Phase transfer of platinum nanoparticles from aqueous to organic solutions using fatty amine molecules

In this report we demonstrate a simple process based on amine chemistry for the phase transfer of platinum nanoparticles from an aqueous to an organic solution. The phase transfer was accomplished by vigorous shaking of a biphasic mixture of platinum nanoparticles synthesised in an aqueous medium and octadecylamine (ODA) in hexane. During shaking of the biphasic mixture, the aqueous platinum nanoparticles complex via either coordination bond formation or weak covalent interaction with the ODA molecules present in the organic phase. This process renders the nanoparticles sufficiently hydrophobic and dispersible in the organic phase. The ODA-stabilised platinum nanoparticles could be separated out from hexane in the form of a powder that is readily redispersible in weakly polar and non-polar organic solvents. The ODA-capped platinum nanoparticles show high catalytic activity in hydrogenation reactions and this is demonstrated in the efficient conversion of styrene to ethyl benzene. The nature of binding of the ODA molecules to the platinum nanoparticles surface was characterised by thermogravimetry, transmission electron microscopy (TEM), X-ray photoemission spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR)     

温控相转移配体及催化(Ⅴ)——单,双-对聚氧乙烯基三苯基膦的合成及其催化性能研究

近年来,水／有机两相催化已成为均相催化多相化研究的主流［１］．其中,新型水溶性膦配体的合成和两相催化新体系的设计尤为引人关注［２］．最近我们发现［３］,聚醚型水溶性膦－铑催化剂在高温下可溶入有机相对反应进行催化,而在冷却后又重返水相和产物分离．本文通...     

Kinetics of Phase Transfer Catalytic Preparation of Benzyl Benzoate

The kinetics is studied for the phase transfer catalytic preparation of benzyl benzoate from sodium benzoate and benzyl chloride with tetrabutylaramonium iodide as catalyst in a well stirred batch reactor. Benzyl chloride is dissolved in toluene as the organic phase and sodium benzoate is dissolved in water as the aqueous phase. The kinetics of the overall reaction is described by a first-order model based on the concentration of benzyl chloride in the organic phase at the later time of the batch reaction. The rate constant increases with an increase of the catalyst concentration while decreases slightly with an increase of the concentration of sodium benzoate under the experimental condition.     

两相催化——均相催化多相化新进展*

评述了水溶性膦配体和两相催化研究领域的进展, 探讨了固载水相催化、温控相转移催化和氟两相体系等新型两相催化体系。两相催化在烯烃的氢甲酰化反应、不饱和化合物的加氢反应以及其它有机反应中获得了广泛的应用。     

乙酸苄酯合成中接枝型三相相转移催化剂的活性及催化反应动力学

采用"接出(grafting from)"方式,将苯乙烯(St)接枝聚合在微米级硅胶表面,然后对接枝的聚苯乙烯进行了氯甲基化(CM)反应,制得了氯甲基聚苯乙烯/硅胶微粒(CMPS/SiO2);使三丁胺与三苯基膦分别与CMPS大分子链上的苄氯基团发生季铵化与季鏻化反应,分别制得了固载有季铵盐与季鏻盐的接枝微粒QN-PSt/SiO2与QP-PSt/SiO2,即制得了两种接枝型三相相转移催化剂.将该催化剂用于苄氯与乙酸钠合成乙酸苄酯的相转移催化反应,并重点考察了催化剂的活性与催化动力学.实验结果表明,两种接枝型三相相转移催化剂QN-PSt/SiO2与QP-PSt/SiO2对乙酸苄酯的合成都具有明显的催化活性,在液-固-液之间可有效地实现反应物种乙酸根的转移;两者相比,季鏻盐型的催化剂QP-PSt/SiO2的催化活性更高;当水相中乙酸钠用量大大过量时,在有机相中苄氯与乙酸根的反应属准一级反应;两个相转移反应体系相比,以QP-PSt/SiO2为催化剂时反应的表观活化能更低.     

Phase transfer and its applications in nanotechnology

As nanoparticle syntheses in aqueous and organic systems have their own merits and drawbacks, specific applications may call for the transfer of newly formed nanoparticles from a polar to a non-polar environment (or vice versa) after synthesis. This critical review focuses on the application of phase transfer in nanoparticle synthesis, and features core-shell structures in bimetallic nanoparticles, replacement reactions in organic media, and catalytic properties of various nanostructures. It also describes the reversible organic and aqueous phase transfer of semiconductor and metallic nanoparticles for biological applications, and the use of phase transfer in depositing noble metals on semiconductor nanoparticles (258 references).     

Catalytic Activity of Alkali Metal Cations for the Chemical Oxygen Reduction Reaction in a Biphasic Liquid System Probed by Scanning Electrochemical Microscopy

Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species or the concomitant oxidation of organic substrates can be enhanced by the separation of products and educts in biphasic liquid systems. Here, the coupled electron and ion transfer processes is studied as well as reagent fluxes across the liquid|liquid interface for the chemical reduction of dioxygen by decamethylferrocene (DMFc) in a dichloroethane-based organic electrolyte forming an interface with an aqueous electrolyte containing alkali metal ions. This interface is stabilized at the orifice of a pipette, across which a Galvani potential difference is externally applied and precisely adjusted to enforce the transfer of different alkali metal ions from the aqueous to the organic electrolyte. The oxygen reduction is followed by H₂O₂ detection in the aqueous phase close to the interface by a microelectrode of a scanning electrochemical microscope (SECM). The results prove a strong catalytic effect of hydrated alkali metal ions on the formation rate of H₂O₂, which varies systematically with the acidity of the transferred alkali metal ions in the organic phase.     

Diffusion‐Regulated Phase‐Transfer Catalysis for Atom Transfer Radical Polymerization of Methyl Methacrylate in an Aqueous/Organic Biphasic System

A concept based on diffusion‐regulated phase‐transfer catalysis (DRPTC) in an aqueous‐organic biphasic system with copper‐mediated initiators for continuous activator regeneration is successfully developed for atom transfer radical polymerization (ICAR ATRP) (termed DRPTC‐based ICAR ATRP here), using methyl methacrylate (MMA) as a model monomer, ethyl α‐bromophenylacetate (EBrPA) as an initiator, and tris(2‐pyridylmethyl)amine (TPMA) as a ligand. In this system, the monomer and initiating species in toluene (organic phase) and the catalyst complexes in water (aqueous phase) are simply mixed under stirring at room temperature. The trace catalyst complexes transfer into the organic phase via diffusion to trigger ICAR ATRP of MMA with ppm level catalyst content once the system is heated to the polymerization temperature (75 °C). It is found that well‐defined PMMA with controlled molecular weights and narrow molecular weight distributions can be obtained easily. Furthermore, the polymerization can be conducted in the presence of limited amounts of air without using tedious degassed procedures. After cooling to room temperature, the upper organic phase is decanted and the lower aqueous phase is reused for another 10 recycling turnovers with ultra low loss of catalyst and ligand loading. At the same time, all the recycled catalyst complexes retain nearly perfect catalytic activity and controllability, indicating a facile and economical strategy for catalyst removal and recycling.

     

温控Noyori配体的合成及在苯乙酮不对称氢转移反应中的应用

设计并合成了一种新型的聚乙二醇单甲醚(MPEG)修饰的温控Noyori配体.将其与[RuCl2.(p-cymene)]2络合形成的催化剂用于水/环己烷两相体系中苯乙酮不对称氢转移反应.以甲酸钠为氢源,考察了反应温度、时间、甲酸钠用量、底物与催化剂摩尔比以及溶剂用量等因素对催化反应的影响.结果表明,反应体系中含催化剂的水相具有浊点,并且催化剂显示出良好的不对称催化性能,在甲酸钠/苯乙酮/催化剂的摩尔比为300:100:1、环己烷/水体积比1:1及30℃的反应条件下反应6h,苯乙酮的转化率为99.7%,产物α-苯乙醇的对映选择性(e.e.)为93.9%.催化剂相易与产物相分离并与直接循环使用,循环使用的催化剂活性明显下降,但产物对映选择性仍保持不变.     

Synthesis of dialkoxydiphenylmethane under phase transfer catalytic condition assisted by ultrasonic irradiation

The synthesis of dialkoxyldiphenylmethanes (DAODPMs) from the reactions of alcohols and dichlorodiphenylmethane (DCDPM) were successfully carried out in a liquid-liquid phase transfer catalytic reaction (LL-PTC). The reactions are greatly enhanced by irradiation with ultrasonic waves. Two sequential reactions in the organic-phase solution proceed to produce the desired product. Only the di-chloro-substituted product dialkoxyldiphenylmethanes (DAODPM) is obtained, indicating that the second reaction is faster than the first one in the organic phase. Explanations for the phenomena of the experimental results are provided.     

Chemoselective Benzylation and Allylation of 4-Nitrobenzaldehyde Promoted by Phase Transfer Catalyst and Metal in Aqueous Media

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Electrochemical Study of s‐Triazine Herbicides Transfer Across the Water/1,2‐Dichloroethane Interface

The transfer of three s‐triazine herbicides, atrazine (ATR), propazine (PRO) and prometrine (PROM), across the water/1,2‐dichloroethane interface was investigated using cyclic voltammetry. A facilitated proton transfer mechanism from the aqueous to organic phase is demonstrated by the analysis of positive peak potential and peak current as a function of pH. It is shown that the determination of 2.5×10^?5 M – 5×10^?4 M concentration of herbicides in aqueous phase may be possible under the experimental conditions employed.     

Phase transfer of oleic acid capped Ni(core)Ag(shell) nanoparticles assisted by the flexibility of oleic acid on the surface of silver

The phase transfer protocols in vogue for the oleic acid capped silver nanoparticles, viz., salt-induced precipitation and redispersion or phosphoric acid-induced method, are examined and compared thoroughly. A comprehensive evaluation with respect to the mechanistic aspects involved is made and the merits and demerits of the different procedures are delineated. It is found that the salt-induced precipitation and redispersion is more versatile in that the precipitate can actually be redispersed in both aqueous and organic media. However, in terms of mechanism both the routes seem to be very similar wherein the orientational change of oleic acid on the silver surface in the two different environments-organic and aqueous-plays a crucial role in the adaptability of the system to the different environments. Subsequently, this change of orientation of oleic acid on silver surface in aqueous and organic media has been utilized to phase transfer Ni-based nanoparticulate systems. The nascent oleic acid-capped Ni nanoparticles, which were synthesized by a foam-based protocol, were dispersible in water but not in nonpolar organic media such as cyclohexane or toluene. Then, just by coating a thin shell of silver on them we could achieve complete phase transfer of the Ni(core)Ag(shell) from aqueous to organic media following similar procedures used for oleic acid-capped silver nanoparticles. Here, the phase transfer seems to be facilitated by the orientational flexibility of oleic acid on the silver surface as opposed to other metal surfaces as evidenced from the infrared and thermogravimetric analyses of oleic acid-capped Ni and Ni(core)Ag(shell) nanoparticles. This orientation-assisted phase transfer method could be generalized and can be adapted to other systems where, if the nascent nanoparticles cannot be phase transferred as is, they can be coated by a silver shell and oleic acid making them suitable for dispersion in both aqueous and organic media.     

Phase transfer catalysis in the chemistry of aliphatic nitrocompounds

The methylation of trinitromethane (TNM) Na-salt under phase transfer catalysis (PTC) conditions was studied in a two-phase system (aqueous solution of TNM Na-salt-CH₃I). The obtained data revealed a relationship between the yield of the methylation product (1,1,1-trinitroethane) and the nature of the phase transfer catalyst and the degree of TNM anion transfer to the organic phase. The kinetic measurements showed that higher efficiency of methylation was achieved under PTC conditions than occurs in a homogeneous reaction due to the fact that the reaction proceeded in the CH₃I medium.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1086–1088, June, 1993.     

Determining the Gibbs energy of ion transfer across water-organic liquid interfaces with three-phase electrodes.

Ions can be transferred between immiscible liquid phases across a common interface, with the help of a three-electrode potentiostat, when one phase is an organic droplet attached to a solid electrode and containing a redox probe. This novel approach has been used in studies to determine the Gibbs energy of anion and cation transfer, ranging from simple inorganic and organic ions to the ionic forms of drugs and small peptides. This method of studying ion transfer has the following advantages: (1) no base electrolytes are necessary in the organic phase; (2) the aqueous phase contains only the salt to be studied; (3) a three-electrode potentiostat is used; (4) organic solvents such as n-octanol and chiral liquids such as D- and L-2-octanol can be used; (5) the range of accessible Gibbs energies of transfer is wider than in the classic 4-electrode experiments; (6) the volume of the organic phase can be very small, for example, 1 microL or less; (7) the experiments can be performed routinely and fast. Herein, the basic 5 principle is outlined, as well as a summary of the results obtained to date, and a discussion on the theoretical treatments concerning the kinetic regime of the three-phase electrodes with immobilized droplets.     

丙烯酰胺在聚乙二醇水溶液中的聚合动力学

用改进溴法对丙烯酰胺 (AM)在聚乙二醇 (PEG)水溶液中聚合动力学进行研究 .在单一和氧化还原引发体系中分别考察了引发剂、单体和PEG用量、不同HLB值乳化剂以及聚合温度等因素对动力学的影响 .得到AM聚合速率与过硫酸铵 (APS)浓度的 0 91次方成正比 ;单一APS和APS 三乙醇胺 (TEA)氧化还原引发体系中的AM聚合表观活化能分别为 96 1和 4 2 3kJ mol.     

Phase-transfer catalytic epoxidation of olefins under liquid-liquid biphasic conditions

The phase transfer catalytic epoxidation of various olefins in the presence of cocatalysts (sodium tungstate and phosphoric acid) and an oxidant (hydrogen peroxide) in an organic/aqueous two-phase medium was investigated. The different conversions and selectivities casued by olefins of different carbon-carbon double bonds are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

反应萃取法合成戊二醛中H3PMoxW12—xO40的催化作用

杂多酸Ｈ３ＰＭｏｘＷ１２－ｘＯ４０是通过其适宜的酸性,氧化性的双功能的配合催化,使Ｈ２Ｏ２氧化环戊烯为戊二醛,液－液相转移反应萃取氧化过程是杂多酸与相转移催化剂形成油溶性配合物,此配合物在相界面被Ｈ２Ｏ２氧化为过氧化杂多酸配合物,过氧化杂多酸配合物在有机相可能机理是Ｈ２Ｏ２氧化杂多酸为过氧化杂多酸。     

Conversion of the surface property of oleic acid stabilized silver nanoparticles from hydrophobic to hydrophilic based on host-guest binding interaction

This paper describes a general method to change the surface property of the oleic acid stabilized silver nanoparticles and successful tranferring of the silver nanoparticles from the organic phase into the aqueous phase. By vigorous shaking of a biphasic mixture of the silver organosol protected with oleic acid and p-sulfonated calix[4]arene (pSC4) aqueous solution, it is believed that an inclusion complex is formed between oleic acid molecules and pSC4, and the protective layer of the silver nanoparticles shifts from hydrophobic to hydrophilic in nature, which drives the transfer of silver nanoparticles from the organic phase into the aqueous phase. The efficiency of the phase transfer to the aqueous solution depends on the initial pSC4 concentration. The pSC4-oleic acid inclusion complex stabilized nanoparticles can be stable for long periods of time in aqueous phase under ambient atmospheric conditions. The procedure of phase transfer has been independently verified by UV-vis, transmission electron microscopy, Fourier transform infrared, and 1H nuclear magnetic resonance techniques.     

Synthesis of polymer-supported phosphonium salts and their use as phase transfer catalysts

Spacer-modified polymer supports have been synthesized through the polymeric Grignard reagent method. Phosphonium-active sites were then introduced into these supports and the polymer-supported phosphonium salts were used as phase transfer catalysts for the nucleophilic substitution reactions. Influences of organic solvent, properties of the spacer and temperature on the catalytic activity have been investigated. Based on the experimental results, it was assumed that there might exist a dissolubility equilibrium of the catalytic site between the organic phase and the aqueous phase. With this idea, the results have been reasonably elucidated.