Alkyl Sulfides Research Articles

Polyfluorination of aryl alkyl sulfides by IF5 with concomitant migration of the arylthio group.

[reaction: see text] In the reaction of p-chlorophenyl alkyl sulfides with IF(5), polyfluorination reaction took place on the alkyl chain with the migration of the arylthio group. Consequently, p-chlorophenyl polyfluoroalkyl sulfides, having 3-7 fluorine atoms depending on alkyl chain length, could be obtained selectively.

Detailed characterisation of sulphur and nitrogen components in a multifunctional, ashless lubricant additive by spectroscopic and chromatographic techniques

AbstractThe work reported here used infrared (IR), multinuclear nuclear magnetic resonance (NMR), and chromatographic techniques to identify and characterise a commercial sulphur‐ and nitrogen‐containing ashless multifunctional additive. The proper assignment of signals in the 1H/13C NMR and IR spectra of the sample has facilitated the identification of different types of sulphur‐ and nitrogen‐containing components. The methodology involves investigation by NMR and IR spectroscopies, thin‐layer chromatography (TLC) and high‐performance liquid chromatogaphy (HPLC) techniques to elucidate the types of components present. This requires the generation of NMR and IR spectral data for standard compounds of alkyl sulphides with different sulphur content and alkyl chain, and nitrogen and sulphur components such as thiadiazole, imidazoline, triazole, etc., and spectral comparison with the spectra of the unknown sample. Further, these components have been separated by silica/alumina column chromatographic and preparative TLC techniques and subsequently analysed for their exact chemical structure by spectroscopic techniques. The combined spectroscopic and chromatographic analyses have yielded the presence of four types of components: di‐t‐octyl polysulphide, di‐t‐octyl thiadiazole, a component containing amine ether functionality, and alkyl amine salts of mono/dialkyl phosphoric acid.

Selective oxidation of sulfides under solvent-free conditions

Alkyl and aryl sulfides can be oxidized under mild, solvent-free conditions with good selectivity. If the oxidant is a mixture of sodium bromate and cation exchange resin, the products are sulfoxides; if it is a mixture of permanganate and copper sulfate pentahydrate, the products are sulfones. The procedures are experimentally simple and the products, obtained in nearly quantitative yields, are easily separated and purified.

XAFS and TOF–SIMS analysis of SEI layers on electrodes

We have used X-ray absorption fine structure (XAFS) in order to analyze the solid electrolyte interface (SEI) layer on the graphite anode and the LiCoO 2 cathode in a lithium-ion battery. The SEI layers on the electrodes in the propylene carbonate (PC)-based electrolyte containing an ethylene sulfite (ES) additive were analyzed based on the different sulfur oxidation states with sulfur K-edge X-ray absorption near-edge structure spectroscopy (S K-edge XANES), X-ray photoelectron spectroscopy (XPS) and time-of-flight–secondary ion mass spectrometry (TOF–SIMS). The SEI layer on the graphite anode was mainly consisted of a sulfite-type compound with an inorganic film like Li 2SO 3 and an organic films like ROSO 2Li. Furthermore, it was proven that the SEI layer on the graphite anode contained alkyl sulfide species. We also found that the SEI layer on the LiCoO 2 cathode also contained alkyl sulfide species.

Triflic Anhydride-Promoted Cyclizationof Sulfides: A Convenient Synthesis of Fused Sulfur Heterocycles

A new approach to the synthesis of annulated sulfur heterocycles based on triflic anhydride-promoted cyclization of the hetaryl(aryl) containing alkyl sulfides was elaborated. Smooth demethylation of initially formed cyclic sulfonium salts by treatment with triethylamine afforded a number of five-, six- and seven-membered fused sulfur heterocycles. Unexpected ring opening took place in the reaction of diethylamine with 5-membered sulfonium salts.

Efficient and Mild Oxidation of Sulfides to Sulfoxides by Iodosobenzene Catalyzed­ by Cr(salen) Complex

Cr(Salen) 1 is found to be an efficient catalyst for the oxidation of various sulfides to sulfoxides with iodosobenzene as terminal oxidant. Both aryl and alkyl sulfides are selectively converted into sulfoxides in excellent yields (>90%).

Substrate Specificity and Enantioselectivity of 4-Hydroxyacetophenone Monooxygenase

The 4-hydroxyacetophenone monooxygenase (HAPMO) from Pseudomonas fluorescens ACB catalyzes NADPH- and oxygen-dependent Baeyer-Villiger oxidation of 4-hydroxyacetophenone to the corresponding acetate ester. Using the purified enzyme from recombinant Escherichia coli, we found that a broad range of carbonylic compounds that are structurally more or less similar to 4-hydroxyacetophenone are also substrates for this flavin-containing monooxygenase. On the other hand, several carbonyl compounds that are substrates for other Baeyer-Villiger monooxygenases (BVMOs) are not converted by HAPMO. In addition to performing Baeyer-Villiger reactions with aromatic ketones and aldehydes, the enzyme was also able to catalyze sulfoxidation reactions by using aromatic sulfides. Furthermore, several heterocyclic and aliphatic carbonyl compounds were also readily converted by this BVMO. To probe the enantioselectivity of HAPMO, the conversion of bicyclohept-2-en-6-one and two aryl alkyl sulfides was studied. The monooxygenase preferably converted (1R,5S)-bicyclohept-2-en-6-one, with an enantiomeric ratio (E) of 20, thus enabling kinetic resolution to obtain the (1S,5R) enantiomer. Complete conversion of both enantiomers resulted in the accumulation of two regioisomeric lactones with moderate enantiomeric excess (ee) for the two lactones obtained [77% ee for (1S,5R)-2 and 34% ee for (1R,5S)-3]. Using methyl 4-tolyl sulfide and methylphenyl sulfide, we found that HAPMO is efficient and highly selective in the asymmetric formation of the corresponding (S)-sulfoxides (ee > 99%). The biocatalytic properties of HAPMO described here show the potential of this enzyme for biotechnological applications.

Oxidative degradation of dimethyl sulfoxide byCryptococcus humicolus WU-2, a newly isolated yeast

A dimethyl sulfoxide (DMSO)-degrading yeast strainCryptococcus humicolus WU-2 was isolated and characterized. When 0.64 mM (50 mg/l) DMSO was added as the sole source of sulfur, DMSO was completely consumed by WU-2 in 48 h and oxidized to dimethyl sulfone with a molar conversion ratio of 83%. WU-2 also oxidized alkyl sulfides such as dimethyl sulfide, ethyl methyl sulfide and diethyl sulfide into the corresponding sulfones, which are odorless compounds.

Mechanism of the oxidation of aromatic sulfides catalysed by a water soluble iron porphyrin.

The oxygen atom transfer-electron transfer (ET) mechanistic dichotomy has been investigated in the oxidation of a number of aryl sulfides by H2O2 in acidic (pH 3) aqueous medium catalysed by the water soluble iron(III) porphyrin 5,10,15,20-tetraphenyl-21H,23H-porphine-p,p',p",p"'-tetrasulfonic acid iron(III) chloride (FeTPPSCl). Under these reaction conditions, the iron-oxo complex porphyrin radical cation, P+. Fe(IV)=O, should be the active oxidant. When the oxidation of a series of para-X substituted phenyl alkyl sulfides (X = OCH3, CH3, H, Br, CN) was studied the corresponding sulfoxides were the only observed product and the reaction yields as well as the reactivity were little influenced by the nature of X as well as by the bulkiness of the alkyl group. Labelling experiments using H(2)18O or H(2)18O2 clearly indicated that the oxygen atom in the sulfoxides comes exclusively from the oxidant. Moreover, no fragmentation products were observed in the oxidation of a benzyl phenyl sulfide whose radical cation is expected to undergo cleavage of the beta C-H and C-S bonds. These results would seem to suggest a direct oxygen atom transfer from the iron-oxo complex to the sulfide. However, competitive experiments between thioanisole (E degree = 1.49 V vs. NHE in H2O) and N,N-dimethylaniline (E degree = 0.97 V vs. NHE in H2O) resulted in exclusive N-demethylation, whereas the oxidation of N-methylphenothiazine (10, E degree = 0.95 V vs. NHE in CH3CN) and N,N-dimethyl-4-methylthioaniline (11, E degree = 0.65 V vs. NHE in H2O) produced the corresponding sulfoxide with complete oxygen incorporation from the oxidant. Since an ET mechanism must certainly hold in the reactions of 10 and 11, the oxygen incorporation experiments indicate that the intermediate radical cation, once formed, has to react with PFe(IV)=O (the reduced form of the iron-oxo complex which is formed by the ET step) in a fast oxygen rebound. Thus, an ET step followed by a fast oxygen rebound is also suggested for the other sulfides investigated in this work.

Determination of volatile alkyl sulfides in wastewater by headspace solid-phase microextraction followed by gas chromatography–mass spectrometry

An analytical procedure based on headspace solid-phase microextraction (SPME) followed by gas chromatography coupled to mass spectrometry in the electron impact mode has been developed for the determination of low-molecular-mass sulfides and disulfides in wastewater. Parameters affecting to the extraction of these volatile alkyl sulfides (VASs) with the SPME, such as the extraction temperature, sample volume, pH and the NaCl addition to the matrix, have been optimised using a polydimethylsiloxane–Carboxen fibre. The linear dynamic range was close to three orders of magnitude for all the studied compounds. Detection limits of 4 ng l −1 for dimethyl sulfide, 0.7 ng l −1 for ethylmethyl sulfide, 5 ng l −1 for diethyl sulfide and 1 ng l −1 for dimethyl disulfide were achieved, with a relative standard deviation between 4 and 6%. The developed analytical methodology was applied to determine those VASs in different wastewaters.

New Preparative Procedure for the Synthesis of Chloroalkyl Sulfides

Reaction of thiols with dihaloalkanes in the system hydrazine hydrate-base leads to alkyl(chloroalkyl) sulfides with different positions of the chlorine atom with respect to sulfur. The developed one-step procedure for the synthesis of such unsymmetrical sulfides is most suitable for arenethiols and alkanethiols having a long polymethylene chain. The reaction mechanism is discussed.

Discovery of new solid phase sulfur oxidation catalysts using library screeningElectronic supplementary information (ESI) available: HPLC conditions. See http://www.rsc.org/suppdata/cc/b1/b108487a/

The discovery of a new solid-supported ligand 5 for the catalytic asymmetric oxidation of aryl alkyl sulfides in up to 72% ee using Ti(OiPr)4 and aqueous H2O2 is reported.

High reactivity of alkyl sulfides towards epoxides under conditions of collagen fixation—a convenient approach to 2-amino-4-butyrolactones

Epoxy crosslinking agents have been investigated for use in the fabrication of bioprosthetic devices, such as heterograft heart valve prostheses. It has been generally assumed that epoxy crosslinking takes place via amino-epoxy reactions. The present study investigated the hypothesis that the reactions of methionine residues with epoxides also can occur in biomaterial crosslinking. A series of model reactions were studied in which a mono-epoxide was combined with individual alkyl sulfides. In the present studies epoxides rapidly alkylate aliphatic sulfides, including methionine derivatives, in buffered aqueous solutions at room temperature and pH close to neutral, forming sulfonium compounds, which are stable at pH 5–7 at temperatures up to 50°C, except for cases in which methionine derivatives with non-protected carboxy groups are used. The rate of reaction remains practically unchanged within the range of pH from 5 to 12, whereas in strongly alkaline media the reverse reaction occurs. This discovery can provide a better understanding of processes occurring in the fixation of bioprosthetic tissues with polyepoxides. It can also develop into a site-specific method to label methionine residues in proteins. The carboxy group-containing sulfonium betaines derived from N-protected methionines undergo cyclization in unexpectedly mild conditions, which can be used as an efficient method for preparation of N-protected 2-amino-4-butyrolactones with sensitive protective groups.

Syntheses, structures, and stabilities of [PPh(4)][WS(3)(SR)](R=(i)Bu,(i)Pr,(i)Bu, benzyl, allyl) and [PPh(4)][MoS(3)(S(t)Bu)

Intermediates in the condensation process of [MS(4)](2)(-) (M = Mo, W) to polythiometalates, in the presence of alkyl halides, had not been reported prior to our communication of [PPh(4)][WS(3)(SEt)] (Boorman, P. M.; Wang, M.; Parvez, M. J. Chem. Soc., Chem. Commun. 1995, 999-1000). We now report the isolation of a range of related compounds, with 1 degrees, 2 degrees, and 3 degrees alkyl thiolate ligands, including one Mo example. [PPh(4)][WS(3)(SR)] (R = (i)Bu (1), (i)Pr (2), (t)Bu (3), benzyl (5), allyl (6)) and [PPh(4)][MoS(3)(S(t)Bu)] (4) have been isolated in fair to good yields from the reaction of [PPh(4)](2)[MS(4)] with the appropriate alkyl halide in acetonitrile and subjected to analysis by X-ray crystallography. Crystal data are as follows: for 1, triclinic space group P1 (No. 2), a = 11.0377(6) A, b = 11.1307(5) A, c = 13.6286(7) A, alpha = 82.941(1) degrees, beta = 84.877(1) degrees, gamma = 60.826(1) degrees, Z = 2; for 2, monoclinic space group P2(1)/c (No. 14), a = 9.499(6) A, b = 15.913(5) A, c = 18.582(6) A, beta = 99.29(4) degrees, Z = 4; for 3, monoclinic space group P2(1)/n (No. 14), a = 10.667(2) A, b = 17.578(2) A, c = 16.117(3) A, beta = 101.67(1) degrees, Z = 4; for 4, monoclinic space group P2(1)/n (No. 14), a = 10.558(3) A, b = 17.477(3) A, c = 15.954(3) A, beta = 101.18(2) degrees, Z = 4; for 5, monoclinic space group P2(1)/n (No. 14), a = 16.2111(9) A, b = 11.0080(6) A, c = 18.1339(10) A, beta = 111.722(1) degrees, Z = 4; for 6, triclinic space group P1 (No. 2), a = 9.4716(9) A, b = 10.4336(10) A, c = 14.4186(14) A, alpha = 100.183(2) degrees, beta = 90.457(2) degrees, gamma = 91.747(2) degrees, Z = 2. Structures 3 and 4 are isomorphous, and 1 exhibits disorder about the tertiary carbon. 6 has been shown to exhibit fluxionality in solution by variable-temperature (1)H NMR studies, and an allyl migration mechanism is implicated in this process. The kinetics for the reaction of [WS(4)](2)(-) and EtBr were measured and suggest an associative nucleophilic substitution (S(N)2) mechanism. The decomposition of the [WS(3)(SEt)](-) ion is shown to be second order with respect to this ion, suggesting the formation of a transient binuclear intermediate. M-S bond cleavage is the predominant step in decomposition of 1-6 to yield alkyl sulfides, alkyl thiols, and polythiometalates such as [PPh(4)](2)[M(3)S(9)]. In contrast, reactions of [PPh(4)](2)[WO(x)()S(4)(-)(x)()] (x = 1, 2) with (t)BuBr result in the additional decomposition product of isobutene, presumably by C-S bond cleavage and beta-hydrogen transfer. Interestingly, the reaction of [PPh(4)](2)[WOS(3)] with BzCl yields 5 as the only isolable W thiolate species.

Synthesis, structure, and interconversion of chiral rhenium oxygen- and sulfur-bound sulfoxide complexes of formula [(η5-C5H5)Re(NO)(PPh3)(OS(Me)R)]+ X−; diastereoselective oxidations of coordinated methyl alkyl sulfides †

Reactions of the chiral chlorobenzene complex [(η5-C5H5)Re(NO)(PPh3)(ClC6H5)]+BF4− (1+ BF4−) and alkyl methyl sulfoxides OS(Me)R (R = a, Me; b, Et; c, i-Pr or d, t-Bu), at −15 °C gave the oxygen-bound sulfoxide complexes [(η5-C5H5)Re(NO)(PPh3)(OS(Me)R)]+ BF4− (2a–2d+BF4−; 94–56%). Above 0 °C, 2a–2d+BF4− rearrange to sulfur-bound linkage isomers [(η5-C5H5)Re(NO)(PPh3)(S(O)(Me)R)]+BF4− (3a–3d+BF4−; 96–20%). The triflate salts 2c,2d+TfO− and 3b,3c+TfO− are analogously prepared from (η5-C5H5)Re(NO)(PPh3)(OTf). Complexes 2b–2d+X− and 3b–3d+X− can exist as two Re, S configurational diastereomers. Stereochemistry is assigned from reactions of (S)- or (R)-1+BF4− with enantiomerically enriched sulfoxides (R)-b–d, and a crystal structure of (SReRS,RReSS)-2d+TfO−·0.5CH2Cl2. Relative diastereomer stabilities, and the basis for the divergent kinetic and thermodynamic oxygen/sulfur binding selectivities, are analysed. The alkyl methyl sulfide complexes [(η5-C5H5)Re(NO)(PPh3)(S(Me)R)]+ X− and dimethyldioxirane react (acetone, −20 °C) to give 3a–3d+X−. Diastereoselectivities (3b–3d+X−) are fair to good. However, some overoxidation to Ph3PO occurs, lowering yields.

Polystyrene-bound cyclo-BINOLs. New heterogeneous ligands for asymmetric catalysis

BINOL and substituted BINOLs, which have been tethered between the 7 and 7′ sites (i.e. ‘cyclo-BINOLs’), can be attached via this linkage to polystyrene resins using a simple acetalization. Efficacy associated with these new ligands is demonstrated in heterogeneous asymmetric catalysis (e.g. aryl alkyl sulfide oxidations, and 1,2-additions of Et 2Zn to aryl aldehydes).

Evidence for the Role of Electron-Withdrawing Power of Functional Groups and [H+] for Electron-Transfer Reaction in Substituted Alkyl Sulfides

The pulse radiolysis technique has been employed to demonstrate the effects of the electron-withdrawing power of functional groups and the H+ concentration on the nature of •OH radical reaction with substituted alkyl sulfides. The intermediate OH adduct and α-thioalkyl radical could be detected in substituted sulfides having a functional group of high electron-withdrawing power. The concentration of H+ required for the formation of solute radical cations appears to correlate with the electron-withdrawing power of the functional group. The reactivity of eaq- toward dialkyl sulfides increases upon the introduction of strongly electron-withdrawing groups which effectively reduce the electron density at sulfur. The transient absorption band (λmax = 310 nm) observed from the reaction of •OH radicals with methyl thioacetic acid (MTA) is assigned to the α-thioalkyl radical formed via an intermediate OH adduct. In highly acidic solutions ([HClO4] ≥ 3 mol dm-3), •OH radicals are able to react with MTA to form dimer radical cations (λmax = 490 nm). The specific one-electron oxidants (Cl2•-, Br2•-, and SO4•-) undergo electron-transfer reaction with the solute; however, the transient absorption band of the dimer radical cation at 490 nm could not be observed, which may be due to unstable nature of the transient species in neutral and slightly acidic solutions. The oxidation potential is determined to be 1.56 V. The decay kinetics of the solute dimer radical cation is discussed in detail, and deprotonation of the solute radical cation is found to be the rate-determining step. The stability constant for the dimer radical cation has been determined to be 10 dm3 mol-1 at 25 °C. The transient species (λmax = 390 nm, k = 3.3 × 109 dm3 mol-1 s-1), formed from the reaction of Br• atom with the solute, is assigned to a three-electron-bonded Br• adduct.

Copper-Mediated Cross-Coupling of Aryl Boronic Acids and Alkyl Thiols

[reaction: see text] The cross-coupling of aryl boronic acids and alkanethiols mediated by copper(II) acetate and pyridine in anhydrous dimethylformamide affords aryl alkyl sulfides in good yield with a wide variety of substituted aryl boronic acids. The method is applicable to the synthesis of aryl sulfides of cysteine.

Mechanism of selective oxidation of organic sulfides with Oxo(salen)chromium(V) complexes

The selective oxidation of organic sulfides to sulfoxides by oxo(salen)chromium(V) complexes in acetonitrile is overall second-order, first-order each in the oxidant and the substrate. The rate constant, k(2), values of several para-substituted phenyl methyl sulfides correlate linearly with Hammett sigma constants and the rho values are in the range of -1.3 to -2.7 with different substituted oxo(salen)chromium(V) complexes. The reactivity of different alkyl sulfides is in accordance with Taft's steric substituent constant, E(S). A mechanism involving direct oxygen atom transfer from the oxidant to the substrate rather than electron transfer is envisaged. Correlation analyses show the presence of an inverse relationship between reactivity and selectivity in the reaction of various sulfides with a given oxo(salen)chromium(V) complex and vice versa. Mathematical treatment of the results shows that this redox system falls under strong reactivity-selectivity principle (RSP).

Oxidation of aromatic sulfides by lignin peroxidase from Phanerochaete chrysosporium.

The reaction of H2O2 with 4-substituted aryl alkyl sulfides (4-XC6H4SR), catalysed by lignin peroxidase (LiP) from Phanerochaete chrysosporium, leads to the formation of sulfoxides, accompanied by diaryl disulfides. The yields of sulfoxide are greater than 95% when X = OMe, but decrease significantly as the electron donating power of the substituent decreases. No reaction is observed for X = CN. The bulkiness of the R group has very little influence on the efficiency of the reaction, except for R = tBu. The reaction exhibits enantioselectivity (up to 62% enantiomeric excess with X = Br, with preferential formation of the sulfoxide with S configuration). Enantioselectivity decreases with increasing electron density of the sulfide. Experiments in H218O show partial or no incorporation of the labelled oxygen into the sulfoxide, with the extent of incorporation decreasing as the ring substituents become more electron-withdrawing. On the basis of these results, it is suggested that LiP compound I (formed by reaction between the native enzyme and H2O2), reacts with the sulfide to form a sulfide radical cation and LiP compound II. The radical cation is then converted to sulfoxide either by reaction with the medium or by a reaction with compound II, the competition between these two pathways depending on the stability of the radical cation.