酸性磷型萃取剂的结构与萃取钴,镍性能关系的研究

考察了一系列二烷基磷酸酯,烷基膦酸单烷基酯和二烷基膦酸对钴(Ⅱ)、镍(Ⅱ)的萃取性能。应用相关分析法探讨了萃取性能与萃取剂分子中取代基的极性效应和空间效应之间的关系。并依据萃合物立体构型的差异解释了萃取剂结构对萃取钴、镍的不同影响。     

异丙基膦酸单烷基酯萃取稀土的化学

本文研究了不同酯烷基结构的异丙基膦酸单烷基酯萃取稀土反应的平衡常数(K_(ex))的差别。异丙基膦酸单β-取代烷基酯具有较高K_(ex)值,而相应的α-取代烷基酯的K_(ex)值则显著下降。此外,镧系收缩的特性扩大了配位体的空间效应,这类效应对化合物的pKa值也有影响。并讨论了异丙基膦酸单十四烷基酯(MANPP)萃取稀土的反应机理,测得该反应的热力学函数,不论K_(ex)值或△G值与原子序数间均具四分组效应。研究了萃取配合物的组成与结构,值得指出的是MANPP在盐酸体系中萃取分离钕、钐的性能均优于硝酸体系。     

一元烷基磷(膦)酸酯萃取稀土的结构与性能的相关分析

本文在确定了一元烷基磷(膦)酸酯萃取稀土的性能主要决定于取代基极性和立体效应的基础上,在继长碳链烷基及烷氧基极性参数σ~P后,又提出了这类化合物萃取稀土反应中的取代基立体参数E_(PA)~(RE)。将这类参数应用到其他的萃取体系也获得良好的相关关系。与反映取代基空间效应的Charton的v参数比较,其E_(PA)~(RE)与v间具良好的线性关系。根据加和性规则,可以求得萃取剂分子中取代基因极性参数和立体参数的总和。由此可计算或预测某些萃取剂的性能,实验值与计算值很接近,这对设计新萃取剂很有帮助,在萃取剂分子设计数学模型的建立中,它提供了重要的结构参数。     

钴萃取研究 Ⅸ.有机磷(膦)酸萃取剂结构与萃取分离钴(Ⅱ)、镍(Ⅱ)性能的研究

本文就三种典型的有机磷(膦)酸萃取剂P_(204)、P_(507)、P_(272)在高氯酸盐体系中对Co(Ⅱ)、Ni(Ⅱ)萃取分离能力进行了比较。 在萃取体系有机相中,上述三种萃取剂与Co(Ⅱ)形成的萃合物均存在粉红色八面体与蓝色四面体构型转化的平衡反应。随着萃取剂分子中氧烷基被烷基取代,反应基团磷氧酰基氧原子上电子云密度增加,酸性降低,与Co(Ⅱ)形成的四面体萃合物稳定性增强,对Co(Ⅱ)/Ni(Ⅱ)分离的能力增加。Co(Ⅱ)四面体萃合物的稳定性是影响Co(Ⅱ)/Ni(Ⅱ)分离效果最主要的因素。这一结论还可通过Co(Ⅱ)/Ni(Ⅱ)萃取分离温度效应与Co(Ⅱ)萃合物构型转化温度效应的一致性得到证实。在所研究的三类有机磷(膦)酸萃取剂结构因素中,磷氧酰基氧原子上的电子云密度是影响Co(Ⅱ)/Ni(Ⅱ)分离效果的关键因素。     

酸性磷(膦)酸酯的合成及其化学结构与萃取钕、钐、镱和钇的性能研究

本文在研究二烷基磷酸、烷基膦酸单烷基酯、二烷基膦酸、单烷基磷酸与单烷基膦酸五种类型酸性磷(膦)酸酯的合成与纯化的基础上,考察了它们的缔合度和萃取稀土的机理,并计算了萃取钕、钐、镱和钇的平衡常数和分离因数。酸性磷(膦)酸酯萃取稀土的平衡常数与其反应基团解离常数密切有关,它们与取代基常数、磷(膦)酸基氧原子电荷密度间均有良好线性关系。酸性磷(膦)酸酯的结构空间位阻对萃取稀土的性能有显著影响。所研究磷(膦)酸酯萃取稀土的选择性随其平衡常数的增大而下降,符合文中提出的溶剂萃取中的反应性-选择性原理。     

烷基磷(膦)酸酯~(31)P NMR的取代基效应

本文利用分子力学计算,将核磁共振中烷基取代基效应的Van der Waal模型扩展到磷酸三烷基酯、烷基膦破二烷基酯、二烷基膦酸烷基酯和三烷基氧化膦。在各类磷化合物中,δ~(31)P和E_(vdw·p)之间存在有良好线性关系。此外,还用分子力学计算方法和变温核磁共振谱方法探讨了一系列烷基膦酸O,O-1,3-亚丙酯和烷基膦酸O,O-1,4-亚丁酯的构型平衡。在气相和非极性溶剂中,前者以烷基处于平键的椅式构型存在,后者以烷基处于平键的扭船式构型存在。     

高位阻有机磷萃取剂的研究——Ⅰ.烃基膦酸单十六烷基酯的合成及其对钴(Ⅱ)、镍(Ⅱ)等金属离子的萃取性能

合成了6个具有高位阻特征的烃基膦酸单十六烷基酯萃取剂,并考察了它们对Co(Ⅱ)、Ni(Ⅱ)、Cu(Ⅱ)、Fe(Ⅲ)和Ca的萃取性能。萃取剂分子中烃基结构的变化对各种金属离子的萃取能力有着不同程度的影响。空间位阻较大的异丙基和环己基化合物具有比2-乙基己基膦酸单2-乙基己基酯(P507)更高的Co-Ni分离能力。     

有机磷(膦)酸萃取剂的结构与萃取分离钴(Ⅱ)、镍(Ⅱ)性能的研究

本文对磷酸二烷基酯(P₂₀₄)、单烷基膦酸单烷酯(P₅₀₇)、二烷基膦酸的结构与萃取Co(Ⅱ)、Ni(Ⅱ)的性能进行了较细致、深入的研究。测定了萃取平衡及温度、pH值、浓度等对平衡的影响。随着萃取剂酸性降低,它们对Co(Ⅱ)/Ni(Ⅱ)的分离效果提高。这与萃取体系有机相中Co(Ⅱ)四面体构型萃合物的稳定性增强相一致。     

一元烷基磷(膦)酸酯萃取钴,镍反应中取代基空间效应的经验参数

本文在考察一元烷基磷(膦)酸酯萃取钴、镍反应平衡常数与取代基结构的定量关系的基础上,提出了酸性磷(膦)酸酯萃取钴、镍反应中反映取代基结构空间效应为主的经验参数EPA[Co]和EPA[NI],这些新标度的建立,不仅使我们可用关系式来描述萃取钴、镍的反应性与取代基结构效应的关系,而且也为选择高效镍、钴分离萃取剂提供了新途径。     

辛基膦酸单辛酯的合成及其萃取镧系元素的结构-性能研究

合成了九个不同辛基结构的辛基膦酸单辛酯,测定了它们的正十二烷溶液在恒定离子强度和不同酸度的硝酸介质中萃取镧、铕和铅的分配比,并以外推法得到了归一化的分配比数值,从而进行了萃取剂结构与性能关系的研究。考察了辛基膦酸单辛酯的烷基支链化程度时萃取镧系元素的能力和分离性能的影响:随着邻近配位基团的烷基支链化程度的增加,其萃取能力下降;但一定的支链对萃取剂分子是必需的,如2-乙基已基膦酸单2-乙基己基酯和正辛基膦酸单1-甲基庚基酯皆具有最佳的分离性能。从空间效应解释了所得的结果。     

THE INFLUENCE OF SUBSTITUENT ELECTRONIC EFFECT ON ETHYLENE OLIGOMERIZATION ACTIVITIES OF BIS(IMINO)PYRIDYL Fe(II) CATALYSTS: A COMBINED MOLECULAR MECHANICS AND CHARGE EQUILIBRATION METHOD

 Bis(imino)pyridyl Fe(II) complexes are important catalysts in ethylene oligomerization for preparing α-olefins. The metal net charge-activity relationship of bis(imino)pyridyl Fe(II) complexes was investigated by molecular mechanics (MM) and net charge equilibration (QEq) method with modified Dreiding force field. It was found that metal net charge was in reverse ratio to ethylene oligomerization activity. Electron-donor substituents with less steric hindrance to the central metal were favorable to Fe complex activity. Metal net charge-activity relationship could be used to assist the design of new Fe oligomerization catalysts with higher activity.     

Quantitative assessment of the stereoelectronic profile of phosphine ligands

The stereoelectronic profile of a variety of phosphine ligands (PR3) have been estimated using a combined approach of quantum mechanics (QM) and molecular mechanics (MM). The quantum mechanically derived molecular electrostatic potential minimum (Vmin) of a PR3 ligand at the phosphorus lone pair region provides a direct measure of the total electronic (Eeff) and steric effects (Seff) of the ligand. The difference between the Vmin of unsubstituted PH3 (Vmin(PH3)) and the Vmin of PR3 is considered as Eeff + Seff. It is found that a two-layer QM-MM ONIOM method comprising PH3 in the inner QM layer and the R groups in the outer MM layer is useful to locate the structure of a PR3 ligand in an electronic effect free environment of the substituents. The Vmin of the ONIOM-optimized PR3 at the phosphorus lone-pair region thus provides the quantification of the steric effect as Seff = Vmin(PH3)-Vmin(ONIOM_PR3). Because Vmin(PR3) contains both Eeff and Seff, the Eeff can be easily defined as Eeff = Vmin(ONIOM_PR3)-Vmin(PR3). A modified form of the symmetric deformation coordinate (S4) is calculated for all of the fully optimized and ONIOM-optimized free phosphines to obtain their S4-based steric effect values. Good linear correlation between S4 of ONIOM-optimized phosphines and the MESP-based Seff values was obtained. Further, the determination of the stereoelectronic profile of PR3 ligands has been achieved, leading to a general classification of the ligands into four categories, namely, ligands with (i) (+Eeff, +Seff), (ii) (+Eeff, -Seff), (iii) (-Eeff, +Seff), and (iv) (-Eeff, -Seff), where plus and minus signs indicate electron donation and electron withdrawal properties, respectively.     

A New Method for Molecular Mechanics

A promising new method for optimizing molecular structures is described. In place of the terms involving bond angles and torsion angles, used in the force fields of conventional molecular mechanics, two-body central forces between atoms are used exclusively, resulting in a considerable computational advantage. The program STRFIT, using this method has been tested by comparing geometries obtained with those found using the popular molecular mechanics program MM2 (Allinger) for a variety of cyclic and acyclic molecules. For unstrained molecules, the difference in steric energy between geometries refined by STRFIT and MM2 is only a few tenths of a kilocalorie and up to about a kilocalorie for strained molecules. Geometry optimization with STRFIT, to a structure that is slightly higher in energy than the structure arrived at by MM2 starting from the same initial starting geometry, is three to eight times faster. A complete new package of programs for conveniently and rapidly doing molecular mechanics calculations is described. It includes a convenient algorithm for the input of approximate molecular structures, a rapid structure-optimizing module using a pure Central force-field approach, and a drawing program designed for use with a dot-matrix printer or a laser printer.     

Steric and hydrophobic effects of substituents in extraction of metal complexes with O,O-dialkyldithiophosphoric acids

The two-phase stability constants (equilibrium constants) of metal complexes MA(n) [M(n)(+) = Ni(II), Zn(II), Cd(II), Pb(II), Tl(I), In(III)] with a series of O,O-dialkyldithiophosphoric acids in the system water-organic solvent) have been determined. By use of correlation analysis the role of the steric and hydrophobic effects of the substituents at the phosphorus atom on the stability constant beta(n) and distribution constant P of the complexes has been elucidated. The data obtained are of use for determining the relationships in the influence of structure of a reagent on its extraction properties and on the conditions for practical application of O,O-dialkyldithiophosphoric acids for metal extraction.     

Reductive elimination of ArCF3 from bidentate Pd(II) complexes: a computational study

The reductive eliminations of ArCF(3) from Pd(II) complexes bearing small- and large-bite-angle phosphane ligands have been investigated using computational methods. QM/QM' and QM/MM studies were applied and complemented with CP2K molecular dynamics investigations. The ligand substituents were varied and a decomposition analysis was performed to allow us to gain insights into the steric and electronic properties of the ligands. The greater reactivity of Xantphos-derived (Xantphos=4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) complexes in the reductive elimination of ArCF(3) is primarily due to the lower repulsive effect of the phoshine substituents in the transition state than in the reactant complex, combined with the increased electronic interaction in the transition state. For DPPE (1,2-bis(diphenylphosphino)ethane), the steric effect of the ligand substituents is greater in the transition state, leading to a higher reaction barrier overall for reductive elimination. There is no direct correlation of the reactivity with the bite angle of the reactant complexes. Only for complexes with large ligand substituents may the bite angle of the Pd complexes be used as a guide for reactivity.     

Simulations of liquid ammonia based on the combined quantum mechanical/molecular mechanical (QM/MM) approach

Two combined quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations, namely, HF/MM and B3LYP/MM, have been performed to investigate the local structure and dynamics of liquid ammonia. The most interesting region, a sphere containing a central reference molecule and all its nearest surrounding molecules (first coordination shell), was treated by the Hartree-Fock (HF) and hybrid density functional B3LYP methods, whereas the rest of the system was described by the classical pair potentials. On the basis of both HF and B3LYP methods, it is observed that the hydrogen bonding in this peculiar liquid is weak. The structure and dynamics of this liquid are suggested to be determined by the steric packing effects, rather than by the directional hydrogen bonding interactions. Compared to previous empirical as well as Car-Parrinello (CP) molecular dynamics studies, our QM/MM simulations provide detailed information that is in better agreement with experimental data.     

Application of parallel processing techniques to improving the efficiency of MM2 molecular mechanics calculations

The application of parallel processing techniques to molecular mechanics calculations is evaluated. Using the standard molecular mechanics package, MM2, four different parallel versions of the program are implemented in a four-processor computing environment. A set of 529 test structures is used to compare the efficiency of the parallel versions of MM2 to a standard serial version of the program. Statistics describing execution times and program execution cycles are gathered and analyzed. The effects of parallel processing overhead and computer system load are explored, and the practical utility of parallel processing in molecular mechanics is estimated. The results of these parallelization experiments indicate that for geometry optimizations requiring significant amounts of computing time an improvement in program execution speed approaching 50% is realizable. © 1993 John Wiley & Sons, Inc.     

Extraction of niobium with phenol-formaldehyde resol oligomer Yarrezin B from peroxide solutions

Extraction of niobium by nitrogen-containing phenol-formaldehyde resol oligomer Yarrezin B from peroxide sulfate solutions was studied. The stoichiometry of extraction was determined. The structure of the extracted complex Nb(O₂)(OH)O₂R(OH)N was predicted by molecular mechanics (MM) and molecular dynamics (MD) methods and the semiempirical ZINDO/1 method (single-point calculations) with the use of the HyperChem Release 8.0.4 program package.