Hydrotalcites as catalysts for the Baeyer-Villiger oxidation of cyclic ketones with hydrogen peroxide/benzonitrile

Hydrotalcites (HTs) in variable Mg/Al ratios were used as catalysts for the Baeyer-Villiger (BV) oxidation of cyclic ketones with hydrogen peroxide. All HTs studied were found to be active in the BV oxidation of cyclohexanone, their activity increases with increasing Mg/Al ratio. The reaction, which was conducted under very mild conditions (viz. atmospheric pressure and a temperature of 70 °C), provided conversions above 70% with 100% selectivity only after 6 h. This outcome was found to require the presence of a nitrile in the reaction medium, so a mechanism involving adsorption of the nitrile and cyclohexanone onto the catalyst is proposed that is consistent with the experimental results. Based on the proposed mechanism, the presence of a surfactant should result in improved conversion and catalytic activity, as was indeed observed with sodium dodecylsulfate in the reaction medium. The best catalyst among those tested was used with other cyclic ketones and found to provide excellent conversion and selectivity results in most cases.     

Determination of Mg, Ti and Cl in Ziegler-Natta catalysts by WDXRF

A method for determination of Mg, Ti and Cl in Ziegler-Natta (ZN) catalysts by wavelength dispersive X-ray fluorescence (WDXRF) spectrometry was developed. For comparative reasons, Ti was determined by spectrophotometry, Mg by complexometry and Cl by argentometric titration. Direct pressing was shown to be unsuitable for sample preparation due to catalyst decomposition. For Ti and Mg measurements, catalyst samples were calcinated at 1000 °C and pressed at 275 MPa. Their determination by the fundamental parameters based on the Ti Ka line measurement was shown to be equivalent to those results obtained by univariate calibration or by the classical methods. Cl was determined by aqueous extraction, followed by deposition on a support. Chloride loss was observed. Fixation of Cl as AgCl on polytetrafluoroethylene (FHLC) millipore membrane afforded the best results. Nevertheless, measurements by WDXRF were shown to be inferior to those obtained by argentometric titration.     

Recycling of osmium catalyst in oxidative olefin cleavage: a chemoentrapment approach

A new chemoentrapment strategy for recycling osmium in the catalytic olefin cleavage reaction is reported. The new strategy utilizes KOH/i-PrOH to generate water-soluble Os(VI) species as a recyclable metal catalyst after the oxidative cleavage reaction. For the recycling of the catalyst, NaIO₄-NaClO₂ was found to be the best combination of secondary oxidants and acetonitrile-water was chosen as an optimal solvent for the best recycling results. The new method allows for an efficient recycling of osmium in the reactions involving mono- and di-substituted olefins with 1 mol % of OsO₄ without any significant side reactions and loss of yield.     

Evaluation of V, Ir, Ru, V-Ir, V-Ru, and W-V as permanent chemical modifiers for the determination of cadmium, lead, and zinc in botanic and biological slurries by electrothermal atomic absorption spectrometry

Permanent modifiers (V, Ir, Ru, V-Ir, V-Ru, and W-V) thermally coated on to platforms of pyrolytic graphite tubes were employed for the determination of Cd, Pb, and Zn in botanic and biological slurries by electrothermal atomic absorption spectrometry (ETAAS). Conventional Pd + Mg(NO₃)₂ modifier mixture was also used for the determination of analytes in slurries and digested samples. Optimum masses and mass ratios of permanent modifiers for Cd, Pb, and Zn in slurry sample solutions were investigated. The 280 μg of V, 280 μg of V + 200 μg of Ir, 280 μg of V + 200 μg of Ru or 240 μg of W + 280 μg of V in 0.2% (v/v) Triton X-100 plus 0.5% (v/v) HNO₃ mixture was found as efficient as 5 μg of Pd + 3 μg of Mg(NO₃)₂ modifier mixture for obtaining thermal stabilization, and for obtaining best recoveries. Optimization conditions of analytes, such as pyrolysis and atomization temperature, characteristic masses and detection limits, and atomization and background peak profiles were studied with permanent and 5 μg of Pd + 3 μg of Mg(NO₃)₂ conventional modifiers and compared with each other. The permanent V-Ir, V-Ru, and W-V modifiers remained stable for approximately 250-300 firings when 20 μl of slurries and digested samples were delivered into the atomizer. In addition, the mixed permanent modifiers increase the tube lifetime by 50-95% when compared with untreated platforms. The characteristic masses and detection limits of analytes (dilution factor of 125 ml g⁻¹) obtained with V-Ir based on integrated absorbance as example for 0.8% (m/v) slurries were 1.0 pg and 3 ng g⁻¹ for Cd, 18 pg and 17 ng g⁻¹ for Pb, and 0.7 pg and 4 ng g⁻¹ for Zn, respectively. The results of analytes obtained by employing V-Ir, V-Ru, and W-V permanent modifier mixtures in botanic and biological certified and standard reference materials were in agreement with the certified values of reference materials.     

Water-tolerant catalyst systems for the bulk cationic polymerization of para-methylstyrene and indene

Water-tolerant catalyst systems have been investigated for the cationic oligomerization of technical-grade p-methylstyrene and indene, for the production of industrially relevant aromatic resins. Systems based on 1-p-tolylethanol and 1-indanol (ROH) as initiators, in association with Cu(OTf)₂, Bi(OTf)₃ (OTf = triflate) and B(C₆F₅)₃ as co-initiators/catalysts, show interesting productivities at 60 °C under air, with as low as 0.2-1.0 mol% catalyst loading. Most of the reactions are not controlled in terms of molecular weights of the products, except for indene oligomerization by the borane catalyst where experimental M_n values match well the theoretical values, as determined by the amount of added initiator over a 5-fold range (with 2-10 mol% vs. monomer). The ROH/tris(pentafluorophenyl)borane system offers the best compromise in terms of productivity and control over the molecular weights of the oligomers, which can be manipulated by the amount of initiator and reaction temperature.     

Effects of acid treatment on activated carbon used as a support for Rb and K catalyst for C2F5I synthesis and its mechanism

In the present work, the activated carbon (AC) support was treated with HCl, HNO₃ and HF solution. The order of catalyst dispersion was as follows: Rb-K/AC-HNO₃ > Rb-K/AC-HF > Rb-K/AC-HCl > Rb-K/AC. The same sequence was also observed for the amount of the acid surface oxygen groups on AC, but not for the basicity of the catalyst. The key role of acid treatment on AC surface chemistry and the basic sites, which are closely related to catalyst dispersion and basicity, is examined to rationalize these findings. On the other hand, a consideration of the reaction mechanism suggests that the reaction proceeds via CF₂ carbenes formed on the catalyst surface as intermediates, followed by carbine disproportionation to CF₃ radicals and CF₃CF₂ radicals, followed by reaction with I₂ to produce CF₃CF₂I, and it was also found that the Rb-K/AC-HCl catalyst with a high dispersion and moderate basicity was helpful for the enhancement of catalytic activity for C₂F₅I synthesis.     

Mg的添加对PtNa/Sn-ZSM-5催化丙烷脱氢反应性能的影响

通过X射线衍射(XRD)、N2吸附、透射电镜(TEM)、NH3程序升温脱附(NH3-TPD)、H2程序升温还原(H2-TPR)和O2程序升温氧化(O2-TPO)等多种表征手段及催化反应性能评价,研究了镁助剂的添加对PtNa/Sn-ZSM-5催化丙烷脱氢反应性能的影响.结果表明:适量Mg的添加(0.3%和0.5%,质量分数)能促进催化剂表面金属粒子的分散,减少反应过程中积碳的产生.Mg的引入能有效抑制催化剂中Sn组分的还原,使更多量的Sn组分以氧化态形式存在,有利于丙烷脱氢反应的进行.但是,过量Mg的加入导致催化剂表面金属颗粒易于发生团聚,高温下Sn组分易于被还原,不利于反应的进行.在本实验中,0.5%Mg加入后PtNa/Sn-ZSM-5催化剂显示出最佳的反应性能,反应7h后,丙烷转化率仍然高达38.7%,对应的丙烯选择性能够维持在95%以上.     

Palladium-catalyzed reactions of acetoxyenynes with triorganoindium reagents

The reaction of 1-acetoxy-2,7- and 2,8-enynes with triorganoindium reagents in the presence of 5 mol % palladium catalyst provides cyclic and/or acyclic substitution products depending upon substrate structure. Enynes bearing secondary acetates, quaternary centers, or heteroatoms furnish high yields of carbocyclic or heterocyclic substitution products. NMR studies show that a single trisubstituted alkene stereoisomer is formed in the reaction. A more atom-efficient procedure for the cyclization-substitution process utilizing heteroleptic indium reagents is presented.     

Microwave-assisted arylation of rac-(E)-3-acetoxy-1,3-diphenylprop-1-ene with arylboronic acids

The palladium-catalyzed arylation of rac-(E)-3-acetoxy-1,3-diphenylprop-1-ene with arylboronic acids was studied under controlled microwave irradiation conditions. A variety of different catalysts, bases, and solvents were explored in order to achieve optimum yields in the shortest possible reaction times. The best isolated yields were obtained using Pd₂(dba)₃·CHCl₃/PPh₃ as the catalytic system, potassium phosphate monohydrate as the base, and toluene/H₂O as a solvent system. Microwave irradiation using 5 mol % of the palladium catalyst for 90 s (max. temp 170 °C) generally afforded the cross-coupling products in good to excellent yields.     

Superacid-catalyzed Friedel-Crafts cyclization of unactivated alkenes

Trifluoromethanesulfonimide is an effective catalyst for Friedel-Crafts cyclizations of simple, nonpolarized alkenes with a variety of pendant arenes. A catalyst loading of 0.5 - 1.0 mol % effects clean cyclization to form 5- to 7-membered carbocycles with generally short reaction times and good to excellent yields under reflux or microwave heating.     

Efficient catalyst turnover in the phosphitylation of alcohols with phosphoramidites

We report a method for catalytic phosphitylation utilizing phosphoramidites. Traditionally, this reaction is inefficient unless an excess of catalyst is present due to catalyst deactivation by an amine by-product. Isocyanate additives have been evaluated for scavenging the amine to facilitate catalyst turnover. A variety of alcohols and phosphoramidites were screened with 5 mol % catalyst. In the presence of additive, 83-97% conversion was achieved in contrast to 7-31% conversion without additive.     

A rapid, one-pot, four-component route to 2H-indazolo[2,1-b]phthalazine-triones

A new, efficient, and environmentally benign protocol for the one-pot, four-component synthesis of 2,2-dimethyl-13-phenyl-2,3-dihydro-1H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione by condensation of phthalic anhydride, hydrazinium hydroxide, aromatic aldehydes, and dimedone catalyzed by Ce(SO₄)₂·4H₂O as an ecofriendly catalyst with high catalytic activity and reusability at 125 °C under solvent-free conditions is reported. The reaction proceeds to completion within 5-10 min in 71-95% yield. To the best of our knowledge, this new procedure provides the first example of an efficient synthetic method for 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione via a four-component reaction.     

Asymmetric Suzuki-Miyaura cross-coupling of aryl chlorides with enhancement of reaction time and catalyst turnover

A series of new chiral phosphonite ligands were evaluated for the palladium-catalyzed asymmetric Suzuki-Miyaura cross-coupling reactions of aryl chlorides. Ligand 4 gave 91% yield and 78% ee with 0.5 mol % catalyst loading for the coupling of aryl boronic acid and aryl chloride in 5 h. When the catalyst loading was lowered to 0.1 mol % the same reaction gave 75% yield and 76% ee.     

Efficient, solventless N-Boc protection of amines carried out at room temperature using sulfamic acid as recyclable catalyst

A simple, rapid, and efficient protocol for the chemoselective N-Boc protection of amines using sulfamic acid as catalyst is described. N-Boc protection of various structurally diverse aliphatic, aromatic, alicyclic, and heterocyclic amines (1°, 2°, 3°) was carried out with (Boc)₂O using sulfamic acid as catalyst (5 mol %) at room temperature under solventless conditions. The advantages of this method are simplicity, shorter reaction times (1-15 min), a cost-effective catalyst, and excellent isolated yields (90-100%); it is also environmentally benign. Moreover, the combined use of ultrasound and sulfamic acid achieves a synergic effect that is especially marked in the N-Boc protection of deactivated (sterically hindered and electron-deficient) amines. The catalyst possesses distinct advantages: ease of handling, cleaner reactions, high activity, and excellent chemoselectivity.     

Thorpe-Ingold effect in copper(II)-catalyzed formal hydroalkoxylation-hydroarylation reaction of alkynols with indoles

The use of Cu(OTf)₂ as a catalyst for tandem hydroalkoxylation-hydroarylation reaction of alkynes tethered with hydroxyl group is reported. The reaction proceeds at 60 °C or even at room temperature with 5 mol % catalyst loading and produces C-3-substituted indoles in good to high yields. The method was shown to be applicable to a broad range of indoles, containing electron-withdrawing and electron-donating substituents, and alkynol substrates bearing sterically demanding substituents in the tether. Interestingly, it was found that Thorpe-Ingold effect is operating for this cyclization reaction. Easy availability and low cost of Cu(OTf)₂ make this method attractive and amenable for large-scale synthesis compared to known literature methods.     

A study of the direct determination of Cd, Cr, Cu, Pb and Zn in certified reference materials of soils by solid sampling electrothermal atomic absorption spectrometry

A simple and rapid method for the direct determination of Cd, Cr, Cu, Pb and Zn in soil was developed. The method was developed using three certified reference materials of soil: Eutric Cambisol, Orthic Luvisols and Rendzina, which differed in their matrix composition. Chemical modifiers were essential to achieve reproducible and interference-free signals for the analytes studied. The best results were obtained with a Pd/Mg(NO₃)₂ admixture for the determination of Cd, Pb and Zn and NH₄F for Cu. The combination of W (as a permanent modifier) and Mg(NO₃)₂ provided well-defined signal profiles for Cr. The following spectral lines were used: Cd 228.8 nm, Cr 520.6 nm, Cu 218.2 nm, Pb 205.3 nm and Zn 307.6 nm. The limit of detection was 4.2 ng g^− 1 for Cd, 1.1 μg g^− 1 for Cr, 0.5 μg g^− 1 for Cu, 1.3 μg g^− 1 for Pb and 8.6 μg g^− 1 for Zn for the maximum sample mass used. Under optimized conditions, the analyte and matrix were separated effectively in situ, and aqueous standards could be used for calibration.     

A three-component reaction between alkenes, secondary phosphanes, and elemental selenium: a novel, efficient, atom-economic synthesis of diselenophosphinic esters

A novel, convenient, atom-economic approach toward the synthesis of diselenophosphinic esters has been developed via the three-component reaction between aryl- or hetarylalkenes secondary phosphanes, and elemental selenium. The reaction proceeds without a catalyst (85 °C, 3 h, 1,4-dioxane) to afford the target compounds in good to high yields.     

Synthesis conditions and activity of various Lewis acids for the fluorination of trichloromethoxy-benzene by HF in liquid phase

The experimental conditions (temperature, reaction time, amount of hydrogen fluoride (HF)) for the comparison of the performances of various Lewis acids in the liquid phase fluorination by HF of the trichloromethoxy-benzene were determined by using SbCl₅ as the reference catalyst. After 1 h reaction at 50 °C, C₆H₅OCCl₃ was totally converted into C₆H₅OCF₃ requiring only 2 mol% of SbCl₅ and a stoichiometric amount of HF. The most efficient catalysts were found to be chlorinated Lewis acids in which the metal is at the state of oxidation +V (SbCl₅, MoCl₅, TaCl₅ and NbCl₅). The appropriate catalyst has to be able to form a nucleophilic complex with HF, which constitutes the actual fluorinating agent and is more efficient than HF alone.     

载体对浸渍型Cu/Mn/Mg/K甲醇裂解催化剂的影响

载体对浸渍型Cu/Mn/Mg/K甲醇裂解催化剂的影响;