solution, while the stereoselectivity of the reaction is only negligible in acetone solution. The system “H2O2–compound 1–MeCO2H” also transforms secondary alcohols into the corresponding ketones with quantitative yields at room temperature within a few minutes; the yields of aldehydes and carboxylic acids in the oxidation of primary alcohols are lower. Terminal aliphatic olefins such as hexene-1 are quantitatively epoxidized by the same system in acetonitrile at room temperature within 20min, while the epoxide yield in the analogous reaction with styrene attains only 60% under the same conditions. Finally, dimethylsulfide can be quantitatively and selectively converted into dimethylsulfoxide within 3h at room temperature. The system “tert-BuOOH–compound 1” also oxidizes alkanes, addition of acetic acids has less pronounced effect on the direction and efficiency of the reaction. Two other checked derivative of Mn(IV) (compounds 2 and 3) as well a porphyrin complex of Mn(III) (compound 4) exhibited lower activity in catalysis of alkane oxidation with tert-BuOOH.

Photosensitized oxygenation of some benzyl sulfides. The role of persulfoxide

Photosensitized oxygenation of some benzyl sulfides. The role of persulfoxide

Nephtys hombergii , a free-living predator in marine sediments: energy production under environmental stress

Nephtys hombergii is a free-living, burrowing predator in marine sediments. The worm is, therefore, exposed to various environmental conditions which tube-dwelling polychaetes of the same habitat most likely do not encounter. The worms have to survive periods of severe hypoxia and sulphide exposure, while at the same time, they have to maintain agility in order to feed on other invertebrates. N. hombergii is adapted to these conditions by utilising several strategies. The species has a remarkably high content of phosphagen (phosphoglycocyamine), which is the primary energy source during periods of environmental stress. With increasing hypoxia, energy is also provided via anaerobic glycolysis (pO2<7 kPa), with strombine as the main end-product. Energy production via the succinate pathway becomes important only under severe hypoxia (<2 kPa), suggesting a biphasic response to low oxygen conditions which probably is related to the worm's mode of life. The presence of sulphide resulted in a higher anaerobic energy flux and a more pronounced energy production via glycolysis than in anoxia alone. Nevertheless, after sulphide exposure under anaerobic conditions of <24 h, N. hombergii is able to recover completely. Although N. hombergii appears to be well adapted to a habitat with short-term fluctuations in oxygen and appearance of hydrogen sulphide, its high energy demand as a predator renders it likely to limit its survival in an environment with longer lasting anoxia and concomitant sulphide exposure.

Singlet Oxygen and the Production of Sulfur Oxygenates of Nickel(II) and Palladium(II) Thiolates.

The metal dithiolate [1,5-bis(2-mercaptoethyl)-1,5-diazacyclooctane]nickel(II) (Ni-1), a sterically hindered analogue (Ni-1), and the palladium analogue Pd-1 react with (1)Delta O(2) to yield a variety of stable and isolable metallosulfones (MS(O(2))R) and metallosulfoxides (MS(O)R). Singlet oxygen was generated both photochemically with the sensitizer Rose Bengal and thermally by decomposition of the 1,4-endoperoxide of 1,4-dimethylnaphthalene. Increased rates and oxygenation yields are observed upon excitation of O(2) from its ground state, (3)Sigma, to the excited state, (1)Delta. The reactions are both solvent and concentration dependent, with sulfones generally favored in acetonitrile and sulfoxides favored in methanol. There is also a ligand and metal effect. The proposed mechanistic pathways involving a persulfoxide precursor to single sulfur site O(2) addition (producing metallosulfones) and adjacent sulfur site O(2) addition (producing metallosulfoxides) are consistent with product distribution, comparison to the much studied oxygenation of organic sulfides, and previous isotopic labeling experiments (J. Am. Chem. Soc. 1996, 118, 1791; 1992, 114, 4601; Inorg. Chem. 1993, 32, 4171).

Marenzelleria cf. viridis and the sulphide regime

To find out how the polychaete Marenzelleria cf. viridis could spread successfully into the habitat of the Darss-Zingst Bodden Chain, one important environmental factor for sediment dwelling animals was examined: hydrogen sulphide. To investigate the stress of this environmental factor, hydrogen sulphide was continuously examined in the pore water of the sediment and burrows of M. cf. viridis. Metabolic activity was recorded by direct and indirect calorimetry. Depending on water temperature, organic matter content of the sediment and salinity, the sulphide concentration in the pore water varied between 1.5 and 4.2 mmol l-1 being high during summer and in winter when the sediment and overlying water was ice covered. In microcosm experiments water of M. cf. viridis-burrows showed variations in sulphide between 145 and 210 µmol l-1 but pore water concentration was much higher (6.5 mmol l-1). In the presence of oxygen animals exhibited an accelerated metabolic rate which was met by a fully aerobic metabolism at Po2 of 20 to 7.5 kPa and sulphide concentration of 215–245 µmol l-1. When oxygen is absent the heat production was only slightly elevated (103%) when compared to the anoxic control. The elevated heat production of the animals during sulphide exposure and oxygen may be due to detoxification processes. In this case thiosulphate is formed probably via mitochondrial oxidation and therefore may account for additional ATP-gain.

Activated carbons from mixtures of coal pitch and FeCl3graphite intercalated compounds

Abstract Processing of granular and powdered activated carbons was performed by carbonization of coal pitch (precursor) loaded with natural polycrystalline graphite particles initially intercalated by iron (III) chloride (chemical activator). The resulting char was steam activated at high temperature. Interactions of hydrogen sulfide and molecular oxygen with the microporous material were studied by means of isothermal adsorption on the pulverized carbon and by temperature-programmed desorption. The results suggest that chemisorption and catalytic oxidation of hydrogen sulfide occur on basic sites resulting from the chemisorption of molecular oxygen on to the iron (II, III) oxide and on the carbon surface.