Micellar Effect on Chromium(VI) Oxidation of Ethanol and Propan-1-ol in Aqueous Acid Media

Cetylpyridinium chloride (CPC) inhibits the Cr(VI) oxidation of ethanol and propan-1-ol while sodium dodecyl sulfate (SDS) catalyzes the title reactions. At higher values of the [surfactant], the rate attains a limiting value. The micellar effect has been explained by considering the preferential partitioning of the reactants in terms of the suggested mechanism. Applicability of the Menger-Portnoy model and Piszkiewicz model to explain the observed micellar effect has been examined. This revised version was published online in June 2006 with corrections to the Cover Date.     

Metal-Free,One-Pot,Rapid Synthesis of Tetrahydropyridines Using Acetic Acid as Solvent and Catalyst at Room Temperature

Acetic acid–promoted, one-pot synthesis of tetrahydropyridines has been developed under metal-catalyst-free conditions via a tandem reaction. High atom economy, good yield, simple procedure, no expensive column chromatography, shorter reaction time, and metal-free and mild reaction conditions are some of the important features of this protocol. The current methodology provides an alternative approach for not only highly substituted tetrahydropyridines (THPs) but also fully substituted tetrahydropyridines (FTHPs) in moderate to good yields. The plausible mechanism for the formation of THPs was greatly promoted by the H⁺ ion coming from acetic acid.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

The Fe Active Sites in FeZSM-5 Catalyst for Selective Oxidation of CH4 to CH3OH at Room Temperature

It was shown recently that iron complexes formed during the thermal treatment of FeZSM-5 zeolite perform single-turnover cycles of methane oxidation to methanol at ambient conditions when nitrous oxide is used as a source of oxygen. The long-living active intermediate is capable of transferring accepted O atom (called -oxygen) into C-H bond of methane to produce methanol at 100% selectivity. The present work is aimed to the identification of iron active sites through a comparison of in situ ⁵⁷Fe Mössbauer spectra of FeZSM-5 after various thermal treatments and reaction stages. It is established that vacuum activation at 900 °C accompanied by a manifold increase of -centers leads to the transformation of inactive Fe³⁺ to the active, coordinatively unsaturated Fe²⁺ states. After -oxygen loading, active Fe²⁺ states transform to a new Fe³⁺ states responsible for further methane oxidation. The latter reaction, as well as reaction with ²H₂, is not fully reversible: part of active Fe³⁺ transforms to other inactive Fe³⁺ form. On the contrary, reaction of -oxygen with CO leads to a complete restoration of the initial, vacuum activated Fe²⁺ states. On the base of joint Mössbauer and catalytic data, the structure and composition of iron active centers are suggested.     

Envirocat EPZ-10: A Solid Acid Catalyst for the Synthesis of 1,8-Dioxo-octahydroxanthenes in Aqueous Medium

An efficient method for synthesis of 1,8-dioxo-octahydroxanthenes using EPZ-10 as a heterogeneous catalyst is developed. In this method, aldehydes and dimedone / cyclohexane-1,3-dione are heated at 70 °C in the presence of a catalytic amount of EPZ-10 in water as a universal solvent, affording the corresponding 1,8-dioxo-octahydroxanthenes in moderate to excellent yields. Also, domino Knoevenagel / hetero-Michael-addition reaction is described in water without any catalyst with excellent yields. The major advantages of this method are excellent yields, short reaction time, and ease of operation. This green protocol works well with dimedone as well as cyclohexane-1,3-dione.     

Au/MBFCN多组分复合型催化剂用于低温催化氧化丙烯制丙烯醛

钼铋系催化剂在丙烯氧化制丙烯醛反应中具有独特优势,但对反应温度、水汽配比的要求均较高.金催化剂的低温催化性能优异且对产物选择性高,我们结合两者的优势,通过调变载体制备过程中沉淀终止时的pH值得到了一系列多组分复合氧化物担载金催化剂(Au/MBFCN).反应结果显示,pH=4、载金量为0.5％(质量分数)时得到的催化剂A...     

Synthesis and Study of Mono-Schiff Base MnIII Complexes with Aza-crown or Morpholino Pendant as Catalyst in Aerobic Oxidation of p-xylene to p-toluic Acid

Novel mono-Schiff base Mn^III complexes with pendant aza-crown or morpholino groups have been synthesized and studied as catalysts in aerobic oxidation of p-xylene to p-toluic acid. The oxidation of p-xylene to p-toluic acid with air at 120 °C under normal atmospheric pressure occured efficiently in the presence of aza-crown ether substituted mono-Schiff base Mn^III complexes. Significant selectivity (up to ~90%) and conversion levels (up to ~38%) were obtained. The effect of the aza-crown ether pendant in Mn^III Schiff base complexes on the oxidation of p-xylene was also investigated by comparison with the morpholino pendant analogues. The addition of alkali metal ions accelerated the rate of conversion of p-xylene to p-toluic acid.     

Catalytic Method for Synthesis of Aspirin by a Green,Efficient and Recyclable Solid Acid Catalyst (Preyssler's Anion) at Room Temperature

Synthesis of aspirin at room temperature via O‐acetylation of salicylic acid in the presence of Preyssler type heteropolyacids has been investigated in order to contribute toward clean technology, which is the most important need of the society. All of the catalysts are recyclable and reusable.     

Acicular Nickel on Carbon Nanofiber as Electrochemical Sensor Electrode for the Rapid Detection of Aqueous and Gaseous Formaldehyde at Room Temperature

The rapid and straightforward detection of formaldehyde (FA) in the environment is crucial for preventing the accidental inhalation of FA and limiting skin exposure to FA. In this study, we developed a simple nickel-based electrocatalytic electrode on carbon nanofibers (CNFs−Ni), which is suitable for rapidly detecting FA at room temperature. Centrifugal electrospinning was used to obtain polyacrylonitrile (PAN) nanofibers, which was subsequently stabilized and carbonized to fabricate the CNFs. Carbonization of the CNFs occurred at various temperatures (T_c=1200, 1300, 1400, and 1500 °C). PAN CNFs served as a highly conductive template for electroless plating under a magnetic field of 500 G to grow acicular nickel. The amperometric responses of the CNFs−Ni to aqueous FA were then measured. A lab-built amperometric gas sensor (CNFs−Ni 1–8), which comprised CNFs with a reduced Ni loading, was used as the electrode for detecting gaseous FA. Scanning electron microscopy (SEM), linear sweep voltammetry (LSV), cyclic voltammetry (CV), and chronoamperometry were used to evaluate the sensitivities of the electrodes. Within the linear range of 0.05–91.5 mM, the CNFs1400-Ni electrode was highly sensitive for detecting aqueous FA (2592 μA mM⁻¹ cm⁻²), as evidenced by the fast response time (6 s). At a low concentration of gaseous FA (0.5 ppm), the laboratory-built FA gas sensor was stable (98.3 %) and had a fast response time (5 s) after 9 h of continuous operation.     

Synthesis and Study of Unsymmetrical Schiff Base Mn(III) Complexes with Pendant Aza-crown or Morpholino Groups as Catalyst in Aerobic Oxidation for p-Xylene to p-Toluic Acid

A series of novel unsymmetrical Schiff base Mn(III) complexes with pendant aza-crown or morpholino groups have been synthesized and studied as catalysts in aerobic oxidation of `p-xylene to p-toluic acid (PTA). The oxidation of p-xylene to p-toluic acid with air at 120°C under normal atmospheric pressure occurred efficiently in the presence of aza-crown ether substituted unsymmetrical Schiff base Mn(III) complexes. Significant selectivity (up to ～90%) and conversion levels (up to ～40%) were obtained. The effect of the aza-crown ring appended in Mn(III) Schiff base complexes on the oxidation of p-xylene were also investigated by comparison with the morpholino group pendant analogues. The addition of alkali metal ions accelerates the rate of conversion of p-xylene to p-toluic acid.     

Fermented Baker's Yeast: An Efficient Catalyst for the Synthesis of Pyran Derivatives in Water at Room Temperature

An environmentally friendly, one-pot synthesis of biologically important pyran derivatives in water is described herein. The advantages of this method are its simplicity, cost-effectiveness, and environmental friendliness. Water was exploited both as reaction media as well as activator of catalyst (fermentation of bakers' yeast). Compared with other methods for synthesis of pyran derivatives, satisfactory results were obtained with good yields under simple experimental procedure.     

A Novel One‐pot Synthesis of Biaryl Derivatives by Sequential Strategies via Suzuki Coupling/Knoevenagel Condensation in Aqueous Medium at Room Temperature

A novel one‐pot synthesis of biaryl derivatives has been developed starting from bromobenzaldehyde and phenylboronic acid in the presence of activated methylene compounds via sequential Suzuki coupling/Knoevenagel condensation in aqueous isopropanol medium at room temperature. Significantly, this strategy afforded a straightforward and efficient approach to construct original biaryls in which a new carbon double bond bound to activated moieties such as nitrile, ester and amide is formed from three simple substrates in a one‐pot procedure. Moreover, a wide scope of substrates could effectively participate in the process affording the target products in moderate to excellent yields.     

A Palladium Nanoparticle–Nanomicelle Combination for the Stereoselective Semihydrogenation of Alkynes in Water at Room Temperature

The addition of NaBH₄ to Pd(OAc)₂ in water containing nanomicelles leads to the generation of H₂ and Pd nanoparticles. Subsequent reduction of disubstituted alkynes affords Z‐alkenes in high yields. These reactions are general, take place in water at ambient temperatures, and offer recycling of the aqueous reaction mixture along with low overall E Factors.     

Aqueous Room Temperature Ionic Liquids as Green Mobile Phases for Liquid Chromatographic Analysis of Nicotine and Cotinine in Serum

Due to the concerns on laboratory environmental safety and human health, aqueous solutions of room temperature ionic liquids (RTILs) were used as environmentally friendly chromatographic mobile phases instead of the conventional volatile organic solvents. The method was applied to the analysis of nicotine and its metabolite, cotinine, in serum, as an example. The separation problems of these alkaloids were solved successfully by RTILs via the suppression of the adsorption between analytes and silanol groups. In comparison with other existing chromatographic methods, the proposed method is environmentally friendly and can obtain better peak symmetry and higher separation efficiency.     

Pressure Dependence of the Acid/Base Equilibria of Methyl Orange in Aqueous Solutions to 1000 bar at 20°C

The pressure dependence on the acid/base equilibria of methyl orange in aqueous solution was measured at 20 °C in the 1–1000 bar range with a newly designed flow-through spectrophotometric cell. Combined chemometric and thermodynamic analyses of the UV-Vis spectrophotometric data were used to extract the dissociation constants as well as the changes in molar volume and isothermal compressibility of methyl orange as a function of pressure. The results show that increasing the pressure promotes the deprotonation of methyl orange, with pK values ranging from 3.505 at 1 bar to 3.445 ± 0.002 at 1000 bar. Increasing the pressure also yields small negative changes in the molar volume ranging from –6.9 cm³·mol⁻¹ at 1 bar to −1.7 cm³·mol⁻¹ at 1000 bar. The isothermal compressibility of methyl orange in this pressure range was estimated using the second derivative of second and third order polynomial fits to the constants, and resulted in a constant value of –48.4 × 10⁻⁴ cm³·mol⁻¹·bar⁻¹ in the former case, but increasing values from –107 × 10⁻⁴ cm³·mol⁻¹·bar⁻¹ at 1 bar to 3.43 × 10⁻⁴ cm³·mol⁻¹·bar⁻¹ at 1000 bar in the latter case. Molar absorption coefficients for the protonated and deprotonated species were also shown to be only slightly effected by pressure changes and can be used to accurately predict the absorption spectra of methyl orange as a function of pressure.     

回收灯用钨丝在H2O2催化氧化环己酮合成己二酸中的应用

以回收灯用钨丝为催化剂前驱物,30％H2O2为氧源,催化氧化环己酮合成了己二酸,反应体系中无须使用有机溶剂、酸性助剂和相转移剂。 IR和TG分析表明,钨丝与H2O2反应生成的新生态过氧钨酸是催化活性成分,合成己二酸后转化为钨酸。 钨丝为催化剂前驱物合成己二酸适宜反应条件为：100 mmol环己酮,50 mL 30%H2O2,钨丝的摩尔用量为环己酮摩尔数的1.5%,回流反应6 h,己二酸收率63.7%。 比相同反应条件下用钨酸和WO3为催化剂的收率高10%~18%。     

Utilization of Solid Acid SO42−/TiO2 as Catalyst to the Three‐Component Mannich Reaction at Ambient Temperature

The three‐component Mannich reaction of among dimethyl malonate, aromatic primary amine, and aromatic aldehyde was made successfully in the presence of solid acidic catalyst SO₄²⁻/TiO₂, with excellent catalytic activity, as compared to SO₄²⁻/γ‐Al₂O₃ and SO₄²⁻/ZnO. To the best of our knowledge, SO₄²⁻/TiO₂ prepared at varied calcination temperatures can perform different intensities of Lewis and Brønsted acidities. Because of this point, under the optimum conditions, the effect of SO₄²⁻/TiO₂ (prepared at 200°C) was much more than that of SO₄²⁻/TiO₂ (prepared at 300°C or 400°C) in the three‐component Mannich reaction. In observing ionization activation mode of the three‐component Mannich reaction, it disclosed that the plausible mechanism possibly undergoes formation of aldimines and transformation of aldimines into β‐amino esters by applying solid acidic catalyst SO₄²⁻/M_xO_y.     

Chemical Oxidation of LiFePO<Subscript>4</Subscript> in Aqueous Medium as a Method for Studying Kinetics of Delithiation

The kinetics of LiFePO₄ oxidation by hydrogen peroxide in aqueous alkaline medium is studied with the use of potentiometric determination of lithium concentration in solution during delithiation. It is demonstrated that the lithium transfer through the reaction-product layer is controlled by diffusion. The activation energy and the diffusion coefficient of the species transferred in the solid phase during the chemical reaction of oxidative delithiation are determined and the parameters of this processes are analyzed.     

室温离子液体作溶剂顶空气-质联用测定药物中溶剂残留

基于室温离子液体无蒸汽压、良好溶解性和分散性的特点,用室温离子液体[bm im][PF6]作溶剂顶空气-质联用测定非那雄胺中二氯甲烷、三氯甲烷及二氧六环的残留量,优化了顶空气-质联用分析条件。二氯甲烷、三氯甲烷及二氧六环的检出限分别为0.2、0.02和0.50 ng,线性相关系数大于0.99;相对标准偏差(RSD)0.39%~4.60%;回收率为90.5%~111.9%。室温离子液体作为顶空溶剂的灵敏度有所提高。     

Self‐Supported Chiral Titanium Cluster (SCTC) as a Robust Catalyst for the Asymmetric Cyanation of Imines under Batch and Continuous Flow at Room Temperature

A robust heterogeneous self‐supported chiral titanium cluster (SCTC) catalyst and its application in the enantioselective imine‐cyanation/Strecker reaction is described under batch and continuous processes. One of the major hurdles in the asymmetric Strecker reaction is the lack of availability of efficient and reusable heterogeneous catalysts that work at room temperature. We exploited the readily hydrolyzable nature of titanium alkoxide to synthesize a self‐supported chiral titanium cluster (SCTC) catalyst by the controlled hydrolysis of a preformed chiral titanium‐alkoxide complex. The isolated SCTC catalysts were remarkably stable and showed up to 98 % enantioselectivity (ee) with complete conversion of the imine within 2 h for a wide variety of imines at room temperature. The heterogeneous catalysts were recyclable more than 10 times without any loss in activity or selectivity. The robustness, high performance, and recyclability of the catalyst enabled it to be used in a packed‐bed reactor to carry out the cyanation under continuous flow. Up to 97 % ee and quantitative conversion with a throughput of 45 mg h^?1 were achieved under optimized flow conditions at room temperature in the case of benzhydryl imine. Furthermore, a three‐component Strecker reaction was performed under continuous flow by using the corresponding aldehydes and amines instead of the preformed imines. A good product distribution was obtained for the formation of amino nitriles with ee values of up to 98 %. Synthetically useful ee values were also obtained for challenging α‐branched aliphatic aldehyde by using the three‐component continuous Strecker reaction.