Organometallic salts as phase transfer catalysts

Six organometallic compounds were tested to see if they could behave as phase transfer catalysts. All of the compounds appeared to catalyze the base hydrolysis of p-nitrophenylacetate in a 2 layer aqueous-organic system.     

Synthesis and characterization of high-barrier polyimide containing rigid planar moieties and amide groups

A high-performance polyimide was prepared by the dipolymerization of 4,4'-diaminobenzanilide (DABA) and pyromellitic dianhydride (PMDA). Due to the introduction of rigid planar moieties and amide groups, the polyimide shows outstanding properties, such as high glass transition temperatures (435 °C), excellent thermal stability (T_d5%, 542 °C, coefficient of thermal expansion, −3.2 ppm K⁻¹), and superior mechanical properties. Most importantly, the polyimide exhibits excellent barrier properties, with oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) low to 7.9 cm³ (m² day)⁻¹ and 5.1 g (m² day)⁻¹, respectively. Wide angle X-ray diffractograms (WAXD), positron annihilation lifetime spectroscopy (PALS) and molecular dynamics simulations reveal that the excellent barrier properties are mainly attributed to the high crystallinity, high extent of in-plane crystalline orientation, and low free volume, which are resulted from the rigid planar structure and strong interchain hydrogen bonding. The high-barrier and thermally stable polyimide has an attractive potential application prospect in the fields of micro-electronics encapsulation and high grade packaging industry.     

Silica gel supported phosphonium salts as micellar and phase transfer catalysts

Phosphonium salts immobilized on silica gel have been found to be both micellar and phase-transfer catalysts. They are able to exchange their parent anions with the anions present in an aqueous solution and promote, in catalytic amounts, the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate to give 2-cyano-5-nitrophenolate, a test for micellar catalysis.     

Inhibition by phase transfer catalysts

While phase transfer catalysts have generally a positive effect on substitution of halides by rhodanide ion in two-phase reaction systems changing the structure of alkyl halide from primary to tert.-alkyl groups, catalysis reverses into inhibition. The assumption that this is due to the change in reaction mechanism from S_N2 to S_N1 was proved on hydrolysis of triphenylmethyl chloride in a two-phase system, where the inhibitory effect of phase transfer catalysts is even more pronounced.

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, , , , . , S_N2 S_N1, , .

     

Polymeric formamides as liquid–liquid phase transfer catalysts

Polymeric formamides were prepared by free radical polymerization of N-methyl-N-vinyl-formamide or N-methyl-N-(4-vinylbenzyl)formamide, and copolymerization of these monomers with styrene. These soluble polymers serve as phase transfer catalysts for several reactions under liquid–liquid biphase conditions. The catalytic activity of copolymers containing styrene unit is affected remarkably by composition, and there are maxima at certain composition in both polymers. However, copolymers with an acrylonitrile co-unit scarcely exhibit catalytic activity. Furthermore, it was found that these polymers can extract all alkali metal ions employed here, and that the extraction ability increases with increasing the density of active sites. From these results, it is demonstrated that catalytic activity strongly depends on both cation extraction ability of polymers and lipophilicity around the active sites in the polymer.     

Phase-transfer catalytic activity of soluble polystyrenes containing crown ether moieties and hydroxyl groups adjacent to the macrorings

Soluble polystyrenes with crown ether structures and hydroxyl groups adjacent to the macrorings were prepared by the reaction of epoxide-containing polystyrenes with monoaza-15-crown-5 or monoaza-18-crown-6. Rate of formation of the polymer-bound alkali cation-crown alkoxide ion pair from the soluble polystyrenes and aqueous NaOH or KOH depended on the loading of crown ether and hydroxyl units and on the size of the macroring. The elimination of HCl from less reactive 2-chloroethylbenzene with aqueous NaOH or KOH in the presence of the soluble polystyrene catalysts under two-phase conditions was limited mainly by the intrinsic reaction rate. The elimination of HBr from more reactive 2-bromoethylbenzene in the presence of the less (11%) ring-substituted polymer catalyst with 18-crown unit was limited by the alkoxide formation rate. © 1994 John Wiley & Sons, Inc.     

Tertiary amine oxides as phase transfer catalysts for substitution and dichlorocyclopropanation reactions

Tertiary amine oxides catalyze a variety of phase transfer reactions, primarily by $\text{in}$$\text{situ}$ deoxygenation to form the tertiary amine or derived catalyst.     

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.     

Synthesis and characterization of new polystyrenes containing tributyltin moieties linked to the aromatic ring through a methylenic spacer

Novel polymeric derivatives bearing tributyltin carboxylate moieties in the side chain were synthesized. The coordination at tin in solution and in the solid state was investigated by both Sn‐NMR and FT‐IR: the metal atom appears completely tetracoordinated in chloroform solution, while in the solid state all polymeric products exhibit both tetra‐ and pentacoordination at tin, the latter increasing with the amount of tin containing units. No evidence of tin leaching by hydrolysis of the organometallic ester was observed for these materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5372–5383, 2004     

Metal complexes as phase transfer catalysts in the synthesis of O-acetylmandelonitrile

The asymmetric synthesis of O-acetylated mandelonitrile derivative was accomplished from PhCHO, KCN, and Ac₂O in a toluene--water system in the presence of transition metal complexes of Schiff"s bases as phase transfer catalysts.     

Developing organoboranes as phase transfer catalysts for nucleophilic fluorination using CsF

Despite the general high fluorophilicity of boron, organoboranes such as BEt₃ and 3,5-(CF₃)₂C₆H₃–BPin are shown herein for the first time, to our knowledge, to be effective (solid to solution) phase-transfer catalysts for the fluorination of certain organohalides with CsF. Significant (up to 30% e.e.) chiral induction during nucleophilic fluorination to form β-fluoroamines using oxazaborolidine (pre)catalysts and CsF also can be achieved. Screening different boranes revealed a correlation between calculated fluoride affinity of the borane and nucleophilic fluorination reactivity, with sufficient fluoride affinity required for boranes to react with CsF and form Cs[fluoroborate] salts, but too high a fluoride affinity leading to fluoroborates that are poor at transferring fluoride to an electrophile. Fluoride affinity is only one component controlling reactivity in this context; effective fluorination also is dependent on the ligation of Cs⁺ which effects both the phase transfer of CsF and the magnitude of the [Cs⋯F-BR₃] interaction and thus the B–F bond strength. Effective ligation of Cs⁺ (e.g. by [2.2.2]-cryptand) facilitates phase transfer of CsF by the borane but also weakens the Cs⋯F–B interaction which in turn strengthens the B–F bond – thus disfavouring fluoride transfer to an electrophile. Combined, these findings indicate that optimal borane mediated fluorination occurs using robust (to the fluorination conditions) boranes with fluoride affinity of ca. 105 kJ mol⁻¹ (relative to Me₃Si⁺) under conditions where a signficant Cs⋯F–B interaction persists.

Simple boranes with the optimal fluoride ion affinity are effective as catalysts for phase transfer nucleophilic fluorination with CsF.     

Novel synthesis of polymeric phase transfer catalysts containing N,N-dialkylacrylamide unit and their catalytic activity

Soluble polymeric phase transfer catalysts (PTCs) containing benzyltributylphosphonium chloride moieties and polar N,N-dialkyl-acrylamide with long alkyl groups such as N,N-dipropylacrylamide, N,N-dibutylacrylamide, N,N-dihexylacrylamide, and N,N-dioctylacrylamide were prepared via two-step reactions from p-chloromethylstyrene and the corresponding N,N-dialkylacrylamide. When the obtained polymers were added, the phase transfer catalyzed reaction of benzylchloride with solid potassium acetate to proceed smoothly. The catalytic activity was strongly affected by the content of phosphonium chloride and the varieties of comonomer unit in the polymeric PTC. The polymeric PTC containing the N,N-dihexylacrylamide unit showed excellent high catalytic activity in a low polar solvent such as the mixed solvent of toluene with 70 vol % n-tridecane. Therefore, the polymer containing lipophilic long chains such as the hexyl group is desirable for polymeric PTC. © 1996 John Wiley & Sons, Inc.     

Revisiting optically active quaternary derivatives made from prolinol as phase transfer catalysts

New non-racemic ammonium salts derived from prolinol have been prepared which are stereogenic both at N and at C. Absolute configurations rest on X-ray structures for 3c and 7a. The new compounds have been tested in a number of known enantioselective phase transfer catalytic (PTC) reactions to gain insight into steric control factors in such processes. Only very moderate e.e.s were observed. A SAMP hydrazone related catalyst (7a) reported by other authors was fully characterized. Racemic reaction products were obtained in two alkylations of diphenylmethylene benzylimine in the presence of this pure catalyst 7a. Very high e.e.s reported previously by others could not be reproduced.     

反应控制相转移催化剂的研究进展

反应控制相转移催化兼具均相和非均相催化的优点,有助于解决催化剂催化活性低及分离回收困难等问题,符合环境友好的要求,所以一直以来备受关注。反应控制相转移现象的形成与催化剂的阴、阳离子结构和溶剂等反应条件密切相关。本文就目前应用广泛的反应控制相转移催化剂的阴、阳离子的结构特点进行综述,最后就反应控制相转移催化体系可能存在的问题和创新方向作了展望。     

Preparation and synthetic application of cellulose-supported phase transfer catalysts

Esterification of potassium cellulosate with chloroacetyl chloride and acryloyl chloride under anhydrous conditions allowed the introduction of chloromethyl and vinyl groups respectively on to the cellulose backbone. Subsequent reactions with tributylphosphine, tributylamine and diethylamine generated a number of immobilized phosphonium and ammonium salts with degrees of functionalization in the range 0.2–0.7 mmol g^?1. These cellulose-supported species were used as phase transfer catalysts in displacement reactions of solid potassium acetate and phenoxide on alkyl halides, and also in the reduction of ketones by sodium borohydride. In favourable cases virtually quantitative conversions were achieved and even non-functionalized cellulose itself displayed some activity. None of the catalysts examined were active in the reduction of acetophenone although the o-hydroxy derivative was readily reduced. At the moment it is not clear whether or not some unfavourable thermodynamic distribution factors are involved; further work is in progress.     

Stereoselective substitution on PVC using phase transfer catalysts

The nucleophilic substitution with sodium benzenethiolate in aqueous suspension in the presence of a phase-transfer catalyst has been studied for two samples of PVC of different tacticities. The kinetics shows two well-defined periods: one period is very fast and involves low conversions that are greater as the isotactic content of PVC increases, while another steady period is slow and its slope seems to depend on physical features, e.g., molecular weight and crystallinity, which would affect the accessibility of nucleophile. The evolution of unreacted syndio, iso, and heterotactic triad contents with degree of substitution has been followed by ¹³C-NMR spectroscopy. Since the content of syndiotactic triads does remain unreacted at the end of the reaction and that of isotactic and heterotactic triad decreases, but at a different rate, the reaction is proved to proceed by a stereospecifically controlled mechanism. The influence of degree of substitution on both the thermal degradation rate and the evolution of UV–Visible spectra of equally degraded samples has been also studied; the highest stability in terms of degradation rate and content of short polyenes is obtained when a specific fraction of isotactic triads has reacted. From the correlation between the results of this work and those previously obtained in solution, some enlightening conclusions about the reaction mechanism are drawn.     

Imidazolium salts as phase transfer catalysts for the dialkylation and cycloalkylation of active methylene compounds

The dialkylation and cycloalkylation reactions of active methylene compounds in the presence of readily available imidazolium salts (ionic liquids) as phase transfer catalysts were performed to afford the respective dialkylated or cycloalkylated products. This method is very efficient for the synthesis of 1,1-disubstituted derivatives and cyclopropane and cyclopentane ring systems in a facile manner.