Unique chemoselective Mukaiyama aldol reaction of silyl enol diazoacetate with aldehydes and acetals catalyzed by MgI2 etherate

Functionalized diazo acetoacetates are prepared by an efficient Mukaiyama aldol reaction between 3-TBSO-2-diazo-3-butenoate with aldehydes and acetals under mild reaction conditions. A variety of substituted aldehydes and the corresponding acetals are both accessible in good to excellent yields through this methodology. MgI₂ etherate (MgI₂·(OEt₂)_n) is the preferred catalyst and, the addition proceeds without decomposition of the diazo moiety. In addition, this MgI₂·(OEt₂)_n-catalyzed Mukaiyama aldol reaction shows unique chemoselectivity towards aldehydes and acetals.     

Structural studies of organometallic compounds in solution: I. Magnesium iodide in diethyl ether and tetrahydrofuran

The structure of 2.8 M MgI₂ in diethyl ether solution and that of 1.7 M MgI₂ in tetrahydrofuran solution have been determined by large angle X-ray scattering measurements. The measurement on the diethyl ether solution was performed at 44°C, on a phase crystallizing at approximately 30°C. In diethyl ether a dimeric structure is found, arranged in a square-planar fashion. The bond lengths are: MgI 2.652(2), II (diagonal) 3.75(2) and II (linear) 5.30 Å. Three diethyl ether molecules are probably coordinated to each magnesium to complete an octahedral arrangement. In tetrahydrofuran the ion MgI⁺ from a dissociated complex predominates. In the MgI₂ complex a tetrahedral arrangement is found. In both the MgI⁺ and MgI₂ complexes the MgI distance is 2.56(2) Å. In the MgI₂ complex the II distance is 4.44(4) Å. In both solutions the MgO and MgC distances were kept fixed at 2.10 and 3.48 Å, respectively. The solubility of MgI₂ in diethyl ether has been shown to be strongly dependent on the water content of the ether; 0.2 M was the highest concentration obtained in anhydrous diethyl ether.     

One-pot Mukaiyama–Mannich reaction of aldehydes,amines and silyl enol diazoacetate catalyzed by MgI2 etherate

Abstract

Three-component Mukaiyama–Mannich reaction of aldehydes, amines, and silyl enol diazoacetoacetate was efficiently carried out to afford δ-amino substituted-α-diazoacetoacetate derivatives catalyzed by 5?mol% of MgI₂ etherate (MgI₂?(OEt₂)_n) under mild and neutral reaction conditions in good to excellent yields.     

Highly efficient and chemoselective direct aldol reaction of acyldiazomethane with aldehydes promoted by MgI2 etherate

College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310032, China MgI₂(Et₂O)_n promoted aldol condensation of various aldehydes with acyldiazomethane was described in the presence of DIPEA in good to excellent yields under mild conditions with high chemoselectivity.     

Highly chemoselective and efficient Strecker reaction of aldehydes with TMSCN catalyzed by MgI2 etherate under solvent-free conditions

Abstract

Strecker reaction of various substituted aromatic aldehydes, heteroaromatic aldehydes, aliphatic aldehydes and α,β-unsaturated aldehydes with trimethylsilyl cyanide (TMSCN) was realized in the presence of 5?mol % of MgI₂ etherate in a mild, efficient and highly chemoselective manner under solvent-free conditions.     

Interaction Between Two Similar Plane Parallel Double Layers for (NH4)2Fe(SO4)2 or (NH4)2Cu(SO4)2 Type Complex Salt Electrolytes at Positive Surface Potential

Interaction energies between two similar plane parallel double layers for (NH₄)₂Fe(SO₄)₂ or (NH₄)₂Cu(SO₄)₂ type complex salt electrolytes at positive surface potential were expanded in a power series and accurate numeral results were given for 0.1 ≤ y _e  < y ₀ ≤ 20. The general expressions were given for the interaction energies of A _ν +B _ν′ +C_ν? type complex salt electrolytes at y > 0. The interaction energies for simple salts NaCl, CaCl₂, Na₂SO₄, FeCl₃, Na₃PO₄, Mg₃(PO₄)₂, Al₂(SO₄)₃, and complex salts (NH₄)₂Fe(SO₄)₂ or (NH₄)₂Cu(SO₄)₂ at y ₀ = 1 were compared. There was hardly difference between these simple salts and this complex salt for the interaction energies. The interaction energy for complex salt (NH₄)₂Fe(SO₄)₂ was close to that for simple salt Na₃PO₄.

Supplemental files are available for this article. Go to the publisher's online edition of the Journal of Dispersion Science and Technology to view the free supplemental file.     

Application of response surface methodology for optimization of the stability of asphaltene particles in crude oil by TiO2/SiO2 nanofluids under static and dynamic conditions

In this work, the onset of asphaltene flocculation for an Iranian crude oil by titration of samples with heptane in the presence and absence of the TiO₂/SiO₂ nanofluids was obtained by Near-IR spectroscopy. Nanoparticles and nanocomposites were characterized by BET, FESEM, EDX, XRD, and XRF analysis. Modeling and optimization of inhibition of asphaltene flocculation process by TiO₂/SiO₂ nanofluids were conducted by response surface methodology (RSM). Under optimum conditions (nanocomposite composition = 0.04 wt% (80%TiO₂:20%SiO₂), salinity = 4.01 wt%, and pH = 3.42), the onset point increased. For nanofluids stability analysis, the optimum nanofluid was compared with the two other nanofluids (SiO₂ and TiO₂) by visual observation method. The results indicated that high stability and surface area of the 80%TiO₂ nanocomposites increase asphaltene adsorption on the particles surface that subsequently increases the onset point. In addition, the optimum nanofluid performance on the carbonate rocks was evaluated by contact angle and core flooding experiments. The 80% TiO₂ nanofluid changed the wettability of carbonate rocks from strongly oil-wet to strongly water-wet condition and also decreased the residual oil saturation and enhanced the oil recovery with an increase in the recovery factor of about 15%.     

Absorption,desorption and interaction of SO2 with the binary system tetraethylene glycol + dimethyl sulfoxide

The gas-liquid equilibrium (GLE) data were determined for the mixture SO₂ + N₂ in the binary system of tetraethylene glycol (TeEG) + dimethyl sulfoxide (DMSO) at T = 298.15–313.15 K and p = 123.15 kPa with the SO₂ partial pressures of 0.4–150 Pa. From GLE data, Henry’s law constants (HLCs) were obtained. When the SO₂ concentration in the gas phase was designed at y_SO2 = 500 ppmv, the SO₂ solubility in the binary system is located in a minimum of 9.36 mol m^?3 in TeEG and a maximum of 80.34 mol m^?3 in DMSO. The SO₂ absorption process was reversible from the five absorption–desorption cycles, and the solvents could repeat utilisation without obvious loss of absorption capacity and the homologous SO₂ desorption efficiency was nearby 98.7%. Furthermore, the spectral consequences illustrated that H-bonding was formed among TeEG, DMSO and SO₂.     

Hierarchically Structure SnO2/ZnO Nanocomposites: Preparation,Growth Mechanism and Gas Sensing Property

SnO₂/ZnO nanocomposite was synthesized from mixed ethanol and water systems and the ethanol-sensing properties of sensors based on SnO₂/ZnO were investigated. The structure and morphology of the products was characterized by x-ray diffraction (XRD) and a field emission scanning electron microscope (FE-SEM). The results showed that the diameter of the liked pine needle SnO₂ was about 40 nm with a length about 300 nm, which are uniformly dispersed on the surface of the ZnO nanosheets. The growth process of the SnO₂/ZnO nanocomposite was discussed. The results of gas sensing properties of SnO₂/ZnO nanocomposite sensor showed high and quick response to ethanol vapor at 5.0 v. This sensor showed the advantages of high selectivity, strong stability, and prompt response/recovery characteristics in detecting ethanol vapor at 5.0 v.     

Interaction between Two Similar Plane Parallel Double Layers for Al2(SO4)3 Type Asymmetric Electrolytes at Positive Surface Potential

The interaction between two similar plane double-layers for Al₂(SO₄)₃ type asymmetric electrolytes was investigated with the aid of λ parameter method. The interaction energies for the system at positive surface potential were expanded in the power series at low and high potential, respectively. The high potential formula can be applied to 0.2 ≤ y_e  < y ₀ ≤ 20. This almost covers with the bounds of all potential, and that the calculative method is relative simple. The accurate numeral results and V′?ξ_d curves were given for y ₀ ≤ 20. When y ₀ ≥ 5, V′ hardly change with y ₀. The interaction energies between two similar plane parallel double layers for the different type electrolytes at y ₀ = 1 were compared. The present results are also fit for Mg₃(PO₄)₂ type electrolytes at negative surface potential.     

Unique chemoselective Clauson-Kass reaction of substituted aniline catalyzed by MgI2 etherate

Clauson-Kass reaction of various substituted aniline, primary aryl amide, and sufonyl amide with 2,5-dimethoxytetrahydrofuran was realized in the presence of 10 mol % of MgI₂ etherate in a mild, efficient, and highly chemoselective manner. Iodide counterion and solvents (i.e., MeCN) played the critical roles for the unique reactivity of this catalytic system.     

NMR and kinetic studies of the interactions of [Au(cis-DACH)Cl2]Cl and [Au(cis-DACH)2]Cl3 with potassium cyanide in aqueous solution

The interactions of [Au(cis-DACH)Cl₂]Cl and [Au(cis-DACH)₂]Cl₃ [where cis-DACH is cis-1,2-diaminocyclohexane] with enriched KCN were carried out in CD₃OD and D₂O, respectively. The reaction pathways of these complexes were studied by ¹H, ¹³C, ¹⁵N NMR, UV spectrophotometry, and electrochemistry. The kinetic data for the reaction of cyanide with [Au(cis-DACH)₂]Cl₃ are k = 18 M^?1s^?1, ?H^≠ = 11 kJ M^?1, ?S^≠ = ?185 JK^?1 M^?1, and E_a = 13 kJ M^?1 with square wave voltammetric (SWV) peak +1.35 V, whereas the kinetic data for the reaction of cyanide ion with [Au(cis-DACH)Cl₂]Cl are k = 148 M^?1s^?1, ?H^≠ = 39 kJM^?1, ?S^≠ = ?80 JK^-1 M^?1, and E_a = 42 kJM^?1 along with SWV peak +0.82 V, indicating much higher reactivity of [Au(cis-DACH)Cl₂]Cl toward cyanide than [Au(cis-DACH)₂]Cl₃. The interaction of these complexes with potassium cyanide resulted in an unstable [Au(¹³CN)₄]^? species which readily underwent reductive elimination reaction to generate [Au(¹³CN)₂]^? and cyanogen.     

A rapid microwave-assisted acid extraction method based on the use of diluted HNO3-H2O2 followed by ICP-MS analysis for simultaneous determination of trace elements in coal samples

Before coal processing such as pyrolysis, liquefaction, gasification and combustion, it is very crucial to monitor the trace element concentration levels as that determines the coal quality. Therefore, the current study describes the development of microwave-assisted acid extraction (MW-AAE) method for extraction of 15 trace elements in coal samples prior to their determination using inductively coupled plasma-mass spectrometry. Diluted HNO₃-H₂O₂ was used in order to reduce reagents amount used, eliminate matrix interferences caused by concentrated acids and to decrease waste produced in analytical laboratories. The optimisation of the proposed extraction method was carried out by using a full factorial design (2⁴) involving four factors; that is, temperature, extraction time, HNO₃ and H₂O₂ concentrations. The optimum conditions for the MW-AAE procedure were found to be 200°C, 5 min, 5 mol L^?1 and 2 mol L^?1 for temperature, extraction time, HNO₃ and H₂O₂ concentrations, respectively. Under optimum conditions, the accuracy of the MW-AAE method was examined by analysing three coal certified reference materials (SARM 18, 19 and 20) and recoveries of 80–115% were achieved for V, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Sr, Zr, Cs, Ba, Pb and U, except for Ti (10–25%) and Hf (27–70%). In addition, the precision of the proposed method, expressed in terms of relative standard deviation (SD) (n = 15), was within the accepted range (≤3.5%). The method detection limits of 0.001–0.57 µg g^?1 for all trace elements under the investigation were similar to the literature reported work, except for Ti (4.00 µg g^?1).     

Efficient and mild Strecker-type reaction of nitrones catalyzed by MgI2 etherate

An efficient Strecker-type reaction of nitrones with trimethylsilyl cyanide (TMSCN) catalyzed by MgI₂ etherate has been achieved in a short time under mild condition. The condensations of aromatic nitrones, heterocyclic nitrones, and aliphatic nitrones with TMSCN are performed in good to excellent yields. Further dehydration of α-cyanohydroxylamine smoothly produced the α-imine nitrile in good yields by hydrolysis with the treatment of 2.0?mol/L HCl in methanol.     

Crystal chemistry of MX · MgX2 · 6H2O type compounds

The following MX · MgX₂ · 6H₂O compounds (double salt hexahydrates) were synthesized by variation of the M⁺ and X^? ions: CsCl · MgCl₂ · 6 H₂O, Li(H₂O)Cl · MgCl₂ · 6H₂O, NH₄Br · MgBr₂ · 6 H₂O, RbBr · MgBr₂ · 6 H₂O, CsBr. MgBr₂ · 6 H₂O, KI · MgI₂ · 6 H₂O, NH₄I. Mgl₂ · 6 H₂O and RbI · MgI₂ · 6H₂O. By X-ray analysis of powder samples the lattice parameters and the space group were determined. On the basis of the results thus obtained, an identification with structural types was carried out. In accordance with the findings, the structure is made up of (M⁺)X₆^?octahedra which are linked into perovskite type units by sharing vertices. Their interstices are occupied by the Mg(H₂O)₆²⁺ octahedra. A “tolerance factor” t which has been calculated on the basis of the proportion of radii and which attains values between 1.045 and 1.061 is a criterion for the upper limit of the area of existence of this structure. Carnallite has a higher to value and, therefore, a different structure.     

Aldol Condensations Catalyzed by PEG400 and Anhydrous K2CO3 Without Solvent

Abstract

Aldol condensations of aromatic aldehydes with ketones under solvent‐free conditions to synthesize α,β‐unsaturated ketones in good to excellent yields using PEG400 and powdered anhydrous K₂CO₃ as catalysts at 90 °C and 120 °C are described.     

Label-Free Detection of DNA Hybridization Based on MnO2 Nanoparticles

Abstract

Nano-MnO₂/chitosan composite film modified glassy carbon electrode (MnO₂/CHIT/GCE) was fabricated and a DNA probe was immobilized on the electrode surface. The immobilization and hybridization events of DNA were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS was applied to the label-free detection of the target DNA. The human immunodeficiency virus (HIV) gene fragment was successfully detected by this DNA electrochemical sensor. The dynamic detection range was from 2.0 × 10^?11 to 2.0 × 10^?6 mol/L, with a detection limit of 1.0 × 10^?12 mol/L.     

Environmentally Friendly and Highly Efficient Co(OAc)2-Catalyzed Aerobic Oxidation to Access 2,6-Di-Electron-Donating Group Substituted 4-Hydroxybenzaldehydes

A highly efficient and green aerobic oxidation has been developed for selectively preparing a series of valuable 2,6-dialkyl-, dialkoxyl-, and alkoxylalkyl-substituted 4-hydroxybenzaldehydes from corresponding 4-cresols in good to excellent yields, using a catalytic system of Co(OAc)₂ · 4H₂O (1.0 mol%)–NaOH (1.0 equiv)–O₂ (1.0 atm) in aqueous ethylene glycol (EG/H₂O = 20/1, v/v) at 50 °C. Furthermore, a plausible mechanism was proposed for the direct oxyfunctionalization of the aromatic methyl group into the aldehyde group.     

An efficient hydrocyanation of α, β-unsaturated diesters with TMSCN catalyzed by MgI2 etherate

Abstract

A mild, efficient and highly regioselective addition of trimethylsilyl cyanide (TMSCN) to α,β-unsaturated diesters has been achieved by using MgI₂ etherate as catalyst under solvent-free conditions. This protocol provides the corresponding β-cyano esters in high yields.     

Sensitive electrochemical detection of bisphenol A with chitosan and urchinlike MnO2 microsphere modified carbon ionic liquid electrode

In this article, a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid N-hexylpyridinium hexafluorophosphate as the binder and the modifier. Then urchinlike MnO₂ microsphere and chitosan (CTS) was further casted on the CILE surface step-by-step to get a modified electrode that was denoted as CTS/MnO₂/CILE. Cyclic voltammetric studies indicated that bisphenol A (BPA) exhibited a well-defined oxidation peak at 0.486 V in 22.83 g L^?1 pH 8.0 Britton?Robinson buffer solution, which was attributed to the electro-oxidation of BPA on the modified electrode. The presence of urchinlike MnO₂ microsphere on the electrode surface could increase the oxidation peak current (I_pa) greatly, which may be due to the larger surface area that could adsorb more BPA on the electrode surface. Electrochemical parameters of BPA on the modified electrode were calculated with the electron transfer coefficient (α) as 0.66 and the apparent heterogeneous electron transfer rate constant (ks) as 0.50 s^?1. Under the optimal conditions, a linear relationship between the I_pa of BPA and its concentration was obtained in the range from 1.37 × 10^–1 mg L^?1 to 182.6 mg L^?1 with the detection limit as 7.31 × 10^–3 mg L^?1 (3σ). The CTS/MnO₂/CILE was applied to the detection of BPA content in different kinds of samples with satisfactory results.