Zr (IV)-ninhydrin supported MCM-41 and MCM-48 as novel nanoreactor catalysts for the oxidation of sulfides to sulfoxides and thiols to disulfides

Modification of MCM-41 and MCM-48 mesoporous materials with bonded aminosilane species, Schiff base preparation by ninhydrin and finally complexation with zirconium, has attracted much attention in order to design catalyst with advanced applications in the oxidation of sulfides to sulfoxides and thiols to disulfides in the presence of hydrogen peroxide. In all oxidation of sulfides to sulfoxids 0.4 mL H₂O₂ used as oxidant in the presence of Zr(IV)-ninhydrin supported MCM-41 (0.01 g) or Zr(IV)-ninhydrin supported MCM-48 (0.005 g) at room temperature and solvent-free condition. Also the best conditions for oxidation of thiols to disulfides with 0.4 mL H₂O₂ were 0.005 g Zr(IV)-ninhydrin supported MCM-41 or Zr(IV)-ninhydrin supported MCM-48 at room temperature and in ethanol. These catalysts are characterized by SEM, XRD, TGA, FT-IR, EDS, ICP and BET analysis. Also the Turn over frequency (TOF) and Turn over number (TON) of catalysts are calculated. Obtained results by these heterogeneous catalysts revealed several advantages including short reaction times, simple workup, easy isolation and reusability.     

Metal–organic framework MOF-199-catalyzed direct and one-pot synthesis of thiols,sulfides and disulfides from aryl halides in wet polyethylene glycols (PEG 400)

A highly porous metal–organic frame work Cu₃ BTC₂ (copper(II)-benzene-1,3,5-tricarboxylate) that is known as MOF-199 was synthesized from the reaction of 1,3,5-benzenetricarboxylic acid and Cu(OAc)₂·H₂O by a solvothermal method and characterized by several techniques including FT-IR, XRD, EDX and scanning electron microscopy. The MOF-199 used as an efficient catalyst for one-pot synthesis of thiols by domino reactions of aryl halides and thiourea, and subsequently conversion to aryl alkyl sulfides and diaryl disulfides in polyethylene glycols (PEGs). A variety of aryl alkyl sulfides can be obtained in good to excellent yields in a relatively short reaction time and in the presence of the trace amount of catalyst. Also, the catalyst can be separated from the reaction mixture by decanting, and be reused without significant degradation in catalytic activity.     

Electrosynthesis of organic compounds. XVI. Cathodic reduction of some haloalkyl naphthyl sulfides and sulfones in nonaqueous solvent

Three aryl haloalkyl sulfur compounds—chloroethyl β-naphthyl sulfide, chloropropyl β-naphthyl sulfide and chloroethyl β-naphthyl sulfone—were subjected to cathodic reduction. The compounds were cathodically electrolyzed under a controlled potential of ?2.00 ± 0.03 V vs SCE on a zinc cathode as the working electrode and a platinum anode as helping electrode in absolute methanol containing Ba(ClO₄)₂ as supporting electrolyte at constant temperature (30°C). The isolated products were alkyl β-naphthyl sulfides, alkyl β-naphthyl sulfones, alkenyl β-naphthyl sulfides, alkenyl β-naphthyl sulfone, β-naphthyl thiols (in case of sulfides), naphthalene and other identified products. Suitable mechanisms are suggested.     

Regioselective ring opening of epoxides with thiols under solvent free and mild conditions using heterogeneous catalyst

A highly effective and mild protocol for ring opening of 1–2 epoxides with thiols in the presence of catalytic amount of HBF₄–SiO₂ under solvent-free conditions is developed. A variety of β-hydroxy sulfides were obtained in high yields with excellent regioselectivity in short reaction times using heterogeneous catalyst for the first time.     

The unusual influence of hetaryl groups on the direct conversion of some secondary alcohols into thiols with Lawesson’s reagent: elucidation of the reaction mechanism

A series of hetaryl-substituted methanols were used for direct conversion into the corresponding thiols by treatment with Lawesson’s reagent in boiling toluene. Unexpectedly, the respective sulfides were formed exclusively. In the case of chiral alcohols, the sulfides were obtained as 1:1-mixtures of meso- and dl-diastereoisomers. In contrast to hetaryl-substituted alcohols, the analogous protocol applied for benzhydryl alcohol led to a mixture of the expected secondary thiol and a bis(diphenylmethyl) trithiophosphonate. Finally, the analogous reactions with ferrocenyl(phenyl)methanol and diferrocenylmethanol, respectively, led to the corresponding thiols in good yield.     

Asymmetric Sulfoxidation of Thioethers with Hydrogen Peroxide in Water Mediated by Platinum Chiral Catalyst

Easy stereoselective oxidation of prochiral aryl alkyl sulfides 2 to the corresponding sulfoxides can be achieved in water‐surfactant medium with inexpensive hydrogen peroxide mediated by the chiral platinum diphosphine complex {[(R)‐BINAP]Pt(μ‐OH)}₂(BF₄)₂ ( 1 ). Remarkable key features of general interest are (i) easy isolation of the products from catalyst by simple diethyl ether/water‐surfactant two phase separation, (ii) catalyst loading as low as 1% mol, (iii) good yields, sulfoxide 3 to sulfone 4 ratio up to 200 : 1 and enantioselectivities up to 88%, (iv) mild experimental conditions.     

Catalytic oxidation of styrene by manganese(II) bipyridine complex cations immobilized in mesoporous Al-MCM-41

Manganese 2,2'-bipyridine (bpy) complex cations, [Mn(bpy)₂]²⁺, have been immobilized in mesoporous Al-MCM-41 (Si/Al=9) and used as a catalyst for the oxidation of styrene by iodosylbenzene, H₂O₂ and tert-butyl hydroperoxide (TBHP). The oxidation products included epoxide, diol and aldehyde. Al-MCM-41-immobilized [Mn(bpy)₂]²⁺ exhibited a higher catalytic activity for styrene oxidation than the corresponding homogeneous catalyst and showed no significant loss of catalytic activity when recycled. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heterogeneous Hydrothiolation of Alkynes with Thiols Catalyzed by Diphosphino-Functionalized MCM-41 Anchored Rhodium Complex

Abstract  

A novel diphosphino-functionalized MCM-41 anchored rhodium complex [MCM-41-2P-RhCl(PPh₃)] was conveniently synthesized by the reaction of diphosphino-functionalized MCM-41 (MCM-41-2P) with RhCl(PPh₃)₃. It was found that this rhodium complex is an efficient catalyst for the hydrothiolation of terminal alkynes with thiols and can be recovered and recycled by a simple filtration of the reaction solution and used for at least ten consecutive trials without any decreases in activity.     

Synthesis,characterization and catalytic study of a novel iron(III)-tridentate Schiff base complex in sulfide oxidation by UHP

An hydrazone Schiff base-iron(III) complex using salicylidene benzoyl hydrazine (L) as ligand has been synthesized and characterized by elemental analyses, IR, ¹H and ¹³C NMR and UV–Vis spectroscopy. Oxidation of sulfides to sulfoxides in one-step was conducted by this complex catalyst using urea hydrogen peroxide (UHP) in mixture of CH₂Cl₂/CH₃OH (1:1) under air at room temperature. The effect of the reaction conditions on the oxidation of methylphenylsulfide was studied by varying the amount of the catalyst, reaction temperature, reaction time and the amount of UHP. The results showed that using this system in the oxidation of sulfides, sulfoxides were obtained as the main products, together with variable amounts of sulfones (?9%), depending on the nature of the substrate.     

Chromium (III) Catalyzed Selective Oxidation of Sulfides to Sulfoxides Using 30% H2O2

Chromium (III) is used as an efficient, recyclable catalyst for selective oxidation of sulfides. The reactions were carried out in 60% acetonitrile (v/v) using 30% H₂O₂. Chromium (III) forms complex with sulfides which is then oxidized by H₂O₂ to form sulfoxides.     

Zirconocene bis(perfluorooctanesulfonate)s-catalyzed acylation of alcohols, phenols, thiols, and amines under solvent-free conditions

Air-stable zirconocene bis(perfluorooctanesulfonate)s [Cp₂Zr(OPf)₂, OPf = OSO₂C₈F₁₇] showing high Lewis acidity and high thermal stability was prepared by reacting Cp₂ZrCl₂ with AgOPf, and examined as a catalyst for acylation reactions. It was found that in the acetylation of various alcohols, phenols, thiols, and amines by equimolar of acetic anhydride, Cp₂Zr(OPf)₂ exhibits high activity and selectivity to desired products under mild and solvent-free conditions. In the acylation of 2-phenylethanol across various acylating reagents, it also shows good catalytic efficiency. In a test of ten cycles, Cp₂Zr(OPf)₂ shows little loss of activity. The results afford a general and efficient method for the acylation of alcohols, phenols, thiols, and amines using zirconium bis(perfluorooctanesulfonate) as catalyst.     

Anchoring of Copper(II) Schiff Base Complex into Aminopropyl-Functionalised MCM-41: A Novel,Efficient and Reusable Catalyst for Selective Oxidation of Alcohols

A copper(II) complex containing tetradentate N₂O₂ Schiff base ligand immobilized into aminopropyl-functionalised MCM-41 (mobile crystalline material number 41), was prepared and characterized by Fourier-transform infrared, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, N₂ adsorption–desorption and inductively coupled plasma analysis techniques. The novel heterogeneous catalyst, MCM-41-pr-NH₂-CuL, can be successfully applied for efficient and selective oxidation of different primary and secondary alcohols to the corresponding carbonyl compounds using hydrogen peroxide as an oxidant in acetonitrile at 60 °C. The effect of reaction parameters such as solvent, amount of catalyst, temperature and kind of oxidant on the oxidation of benzyl alcohol was also studied. The prepared catalyst could be recovered and reused four times without important loss of its catalytic performance. The heterogeneous MCM-41-pr-NH₂-CuL catalyst was found to be catalytically more active in the oxidation of alcohols compared to the similar type of copper(II) Schiff base complex in homogeneous media under the same reaction conditions.     

Silica sulfuric acid promoted selective oxidation of sulfides to sulfoxides or sulfones in the presence of aqueous H2O2

Alkyl and aryl sulfides are oxidized to the corresponding sulfoxides or sulfones in excellent yields with aqueous hydrogen peroxide in the presence of silica sulfuric acid as an efficient solid acid catalyst. The oxidation of alkyl and aryl sulfide proceeds at 25–90°C and the corresponding sulfoxides or sulfones was selectively obtained by controlling the amounts of H₂O₂ and catalyst.     

Selective and efficient oxidation of sulfides and thiols with a 1,1,3,3-tetramethylguanidine/Br2 complex

The 1,1,3,3-tetramethylguanidine/Br₂ complex has been found to be an efficient reagent for the selective oxidation of aliphatic and aromatic sulfides to the corresponding sulfoxides and the oxidative coupling of thiols to disulfides. 1,1,3,3-Tetramethylguanidine can be recovered at the completion of the reaction and reused.     

MCM-41 supported CuO/Bi2O3 nanoparticles as potential catalyst for 1,4-butynediol synthesis

CuO/Bi₂O₃ (CuO/Bi₂O₃/MCM-41) nanoparticles supported on MCM-41 were synthesized by a facile impregnation method. The products were characterized by nitrogen adsorption/desorption, X-ray diffraction (XRD), H₂ temperature programmed reduction (H₂-TPR) and scanning electron microscopy (SEM). XRD patterns indicated the presence of crystalline CuO and Bi₂O₃ phase for CuO/Bi₂O₃/MCM-41 catalyst. TPR results revealed CuO nanoparticles were dispersed well on MCM-41. SEM results showed that the nanoparticles were located on the MCM-41. The activity of the catalysts towards ethynylation of formaldehyde for 1,4-butynediol synthesis was evaluated at atmospheric pressure. Compared with unsupported CuO/Bi₂O₃ and commercial Cu/Bi-based catalyst, CuO/Bi₂O₃/MCM-41 catalyst showed maximum conversion (51%) and selectivity (94%) towards 1,4-butynediol. The results show that CuO/Bi₂O₃ catalysts supported on MCM-41 have potential for 1,4-butynediol synthesis in industrial application.     

Determination of forms of organic sulfur in coal by step-wise oxidation with perchloric acid-ferric perchlorate mixture

Differentiation of organic sulfur forms in coal by step-wise oxidation with a mixture of perchloric acid (HClO₄) and ferric perchlorate (Fe(ClO₄)₃) was studied. Various organic sulfur compounds were oxidized with HClO₄ solution containing Fe(ClO₄)₃, and the amounts of sulfate formed during reaction were measured. The compounds can be grouped into three categories according to their reactivities as follows: (1) easily oxidized ones, i.e. disulfides, for which almost all of the sulfur was converted to sulfate after oxidation, (2) less reactive ones including aliphatic sulfides, aliphatic and aromatic thiols (20–30% of sulfur in these compounds was oxidized to sulfate), and (3) relatively stable ones, i.e. thiophenes and aromatic sulfides, from which no sulfate was formed. Samples of Illinois No. 6 and Bevier coals were also reacted with HClO₄ solutions containing increasing concentration of Fe(ClO₄)₃. The organic sulfur in these coals could be differentiated into various groups according to their reactivities.     

Preparation and applications of a polymer supported peroxotungstate complex as a novel polymeric oxidizing agent

A polymer supported anionic peroxotungstate compound [Amb]₂[W₂O₃(O₂)₄] is prepared and characterized by conventional methods. Its use as a stoichiometric oxidizing agent for a variety of organic compounds is described. With this reagent alcohols are converted to the corresponding carbonyl compounds. Decarboxylation of α-hydroxy acids proceeds quantitatively. Also thiols are converted to disulfides, hydroquinones to quinones, benzylamines to carbonyl compounds, tertiary amines to the N-oxides, phosphines to phosphine oxides, and sulfides to sulfones. Deprotection of oximes and oxidative deprotection of silyl ethers proceed easily.     

Oxidation and Oxidative Bromination Reactions Catalyzed By a Reusable Polymer-Anchored Iron(III) Complex in Water at Room Temperature

A polymer-anchored iron(III) catalyst was synthesized and characterized. Its catalytic activity was evaluated for the oxidation of various alkenes, sulfides, aromatic alcohols and ethylbenzene with 30 % H₂O₂ as the oxidizing agent. The catalyst was also effective for the oxidative bromination reaction with 80–100 % selectivity of monobrominated products with H₂O₂/KBr at room temperature. The above reactions require a minimum amount of H₂O₂ and short reaction time. Most importantly, all the above reactions occur in aqueous medium. The catalyst can be facilely recovered and reused six-atimes without significant decrease in its activity and selectivity.     

3,5‐Dimethylpyrazolium Fluorochromate(VI)‐Catalysed Oxidation of Organic Substrates by Hydrogen Peroxide under Solvent‐Free Conditions

3,5‐Dimethylpyrazolium fluorochromate (VI), C₅H₈N₂H[CrO₃F], DmpzHFC , serves as an efficient catalyst for oxidation of primary, secondary and allylic alcohols to the corresponding carbonyl compounds using H₂O₂ at room temperature under solvent‐free conditions. Oxidation of methyl phenyl sulfides and triphenylphosphine were also carried out successfully.     

Activities of unsupported second transition series metal sulfides for hydrodesulfurization of sterically hindered 4,6‐dimethyldibenzothiophene and of unsubstituted dibenzothiophene

The applicability of transition metal sulfides (TMS) from the second transition series in deep hydrodesulfurization (HDS) was examined and compared to that of a traditional, supported CoMo/Al₂O₃ catalyst. Sulfides of Nb, Mo, Ru, Rh and Pd were studied for HDS of dibenzothiophene (DBT) and 4,6‐dimethyldibenzothiophene (4,6‐Me₂DBT). Measurements were carried out with unsupported TMS samples at different temperatures and H₂S partial pressures. The trend in DBT HDS activities agreed quite well with those found by previous authors. It was furthermore found that the activities of the metal sulfides towards the sterically hindered molecule 4,6‐Me₂DBT closely followed those for DBT. This is somewhat surprising since the direct sulfur abstraction route was of major importance for DBT while the prehydrogenation route, in which ring‐hydrogenation in the DBT skeleton precedes desulfurization, was prevalent for 4,6‐Me₂DBT. This suggests that common steps are involved in the two routes. For the unsupported metal sulfides, ring‐hydrogenated but not desulfurized DBT and 4,6‐Me₂DBT products were found in much larger amounts than for supported and promoted MoS₂‐based catalysts. This can be rationalized as being due to a relatively higher hydrogenation/desulfurization selectivity ratio for the different transition metal sulfides. Inhibition by H₂S was found to be most pronounced near the center of the transition series. This revised version was published online in July 2006 with corrections to the Cover Date.