Alkyl Aryl Sulfides Research Articles

Oxidation of Sulfides to Sulfoxides and Sulfones with 30% Hydrogen Peroxide under Organic Solvent‐ and Halogen‐Free Conditions.

Abstract Aromatic and aliphatic sulfides are oxidized to sulfoxides or sulfones in high yield with 30% hydrogen peroxide under organic solvent- and halogen-free conditions. Dialkyl and alkyl aryl sulfides are cleanly oxidized to sulfoxides using aqueous hydrogen peroxide without catalysts. The best catalyst for the sulfone synthesis consists of sodium tungstate, phenylphosphonic acid, and methyltrioctylammonium hydrogensulfate. Co-existing primary or secondary alcohol or olefinic moieties are unaffected under such conditions.

Synthesis of Aryl Sulfones

Methods available for the synthesis of diaryl and monoaryl monoalkyl sulfones are reviewed. The main methods employed involve alkylation of salts of sulfinic acids, acidcatalysed condensation of sulfonic acids with aromatic hydrocarbons, and oxidation of diaryl and alkyl aryl sulfides. Oxidation by peracids, N-oxides (catalysed by tetra-n-propylammonium perruthenate), periodate (catalysed by ruthenium trichloride), and oxone® (potassium hydrogen persulfate), are highlighted.

Oxidation of sulfides to sulfoxides and sulfones with 30% hydrogen peroxide under organic solvent- and halogen-free conditions

Aromatic and aliphatic sulfides are oxidized to sulfoxides or sulfones in high yield with 30% hydrogen peroxide under organic solvent- and halogen-free conditions. Dialkyl and alkyl aryl sulfides are cleanly oxidized to sulfoxides using aqueous hydrogen peroxide without catalysts. The best catalyst for the sulfone synthesis consists of sodium tungstate, phenylphosphonic acid, and methyltrioctylammonium hydrogensulfate. Co-existing primary or secondary alcohol or olefinic moieties are unaffected under such conditions.

Anthracene-Bound Sulfonium Salts. Highly Efficient Photoinitiators for Cationic Polymerization. A New Synthesis of Sulfonium Salts which Avoids the Use of Silver Salts.

The low absorptivity of triarylsulfonium salts above 320nm limits their utilization of longer wavelength emission from light sources. Herein we report the synthesis and photoactivity of anthracene-bound sulfonium salts, in which the sulfonium salt is insulated from the anthracene chromophore by a saturated chain. The salts efficiently absorb radiation between 330-410nm owing to the strong anthracene absorptivity in this spectral region. The efficiency of utilization of the absorbed radiation for generating cationic initiators is strongly dependent on the substituents attached to the sulfonium ion. Evidence is presented in support of generation of initiators for cationic polymerization by photoinduced electron transfer from the anthracene chromophore to the sulfonium group, wherein the efficiency of electron transfer is dependent on the sulfonium ion substituents. A new synthesis of sulfonium salts is also provided, which occurs by direct alkylation of diaryl, dialkyl and arylalkyl sulfides by oxiranes in the presence of strong acids having non-nucleophilic anions.

ChemInform Abstract: Alkyl- and Arylthiodediazoniations of Dry Arenediazonium o-Benzenedisulfonimides. Efficient and Safe Modifications of the Stadler and Ziegler Reactions to Prepare Alkyl Aryl and Diaryl Sulfides.

The reaction between dry arenediazonium o-benzenedisulfonimides 1 and sodium thiolates in anhydrous methanol represents an efficient and safe procedure, of general validity, for the preparation of unfunctionalized or variously functionalized alkyl aryl and diaryl sulfides. As a rule, the reaction temperature was maintained at 0−5 °C for the alkylthiodediazoniations and at room temperature (20−25 °C) for the arylthiodediazoniations. The sulfide yields are generally high; of the 63 considered examples, 43 gave yields greater than 80% and 13 were between 70% and 80%. Lower yields were obtained only when sterically hindered diazonium salts or thiols were used. A good amount of the o-benzenedisulfonimide (8) was always recovered from the reactions and could be reused to prepare salts 1. The copious experimental data collected in homogeneous conditions have offered several starting points for the study of the mechanism of these reactions.

Fluorous Biphasic Catalytic Oxidation of Sulfides by Molecular Oxygen/2,2-Dimethylpropanal

The use of perfluoroalkyl-substituted cobalt complexes as catalysts for the oxidation of alkyl aryl sulfides with molecular oxygen/2,2-dimethypropanal has been studied in a fluorous organic biphasic system. The addition of very small amounts of a CoII−tetraarylporphyrin (Co-4) led to increased substrate conversions (67−100%). Sulfoxide was generally obtained as the main product, together with variable quantities of sulfone (0−100%), depending on the nature of the substrate. A perfluoroalkyl-substituted CoII−phthalocyanine (Co-6) proved to be less efficient with regard to substrate conversion (40−78%), but afforded sulfoxides selectively. Although the mechanism has not been investigated in detail, the reaction probably proceeds through a free-radical oxidative process, initiated by the CoII complexes. The attempts at recycling the catalysts through phase separation were partly ineffectual owing to their instability under the reaction conditions, which is more pronounced in the case of Co-6.

Reduction of inner sulfonium salts, thioethers, and sulfones derived from closo-[B12H12]2- by lithium in methylamine: a new route to mercaptododecaborates.

Anions [Me2SB12H11]- (2) and [MeSB12H11]2- (3) can be reduced by excess lithium in methylamine at -15 degrees C to yield [HSB12H11]2- (1) after workup. Such behavior toward this reducing system is similar to that of alkyl aryl sulfides. The sulfone [MeSO2B12H11]2- (12) also yields 1 as a major boron product upon reduction, while alkyl aryl sulfones produce the corresponding arenes under the same conditions. Similarly, isomers of (Me2S)2B12H10 (4-6) are reduced by lithium in methylamine yielding dithiols [(HS)2B12H10]2- (7-9). The tetrabutylammonium salts of 1 and 7-9 are obtained in 80-90% yields and characterized by multinuclear NMR and mass spectrometry, the latter three compounds being isolated and characterized for the first time. The reduction reaction provides access to dithiols 7-9 for biological evaluation and use in synthesis. Thus, 2 and 4-6 can be easily converted to [R2SB12H11]- and (R2S)2B12H10 in a two-step reduction-alkylation procedure. 1,2-(Bn2S)2B12H10 (13) obtained by alkylation of the reduction product of 4 by benzyl chloride was characterized by single-crystal X-ray diffraction analysis. Crystal data for 1,2-(Bn2S)2B12H10.CD3CN: C2/c (No. 15), a = 13.666(1) A, b = 16.978(1) A, c = 14.667(1) A, beta = 91.08(1) degrees, Z = 4.

Electrophilic Substitution of Phenols with α,α′-Dioxothiones andortho-Thioquinones

α,α′-Dioxothione 1a and ortho-thioquinones 2a and 2b are able to react with several phenols and N,N-dimethylaniline to give the corresponding alkyl aryl or diaryl sulfides. The mechanism of this reaction was proved to be an electrophilic aromatic substitution undergone by the highly polarised carbon−sulfur double bond. Following this procedure, the atropoisomeric biphenyl compound 26 was also prepared.

Alkyl- and arylthiodediazoniations of dry arenediazonium o-benzenedisulfonimides. Efficient and safe modifications of the stadler and ziegler reactions to prepare alkyl aryl and diaryl sulfides

The reaction between dry arenediazonium o-benzenedisulfonimides 1 and sodium thiolates in anhydrous methanol represents an efficient and safe procedure, of general validity, for the preparation of unfunctionalized or variously functionalized alkyl aryl and diaryl sulfides. As a rule, the reaction temperature was maintained at 0-5 degrees C for the alkylthiodediazoniations and at room temperature (20-25 degrees C) for the arylthiodediazoniations. The sulfide yields are generally high; of the 63 considered examples, 43 gave yields greater than 80% and 13 were between 70% and 80%. Lower yields were obtained only when sterically hindered diazonium salts or thiols were used. A good amount of the o-benzenedisulfonimide (8) was always recovered from the reactions and could be reused to prepare salts 1. The copious experimental data collected in homogeneous conditions have offered several starting points for the study of the mechanism of these reactions.

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.

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.

Photoinduced hydrogen- and electron-transfer processes between chloranil and aryl alkyl sulfides in organic solvents. Steady-state and time-resolved studies

The photochemical behavior of three aryl alkyl sulfides, thioanisole (TA), benzyl phenyl sulfide (BPS) and 4-methoxybenzyl phenyl sulfide (MBPS), sensitized by triplet chloranil (CA), was investigated by nanosecond laser flash photolysis and steady-state irradiation in CH2Cl2 and MeCN. The nature of the transients detected upon 355-nm laser excitation was independent of the molecular structure of the aryl alkyl sulfides but strongly affected by the solvent polarity. In particular, in CH2Cl2 the quenching process of triplet CA by aryl alkyl sulfides was accompanied by H-transfer, with formation of the CAH• and TA(-H)•/BPS(-H)•/MBPS(-H)• radicals. In contrast, a charge transfer process between triplet CA and aryl alkyl sulfides, with formation of the radical anion CA•− and radical cations of aryl alkyl sulfides, occurred in MeCN. In this solvent, a transient detected at long delay time was tentatively assigned to the anion CAH− formed by H-transfer between radical ions. In all experiments, transient species were characterized in terms of second-order decay rate constants and quantum yields of formation. Steady-state irradiation of the CA/TA system led to the stable photoadduct C6H5SCH2OC6Cl4OH in both CH2Cl2 and MeCN with quantum yields of 0.033 and 0.27, respectively. In contrast, aldehydes, thioacetals, and disulfides were the main products obtained upon irradiation of the CA/BPS and CA/MBPS systems. The photoaddition products were not observed, probably owing to their low stability. The nature of the photoproducts formed by irradiation of CA/aryl alkyl sulfides was independent of solvent properties, even though the reactivity was higher in MeCN than in CH2Cl2 .

Mn-salen catalyzed nitrene transfer reaction: Enantioselective imidation of alkyl aryl sulfides

Enantioselective imidation of alkyl aryl sulfides was achieved by using ( R, R)- or ( R, S)-Mn-salen complex [( R, R)-3 or ( R, S)-3] as a catalyst. The optimum reaction conditions are dependent upon the substrates examined. For example, the imidation of alkyl phenyl sulfides with PhI=NTs using Mn-salen complex ( R, R)-3 as a catalyst in the presence of N-methylmorpholine N-oxide showed high enantioselectivity (up to 89% ee). On the other hand, the reaction of methyl 2,4-dinitrophenyl sulfide was effected (97% ee) by using Mn-salen complex ( R, S)-3 as the catalyst in the absence of N-methylmorpholine N-oxide.

A Mild and Efficient Procedure for the Oxidation of Organic Sulfides to Sulfones by Use Of Urea-Hydrogen Peroxide/Trifluoroacetic Anhydride System

Selective, mild and safe oxidation of dialkyl-, diaryl- and alkyl-aryl sulfides to the corresponding sulfones was achieved by using of urea-H2O2/trifluoroacetic anhydride system.

Enantioselective Ti(IV) Sulfoxidation Catalysts Bearing C3-Symmetric Trialkanolamine Ligands: Solution Speciation by 1H NMR and ESI-MS Analysis

Sulfoxidation catalysts generated from titanium(IV) isopropoxide and enantiopure trialkanolamine ligands promote the enantioselective oxidation of aryl alkyl sulfides to the corresponding sulfoxides even at low (1−2%) catalyst loadings. Electrospray ionization mass spectrometry (ESI-MS), in combination with conventional low-temperature NMR techniques, provides a powerful tool for understanding the unique nature of these catalysts. Tetradentate ligation of the titanium atom by the trialkanolamine ligand provides a highly robust titanatrane core which is retained even in hydroxylic solvents and/or under acidic conditions. In contrast, the remaining apical coordination site is shown to be substitutionally labile. Previously ill-defined species formed when the catalyst is generated in situ with a slight excess of trialkanolamine are shown to consist of discrete 2:1, 3:2, and 4:3 oligomers in which the excess trialkanolamine bridges multiple titanatrane units. In the presence of excess tert-butyl hydroperoxide, all of the precatalyst species are cleanly converted to a mononuclear titanium(IV) peroxo complex which serves as the active sulfoxidation catalyst. Ab initio molecular orbital calculations were used to probe the structure and position of protonation of the catalytic species. Other ionization techniques (fast ion bombardment or electron impact) proved less useful than ESI-MS due to high levels of fragmentation during the ionization process.

Asymmetric Synthesis with the Enzyme Coprinus Peroxidase: Kinetic Resolution of Chiral Hydroperoxides and Enantioselective Sulfoxidation.

The enzyme Coprinus peroxidase (CiP) was employed for the kinetic resolution of racemic hydroperoxides 1 and the asymmetric sulfoxidation of prochiral sulfides 4. Eleven hydroperoxides 1a-k were reduced by CiP and guaiacol as reductant under conditions of kinetic resolution with enantioselectivities of up to >98% for the (S)-hydroperoxide 1 and 90% for the (R)-alcohol 2. In the absence of a reductant, the hydroperoxide 1a afforded with CiP enantiomerically enriched hydroperoxide 1a (ee up to 54%) and alcohol 2a (ee up to 40%), as well as ketone 3a (which is also formed simultaneously in all other reactions) and molecular oxygen. Catalase activity was established for CiP with hydrogen peroxide. When aryl alkyl sulfides 4 were used as oxygen acceptors, three products, sulfoxides 5, alcohols 2, and hydroperoxides 1, were obtained, all in enantiomerically enriched form. The highest ee value (89%) was achieved for the sulfoxide derived from naphthyl methyl sulfide (4f). Thus, CiP may be utilized for the asymmetric synthesis of optically active hydroperoxides 1, alcohols 2, and sulfoxides 5.

Stereoselective catalytic sulfoxidations mediated by new titanium and zirconium C3, trialkanolamine complexes

Abstract

An Efficient Method for the Oxidation of Organic Sulfides to Sulfones

Mild and safe oxidation of dialkyl-, diaryl- and alkyl-aryl sulfides (1a-m) to the corresponding sulfones (2a-m)by using urea-hydrogen peroxide/formic acid system is reported.

Studies on the Oxidation of some Sulfides with Pyridinium Dichromate in Acetonitrile medium

The kinetic behaviours of oxidation of dialkyl, alkyl aryl and diphenyl sulfides are quite different with pyridinium dichromate in acetonitrile medium; studies indicate the involvement of a sulfur cation free radical intermediate in diphenyl sulfide oxidation; electron releasing and withdrawing groups retard the reactivity of aryl methyl sulfides; the observed non-linear concave downwards type Hammett plot is well explained by assuming shifts in the rate-limiting step within the same overall reaction pathway.

Studies on the Oxidation of some Sulfides with Pyridinium Dichromate in Acetonitrile medium

The kinetic behaviours of oxidation of dialkyl, alkyl aryl and diphenyl sulfides are quite different with pyridinium dichromate in acetonitrile medium; studies indicate the involvement of a sulfur cation free radical intermediate in diphenyl sulfide oxidation; electron releasing and withdrawing groups retard the reactivity of aryl methyl sulfides; the observed non-linear concave downwards type Hammett plot is well explained by assuming shifts in the rate-limiting step within the same overall reaction pathway.