Phase Transfer Catalytic System Research Articles

Polyetheretherketone fiber-supported polyethylene glycols for phase-transfer catalysis in its surface layer

Cleaner and more efficient catalytic processes are becoming more relevant to the synthetic chemistry for reducing wastes. And herein, a commercially available ultra-high strength textile fiber polyetheretherketone (PEEK) was directionally modified by post-functionalization procedure to graft polyethylene glycols (PEG) into its surface layer to form a hydrophilic interface, and the resulted PEEK-PEG materials capable of acting as the supported phase-transfer catalysts for sorts of organic conversions in a cleaner manner were reported. The fiber samples generated during the preparation and utilization processes were observed and characterized in detail by various techniques such as morphology, mechanical properties, elemental analysis, FTIR spectroscopy and X-ray diffraction and TG analysis, and rest assured that the strategy was dependable. Moreover, the phase-transfer catalytic performance of the fiber-supported catalyst PEEK-PEG was verified in different kinds of substitution reactions, and the effects of PEG type, PEG loading and the correspondingly reaction conditions on the phase-transfer catalytic system were inspected meticulously, which were further conducive to sustain the proposed phase-transfer catalytic mechanism, and with the synergistic effect of the fiber support and PEG chain in the hydrophilic interface to afford the substitutions proceeded smoothly to obtain good to excellent product yields. Additionally, the fiber catalyst could be recycled simply and reused over 15 cycles with excellent stability under the strong caustic condition, and the catalytic system could be enlarged to the gram-scale in a spinning basket reactor, to provide a cleaner manner for phase-transfer catalysis in organic conversions with the potential of industrial application.

Catalytic Aerobic N-Nitrosation by Secondary Nitroalkanes in Water: A Tandem Diazotization of Aryl Amines and Azo Coupling

Secondary nitroalkanes underwent oxygen-mediated nitro-nitrite isomerization, serving as versatile N-nitrosating agents under aerobic conditions. To capitalize on the newly discovered aerobic nitro-nitrite isomerization phenomenon, a phase-transfer catalysis system employing KSeCN and TBAI was developed, in which the tandem diazotization and azo coupling with nitroalkanes as well as N-nitrosation of amines were accomplished. The current tandem diazotization and azo coupling strategy provides a facile synthesis of areneazo-2-(2-nitro)propane derivatives, a safe synthetic alternative to aryl diazonium salts.

Quaternary ammonium salt functionalized polyetheretherketone fiber: A novel fibrous material for phase-transfer catalysis

Herein, the commercially available ultra-high-strength textile fiber polyetheretherketone (PEEK) was directionally functionalized by afterward immobilization procedures to graft quaternary ammonium salts into its surface layer, and the resulted fibrous materials were capable of acting as the heterogeneous-supported phase-transfer catalysts were presented in the etherification of halogenated nitrobenzenes for the synthesis of nitroanisoles. The acquiring fiber samples from different processes were observed and characterized detailedly by diversified technologies of morphologies, mechanical properties, elemental analysis, FTIR spectroscopy, X-ray diffraction, and thermogravimetric analysis to confirm the reliability of this methodology. Moreover, the effect of functionalized degree on the PEEK fiber was inspected, and the phase-transfer catalytic system mediated by the fibrous material showed superior performance in terms of simple procedures, high yields of nitroanisoles (up to 99%), and excellent recyclability (over 30 cycles). Additionally, the newly developed fibrous catalyst exhibited superior stability (at least for 4 months) and effectively gram-scale operation in a concise spinning basket reactor, which is very attractive for various phase-transfer catalysis reactions in chemical productions.

Catalytic enantioselective 5-endo-bromocycloetherification of unactivated cyclic alkenes

This study reports the development and scope of catalytic enantioselective 5-endo-trig bromocycloetherification of six-membered unactivated alkenes having a hydroxyethyl group. The proposed reaction occurs in a chiral anionic phase-transfer catalytic system using a combination of a binaphthol-based chiral phosphoric acid and a derivative of DABCO bromine complex to provide bicyclic tetrahydrofuran-fused 6-membered products, which bear a bromo group at the bridgehead position with complete diastereoselectivity and good to high enantioselectivity. Results show that the enantioselectivity depends on the solvent system and substituents at the 3,3′-position of the catalyst. Thus, the best result can be obtained using a catalyst that has 2,4,6-tricyclohexylphenyl groups at the 3,3′-positions in a mixture of fluorobenzene and n-heptane. In addition, the construction of a quaternary carbon center with the retention of configuration via a radical mediated allylation of the tertiary bromo group in the product was reported.

Styrene epoxidation catalyzed by polyoxometalate/quaternary ammonium phase transfer catalysts: The effect of cation size and catalyst deactivation mechanism

Catalytic epoxidation of alkenes is an important type of organic reaction in chemical industry, and the deep insight into catalyst deactivation will help to develop new epoxidation process. In this work, series of quaternary ammoniums bearing different cationic sizes, i.e. MTOA+ (methyltrioctylammonium, [(C8H17)3CH3N]+), HTMA+(hexadecyltrimethylammonium, [(C16H33)(CH3)3N]+) and DMDOA+ (dimethyldioctadecylammonium, [(C18H37)2(CH3)2N]+) were incorporated with polyoxometalate (POM) anions to prepare phase transfer catalysts (PTCs), which were used in the styrene epoxidations. Among them, (MTOA)3PW4O24 exhibits the best catalytic performance judged from the highest styrene conversion rate (52%) and styrene oxide selectivity (93%), during which the styrene epoxidation conditions were optimized. Meanwhile, the deactivation mechanism of this kind of PTCs was proposed firstly, i.e. in the case of low H2O2 content, the oxidant can only be used in the styrene epoxidation, in which the catalyst can transform into stable Keggin-type POM. But when the content of H2O2 is higher, the excess H2O2 can re-activate the Keggin-type POM into active (PW4O24)3− anions, which can trigger the ring-opening polymerization of styrene oxide. Consequently, the catalyst is deactivated by adhered poly(styrene oxide) irreversibly, which was determined by NMR spectra. In this situation, the active moiety {PO4[WO(O2)2]4}3− in phase-transfer catalytic system can break into some unidentified species with low W/P ratio with the presence of epoxides. This work will be beneficial for the design of new PTCs in alkene epoxidation in fine chemical industry.

A novel thermoregulated phase-transfer catalysis system for chiral nano-Pt-catalyzed asymmetric hydrogenation

The chiral ionic liquid CILTPT-MS [CH3(OCH2CH2)16CD]+[CH3SO3]− (CD = cinchonidine) is found to exhibit cloud point character. Due to this cloud point character, a CILTPT-MS-stabilized chiral nano-Pt catalyst is prepared and utilized to realize transfer in a H2O–1-pentanol biphasic system by simply changing the temperature. Therefore, a fluorine-free, thermoregulated phase-transfer catalysis system is developed and applied to the asymmetric hydrogenation of α-ketoesters with enantiomeric excess of >99% and excellent conversion. In addition, the chiral nano-Pt catalyst can be easily separated and reused efficiently.

Biofuel upgrade reactions via phase-transfer catalysis of methanotrophs

Methane, one of the six major greenhouse gases, poses a serious environmental problem with the potential for global warming 20 times that of CO2. Although a large amount of methane is generated worldwide, its recovery and utilization are very low. One of the environmentally friendly ways to use methane is the biological gas-to-liquids (Bio-GTL) process, in which methane is biologically converted to useful products by microorganisms. Methanotrophs are strains that can convert methane to methanol at ambient conditions using methane monooxygenase (MMO). Here, we report an efficient phase-transfer catalysis system for methane-to-methanol conversion using methanotrophs. The methanotroph used in the work is Methylomicrobium alcaliphilum 20Z of which the methanol dehydrogenase (MDH) enzyme is removed to enhance methanol accumulation. The phase-transfer catalysis system does not require any separation processes and facilitates the mass transfer of methane gas, thereby increasing the methanol productivity and lowering the production cost. The methanol productivity is 0.717g/L/h, which is superior to the results reported to date. In addition, the use of a cellulose-membrane reactor system enables multiple biocatalytic reactions without a significant decrease in productivity.

Facile construction of thermo-responsive Pickering emulsion for esterification reaction in phase transfer catalysis system

In this paper, a thermo-responsive Pickering emulsion (PE) is constructed for the esterification reaction in the phase transfer catalysis (PTC) system. Silica nanoparticle modified by alkyl polyoxyethylene ether and tetrabutylammonium bromide (TBAB) is the highly efficient thermo-responsive Pickering emulsifier to stabilize the diisopropyl ketone-in-water emulsion. PEs can keep stable at room temperature for 3 days and demulsify only in the condition of elevated temperature and agitation, which causes the easy product separation and aqueous phase recycling. The adsorption of TBA+ and nonionic surfactant via electrostatic interaction and hydrogen bonding, respectively, can increase the hydrophobicity and the emulsifying capacity of silica nanoparticle. The ion-pair of TBA+ and reactant anion is generated and can be transferred into the organic phase, initiating the bond-forming reaction. The modifying effect of polyoxyethylene ether is weakened with the increase of temperature due to the loss of the hydrogen bonding interaction, resulting in the demulsification of PEs. Moreover, the cloud point of polyoxyethylene ether is the temperature for the complete separation of two phases. In this PTC system, the conversion rate for the esterification can reach to 92 % and the aqueous phase can be reused at least 5 times without sacrifice of the catalytic activity, demonstrating the potential application in industry.

Specific Features of Phase Transfer Catalytic Glycosylation of 2-Mercaptobenzimidazole

The reaction of 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-glucopyranosyl chloride with 2‑mercaptobenzimidazole under conditions of the phase transfer catalysis was studied and specific features of the phase transfer process were evaluated. It was found that the corresponding N- and S-β-D-glucosaminides were the major glucosaminylation products. Glucosaminylation of 2-mercaptobenzimidazole in an anhydrous methylene chloride–sodium hydride phase transfer catalytic system was shown to proceed regiospecifically. The structures of the synthesized compounds were characterized using 1H NMR spectroscopy and mass spectrometry.

Cotton Fabric-Supported Cationic Acrylate Polymer as an Efficient and Recyclable Catalyst for Williamson Ether Synthesis Reaction in Solid-Liquid-Liquid Phase Transfer Catalysis System.

Cotton-based catalytic fabric (CCF) was prepared by the simple padding-drying method with the copolymer of five functional monomers as the modifier and was applied in the solid–liquid–liquid phase-transfer catalysis (SLL-PTC) system. Effects of the structure of the function monomer, the content of the cation, and the loading amount on the catalytic activity of CCF were investigated. The lipophilicity, disperse extent of cationic center, and the accessory to the ion for CCF were influenced by the structure and content of the function monomer. The organic phase was adsorbed on the surface of the catalytic fabric, and the novel catalytic cycle in the PTC system was initiated. The anion in the aqueous phase diffuses through the interfacial region to the site for ion exchange. Bond-forming reaction was initiated in the interfacial region between the organic phase on the fabric and the aqueous phase. The conversion rate for Williamson ether synthesis reaction reached 92%, and CCF could be reused five times in this SLL-PTC system.

Synthesis of 1-butoxy-4-tert-butylbenzene under The Effect of Multi-site Phase Transfer Catalysis System – A Kinetic Study

Phase transfer catalysis technique proved to be a useful method for synthesizing various organic compounds under heterogeneous reactions and recognized as a viable environmentally friendly. The influence of a new multi site phase transfer catalyst (MPTC) is the synthesis of 1-butoxy-4-tertbutylbenzene from 4-tert-butylphenol with 1-bromobutane (BB) under heterogeneous solid-liquid condition using potassium hydroxide as a base at 60 °C. The higher conversion of 1-bromobutane was achieved by using the synergistic condition of multi-site phase transfer catalyst in better efficacy. The reaction rate enhanced by decreases the volume of water. The apparent the reaction rate was found to be pseudo-first order kinetics. The apparent rate constant was increased linearly with the increase in the concentration of various parameters, such as: MPTC, temperature, potassium hydroxide, and stirring speed. The activation energy (Ea) was also calculated through the Arrhenius plot. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

A Kinetic Study on the Synthesis of N-arylation of Indole Under Synergetic Effect of Multi-Site Phase Transfer Catalysis System

Background:Phase transfer catalysis technique is recognized as an attractive method for synthesizing several organic compounds under heterogeneous reaction.Methods:In this study, the effect of Multi-site Phase-Transfer Catalyst (MPTC) was tested during the synthesis of 1-(4-nitrophenyl)-1-indole from 1-chloro-4-nitrobenzene (CNB) and indole in a heterogeneous solid-liquid condition using sodium hydroxide at 50°C.Results:In a synergetic condition, in the presence of MPTC the conversion of 1-chloro-4- nitrobenzeneyield was increased, which is proved the efficacy of this catalyst. In addition, the rate of this reaction was also enhanced by the change in volume of water.Conclusion:The apparent reaction rate was found to be of pseudo-first-order kinetics. MPTC is a promising tool for many organic reactions. Therefore, increase the rate constant can be achieved by various parameters, such as temperature, MPTC, sodium hydroxide, and stirring speed.

Enantioselective Synthesis of Multifunctionalized 4H-Pyrans via Formal [4 + 2] Annulation Process by Bifunctional Phosphonium Salt Catalysis.

A highly enantioselective formal [4 + 2] annulation involving electron-deficient allenes as C2-synthons has been developed under bifunctional phosphonium salt catalysis. With this catalytic protocol, a wide range of synthetically interesting and highly functionalized chiral 4H-pyran derivatives were readily prepared in good yields (up to 99%) with outstanding diastereo- and enantioselectivities (up to >20:1 dr, up to >99.9% ee). The utility and the practicality of this method were demonstrated by the gram-scale reaction and facile elaboration. Of note, this is the first example of an asymmetric annulation reaction involving allenic reactants under a phase-transfer catalysis system.

Ultrasound-Assisted Green Synthesis of Dialkyl Peroxides under Phase-Transfer Catalysis Conditions

The dialkyl peroxides, which contain a thermally unstable oxygen–oxygen bond, are an important source of radical initiators and cross-linking agents. New efficient and green methods for their synthesis are still being sought. Herein, ultrasound-assisted synthesis of dialkyl peroxides from alkyl hydroperoxides and alkyl bromides in the presence of an aqueous solution of an inorganic base was systematically studied under phase-transfer catalysis (PTC) conditions. The process run in a tri-liquid system in which polyethylene glycol as a phase-transfer catalyst formed a third liquid phase between the organic and inorganic phases. The use of ultrasound provided high yields of organic peroxides (70–99%) in significantly shorter reaction times (1.5 h) in comparison to reaction with magnetic stirring (5.0 h). In turn, conducting the reaction in the tri-liquid PTC system allowed easy separation of the catalyst and its multiple use without significant loss of activity.

Asymmetric Three-Component Cyclizations toward Structurally Spiro Pyrrolidines via Bifunctional Phosphonium Salt Catalysis.

Asymmetric multicomponent reactions toward optically pure compounds are highly attractive but extremely challenging. Presented herein is a highly diastereo- and enantioselective three-component cyclization of exocyclic alkenes with aldehydes and amino esters, which was enabled by bifunctional phosphonium salt catalysts. A wide range of multiply substituted spiro pyrrolidine derivatives were prepared in high yields with excellent stereoselectivities. Of note, this is the first example of a catalytic asymmetric three-component reaction with a phase-transfer catalysis system.

Dipeptide-Based Phosphonium Salt Catalysis: Application to Enantioselective Synthesis of Fused Tri- and Tetrasubstituted Aziridines

Over the past decades, phase-transfer catalysis (PTC), generally based on numerous chiral quaternary ammonium salts, has been recognized as a powerful and versatile tool for organic synthesis in both industry and academia. In sharp contrast, PTC involving chiral phosphonium salts as the catalysts is insufficiently developed. Recently, our group realized the first enantioselective aza-Darzens reaction for preparing tri- and tetrasubstituted aziridine derivatives under bifunctional phosphonium salt catalysis. This article briefly discusses the recent development in asymmetric reactions (mainly including nucleophilic additions and cyclizations) promoted by chiral quaternary phosphonium salt catalysts. We expect that more catalytic asymmetric reactions will be developed on the basis of such new phase-transfer catalytic systems in the near future.

Single-stage synthesis of alkyl-H-phosphinic acids from elemental phosphorus and alkyl bromides

Elemental phosphorus (red or white) reacts with alkyl bromides at 60–62 °C in the phase-transfer catalytic system KOH/H2O/PhMe/Et3BnNCl to afford alkyl-H-phosphinic acids in up to 47% yield.

Synergetic effect of multi-site phase transfer catalysis system mediated free radical polymerization of acrylonitrile – a kinetic study

In this work, the kinetics and mechanism of free radical polymerization of acrylonitrile (AN) using potassium peroxydisulphate (PDS-K2S2O8) as a water soluble initiator in the presence of synthesized 4,4'-dihexadecyl-1,1'-bipyridine diiumdichloride (DHBPDDC) as multi-site phase-transfer catalyst (MPTC) has been investigated. The polymerization reaction were carried out under nitrogen atmosphere and unstirred condition at constant temperature 60+1°C in ethyl acetate/water biphasic medium. The effects of variation of monomer(AN), initiator(PDS) and catalyst(MPTC) solvent polarity and temperature on the rate of polymerisation (Rp) were ascertained. The order with respect to monomer(acrylonitrile) was found to be unity. The order with respect to initiator and catalyst was found to be 0.51, 0.48 respectively. However, an increase in the polarity of the solvent has slightly increased the rate of polymerization value (Rp). Based on the results obtained, a suitable kinetic mechanism scheme has been proposed to account for the experimental observations and its significance was discussed. The other thermodynamic parameters such as entropy of activation ((∆S#), enthalpy of activation (∆H#) and free energy of activation (∆G#) have been calculated.

Catalytic Process for the Hydroxide-Initiated Reaction of the “Weakly Acidic” Substrate in the Third-Liquid Phase-Transfer Catalytic System

Generation processes of the third phase and the carbanion for Horner−Wadsworth−Emmons (HWE) reaction of the “weakly acidic” substrate in the third−liquid PTC (TLPTC) system were investigated. The third phase was consisted of Et2PO4− (diethyl phosphate anion), Br− and TBA+ (tetrabutylammonium), and the mole of Et2PO4− was 6.65 times of that of TBA+. The true catalyst was the complex of TBA+Et2PO4− and TBAB. Excess Et2PO4− could be associated with TBA+Et2PO4−, resulting the generation of the third phase. The “true” catalyst showed a higher catalytic activity and the reaction equilibrium constant for the third phase cycle was 26−times of that for the organic phase cycle. Results from background reaction, interfacial tension and H−D exchange reaction experiments suggested that the phosphonate were deprotonated by “naked” OH− without help of the catalyst. These novel generation processes of the third phase and the carbanion were the key factors for this efficient TLPTC system.

2-Mercaptobenzoxazole as a Novel Sulfur Transfer Agent in the Cu-Catalysed “On-Water” Synthesis of Symmetrical or Unsymmetrical Sulfides under Phase Transfer Catalysis Conditions

Aim and Objective: In the chemical literature, there is very little data about copper catalysed synthesis of diaryl sulfides in water. In this work we present a novel highly selective Cu-catalysed “on-water” method of the synthesis of symmetrical and unsymmetrical sulfides from aryl iodides and 2-mercaptobenzoxazole as a novel sulfur transfer agent. Material and Method: 2-Mercaptobenzoxazole was presented as a novel sulfur transfer agent. Novel Cucatalysed “on-water” method for the selective synthesis of diaryl sulfides from diaryl iodides in the phase transfer catalytic system 2-mercaptobenzoxazole / CuI / proline/ KOH/ Adogen 464 was developed. Results: We have elaborated the novel catalytic system 2-mercaptobenzoxazole / KOH / CuI / Adogen464 / proline for the synthesis of diaryl sulfides from corresponding aryl iodides in water. The products were isolated in 30-76% yields. Modification of the presented method was successfully applied in the preparation of unsymmetrical sulfides. For example, benzylphenylsulfide and benzyl(3-fluorophenyl)sulfide were selectively prepared in 68% and 57% yields, correspondingly, by three-component, one-pot coupling reaction in the system PhCH2Br (1 mmol) / ArI (1 mmol) / 2-meracaptobenzoxazole (1 mmol) / CuI (20 mol.%) / proline (20 mol.%)/ Adogen464 / H2O at 160°C. Conclusion: Thus, novel Cu-catalyzed “on-water” method for the synthesis of symmetrical and unsymmetrical sulfides in the system aryl iodides (and benzyl bromide) /2-mercaptobenzoxazole / KOH / CuI / Adogen464 / proline / H2O was presented. Interestingly, similar reaction of 2-mercaptobenzothiazole in the above system led only to 2-arylsulfanylbenzothiazoles. According to our point of view, the presented method is the best for the selective preparation of sulfides possessing NH2, Br and F functional groups. Keywords: 2-Mercaptobenzoxazole, diaryl sulfides, alkyl aryl sulfides, benzyl bromide, aryl iodides, Cu-catalysis, “on-water” phase transfer catalysis, sulfur transfer.