Use Of Phase Transfer Catalysts Research Articles

Ionic Liquids: Advances and Applications in Phase Transfer Catalysis

Ionic liquids are a family of liquids that are composed entirely of ions and usually have melting points lower than 100 °C. Extensive research, along with the ever-growing interest of the scientific community, allowed for the development of a multitude of ionic liquids with low melting points. Such compounds are considered neoteric materials as well as ideal, custom-made solvents for a variety of different chemical transformations. In this regard, the importance of phase transfer catalysis is evident in a diversity of substrates and reactions. The use of phase transfer catalysts allows the reaction to proceed, facilitating the transfer of otherwise insoluble reactants to the desired phase. Recent scientific advances led to the emergence of ionic liquids, which are excellent candidates as phase transfer catalysts. The inherent fine-tuning capability of these molecules, along with the potential of phase transfer catalytic reactions, epitomize the sustainable aspect of this field of research. Herein, a cohesive report of such applications will be presented, including the period from the last decade of the 20th century up to date.

Mass transfer intensification of 2-methyl-5-nitrotetrazole synthesis in two-phase liquid–liquid Taylor flow in microreactor

Alkylation of 5-nitrotetrazole sodium salt with dimethyl sulfate was carried out under two-phase Taylor flow conditions in a system “dichloromethane-water” in a microreactor of 1.22 mm diameter. A comparative analysis was performed of the specific interfacial area, the surface and volume mass transfer coefficients with respect to results obtained in the presence of phase transfer catalysis in a batch reactor with a magnetic stirrer (MM) or a high speed rotor disperser (HSD). It was shown that regardless of the larger drops formed in the microreactor (and an essentially less value of the specific interfacial area a) as compared to the HSD reactor the surface mass-transfer coefficient (kL) attained in the microreactor is 15 and 208 times higher (in MM and HSD reactors correspondingly) in the absence of the phase transfer catalyst and 3.17 (MM) and 36.2 (HSD) times higher at the application of the latter. Without phase transfer catalyst the volume mass transfer coefficient (kLa) in the microreactor is 15.2 (MM) and 6.8 (HSD) times larger than in batch reactors. At the use of the phase transfer catalyst the volume mass transfer coefficient (kLa) in the microreactor is 3.24 (MM) and 1.2 (HSD) times larger than in batch reactors, even though interfacial area in HSD 30 times higher than that in the microreactor.The application of microreactors in future may provide a possibility to eliminate the use of phase transfer catalysts and high speed mixing devices and would lower the hazard level of the corresponding processes.

Accelerated Two-Phase Oxidation in Microdroplets Assisted by Light and Heat without the Use of Phase-Transfer Catalysts

Two-phase oxidation of alcohols to corresponding aldehydes could be achieved without any phase-transfer catalyst in microdroplets. Herein, we realized reaction acceleration for two-phase oxidation in microdroplets using diluted oxidants under light and thermal irradiation. Lights of short wavelengths were more desirable to reaction acceleration than lights of long wavelengths. However, yields were dramatically improved by moderate heating but reversely decreased by excess heat owing to crystallization. The yields with 5-fold diluted NaOCl solution under light and thermal irradiation were comparable to those with undiluted NaOCl in the absence of light and heat. The dilution of NaOCl not only improved robustness of the sprayer (no salt deposition at the capillary tip) but also met the requirements of green chemistry.

Two-Phase Reactions in Microdroplets without the Use of Phase-Transfer Catalysts.

Many important chemical transformations occur in two-phase reactions, which are widely used in chemical, pharmaceutical, and polymer manufacturing. We present an efficient method for performing two-phase reactions in microdroplets sheared by sheath gas without using a phase-transfer catalyst. This avoids disadvantages such as thermal instability, high cost, and, especially, the need to separate and recycle the catalysts. We show that various alcohols can be oxidized to the corresponding aldehydes and ketones within milliseconds in moderate to good yields (50-75 %). The scale-up of the present method was achieved at an isolated rate of 1.2 mg min-1 for the synthesis of 4-nitrobenzylaldehyde from 4-nitrobenzyl alcohol in the presence of sodium hypochlorite. The biphasic nature of this process, which avoids use of a phase-transfer catalyst, greatly enhances synthetic effectiveness.

Reaction Engineering of Microchannel Catalytic Reactors for Green Process

It is essential to introduce green sustainable chemical process into developing countries. Use of microchannel reactors is one of the future solutions. Especially, application of multiphase catalytic system should be studied in the reaction engineering view point. Examples of application of catalysts to microchannel reactors were introduced such as: Use of phase transfer catalysts in multi phase parallel flow reactors, Use of phase transfer catalysts with the aid of ultrasonic irradiation in multiphase slug flow capillary reactors and Preparation of gas phase tube wall type catalytic reactors which were evaluated with microscopic FT-IR and UV spectrometer.

Asymmetric chemoenzymatic synthesis of N-acetyl-α-amino esters based on lipase-catalyzed kinetic resolutions through interesterification reactions

Several phenylalanine analogs have been synthesized through a four-step route starting from easily available ethyl acetamidocyanoacetate. In a first reaction, and making use of phase transfer catalysts, this compound reacted with several alkyl halides, being benzyltributylammonium chloride identified as the best one for the production of a series of quaternary amino acids in moderate to excellent yields (52–95%). Then, the corresponding N-acetyl-phenylalanine methyl and allyl ester derivatives were obtained through acidic hydrolysis, esterification, and N-acetylation. Rhizomucor miehei lipase was found as a versatile enzyme for the resolution of these amino esters, finding the best results through interesterification reactions with butyl butyrate in acetonitrile. A great influence in the stereoselectivity was found depending on the chemical structure of the compound, achieving for the non- or para-substituted in the phenyl ring excellent stereoselectivities, being moderate for the meta-nitro derivative, while the ortho-nitro amino ester did not react.

ChemInform Abstract: Biodiesel Production by Ultrasound‐Assisted Transesterification: State of the Art and the Perspectives

AbstractReview: 102 refs.

Phase Transfer Catalysts Drive Diverse Organic Solvent Solubility of Single-Walled Carbon Nanotubes Helically Wrapped by Ionic, Semiconducting Polymers

Use of phase transfer catalysts such as 18-crown-6 enables ionic, linear conjugated poly[2,6-{1,5-bis(3-propoxysulfonicacidsodiumsalt)}naphthylene]ethynylene (PNES) to efficiently disperse single-walled carbon nanotubes (SWNTs) in multiple organic solvents under standard ultrasonication methods. Steady-state electronic absorption spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM) reveal that these SWNT suspensions are composed almost exclusively of individualized tubes. High-resolution TEM and AFM data show that the interaction of PNES with SWNTs in both protic and aprotic organic solvents provides a self-assembled superstructure in which a PNES monolayer helically wraps the nanotube surface with periodic and constant morphology (observed helical pitch length = 10 ± 2 nm); time-dependent examination of these suspensions indicates that these structures persist in solution over periods that span at least several months. Pump-probe transient absorption spectroscopy reveals that the excited state lifetimes and exciton binding energies of these well-defined nanotube-semiconducting polymer hybrid structures remain unchanged relative to analogous benchmark data acquired previously for standard sodium dodecylsulfate (SDS)-SWNT suspensions, regardless of solvent. These results demonstrate that the use of phase transfer catalysts with ionic semiconducting polymers that helically wrap SWNTs provide well-defined structures that solubulize SWNTs in a wide range of organic solvents while preserving critical nanotube semiconducting and conducting properties.

Microwave assisted phase-transfer catalytic ethoxylation of p-chloronitrobenzene—A kinetic study

p-Ethoxynitrobenzene was synthesized by the reaction of p-chloronitrobenzene with potassium ethoxide in a homogeneous system using benzyltriethylammonium chloride (BTEAC, QCl) as a phase-transfer catalyst at 50 °C under microwave irradiation conditions. The use of phase-transfer catalysts and microwave has been compared and demonstrated in this nucleophilic substitution reactions. The kinetics of the reaction depends on the effect of phase-transfer catalysts, amount of catalyst, amount of potassium hydroxide, volume of ethanol and temperature on the conversion of the reaction were investigated.

Ethoxylation of p-chloronitrobenzene using phase-transfer catalysts by ultrasound irradiation – A kinetic study

Ethoxy-4-nitrobenzene was synthesized by the reaction of 4-chloronitrobenzene with potassium ethoxide in a homogeneous system using benzyltriethylammonium chloride (QCl) as a phase-transfer catalyst at 50 °C under ultrasound irradiation conditions. The use of phase-transfer catalysts and ultrasound has been compared and demonstrated in this nucleophilic substitution reactions. The kinetics of the reaction depends on the effect of amount of catalyst, quaternary ammonium salts, agitation speed, amount of potassium hydroxide, amount of ethanol, temperature and the frequency of the ultrasound waves on the conversion of the reaction.

Sulfate catalysed multicomponent cyclisation reaction of aryl isocyanates under green conditions

Sulfate anion, as a novel anionic catalyst, promotes the multicomponent cyclisation of aryl isocyantes to give heterocyclic symmetrical isocyanurates selectively under solvent-free conditions. The use of phase transfer catalysts reduces reaction times by 4-16 times.

Oxidative Dimerization: Pd(II) Catalysis in the Presence of Oxygen Using Aqueous Media.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Oxidative dimerization: Pd(II) catalysis in the presence of oxygen using aqueous media

Reported herein is a method for the formation of symmetric biaryls and dienes via oxidative dimerization of aryl and alkenyl boronic acids. These conditions utilized Pd(II) catalysts under an oxygen atmosphere with water as the solvent. The use of phase transfer catalysts promoted efficient and mild syntheses of a wide range of materials.

An Improved Route for Ring Expansion of Five-Membered Heterocyclic Compounds by Use of Phase Transfer Catalysts

An Improved Route for Ring Expansion of Five-Membered Heterocyclic Compounds by Use of Phase Transfer Catalysts

Surface modification of poly(vinylidene fluoride) by alkaline treatment Part 2. Process modification by the use of phase transfer catalysts

A detailed study of the alkaline modification of poly(vinylidene fluoride) (PVdF) by a phase transfer catalyst (PTC) medium has been carried out by X-ray photoelectron spectroscopy, (XPS), secondary ion mass spectrometry (SIMS) and Raman spectroscopies, to determine the composition of the modified surface layer. The study indicates the formation of a surface layer consisting of conjugated CC bonds, concomitant with surface defluorination and the inclusion of oxygen functionalities on treatment. A previous investigation studied the affect of alkaline treatment, however without the use of PTCs (Ross GJ, Watts JF, Hill MP, Morrissey P. Surface modification of poly(vinylidene fluoride) by alkaline treatment. 1. The degradation mechanism Polymer 2000;41: 1695–96.), that produced a surface layer with different functionalities. A mechanism for the degradation process in the presence of a PTC is proposed in this paper, which includes the formation of the polyene structure followed by hydroxide attack to yield hydroxyl and carbonyl groups and more complex oxygen functionalities.

Potassium borohydride reductions of immobilised ketosteroids

Abstract Ketosteroids absorbed into various insoluble supports (powdered polyethylene, microporous 2% crosslinked polystyrene beads, macroporous highly crosslinked polystyrene beads, silica gel and alumina) can be reduced using aqueous potassium borohydride. The use of phase transfer catalysts generally raises yields. In the case of 6-ketosteriods the supported reactions often follow a stereochemical course significantly different from that of analogous reactions in solution. This is attributed to the adsorbtion of the steroid onto the inner surfaces of the supports. In these cases reduction of the ketosteroid by alkoxyborohydrides is substantially suppressed and thus most of the reduction is brought about by BH4− itself, a relatively sterically undemanding reductant. The net result is that whilst reductions of 6-ketosteroids in solution by potassium borohydride typically gives the 6α- and 6β-alcohols in the ratio 15:85, with the supported steroid the ratios can be as high as 90:10.

Reactions of nitrochlorobenzenes with sodium sulfide: change in selectivity with phase-transfer catalysts

o-Nitro- and p-nitrochlorobenzene were reduced to the corresponding chloroanilines with aqueous solutions of sodium sulfide both in the presence and absence of a phase-transfer catalyst. The use of phase-transfer catalysts, with solid sodium sulfide, was found to change the course of the reaction completely to dinitrodiphenyl sulfide. The role of mass transfer in the system was assessed with m-nitrochlorobenzene as the organic substrate.

Use of phase transfer catalysts to aid initiation in suspension vinyl polymerization

In suspension vinyl polymerization of water immiscible monomers, the polymer yield is very low when water soluble initiator is used, because the free radicals generated in the aqueous phase do not get the opportunity to initiate polymerization. However, in conjunction with a phase transfer catalyst, the radical precursor is transferred into the organic phase, where the generated free radicals cause vinyl polymerization, just as an organic soluble initiator does.

Excursions into multiphase reactions

Multiphase reactions are ubiquitous in the chemical industry and a rational analysis of reactors where they are conducted requires an intimate knowledge of chemical kinetics, thermodynamics, mass transfer and fluid mechanics. In many situations in practice, conducting reactions in multiphase systems is advantageous as compared to that in a single liquid phase system.The use of phase transfer catalysts, micellar catalysts, emulsifiers, hydrotropic agents etc., can significantly enhance the rates of multiphase reactions. A change-over from gas-liquid to liquid-liquid mode of operation could also have favourable influence. Solid-liquid reactions have received limited attention and many aspects need to be studied intensively. Three-phase reactions offer some fascinating features. The effect of solid particles, which may be sparingly soluble reactant, catalyst or even alien material, can be very substantial.Multiphase biochemical and electrochemical reactions have many unique features and such reactions are becoming increasingly important. Novel strategies of conducting multiphase reactions have been developed of late, though there are plenty of problems yet to be tackled.

Preparation of ω‐123I‐labelled fatty acids by 123I‐for‐Br exchange: Comparison of three methods

AbstractLong chain ω‐123‐I‐labelled fatty acids such as 16‐I‐hexadecanoic‐, 17‐I‐heptadecanoic‐, and 16‐I‐hexadec‐9‐enoic acid have been prepared without adding carrier by nucleophilic 123I‐for‐Br exchange in acetone, in the melt, and by use of phase transfer catalysts in non‐polar solvents. While preparation in refluxing acetone required reaction times of more than 2 hours to reach saturation yields, halogen exchange in molten bromofatty acids at temperatures of about 150 °C gave rise to yields of about 80% of radiochemically pure 17‐123I‐heptadecanoic acid within only 5 minutes. Comparable yields were also obtained using Kryptofix 221 in refluxing toluene after 10 minutes.