环状碳酸酯低聚物的合成及其开环聚合的研究

环状碳酸酯低聚物的合成及其开环聚合的研究陈雨萍魏玮李革（中国科学院化学研究所工程塑料国家重点实验室北京１０００８０）关键词环状碳酸酯低聚物，聚碳酸酯，开环聚合环状单体的开环聚合在合成高聚物方面具有突出的优点，即在聚合过程中没有副产物、热效应低、聚合...     

Synthesis of siloxane stationary phases for capillary gas chromatography and supercritical fluid chromatography

A comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, ¹H NMR, ²⁹Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free-radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV-1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography.     

Voltammetric behaviour and determination of moxifloxacin in pharmaceutical products and human plasma

The oxidative behaviour of moxifloxacin was studied at a glassy carbon electrode in different buffer systems using cyclic, differential pulse, and Osteryoung square-wave voltammetry. The oxidation process was shown to be irreversible over the entire pH range studied (2.0–10.0) and was diffusion-controlled. The methods were performed in Britton–Robinson buffer and the corresponding calibration graphs were constructed and statistical data were evaluated. When the proposed methods were applied at pH 6.0 linearity was achieved from 4.4×10^–7 to 1.0×10^–5 mol L^–1. Applicability to tablets and human plasma analysis was illustrated. Furthermore, a high-performance liquid chromatographic method with diode-array detection was developed. A calibration graph was established from 4.0×10^–6 to 5.0×10^–5 mol L^–1 moxifloxacin. The described methods were successfully employed with high precision and accuracy for estimation of the total drug content of human plasma and for pharmaceutical dosage forms of moxifloxacin.     

Interactions of aliphatic β-amino-β-trifluoromethylvinyl ketones with ethylenediamine

The reactions of aliphatic β-amino-β-trifluoromethylvinyl ketones with an excess of ethylenediamine at room temperature afforded the corresponding 2,3-dihydro-1H-1,4-diazepines or substituted 2-acetonyl-2-trifluoromethylimidazolidines (the latter were obtained when the approach to the carbonyl group was sterically hindered). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2305–2308, November, 1998.     

Formation of Tertiary 3-Nitro Allylic Alcohol by Condensation of 2-Chloroiso- butyrophenone with Nitromethanide Anion: Estimation of Gibbs Free Enthalpies of Reaction in Solution for the Reaction Mechanism [1]

Summary. The reaction of 2-chloroisobutyrophenones and nitromethanide anion gives stereoselectively (E)-3-nitro allylic alcohols. The Gibbs free enthalpies of reaction in DMSO for carbanion addition, epoxide formation, and rearrangement to 3-nitro allylic alcohol, as elementary steps for the reaction, were estimated from corresponding neutral gas reactions and using a thermodynamical approach to the transfer of gaseous compounds to DMSO. A criterion for assigning the sign of affinity of liquid compounds to DMSO was developed on the basis of the Gibbs enthalpies of liquefaction. The information obtained on reaction rate and thermodynamic viability of the steps indicates that carbanion addition is the rate-determining step.In memory of Prof. Dr. M. Ballester, deceased on April 6, 2005     

LiBF4: a mild and novel reagent for the OH insertion reactions of α-diazoketones

Lithium tetrafluoroborate (10 mol%) is found to catalyze efficiently the OH insertion reactions of α-diazoketones with various alcohols including benzylic, allylic, propargylic and cyclopropyl carbinols to produce the corresponding α-alkoxy ketones in excellent yields with high selectivity. A solution of 10 mol% of LiBF₄ in acetonitrile provides a convenient reaction medium to carry out the OH insertion reactions under mild and neutral conditions.     

Chemoselective synthesis of multiple epoxy-bridged tetrahydropyranone ring systems

Bis- as well as tris-tetrahydropyranone ring systems were obtained via multiple tandem cyclization-1,3-dipolar cycloaddition reactions of α-diazo ketones with ketone as well as aldehyde functional groups in a chemoselective manner.     

Electrochemical Determination of Ascorbic Acid in Room Temperature Ionic Liquid BPPF6 Modified Carbon Paste Electrode

A room temperature ionic liquid N‐butylpyridinium hexafluorophosphate (BPPF₆) was used as a binder to make an ionic liquid modified carbon paste electrode (IL‐CPE), which showed good characteristics such as simple preparation procedure, fast electrochemical response and good conductivity. The electrochemical oxidation of ascorbic acid (AA) on the new IL‐CPE was carefully studied. The oxidation peak potential of AA on the IL‐CPE appeared at 109 mV (vs. SCE), which was about 338 mV decrease of the overpotential compared to that obtained on the traditional carbon paste electrode (CPE) and the oxidation peak current was increased for about four times. The electrochemical parameters of AA on the IL‐CPE were calculated with the charge transfer coefficient (α) and the electrode reaction rate constant (k_s) as 0.87 and 0.800 s^?1, respectively. Based on the relationship of the oxidation peak current and the concentration of AA a sensitive analytical method was established with cyclic voltammetry. The linear range for AA determination was in the range from 1.0×10^?5 to 3.0×10^?3 mol/L with the linear regression equation as I_p (μA)=?2.52–0.064C (μmol/L) (n=13, γ=0.9942) and the detection limit was calculated as 8.0×10^?6 mol/L (3σ). The proposed method was free of the interferences of coexisting substances such as dopamine (DA) and amino acids etc., and successfully applied to the vitamin C tablets determination.     

Single‐Wall Carbon Nanotube Paste Electrodes: a Comparison with Carbon Paste,Platinum and Glassy Carbon Electrodes via Cyclic Voltammetric Data

A new carbon electrode material, obtained by mixing single wall carbon nanotubes (SWNTs) with a mineral oil binder is studied. Carbon nanotube pastes show the special properties of carbon nanotubes combined with the various advantages of composite electrodes such as a very low capacitance (background current) and the possibility of an easy preparation, modification and renewal. A better knowledge of the characteristics of electrode reactions at carbon nanotube paste (CNTP) electrodes was obtained studying the electron transfer rates of various redox couples under different pretreatment conditions. A critical comparison with carbon paste (CP), platinum (Pt) and glassy carbon (GC) electrodes was also carried out. Capacitance and resistance values were also calculated for all electrodes investigated. Both untreated and treated CNTP electrodes showed a low resistance while the capacitance was markedly reduced with CNTP electrodes previously treated with concentrated nitric acid. An electrochemical pretreatment on CNTP electrodes was developed which showed an excellent result towards two‐electron quinonic structure species. After this treatment the heterogeneous standard rate constants for p‐methylaminophenol sulfate (MAP) and dopamine resulted to be significantly higher (2.1×10^?2 cm/s and 2.0×10^?2 cm/s, respectively) than those obtained with the other electrodes studied. Reproducibility, stability and storage characteristics of CNTP electrodes were also reported.     

A novel deacylation during the amination of trifluoromethyl β-dicarbonyl compounds

Starting from trifluoromethyl β-dicarbonyl compounds, a rare loss of CF₃CO was observed in the amination reactions performed under heterogeneous conditions using NsONHCO₂Et as the aminating agent and CaO or NaH as the base, while corresponding nonfluorinated β-dicarbonyl compounds under analogous conditions give non deacylated aminated compounds. This reaction can facilitate a direct synthesis of N-substituted α-amino esters or α-amino ketones.