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1.
The effect of organic modifier concentration on retention and selectivity of two piperazine diastereomers in a typical n-octadecyl-bonded silica (ODS) column was investigated at pH 6.4 and pH 3.0 using phosphate-buffered acetonitrile (MeCN/H2O) and methanol (MeOH/H2O) mobile phases. The results show the logarithmic retention factors decrease with increasing organic concentration in a less rectilinear fashion in the MeCN/H2O system than in the MeOH/H2O system at high organic concentrations at both pHs. At pH 6.4, the MeOH/H2O system provided significantly higher diastereomer selectivity than the MeCN/H2O system, which can be ascribed to the hydrogen bonding interaction of methanol (as a hydrogen donor) with the piperazine amine moiety of the solute (as a hydrogen acceptor). At pH 3.0, both mobile phases provided high selectivity, in which both acetonitrile and methanol acted as hydrogen acceptors, while the protonated amine acted as the hydrogen donor. The effect of temperature on retention and selectivity was also studied in the two mobile phase systems at both pHs. It was found that at pH 6.4 the retention and selectivity were enthalpically driven in the MeOH/H2O system, while entropically driven in the MeCN/H2O system. However, the retention was entropically driven and the selectivity enthalpically driven in both systems at pH 3.0. Locally preferential solvating and hydrogen bonding effects are proposed to explain the anomalous retention and selectivity behaviors.  相似文献   

2.
Hiroto Kaku 《Tetrahedron》2010,66(48):9450-9455
Racemic 2-monosubstituted cycloalkanones were converted to R-isomers when TADDOLs (e.g., 1a, b) were used as host molecules in alkaline aqueous MeOH. The efficiency of this thermodynamically controlled deracemization was strongly influenced by the mixture ratio of the solvent, H2O/MeOH. Based on this finding, an improved method of preparing (R)-2-monosubstituted cycloalkanones with higher optical purity was developed. For example, (R)-2-(4-methylbenzyl)cyclohexanone (5) was obtained in 85% yield with 98% ee, when a 1:1 mixture of H2O/MeOH was used as the solvent in the presence of 1a.  相似文献   

3.
Catalytic hydrodechlorination of chlorobenzene (CB) was carried out in the liquid phase in a mixture of methanol/water (MeOH/H2O) at 30°C and 2kg/cm2 pressure. The reaction orders with respect to CB and H2 pressure were one and zero, respectively. Addition of NH4OH in the reaction produces a decrease in the activity (TOF). Solvent effect shows the following order of activity: H2O>MeOH/H2O>EtOH/H2O>MeOH.  相似文献   

4.
P. L. Zhu 《Chromatographia》1985,20(7):425-433
Summary In RPLC the dead volume can be defined as the difference between the maximum column hold-up volume and the volume of the adsorbed phase. The composition of the adsorbed phase depends on the composition of the mobile phase and therefore, the dead volume also varies with it. In this work, the alkyl bonded phase acetonitrile (ACN)-water mobile phase system is investigated. In the system, deuterated water (D2O) and deuterated acetonitrile (D-ACN) are retained due to the isotopic dilution effect. By means of D2O and D-ACN, the absolute adsorption isotherm of the organic modifier ACN is measured. Based on the isotherm, the chromatographic behaviour of ACN, D-ACN and D2O, the variation of the dead volume with the composition of the mobile phase, and the approach to determine the maximum column hold-up volumn are explained. In addition, the various approaches to determine the dead volume are compared and the recommendations are given for the case of common unbuffered binary systems (MeOH/H2O, THF/H2O and ACN/H2O).  相似文献   

5.
Racemic α-monosubstituted cyclopentanones were converted to optically active forms by a thermodynamically controlled deracemization using TADDOL-type host molecule 1 in alkaline aqueous MeOH. The efficiency of this conversion was strongly influenced by the ratio of the solvent components (H2O/MeOH) and the functionality and architecture of the α-side-chain on the cyclopentanones. For example, (R)-2-(2-benzyloxyethyl)cyclopentanone (9) was obtained in 89% yield with 97% ee using a 7:3 mixture of H2O/MeOH as the solvent. X-ray analytical studies were also carried out and disclosed the nature of this chiral molecular recognition process in the solid phase.  相似文献   

6.
Styrene is hydrogenated to ethylbenzene and hydroformylated to 2- and 3- phenylpropanol by CO and H2O in the presence of a Fe3(CO)12 + Et3N + NaOH catalyst system at 140°C and 100 bar in H2O/MeOH. The product composition depends strongly on the H2O/MeOH ratio (A); alcohol formation is favoured at A  3/1 and ethylbenzene formation at A  1/2. 1,3-Diphenylbutane is formed as by-product.  相似文献   

7.
The stoichiometric reaction of NiCl2·6H2O with sodium 4-imidazoleacetate Na(IA) in absolute MeOH yields blue crystals of Ni(IA)2·4H2O·2MeOH (1). This product decomposes rapidly in air, losing two MeOH molecules and producing Ni(IA)2·4H2O (2). Compound (1) when left in the mother liquor, slowly recrystallizes forming [Ni(IA)2(MeOH)2] (3), which is stable in air and suitable for single crystal X-ray diffraction studies. These crystals consist of slightly distorted octahedral coordination units in which the carboxylic oxygen, imidazole N3 nitrogen and the MeOH oxygen atoms act as coordination centers. The i.r. features, due to MeOH molecules, were employed to characterize the compounds studied. The reflectance spectrum of (3) was interpreted on the basis of octahedral and tetragonal symmetry of the NiO4N2 chromophore.  相似文献   

8.
空气污染各组分对甲烷超声速燃烧性能的影响   总被引:3,自引:0,他引:3  
侯凌云  杨缙  马雪松  刘巍 《物理化学学报》2010,26(12):3150-3156
在与甲烷详细化学反应机理对比验证基础上,采用18组分24步简化反应机理模拟甲烷超声速燃烧过程,从化学动力学和热力学角度用数值方法研究了乙醇燃烧加热空气中的七种主要污染组分(H2O,CO2,O,OH,CO,H,H2)对甲烷超声速燃烧性能的影响.分析结果表明:在一定条件下,进口空气中污染组分H2O的增加造成平均比热容增加,总温降低,并作为第三体抑制甲烷的燃烧过程,使超燃室的性能下降;CO2因大分子量特性使燃气平均分子量增大,降低超燃室做功能力,H2O和CO2两组分对甲烷超燃性能都起消极作用;污染组分自由基H、O、OH和燃烧中间产物CO、H2使燃烧室燃烧效率上升,对甲烷超燃性能起积极作用.  相似文献   

9.
The kinetics of oxidation of benzhydrol and its p-substituted derivatives (YBH, where Y=H, Cl, Br, NO2, CH3, and OCH3) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT), catalyzed by ruthenium(III) chloride, in the presence of hydrochloric acid in 30% (v/v) MeOH medium has been studied at 35°C. The reaction rate shows a first-order dependence on [CAT]O and a fractional-order each on [ YBH]O, [Ru(III)], and [H+]. The reaction also has a negative fractional-order (−0.35) behavior in the reduction product of CAT, p-toluenesulfonamide (PTS). The increase in MeOH content of the solvent medium retards the rate. The variation of ionic strength of the medium has negligible effect on the rate. Rate studies in D2O medium show that the solvent isotope effect, k′H2O/k′D2O, is equal to 0.60. Proton inventory studies have been made in H2O(SINGLEBOND)D2O mixtures. The rates correlate satisfactorily with Hammett σ relationship. The LFE relationship plot is biphasic and the reaction constant ρ=−2.3 for electron donating groups and ρ=−0.32 for electron withdrawing groups at 35°C. Activation parameters ΔH, ΔS, and ΔG have been calculated. The parameters, ΔH and ΔS, are linearly related with an isokinetic temperature β=334 K indicating enthalpy as a controlling factor. A mechanism consistent with the observed kinetics has been proposed. © 1997 John Wiley & Sons, Inc.  相似文献   

10.
The influence of the addition of different amounts of MeOH, H2O, and HCOOH on the activity of supported palladium catalyst in the copolymerization of CO with ethylene and the kinetic regularities of this reaction were studied for the first time. The maximum yield of the copolymer is attained when MeOH and H2O or HCOOH and H2O are simultaneously introduced into the reaction medium (toluene). The results obtained are consistent with the concepts about the role of protic agents in the formation of active intermediates and polymer molecules in the copolymerization of CO with ethylene in the presence of the homogeneous catalytic systems.  相似文献   

11.
A mixture of cosolvents is described that significantly improves the solubility of most pharmaceutical compounds. The mixture consists of equal volumes of MeOH, 1,4‐dioxane, and MeCN, thereby containing polar and nonpolar solvents, and is referred to as MDM (from MeOH, dioxane, and MeCN). MDM is mixed with H2O until the required composition is reached. The utility of this system is that it enables analytical measurements to be performed on a wide range of compounds where measurements would be impaired in aqueous solution. We present the physicochemical characteristics of MDM/H2O mixtures (density, dielectric constant, psKw) and the principles of pKa measurement in this solvent/H2O mixture. We also present pKa values in H2O of several drug compounds determined from values measured in MDM/H2O mixtures.  相似文献   

12.
The effect of the concentration of water on the rate of reduction of molecular nitrogen to hydrazine by niobium(iii) hydroxide in alkaline H2O−MeOH and D2O−MeOD mixtures was studied. In both cases, the reaction rate is maximum when [H2O]=4 mol L−1, and the inverse isotopic effect (K D/k H>1) is observed when [H2O]<20 mol L−1. Similar regularity was observed for the reaction of hydrogen elimination. It was found that HD is formed in the H2O−MeOH system in the presence of D2. The conclusion was made that the ratedetermining stage in hydrazine formation is the transfer of a hydride ion to the dinitrogen molecule coordinated to the binuclear NbIII center. A kinetic scheme satisfactorily explaining the effect of the concentration of water ([H2O]=1.5−49.0 mol L−1) on the reaction rate constant was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1600–1604, September, 1997.  相似文献   

13.
The dynamic viscoelastic behavior of a concentrated solution of silk fibroin dissolved in the “MU” solvent is measured. The dynamic viscosity η′ and dynamic elasticity G′ increase with increasing concentration of silk fibroin at constant frequency; however, the increasing frequency decreases η′ and G′ at a constant concentration of silk fibroin. When the mixing ratio of C2H5OH/H2O in the “MU” solvent is increased at a constant concentration of LiBr·H2O, η′ and G′ sharply increase at constant frequency. If the LiBr·H2O concentration is varied in the “MU” solvents whose ratio of C2H5OH/H2O is kept constant at 100 : 0, both η′ and G′ are greater for LiBr·H2O concentrations of 50% by weight compared to concentrations of 40% by weight. The dependence of η′ on the temperature of the solution can be predicted by Andrade's viscosity equation. Spinnability improves when the SF concentration is increased. © John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1955–1959, 1997  相似文献   

14.
Blooms of Ostreopsis spp. have been recently reported along the Mediterranean coasts of Spain, France, Italy, and Greece posing serious risks to human health. Occurrence of Ostreopsis spp. may result in palytoxin contamination of seafood and, in order to prevent sanitary risks, the need exists to develop efficient extraction procedures to be coupled to rapid and sensitive monitoring methods of palytoxin-like compounds in seafood. In the present study, the best conditions for both extraction of palytoxin from seafood and palytoxin quantification by using liquid chromatography tandem mass spectrometry (LC-MS/MS) were investigated. Three seafood matrices (mussels, sea-urchins, and anchovies) were selected and five different extraction systems were tested, namely: the official protocol for extraction of lipophilic toxins and various aqueous methanol or acetonitrile solutions (MeOH/H2O 1:1, MeOH/H2O 8:2, MeCN/H2O 8:2 and MeOH 100%). Extraction with MeOH/H2O 8:2 provided the best results in terms of accuracy and matrix interference on LC-MS/MS detection of palytoxin. Accuracy and intra-day reproducibility (n = 3) were evaluated for all the selected matrices but only for mussels at three spiking concentration levels, including the provisional limit proposed by the Community Reference Laboratory for marine biotoxins (250 μg kg−1). Limits of quantitation of palytoxin in mussels, sea-urchins and anchovies tissues were calculated using matrix-matched standards; taking into account extraction efficiency of MeOH/H2O 8:2, they resulted to be 228, 343, and 500 μg kg−1, respectively.  相似文献   

15.
The electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS) using charged electrospray water droplets realized the atomic and molecular level etching with leaving little damage on the surface. In this work, the binary mixtures of water and alcohols (methanol and 2‐propanol) were examined as the charged electrospray droplets. The increase of desorption efficiency and softer ionization are observed for rhodamine B and bradykinin with higher content of alcohols. The etching rates for SiO2 and polystyrene 35000 were found to be more or less the same for 100% H2O and H2O/MeOH projectiles. However, 60 vol.% 2‐propanol gave much lower etching rates than the water/methanol system for polystyrene 35000. This indicates that there is a marked difference in the energy dissipation processes between methanol and 2‐propanol projectiles for soft‐material target. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

16.
A series of (Y(AcO)3·4H2O—Q—Solv) solutions (Q is monoethanolamine (MEA), diethanolamine (DEA), en, dien; Solv = MeOH, EtOH, PriOH, BuOH) was studied to choose the metal-organic precursor for surface smoothing treatment of metallic tapes by chemical deposition of nanocrystalline yttria films. Based on the results of viscosity, wetting angle, and thermal stability measurements, a solution (Y(AcO)3·4H2O—dien—PriOH) was proposed as a new metal-organic precursor. After chemical deposition of nanocrystalline yttria films about 300 nm thick on a Hastelloy C-276 metallic tape the surface roughness was reduced by a factor of 11 (from 9.0 to 0.8 nm on a surface area of 5×5 μm2).  相似文献   

17.
The thermoreversible phase transition of poly(N‐isopropylacrylamide) randomly labeled with a spin label, 4‐amino‐2,2′,6,6′‐tetramethylpiperidine 1‐oxide (TEMPO), and a fluorescent dye, 4‐(pyren‐1‐yl)butyl (PNIPAM‐Py‐T), in different H2O/MeOH mixtures was studied by turbidimetry, continuous‐wave electron paramagnetic resonance spectroscopy (CW‐EPR), and fluorescence spectroscopy. The macroscopic phase diagram of PNIPAM‐Py‐T in H2O/MeOH measured by turbidimetry was identical to those of poly(N‐isopropylacrylamide) (PNIPAM) and of TEMPO‐labeled PNIPAM (PNIPAM‐T) in H2O/MeOH mixtures. However, distinct differences among the three polymers were detected in their solvent‐dependent EPR and fluorescence‐spectroscopic properties. The EPR spectra were analyzed in terms of the isotropic hyperfine coupling constants, which monitor the variation in environmental polarity of the radical labels occurring for the conformational transitions of the polymer as a function of temperature, as well as the correlation time for reorientation motion, the increase of which is indicative of the increased viscosity of the radical environment and interactions occurring between the radical and other surface groups of the precipitated polymer, if compared to the soluble polymer. The fluorescence of Py in PNIPAM‐Py‐T displayed contributions from isolated excited pyrenes (monomer emission) and from preformed pyrene ground‐state aggregates (excimer emission). The quantum efficiencies of monomer and excimer emission were monitored as a function of solvent composition. By the two experimental approaches, we demonstrate the profound influence of the PNIPAM‐attached pyrene units in increasing the hydrophobicity of the nanodomains formed upon heat‐induced precipitation of PNIPAM‐Py‐T.  相似文献   

18.
The reaction of salicylaldoxime (H2salox) with MnCl2·4H2O and NEt4OH in MeOH affords the trinuclear manganese complex (NEt4)[Mn3O(salox)3(MeOH)2(H2O)2Cl2]·MeOH (1·MeOH). A similar reaction of 1·MeOH was carried out using MnBr2·4H2O to obtain the hexanuclear manganese complex (NEt4)3{NaBr2[Mn3O(salox)3(H2O)4Br2]2} (2). The reaction of 2-hydroxy-4-methoxybenzaldehyde oxime (4-MeO-H2salox) and Mn(ClO4)2·6H2O with 1,2-di(4-pyridyl)ethylene (dpe) in MeOH/DMF mixtures yields the one-dimensional complex {[Mn3O(4-MeOsalox)3(dpe)1.5(DMF)2(H2O)](ClO4)}n (3·DMF·H2O). Complex 1·MeOH shows a typical structure of a [MnIII3O]7+ core, and complex 2 contains a dimer [MnIII3O]7+ core connected by a Na+ ion. Complex 3 has a one-dimensional chain structure constructed from [MnIII3O]7+ units linked by dpe ligands. Magnetic analysis shows that all three complexes exhibit antiferromagnetic interactions between the MnIII ions.  相似文献   

19.
Conductivities of KF and CsF in methanol at 25°C   总被引:1,自引:0,他引:1  
Electrolytic conductivities of KF and CsF in methanol solution have been determined at 25°C. The single ion molar conductivities of the fluoride ion, obtained from the two salts are in excellent agreement and indicate that the F? ion is highly solvated in methanol (MeOH). Combination of the present and literature data for related salts in both water and MeOH indicate that while the primary solvation of ions may be more extensive in H2O there is considerable enhancement of the secondary solvation sheath in MeOH. Recalculation of high precision literature conductivity data using a consistent mathematical approach indicates that ion pair formation constants for simple 1:1 electrolytes in MeOH are 1 or 2 orders of magnitude greater than in H2O. This is shown to be entirely due to the less favorable solvation of ions in MeOH, as the Gibbs energies of transfer of the neutral ion pairs MX from H2O to MeOH are also unfavorable. Calculations also show that ion association in MeOH is strongly influenced by coulombic interactions whereas in H2O short range interactions are generally more important.  相似文献   

20.
The complexes of Tl+, Pb2+ and Cd2+ cations with the macrocyclic ligand, dicyclohexano-18-crown-6\linebreak(DC18C6) were studied in water/methanol (H2+O/MeOH), water/1-propanol (H2+O/1-PrOH), water/acetonitrile (H2+O/AN), water/dimethylformamide (H2+O/DMF), dimethylformamide/acetonitrile (DMF/AN), dimethylformamide/methanol (DMF/MeOH), dimethylformamide/1-propanol (DMF/1-PrOH) and dimethylformamide/nitromethane (DMF/NM) mixed solvents at 22 °C using differential pulse polarography (DPP), square wave polarography and conductometry. In general, the stability of the complexes was found to decrease with increasing concentration of water in aqueous/non-aqueous mixed solvents with an inverse relationship between the stability constants of the complexes and the concentration of DMF in non-aqueous mixed solvents. The results show that the change in stability of DC18C6.Tl+, vs the composition of solvent in DMF/AN and DMF/NM mixed solvents is apparently different from that in DMF/MeOH and DMF/1-PrOH mixed solvents. While the variation of stability constants of the DC18C6.Tl+ and DC18C6.Pb2+ complexes vs the composition of H2+O/AN mixed solvents is monotonic, an anomalous behavior was observed for variations of log Kf vs the composition of H2+O/1-PrOH and H2+O/MeOH mixed solvents. The selectivity order of the DC18C6 ligand for the cations was found to be Pb2+ > Tl+ > Cd2+.  相似文献   

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