Phase Transfer Catalytic System Research Articles

Evaluation of Ligno Boost™ softwood kraft lignin epoxidation as an approach for its application in cured epoxy resins

In this study, modification of LignoBoost™ softwood kraft lignin with epichlorhydrin in water-organic solvents media was realized. Lignin-based epoxy resins were obtained by two ways: acetone extraction of glycidylated lignin or glycidylation of the acetone soluble lignin fraction. The effect of glycidylation regimes on the yields of acetone soluble fractions, their functional composition and physical-chemical characteristics was investigated using wet chemistry methods, FTIR spectroscopy, size exclusion chromatography (SEC) and differential scanning calorimetry (DSC). The positive effect of the biphasic phase transfer catalytic system – KOH/quaternary ammonium salt – on glycidylation of both phenolic and aliphatic hydroxyl groups was testified, exemplified using a lignin-like model compound – 4-hydroxy-3-methoxylbenzyl alcohol (vanillyl alcohol). The partial substitution (up to 10%) of commercial epoxy resin on the basis of bisphenol A (Araldite® LY1564) by lignin-based epoxy resin significantly increased the viscosity of resin. Therefore, the possible practical application of lignin-containing epoxies as adhesive, mastic or crack filler instead of binder for fiber reinforced composites was considered. A tendency towards increasing Young’s modulus of cured lignin-containing epoxies, compared with the case of the reference composition, was observed. The lignin chemically incorporated into the matrix of cured commercial epoxy resin acts as a charcoal formation promoter in high temperature treatment.

Sustainability Improvements through Catalyst Recycling in a Liquid–Liquid Batch and Continuous Phase Transfer Catalyzed Process

Phase transfer catalysis (PTC) is a potentially useful approach to processing but often uses environmentally problematic substances that typically end up in waste streams. The sustainability benefits of catalyst recovery from a third liquid layer in a PTC system were investigated for the O-alkylation of 3-phenyl-1-propanol. The system was operated in both the batch and the continuous modes. The formation of a third liquid phase and using it to recover catalyst reduces equipment footprint, product loss through the waste, and VOC emissions and improves energy efficiency compared to the equivalent process designed without the third liquid layer, but at the expense of higher costs, higher E factor, and lower volume efficiency. Overall, continuous phase transfer catalyst recycling is better than the equivalent batch process in volume efficiency, in-process inventory, mass efficiency, E factor, VOC emission, equipment footprint, and operating cost. However, the batch process with batch catalyst recycling is sti...

Structure and Dynamics of Host/Guest Complexation at the Liquid/Liquid Interface: Implications for Inverse Phase Transfer Catalysis

β-Cyclodextrin (β-CD) enhances the rate of the biphasic SN2 reaction between 1-bromooctane and anionic nucleophiles in an adjacent, immiscible aqueous phase. In this work, molecular dynamics simulations were used to study the mass-transfer component of this inverse phase transfer catalysis system. The orientation of the solvent molecules around the β-CD molecule was investigated in detail, revealing the preferred position of the 1-bromooctane guest within the β-CD host molecule. Potentials of mean force for the insertion/extraction of the guest molecule were calculated in the two bulk solvents and at the liquid/liquid interface. The findings of these orientational and energetic studies suggest a logical exchange mechanism facilitated by β-CD.

Asymmetric fluorinative dearomatization of tryptamine derivatives.

An asymmetric fluorinative dearomatization reaction of tryptamine derivatives was developed by using a chiral anion phase transfer catalyst (PTC) system, and the preliminary results of the reaction mechanistic study were achieved. This method is characterized by a simple operation, facile introduction of a fluorine atom in a highly enantioselective manner and construction of two contiguous quaternary stereogenic centers.

Kinetic Study for the Synthesis of 1-nitro-4-(prop-2-ynyloxy) benzene in Solid-Liquid PTC Condition

Background: Currently, phase transfer catalysis is an experimental technique which is environmentally benign technique have become immensely popular in promoting various reactions. Methods: The reaction between 4-nitrophenol and propargyl bromide was carried out in a solid-liquid biphasic phase transfer catalytic system using potassium carbonate as base at 40°C. Results: Trace amount of water is introduced to the reaction system to enhance the reaction rate. The higher conversion of propargyl bromide was achieved in the presence of tetra-n-butylammonium bromide (TBAB) as catalyst. From the experimental evidence there is no side products were observed during or after the reaction. Conclusion: Various parameters were conducted to increase the conversion of propargyl bromide such as, stirring speed, various PTCs, temperature and amount of TBAB loading. All the experiments were conducted to obey pseudo-first order rate law. Apparent activation energy was also determined from the Arrhenius plot. Keywords: Phase transfer catalyst, 4-nitrophenol, propargyl bromide, kinetics, 1-nitro-4-(prop-2- ynyloxy)benzene, solid-liquid reaction.

Novel kinetics model for third-liquid phase-transfer catalysis system of the “complex” carbanion: Competitive role between catalytic cycles

Kinetic model for Horner–Wadsworth–Emerson (HWE) reaction of the “complex” carbanion in the third-liquid phase-transfer catalysis (TLPTC) system was proposed and the factors that influenced the model parameters were investigated in details. The generation process and the composition of the third phase revealed that there were two catalytic cycles (the third phase reaction and the organic phase reaction) in this TLPTC system. Kinetic model which consisted of ion-exchange reaction rate constant, bond-forming reaction rate constant and the contribution ratio between each two catalytic cycle was deduced. Distribution of the carbanion ion-pair between the third phase and the organic phase caused the competitive relationship between these two catalytic cycles. Third phase was the preferred region for the bond-forming reaction, and which contribution was always 5–6 times higher than that of the organic phase reaction. Reaction rate of each catalytic cycle was also affected by lipophilicity of the anion in this TLPTC system. The steric hindrance, lipophilicity of the catalyst cation and polarity of the third phase were primary factors influencing catalyst activity.

Mechanism and kinetics of Horner–Wadsworth–Emmons reaction in liquid–liquid phase-transfer catalytic system

Liquid–liquid phase-transfer catalytic (LL-PTC) system suitable for symmetric distyryl compounds could not be used to synthesize asymmetric derivates. Relatively low value, the time-dependence of the interfacial tension with only phosphonate in the organic phase and high background reaction rate demonstrated that “weakly acidic” phosphonate was adsorbed on the interfacial layer and deprotonated by excess “naked” OH− without the help of the catalyst. Phase-transfer catalyst participated in the transfer process of the carbanion and accelerated the bond-forming reaction. However, the distributing region for the carbanion ion-pair in this PTC system was dependent on the usage of the catalyst and the mechanism would change from the interfacial mechanism to the extraction mechanism. Accordingly, the mechanism including adsorption, deprotonation, ion-exchange reaction, distribution and bond-forming reaction was proposed, and the kinetic model was performed. The activation energy and the dependence of catalytic activity on lipophilicity and accessibility parameter also supported the proposed mechanism. The rate-determining step was not the bond-forming reaction for each mechanism and the apparent reaction rate was relevant to the generation rate of the carbanion and the ion-exchange reaction rate.

Toward Understanding the Mechanism of Phase Transfer Catalysis with Surface Second Harmonic Generation

Phase transfer catalysis (PTC) is nowadays an important technique of organic synthesis. There are numerous indications that its key processes take place at the boundary between immiscible phases; however, this has not been proved by direct observations of interfaces separating the phases. Here, we demonstrate how surface second harmonic generation (SSHG) can be used for direct observation and identification of species adsorbed at the interface during a PTC reaction. The model system consisted of an organic (chlorobenzene) and aqueous (saturated solution of NaOH) phases with pH indicator (thymolphthalein, ThPh) used as a reactant. SSHG measurements allowed monitoring the surface concentration of ThPh anions at the interface and recording the kinetics of adsorption and deprotonation of ThPh. The results confirmed that deprotonation indeed occurs in the interfacial region. The proposed technique is relatively simple and general and can be used in a variety of PTC systems; therefore, its application will unve...

Study on Oxidative Desulfurization Catalyzed by Organic-inorganic Heteropolyacids as Phase Transfer Catalyst

In this paper, organic-inorganic heteropolyacids were prepared, including [π-C5H5NC16H33]3[PW4O16], [π-C5H5NC16H33]3[PMo4O16], [π-C5H5NC12H25]3[PW4O16] and [π-C5H5NC12H25]3[PMo4O16]. The efficiency of oxidative desulfurization was investigated on the four kinds of catalysts under the same conditions using the simulated oil prepared by dissolving organo-sulfur in normal octane. The results show that the catalytic activity of [π-C5H5NC16 H33]3[PW4O16] is the best. The catalytic activity of these heteropolyacids was following the order of [π-C5H5NC16H33]3[PW4O16] > [π-C5H5NC12H25]3[PW4O16]>[π-C5H5NC16H33]3[PMo4O16]>[π-C5H5NC12H25]3[PMo4O16]. Under the optimal experimental conditions, pre-reaction time between H2O2 and the catalyst being 10 min, reaction temperature being 60 °C, O/S molar ratio being 10, the amount of catalyst being 1 wt% of n-octane, and the catalyst being [π-C5H5NC16H33]3[PW4O16], the dibenzothiophene (DBT) conversion was nearly 100% after 60 min. The catalyst [π-C5H5NC16H33]3[PW4O16] can be reclaimed by auto precipitation due to the exhausting of H2O2. The results show that organic-inorganic heteropolyacids are phase transfer catalyst and oxidative desulfurization system belongs to the phase transfer catalysis system controlled by reaction. The catalytic activity of the recycled [π-C5H5NC16H33]3[PW4O16] is almost the same as the fresh. Then, the efficiency of oxidative desulfurization was investigated with different simulated oils using DBT, thiophene (TH), benzothiophene (BT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), respectively. Under the same conditions, the efficiencies of oxidative desulfurization decrease in the order of DBT>4,6-DMDBT>BT>TH, the result was influenced by electron density on the sulfur atoms and the steric hindrance. It showed that the final desulfurization product of TH, BT, DBT and 4,6-DMDBT was 2 4 SO , 4 SO , DBT sulphone and 4,6-DMDBT sulphone, respectively. [π-C5H5NC16H33]3[PW4O16] used in desulfurization of the real diesel and the sulfur removal rate was 92.7%. The sulfur content was reduced from 355 mg/kg to 26 mg/kg. Furthermore, by studying the kinetics of DBT oxidation by H2O2, the reaction order was found to be 1st to DBT. The activation energy ranged from 47.9 kJ/mol to 55.4 kJ/mol by different organic-inorganic heteropolyacids. It indicates the reaction process is quite fast in ODS. The new type of catalysts has a broad development prospect in oil desulfurization.

TRIMETHYLSILYLCYANATION OF HETEROAROMATIC KETONES IN THE CsF/18-CROWN-6/BENZENE PHASE-TRANSFER CATALYTIC SYSTEM

The trimethylsilylcyanation of heteroaromatic ketones in the Me 3 SiCN/CsF/18-crown-6/benzene phase-transfer catalytic system has been studied. The reaction products have been isolated selectively in yields of up to 95%. Authors: E. Abele, R. Abele, I. Mazheika, and E. Lukevics. English Translation in Chemistry of Heterocyclic Compounds , 1999, 35 (8), pp 943-946 http://link.springer.com/article/10.1007/BF02252162

Synthesis of stilbene, 1,4-distyrylbenzene and 4,4′-distyrylbiphenyl via Horner–Wadsworth–Emmons reaction in phase-transfer catalysis system

Stilbenes, 1,4-distyrylbenzenes and 4,4′-distyrylbiphenyls were synthesized via Horner–Wadsworth–Emmons (HWE) reaction in liquid–liquid (LL) and solid–liquid (SL) phase transfer catalysis (PTC) systems. The effect of the side reaction, reactants and the third phase on the activity of HWE reaction were investigated. For aldehydes bearing electron-donating substitute, the yields were more than 90% and the products were all (E)-isomers in both PTC systems. The SL-PTC system was milder than LL-PTC system for HWE reaction due to the different mechanisms. The side reaction of aldehyde was similar to Cannizzaro reaction, whereas the molar ratio of benzoic acid to benzyl alcohol as the products was not 1:1. The limited third phase was discovered to exist in LL-PTC system. In SL-PTC system, the third phase could increase substantially the reaction rate. Moreover, the aqueous phase in LL-PTC system could be reused four times without sacrifice of the yield and reaction rate.

ALKYLATION OF HETARYL METHYL KETONES BY PROPARGYL BROMIDE UNDER PHASE-TRANSFER CATALYSIS CONDITIONS

The alkylation of aryl and hetaryl methyl ketones by propargyl bromide using the phase-transfer catalysis system KOH (s)/18-crown-6/benzene is studied. The corresponding C-trialkylated products are selectively obtained in 34-78% yields. Authors: E. Abele, R. Abele, Yu. Popelis, I. Mazheika, and E. Lukevics. English Translation in Chemistry of Heterocyclic Compounds , 1999, 35 (4), pp 436-438 http://link.springer.com/article/10.1007/BF02319330

A kinetic and spectroscopic study on the polyoxometalate species in a reaction-controlled phase transfer catalytic epoxidation system

An excellent catalytic epoxidation system containing [π-C5H5N(CH2)15CH3]3[PW4O32]/H2O2/ethyl acetate/olefin has been prepared and shown to exhibit a unique reaction-controlled phase transfer behavior. The composition and structural changes of the catalyst [π-C5H5N(CH2)15CH3]3[PW4O32] (I) before, during and after reaction were investigated by 31P NMR, 31P MAS NMR, 183W NMR, IR, Raman and UV–Vis spectroscopy. The 31P MAS NMR and 31P NMR confirmed that the original catalyst was a mixture of heteropoly tungstophosphates. According to the 31P NMR and 183W NMR analysis, new phosphoperoxotungstate species, [PWxOy]z−, were produced in this catalytic system instead of the well known species of {PO4[WO(O2)2]4}3−. The active species of phosphoperoxotungstate containing many peroxo bonds should be similar to [(PO4){WO(O2)2}4]3−. The species degraded from H3PW12O40, H2O2 and quaternary ammonium were very complicated and the compositions were mainly dependent on the ratio of H2O2 to H3PW12O40.

Kinetics and mechanism of Horner–Wadsworth–Emmons reaction of weakly acidic phosphonate in solid–liquid phase-transfer catalysis system

Homer–Wadsworth–Emmons (HWE) reaction of diethyl benzylphosphonate (DEBP, pKa = 27.55) with aldehyde was performed in a solid–liquid phase-transfer catalysis (SL–PTC) system using sodium hydroxide as the solid phase. Various parameters that influenced the pseudo-first-order rate constant including stirring speed, catalysts, salt, water and temperature were investigated to explore the process of the generation and transfer of the active intermediate. A reasonable interfacial mechanism of the PTC reaction of the weakly acidic substrate was proved for the first time. HWE reactions under SL–PTC conditions showed high activity and geometric selectivity. It is anticipated that this simple and controllable synthesis method should provide a new idea for HWE reaction in chemical industry. • HWE reaction of weakly acidic phosphate was developed in SL-PTC system. • The reaction kinetics was investigated under the pseudo-first-order conditions. • The interfacial mechanism for SL-PTC reaction of weakly acidic substrate was proved. • This reaction showed high activity and geometric selectivity at low temperatures.

Physico-Chemical Studies of Reactions of Alkalytion of Schiff,s Bases

The Schiff’s Bases (N-arylidene benzylamines) (1-29) have been alkylated with different alkyl halides by applying solid-liquid phase-transfer catalysis system (solid K2CO3, CH3CN, TBAB). The products were identified as the corresponding alkylated Schiff’s bases, by analyses of their spectral data (UV, IR, NMR, MS). The mechanism of the reaction was investigated on the basis of theoretical approach using semi-empirical AM1 module in the CS ChemOffice molecular modeling package.

(C18H37)2(CH3)2N]7[PW11O39]: a temperature-controlled phase transfer catalyst for olefin epoxidation

A novel temperature-controlled phase transfer catalytic system based on [(C18H37)2(CH3)2N]7[PW11O39] for olefin epoxidation was demonstrated. The reaction was conducted in a non-chlorinated solvent of ethyl acetate with hydrogen peroxide. The catalyst was easily recovered and reused even ten cycles without loss in activity and selectivity.

ChemInform Abstract: Selective and Simple Phase-Transfer Catalyzed Synthesis of Disulfides from Thiols.

Two novel methods of synthesis of disulfides from thiols or their Na salts in the phase transfer catalytic system CBr4/18-crown-6/benzene or toluene are developed and the products isolated in 67–88% yields.

ChemInform Abstract: Trimethylsilylcyanation of Heteroaromatic Ketones in the CsF/18-crown-6/benzene Phase-Transfer Catalytic System.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ESI–MS study of copper chloride/phase-transfer catalytic systems for oxidation of cumene with 1-methyl-1-phenylethyl hydroperoxide

Oxidation of cumene with 1-methyl-1-phenyl- ethyl hydroperoxide in the presence of copper chloride/ phase transfer catalytic systems was investigated by ESI- MS. For catalytically active copper(II) chloride/crown ethers, copper(II) chloride/crown ethers/alkaline metal salts, and copper(II) chloride/tetrabutylammonium chloride systems, the presence of a few kinds of copper complexes in the organic phase was detected by use of ESI-MS. When copper(II) chloride/podand systems were used, the con- version of hydroperoxide and the yield of oxidation product were close to zero, although the concentration of copper complexes in the organic phase was high. Addition of bis(2-hydroxyethyl) ether to the catalytically active copper(II) chloride/18-crown-6 system resulted in an inhibition effect.

Liquid–liquid–liquid phase-transfer catalysis for cleaner and selective etherification of p-hydroxy-biphenyl with benzyl chloride to 1,1′-biphenyl-4-(phenylmethoxy)

Conversion of bi-liquid phase transfer catalysis (PTC) into a tri-liquid PTC system presents several advantages in terms of enhancement of reaction rates and selectivity. These improvements lead to a minimization of waste, reduction in reactor volume and processing times by orders of magnitude in comparison with a liquid–liquid PTC process. The O-alkylation (etherification) of 4-hydroxybiphenyl with benzyl chloride to 1,1′-biphenyl-4-(phenylmethoxy) was carried out under L-L-L PTC system with 100% selectivity at 50°C. The resulting product is commercially used in fine chemical industry and to produce novel materials. The catalyst-rich third phase can be recycled many times, thereby leading to profitability and waste minimization. A reaction mechanism and kinetic model are developed and validated against experimental data, which include the effect of different variables on reaction rates and selectivity.