Phase-transfer Reaction Research Articles

Didecyldimethylammonium bromide (DDAB): a universal, robust, and highly potent phase-transfer catalyst for diverse organic transformations

Didecyldimethylammonium bromide (DDAB) has been scrutinized in comparison with traditional phase-transfer catalysts in variety of liquid–liquid reactions. It was found to be an exceptionally comprehensive, durable, and highly efficient phase-transfer catalyst (PTC) in a number of representative organic transformations such as C- and N-alkylations, isomerization, esterification, elimination, cyanation, bromination, and oxidation under very mild conditions of temperature and mixing. It was confirmed that DDAB is an exceedingly accessible and concurrently a highly liphophilic phase-transfer catalyst. This unprecedented characteristic renders DDAB to be a multipurpose catalyst that functions effectively both in mass transfer controlled and chemically controlled phase-transfer reactions.

Microwave‐Accelerated Suzuki—Miyaura Coupling Reactions Using Potassium Aryltrifluoroborates.

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KINETIC STUDY OF THE SYNTHESIS OF DICHLOROCYCLOPROPANE BY TRIALKYLAMMONIUM PROPANSULTANS AS NEW PHASE-TRANSFER CATALYSTS

In this work, the synthesis of dichlorocyclopropane, from a phase-transfer catalyzed reaction of chloroform and olefins (1-octene or 1,7-octadiene), was carried out in an alkaline solution of NaOH/chloroform two-phase medium. Trialkylammonium propansultan, a zwitterionic compound, acts as a new phase-transfer catalyst of high reactivity to produce high yields of dichlorocyclopropane. Dichlorocarbene (:CCl2), which is an active species to react with olefins to produce dichlorocyclopropane in the organic phase, is generated from the reaction of chloroform, sodium hydroxide, and trialkylammonium propansultan as phase-transfer catalyst at the interface between two phases. The dichlorocyclopropanation is dramatically enhanced by adding a small quantity of trialkylammonium propansultan. An interfacial reaction mechanism was proposed to explain the reaction characteristics. A pseudo first-order rate law is used to describe the reaction rate at high alkaline concentration solution (>50 wt% NaOH). There is detailed investigation of the reaction kinetics, including the effect of the reaction conditions—the agitation speed, temperature, phase-transfer catalysts and their amounts, the amount of chloroform, the amount of 1-octene, inorganic salt (NaCl and Na2SO3), and alkali concentration—on the conversion of 1-octene.

Methanolysis of triacylglycerols by organic basic catalysts

AbstractMethanolysis of rapeseed and soybean oil was studied using organic basic catalysts at boiling with reflux. The molar ratio methanol/free fatty acids (FFA) amounted to approx 2.8 : 1. The catalyst (guanidine carbonate) is used at concentrations between 0.5 and 1.3 wt‐% with respect to the oil. During boiling at reflux, guanidine carbonate disintegrates into guanidine and gaseous carbon dioxide. This is a very special reaction; other alcohols such as ethanol, propanol, etc. do not react in this way with guanidine carbonate. Under these conditions, the reaction mixture consists of two phases. The catalyst is mainly dissolved in the methanol phase. The rate of the phase transfer reaction is increased by stirring. With guanidine carbonate as a catalyst, neutralized rapeseed oil yielded, within 45 min and in one step, a product that meets the European Norm for biodiesel. Degummed and dried crude rapeseed oil contains ca. 1 wt‐% FFA, whereas crude degummed and dried soybean oil contains 0.3–0.7 wt‐% FFA. During catalysis with guanidine carbonate, the FFA are transformed into their methyl esters to about 60–70% at low concentrations in the crude oil (approximately up to 1–1.5%). Neutralization of the degummed and dried crude oil proved to be unnecessary in such cases.

Superoxide catalyzed oxidation of 4-alkylsubstituted pyrazol-5-ones to 4-alkyl-4-hydroxysubstituted pyrazol-5-ones

Superoxide ion, generated in situ by the phase transfer reaction of potassium superoxide and tetraethylammonium bromide, brings about an easy oxidation of different 4-alkylsubstituted pyrazol-5-ones to yield 4-alkyl-4-hydroxy pyrazol-5-ones in reasonably good yields.

Magnetic nanoparticle-supported crown ethers

Magnetic nanoparticle (MNP)-supported crown ethers were successfully prepared and evaluated as catalysts for solid-liquid phase-transfer reactions; the catalytic activities of the MNP-supported crown ethers were not inferior to those of non-supported crown ethers; after the reactions, the catalysts could be readily separated using an external magnet and reused without significant loss of catalytic efficiency.

Microwave-Accelerated Suzuki-Miyaura Coupling Reactions Using Potassium Aryltrifluoroborates

The microwave-accelerated Suzuki-Miyaura coupling of bromoarenes and potassium aryltrifluoroborates in good to excellent yields is described. The method does not require the use of phosphine ligands or phase-transfer catalysts and reactions are complete in 20 minutes.

SYNTHESIS OF DIALKOXYMETHANE AT HIGH ALKALINE CONCENTRATION VIA PHASE TRANSFER CATALYSIS

The phase-transfer catalytic reaction (PTC) of 2,4,6-tribromophenol and dibromomethane by quaternary ammonium salt was carried out in a high alkali content of KOH/dibromomethane two-phase medium. A large conversion of 2,4,6-tribromophenol is obtained at a region of high KOH content. Dibromomethane acts both as the organic-phase reactant and the organic solvent; thus, no extra organic solvent is required. Two main products, i.e., α -bromomethyl 2,4,6-tribromophenyl ether (mono-substituted product) and bis-(2,4,6-tribromophenoxide)methane (bis-substituted product), were detected in the solution during the phase-transfer catalytic reaction. The active catalyst (tetrabutylammonium 2,4,6-tribromophenoxide, ArOQ), which was produced from the reaction of 2,4,6-tribromophenol, potassium hydroxide, and tetrabutylammonium bromide (TBAB or QBr), is purified as the crystalline product from the reaction solution. A kinetic model is developed to describe the behaviors of the two organic-phase reactions on the basis of the experimental observation. The two intrinsic rate constants of the two organic-phase reactions, which are the rate-determining steps of the whole reaction system, are determined. Effects of the reaction conditions, such as agitation speed, amount of water, amount of TBAB catalyst, temperature, and amount of dibromomethane, quaternary ammonium salts, and inorganic salt KBr, on the conversion of 2,4,6-tribromophenol and the reaction rate are investigated in detail.

Semi-Continuous Gas-Liquid Phase-Transfer Catalyzed Reaction of o-Phenylene Diamine and Carbon Disulfide by Tetrabutylammonium Hydroxide

The phase-transfer catalyzed reaction of o-phenylene diamine and carbon disulfide to synthesize 2-mercaptobenzimidazole (MBI) in a gas phase/liquid-phase solution two-phase medium was carried out in a semi-continuous reactor. Tetrabutylammonium hydroxide (TBAOH or QOH), which is an active compound, was used as the catalyst to promote the reaction rate. The liquid-phase solution contains the mixture of ethanol and water in an appropriate volume ratio. The gas-phase CS2/CH2Cl2 mixture of a higher temperature was continuously introduced to the reactor for reaction. The main advantage of the present system is that the reaction is carried out at a relatively higher temperature in the semi-continuous reactor. The gas-phase CS2/CH2Cl2 mixture first dissolves in the EtOH/H2O liquid-phase solution and reacts with QOH in the liquid-phase solution to produce an active intermediate (HOCS2(superscript -)Q(superscript +)). Then, this active intermediate further reacts with o-phenylene diamine to produce the desired product MBI. Based on the experimental observation, a reaction mechanism is proposed. A kinetic model, which considers the two-step reactions was developed, and a pseudo first order rate law is sufficient to describe the reaction. The effects of the reaction conditions, such as the amount of QOH, the agitation speed, the initial concentration of carbon disulfide, the flow rate of gas phase, the amount of o-phenylene diamine, the volume ratio of EtOH/H2O and the temperature, on the conversion of o-phenylene diamine and the apparent rate constant (k(subscript app) are investigated in detail.

Phase-Transfer Catalytic Reaction of Ethyl-2-Bromolsobutyrate and Phenol: Effects of Water and Temperature

The phase-transfer catalytic reaction (PTC) of ethyl-2-bromoisobutyrate and phenol for synthesizing ethyl-2-phenoxyisobutyrate was carried out in KOH solution/organic solvent two-phase medium. Tetrabutylammonium bromide (TBAB) was employed as the phase-transfer catalyst. The occurrence of the reaction on the interface between the organic and aqueous phases is discussed. A rational reaction mechanism is proposed here and used to build the kinetic model. Hydrolysis of the bromo-alkyl bond (Br-C bond) and the ester functional group (-COOR) was found to take place in an alkaline aqueous solution. The effects of the amount of water on the conversion of ethyl-2-bromoisobutyrate, the fractional yield of hydrolyzing ethyl-2-bromoisobutyrate, the fractional yield of hydrolyzing ethyl-2-phenoxy-isobutyrate, and the fractional yield of ethyl-2-phenoxyisobutyrate (ether-ester product) are investigated in detail.

A new type of B-podand catalysts for solid–liquid phase transfer reactions

Boron podands 1– 4 (B-podands) were studied as strong complexing agents of alkali metal cations and very powerful catalysts in typical anion promoted reactions under solid–liquid conditions, even in chlorobenzene and acetonitrile. The results were comparable with the catalytic activity of classical phase transfer catalysts: crown ethers, polyethylene glycols (PEG) and previously studied Si-podands.

Influence of the physical properties and handling of silica gel modified carbon paste electrodes on the phase transfer of solved Cu(II) ions

Carbon paste electrodes (CPE) modified with natural minerals might be utilised to mimic adsorption/desorption reactions at natural interfaces. As a step towards this aim, several properties and application conditions of CPEs, modified with silica gel, were tested for their influence on phase transfer reactions of solved Cu(II)–tetrammine complex ions. The peak current recorded during the anodic stripping of adsorbed Cu(II) species increased with increasing diameter of the circular electrode surface. A silica gel content of 29 mass percent yielded the highest peak current at otherwise constant exposition conditions. A substitution of graphite by glassy carbon did not enhance the electrode sensitivity. The peak current increased with increasing exposition time (up to 20 min) and with decreasing size of the modifier particles. Typically between 12% and 22% of the solved Cu ions were adsorbed onto the electrode surface and between 15% and 20% of this Cu fraction was subsequently removed by stripping and electrode regeneration. Despite the incomplete electrode regeneration the mass transfer ratios of the Cu(II) species were relatively constant during several application cycles.

Effect of Alternating Pumping of Two Reactants into a Microchannel on a Phase Transfer Reaction

AbstractAlternating pumping of two reactants into a microchannel was found to provide, in comparison with batch processes, a more effective mixing and an increased yield for a particular organic reaction which uses a phase transfer catalyst. The superiority of the microreactor method increased with the frequency of alternation of the pumping of the two liquids.

O-Alkylation of a lignite humic acid by phase-transfer catalysis

A mild phase-transfer catalytic reaction has been conducted to O-alkylate the acidic functions of a lignite humic acid (HA), using tetrabutylammonium hydroxide as the phase-transfer catalyst. The HA acidic functional groups were made to react, in tetrahydrofuran, by nucleophilic substitution with several alkyl halides-methyl iodide, and ethyl, propyl, and butyl, and benzyl bromide. The occurrence of the O-alkylation reaction was assessed by elemental analysis and 1H NMR, CPMAS 13C NMR, and FTIR spectroscopy. Bonding of alkyl groups increased the carbon and hydrogen content and the H/C ratios of all the humic reaction products. Increased nitrogen in the reaction products suggested incomplete removal of the phase-transfer catalyst after purification of the alkylated HA. 1H NMR and CPMAS 13C NMR spectra of alkylated products provided evidence of the successful occurrence of the alkylation reactions. Infrared spectra confirmed the NMR results, revealing the characteristic absorption of newly formed alkyl and aryl ethers and esters in the alkylated products and C-H stretching in the aromatic ring of the benzylated derivative. These findings indicate that humic matter can be successfully alkylated with several different alkylating groups by catalysed phase-transfer reaction. This O-alkylation reaction has the advantage of being mild, versatile, and high-yielding compared with traditional methylation reactions applied to HA. The possibility of introducing different alkyl groups into the HA by a mild phase-transfer reaction may become useful by enabling improved fractionation of humic supramolecular associations and further understanding of the molecular nature of humic substances.

Enantioselective Alkylation of Reissert Compounds in Phase Transfer Catalysed Reactions

Isoquinoline Reissert compounds were alkylated under phase-transfer reaction conditions using chiral quaternary ammonium salts derived from Cinchona alkaloids as catalysts. The best stereoselectivity (ee up to 65%) was achieved in the alkylation of 1-cyano-2-phenoxycarbonyl-1.2-dihydroisoquinoline (1d), catalysed by N-benzylcynchoninium bromide (3a), carried in toluene/50% NaOH biphasic system.

Study of mass transfer performance of naproxen acid and ester through a multiphase enzyme-loaded membrane system

The aim of this work was to identify the transport properties of phase-transfer reaction components through a multiphase enzyme-loaded membrane system. The multiphase system is of interest for the preparation of a two-separate phase enzyme membrane reactor (TSP-EMR) applied for the enantioselective conversion of racemic ester of naproxen into the corresponding S-naproxen acid. In this work, the transport properties of the system have been measured in absence of biochemical reaction. Therefore, the overall mass transfer coefficients of reactant (naproxen ester) and product ( S-naproxen acid) through the two-separate phase membrane system have been measured using deactivated enzyme-loaded membrane. The multiphase system of interest is composed of an organic and an aqueous phase separated by a polymeric membrane containing the immobilized enzyme. The enzyme was immobilized alone or in presence of oil/water emulsion, in order to either improve enzyme distribution at the o/w interface than transport of reaction components through the membrane. The mass transfer rate through the membrane as a function of axial velocity was evaluated. The transport performance through the membrane itself, the membrane loaded with enzyme, and the membrane loaded with enzyme in presence of emulsion was studied.

Synthesis and self‐catalyzed phase transfer reaction of novel methacrylate polymers

AbstractEthyl α‐chloromethylacrylate was converted to an ester derivative using 5‐chlorovaleric acid in a single step. The homopolymerization of the new monomer (CEMA) and its copolymerization with methyl methacrylate were performed using photoinitiator Irgacure 651. The polymers were reacted with N,N‐dimethyldodecylamine to obtain polymers with pendant quaternary ammonium (QA) moieties. The polymers with pendant QA groups were used in self‐catalyzed phase transfer reactions with sodium phenoxide and 1‐dodecanethiol. The syntheses of the monomer and polymers were followed by FTIR, 1H NMR, and 13C NMR. The average polymer molecular weights and polydispersities were determined by size exclusion chromatography. Thermal analysis was carried out using thermogravimetric analysis and differential scanning calorimetry. The copolymer composition, degree of quaternization, and degree of conversion in phase transfer reaction were determined by 1H NMR. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5844–5854, 2005

Recent Progress in the Asymmetric Organocatalysis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Phase-behavior and solid–liquid phase-transfer catalytic activity of tetrabutylammonium bromide

The addition of water to tetrabutylammonium bromide (TBABr)/benzene/sodium bromide ternary component systems induced the separation of TBABr-rich liquid phase (L phase) prior to the appearance of an aqueous phase (W phase). The L phase was assumed to be a bicontinuous phase similar to a microemulsion based on the phase composition. TBABr catalyzed the “solid–liquid” phase-transfer reaction of decyl methanesulfonate with sodium bromide either when the L phase was fully hydrated or after a distinct W phase was formed. The phase-transfer catalytic activity was correlated to the phase behavior of TBABr/benzene/water/NaBr four-component system. The difference and similarity between TBABr and tetrabutylphosphonium bromide (TBPBr) were discussed based on the microstructure of the phases formed by TBABr and TBPBr under the phase-transfer catalytic reaction conditions.

Enantio‐ and Diastereoselective Catalytic Mannich‐Type Reaction of a Glycine Schiff Base Using a Chiral Two‐Center Phase‐Transfer Catalyst

Optically active α,β-diamino acids are prepared under asymmetric phase-transfer reaction conditions from a glycine Schiff base and N-protected imines with a tartrate-derived diammonium salt (TaDiAS) as the phase-transfer catalyst (see scheme; Boc=tert-butoxycarbonyl). Chemoselective deprotection of the N atoms allows straightforward transformations of the α,β-diamino acid products to be carried out.