电化学方法固定CO2用于2-羟基-2-(4-甲氧基苯基)-丙酸甲酯的合成

在一室型电解池中, 以饱和CO₂的N,N-二甲基甲酰胺(DMF)为溶液, Mg为牺牲阳极, 不锈钢、钛、铜、镍和银为工作电极, 通过电化学方法固定CO₂, 在恒电流电解的条件下研究了对甲氧基苯乙酮的电羧化反应, 得到了重要的有机合成中间体2-羟基-2-(4-甲氧基苯基)-丙酸甲酯. 电羧化产率受支持电解质种类、电极材料、电流密度、电解电量和反应温度等影响. 经过反应条件的优化, 目标产物在恒定电流密度为5.0 mA/cm²的条件下产率达到63%. 同时, 以玻碳电极-Pt丝螺旋电极-Ag/AgI/I^-为三电极体系, 研究了对甲氧基苯乙酮的电化学行为, 根据底物在通入CO₂前后循环伏安图的变化推测了对甲氧基苯乙酮的电羧化反应机理.     

Electrocarboxylation of haloacetophenones at silver electrode

Electrocarboxylation of haloacetophenones 1 has been carried out in an undivided cell equipped with silver cathode and Mg sacrificial anode in N,N-dimethylformamide. The electroreduction behavior of these haloacetophenones at the Ag electrode was investigated using cyclic voltammetry. The electrocatalytic ability of Ag facilitated C–X bond cleavage. Methyl 4-acetylbenzoate 2 was obtained as the principal product, accompanied by acetophenone 3 and methyl 2-hydroxy-2-phenylpropanoate 4. The performances of the process were found to be dependent on synthetic conditions, such as cathode material, supporting electrolyte, electric charge, current density, and temperature. Higher yields were obtained by changing from chloro to bromo to iodo derivatives, and from ortho to para to meta isomers.     

Electrocarboxylation of Anthrone to Anthracene-9-carboxylic Acid in the Presence of CO2

Electrocarboxylation of anthrone in the presence of CO2 to anthrance-9-carboxylic acid directly was carried out. The electroreduction behavior of anthrone was examined by cyclic voltammetry in the absence and presence of CO2. Then the influences of the supporting electrolytes, temperature, electrode material and anthrone concentration on the carboxylation yield were investigated. Under the optimized conditions, anthrancene-9-carboxylic acid was obtained in a good yield(96.1%).     

无负载的纳米银电极：一种用于1-溴乙基苯与 CO2电羧化的高效催化剂

CO2作为主要的温室气体, CO2固定利用引起了广泛的关注,同时它还是一种丰富无毒的 C1资源,将其作为原料合成高附加值的化学品,不仅可以缓解温室效应,而且还可以缓解能源危机,具有重要的经济和战略意义.在 CO2的资源化利用中,制备2-苯基丙酸意义重大.2-苯基丙酸是一种重要的医药中间体,可用于合成布洛芬、酮洛芬等用途广泛的药剂.因此,其制备方法引起了人们的广泛关注.
　　在典型的合成2-苯基丙酸均相催化体系中,经常使用Co, Ni和Pd等过渡金属催化剂,虽然得到的目标产物产率较高,但催化剂成本高,且很难循环使用,从而限制了其实际使用.
　　电催化法为2-苯基丙酸的合成提供了一条新的途径.本课题组利用手性钴配合物作为催化剂电羧化不对称合成了手性2-苯基丙酸,其产率和 ee值分别为37%和83%.此外,我们还制备了 Co负载的纳米 Ag电极,以其为工作电极不对称羧化1-溴乙基苯与 CO2反应,得到目标产物2-苯基丙酸的产率为58%, ee值为73%.
　　在前期工作的基础上,本文利用无负载的纳米银电极(Ag NPs)为工作电极,电催化1-溴乙基苯与 CO2羧化制备2-苯基丙酸.银纳米电极是利用水合肼还原 AgNO3溶液经抽滤、干燥、压片而成.为了研究 Ag NPs催化 CO2与1-溴乙基苯反应,在一室型电解池中,以 Ag NPs为阴极,镁电极为牺牲阳极,以 CH3CN-TEAI (0.1 mol/L)溶液为电解质溶液,底物浓度为0.1 mol/L,饱和 CO2的氛围下进行恒电流电解,经后处理,可得目标产物2-苯基丙酸.为了提高2-苯基丙酸的产率,我们探讨了工作电极、电解电量、电流密度以及反应温度等条件对反应的影响,从而得到优化条件为反应温度0℃、电解电量2.5 F/mol、电流密度5 mA/cm2,此时2-苯基丙酸的产率可达98%.
　　在优化条件下,我们还研究了一系列苯基卤代物,如溴化苄、溴苯、α-溴苯乙酸、2-溴代萘、二苯基溴甲烷和1-氯乙基苯的电羧化反应.反应后可以得到相应的羧酸,并取得较好的收率(67%?88%).结果表明,纳米银电极对催化该类反应具有很好催化活性和普适性.本文所采用的条件都比较温和,无需高温或高压.
　　在最优条件下,所制纳米银电极可重复使用至少10次,且保持催化活性不变.经过 X射线衍射和扫描电镜表征发现,重复使用后纳米银电极的组成和微结构都保持不变.因此,该纳米银电极具有制备方法简单、催化活性高,稳定性好等特点,具备一定的应用前景.     

In silico correlation of enantioselectivity for the TADDOL catalyzed asymmetric hetero-Diels-Alder reaction

The reverse-docking of a TADDOL organocatalyst to rigid transition state models of catalyst-free reactions (TS-models) for an asymmetric hetero-Diels-Alder reaction is described. In previous reports, reverse-docking of similar organocatalysts to rigid TS-models showed promise for generating transition state models for the catalyzed reaction, and revealed clear energetic trends favoring the experimentally preferred product enantiomers. Although results indicated a mode of catalysis consistent with experimental data, relative docking energies between TS-model enantiomers were too great to allow for in silico correlation to experimentally observed enantiomeric excesses (ee). Several changes were made to the reverse-docking algorithm, EM-Dock, allowing for the first reported correlation to experimentally reported ee values based solely on reverse-docking and molecular mechanics energies.     

Electrochemical carboxylation with carbon dioxide

Studies carried out in the past two years on electrochemical fixation of carbon dioxide with carbon-carbon bond formation, so-called electrochemical carboxylation or electrocarboxylation, are reviewed. Among about twenty papers on electrochemical carboxylation published from 2014 to the present, recent advances in electrochemical carboxylation regarding asymmetric carboxylation, sacrificial anode-free carboxylation, and carboxylation following aryl radical cyclization are focused on and discussed.     

Capillary array electrophoresis for the research of asymmetric transformation reaction of L-proline to D-proline

One asymmetric transformation reaction of L-proline (L-Pro) to D-proline was studied by a home-made capillary array electrophoresis (CAE) for the first time. The aldehyde catalysts and the organic acid solvents for the asymmetric transformation reaction were rapidly screened and the enantiomeric excess values of the asymmetric product of L-Pro were directly obtained from the electrophoretogram of CAE.     

Direct asymmetric aldol reaction catalyzed by nanocrystalline magnesium oxide

Nanomaterials with their three-dimensional structure and defined size and shape are considered to be suitable candidates for proper alignment with prochiral substrates for unidirectional introduction of reacting species to induce an asymmetric centre. The reusable and suitably aligned nanocrystalline magnesium oxide catalyzed direct asymmetric aldol reaction afforded the chiral β-hydroxy carbonyl compounds in good yields and moderate ee's.     

Enantiomeric separation of glycidyl tosylate by CE: Application to the study of catalytic asymmetric epoxidation of allyl alcohol

A CE method using CDs as chiral selectors was developed and validated to achieve the separation of glycidyl tosylate enantiomers originated by in situ derivatization of glycidol enantiomers obtained in asymmetric epoxidation of allyl alcohol with chiral titanium‐tartrate complexes as catalysts. The effects of the nature, pH and concentration of the buffer, the nature and concentration of chiral selector, the addition of SDS, methanol, ethanol or 2‐propanol, the capillary temperature, the effective capillary length and the applied voltage on the chiral resolution of glycidyl tosylate enantiomers were investigated. The best separation conditions were achieved using a Tris‐borate buffer mixture (50 and 25 mM, respectively) at pH=9.3 with a dual CD system consisting of 2.5% succinyl‐β‐CD and 1.0% β‐CD w/v at 15°C. A baseline separation (resolution～2.0) of the glycidyl tosylate enantiomers was obtained in a relatively short time (less than 12 min). Satisfactory results were obtained in terms of linearity (r>0.99) and intermediate precision (RSD below 8.5%). The LOD and LOQ were 3.0 and 10.0 mg/L, respectively, and the recoveries ranged from 99.8 to 108.8%. Finally, the method was applied to the determination of the enantiomeric excess and the yield obtained in the asymmetric epoxidation of allyl alcohol employing chiral titanium‐tartrate complexes as catalysts after an in situ derivatization of glycidol enantiomers to glycidyl tosylate.     

Catalyst electronic polarizability and enantiomeric excess in asymmetric hydrogenation

In the classical rhodium-diphosphine complexes-catalyzed asymmetric hydrogenation of enamide substrates, examination on the role of catalyst electronic polarizability in the origin of enantioselectivity reveals its linear free energy relationship with the product enantiomeric ratio that is much more pronounced than analogous correlation with steric effect in the same systems. From a conceptually novel scenario, this work suggests that the often-overlooked chiral catalyst local polarizability property may function as a controlling force in enantioselection thus has important implication in rational catalyst design.     

Direct asymmetric aldol reactions catalyzed by nanocrystalline copper(II) oxide

The direct asymmetric aldol reactions of aromatic and heteroaromatic aldehydes with acetone to afford chiral β-hydroxy carbonyl compounds in good yields and good to moderate enantioselectivities are realized using nanocrystalline copper(II) oxide in the presence of (1S,2S)-(−)-1,2-diphenylethylenediamine at −30 °C. The catalyst can be reused for four cycles with consistent activity and enantioselectivity.     

AOT-水-正庚烷微乳液中脂肪酶催化拆分消旋布洛芬的研究

以手性高效液相色谱分析法为检测手段,研究了AOT-水-正庚烷微乳液反应介质中,脂肪酶催化消旋布洛芬的不对称酯合成反应。结果表明,在此反应介质中,消旋布洛芬与正辛醇能顺利地进行酯合成反应,转化率达0．3613,产物为光学纯度很高的S-构型布洛芬辛酯,其对映体过量值为0．9732。微乳液中的含水量叫。值（水与表面活性剂的摩尔数比）及AOT浓度主要影响酯合成反应转化率,对产物对映体过量值没有太大的影响;不同链长的脂肪醇不仅影响酯合成反应速率及其对应的最佳ω0值,还影响产物的对映体过量值。     

Chromatographic separation of asymmetric organosilicon compounds on cellulose and amylose stationary phases. The stereochemistry of functional transformation reactions

Summary Silicon compounds, especially silanes, have been separated on cellulose carbamate and amylose carbamate stationary phases. Reasonable recognition is achieved in the separation of organosilicon compounds on cellulose carbamate. Stereoselectivity at the asymmetric silicon center in functional transformation reactions is discussed.     

Convenient synthesis of highly optically active 2,3,4,6-tetrasubstituted tetrahydropyrans via Prins cyclization reaction (PCR) of optically active homoallylic alcohols with aldehydes

Prins cyclization reaction (PCR) of optically active homoallylic alcohols, R^aC^*H(OH)CH₂CHCHCH₃ (1-substituted but-2-en-1-ol), with aldehydes (R^bCHO) in the presence of an acid-catalyst (HX) affords (2-R^b,3-CH₃,4-X,6-R^a)-tetrasubstituted tetrahydropyrans highly stereoselectively in good yields.     

核磁共振技术测定联萘酚的对映体纯度

手性联萘酚((±)-BINOL)制备是国内高校常开设的一个实验,其产品的对映体纯度测试是实验的重要一环。以2-甲酰基苯硼酸和(S)-(?)-1-苯乙胺的混合物作为手性试剂与联萘酚发生Bull-James Assembly反应,以此设计了核磁共振氢谱(¹H NMR)测定联萘酚对映体纯度的实验。实验结果表明,通过反应生成的对映体混合物的核磁信号,能准确地计算出(±)-BINOL的对映体纯度。以选定的苯环氢核信号计算出的(R)-BINOL含量与理论ee值有着良好的线性关系(R²=0.9999)。此实验方法能够快速完成大量学生样品的测量,同时大大减少实验废液的产生量。学生通过此实验可对核磁共振技术有更进一步的了解。     

Synthesis of 2-arylpropionic acids by electrocarboxylation of benzylchlorides catalysed by PdCl2(PPh3)2

Electrochemical carboxylation of benzylchlorides catalysed by Pd(II) complex afforded 2-arylpropionic acids in good yields under atmospheric pressure of carbon dioxide at constant current of 10 mA cm⁻². Mechanistic and electrochemical studies revealed the cooperative role of reduced palladium species in the activation of carbon dioxide.     

Quantification of very low enantiomeric impurity of efaroxan using a dual cyclodextrin system by capillary electrophoresis

A rapid method for the enantiomeric purity determination of efaroxan has been developed by capillary electrophoresis (CE) using a dual cyclodextrin (CD) system. The influence of the nature and the concentration of CDs on separation parameters has been studied. High resolution (R_s = 7) and peak efficiency (104 000-121 000 theoretical plates) values were obtained for efaroxan enantiomers by adding two cyclodextrins, one neutral (7.5 mM DM-β-CD) and the other negatively charged (3 mM CM-β-CD) to the running buffer composed of 100 mM phosphoric acid-triethanolamine (pH 3). These resolution and peak efficiencies values allowed the quantitation of the (S)-enantiomer of efaroxan at very low enantiomeric excess even if the minor component migrates after the major one. This method was fully validated for the enantiomeric impurity determination of the (S)-form of efaroxan at the 0.05% level. Calibration curve, expressed by the peak areas ratio versus the enantiomeric purity was linear over the 0.05-1% enantiomeric impurity range (r² = 0.9996). Limits of detection (LOD) and quantification (LOQ), expressed in term of (S)-enantiomer impurity were 0.02% and 0.05%, respectively. The accuracy of the method at 0.12%, 0.50% and 0.80% enantiomeric impurity levels for the (S)-form were determined. Recoveries were in 94-102% range for each quality control sample and were determined with good precision (intra-day R.S.D. = 3.54%, inter-day R.S.D. = 5.33%).     

Na 掺杂对硅酸锂吸收CO2性能的影响

通过高温固相反应法, 在添加不同比例Na2CO3的条件下, 合成出一系列可在高温500～750 ℃之间直接吸收CO2的硅酸锂材料. 利用扫描电子显微镜、X射线粉末衍射仪分别观察和评价了合成材料的表面形貌与结构特征, 用热重分析仪测量了硅酸锂材料的CO2吸收性能. 实验结果表明, 通过适量Na元素的掺杂, 能够提高硅酸锂材料吸收CO2的性能, 当Na2CO3的添加量x=0.02时, 合成的硅酸锂材料在CO2气氛下, 于700 ℃恒温保持约15 min即可达到吸收平衡, 材料的吸收量为(46±0.6)%(w), 与未经掺杂的材料相比, 吸收容量有所提高. 此外, 气氛中CO2的浓度对材料吸收CO2的速率有较大影响.     

Verification of the need for optical purity measurement of chiral pesticide standards as agricultural reference materials

In this study, optical purity measurement was performed on eight kinds of commercially available pesticide, namely, Dimethenamid-P, Dichlorprop-P, Fluazifop-P butyl, Indoxacarb, Metalaxyl-M, Mecoprop-P, Quizalofop-P ethyl, and Uniconazole-P, in both enantiomer and racemate forms. Chiral separation of each pesticide was achieved by using HPLC with a photodiode-array (PDA) detector and a circular dichroism (CD) detector, which were connected in series. The chiral column used for the enantiomeric separation was a normal phase Chiralpak AD-H column. The mobile phase was n-hexane, with various alcohols added as polar modifiers. The study included investigation of the effects on enantiomeric separation of the percentage of alcohol used, the presence or absence of acid in the mobile phase, and the column temperature, and the optimum detection wavelengths of both PDA and CD detectors. Enantiomeric excess (ee) was calculated as an expression of optical purity. As a result, the ee of some pesticides investigated was approximately (over 95%) in accord with the data provided by manufacturers. However, the ee of Indoxacarb, Uniconazole-P, Quizalofop-P ethyl, and Fluazifop-P butyl was in the range 34.1–94.5%. These results suggest that there is a need to conduct optical purity tests, in addition to a chemical purity test, for optically active pesticides. Presented at BERM-11, October 2007, Tsukuba, Japan.