Phase Transfer Catalytic System Research Articles

Effect of third-phase properties on benzyl- n-butyl ether synthesis in phase transfer catalytic system

The production of benzyl- n-butyl ether from benzyl chloride and n-butanol is studied in phase transfer catalytic system. A third phase is formed when polyethylene glycol (PEG) and dodecane are used as the phase transfer catalyst (PTC) and an organic solvent, respectively. The production rate at the three-phase system is higher by seven times than that at the two-phase system. The ether production rate and its selectivity are dependent on the initial concentration of n-butanol. These are affected by the properties of the third phase, especially the concentrations of n-butanol and water in the third phase. n-Butanol reacts with benzyl chloride and potassium hydroxide simultaneously. The reaction between n-butanol and potassium hydroxide occurs in the aqueous phase. Then, the selectivity of ether on a basis of initial n-butanol is below 0.6 in a stirred tank batch reactor. The selectivity is much improved at 0.9 by using a static triphase batch reactor in which the organic and aqueous phases are separated by the third phase. The interphase mass transfer can be accelerated by ultrasonic device.

Characteristics of third phase for reaction of benzyl chloride with sodium sulfide in phase transfer catalytic system

The purpose of this study is to investigate how the property of third phase affects the reaction rate in a phase transfer catalytic reaction system. Dibenzyl sulfide was produced by the reaction between sodium sulfide in an aqueous phase and benzyl chloride in an organic phase by using tetrahexylammonium bromide ((Hex) 4NBr) as a phase transfer catalyst. As the concentration of sodium sulfide in the aqueous phase and the temperature increased, the third phase was more easily formed. Three types for temperature dependencies on the reaction rate were observed. The reaction rate in one type initially increased, suddenly decreased, and then increased again. The other reaction rates in two types increased with the increase in temperature but the difference between them was 20–50 times at the same temperature. These behaviors could be explained by the property of third phase, especially, the lipophilicity or the hydrophilicity.

Probing the Coupling of Charge-Transfer Processes Across Liquid/Liquid Interfaces by the Scanning Electrochemical Microscope

The feedback mode of the scanning electrochemical microscope (SECM) is used to induce and measure charge-transfer coupling (CTC) between two ion-transfer (IT) processes across liquid/liquid interfaces. Results are interpreted using a general model for coupling processes under steady-state conditions that is also applicable to other modes of coupling such as IT−ET and ET−ET (ET = electron transfer). The measured feedback curves demonstrate the effect of mass-transfer limitations in these processes on the potential across the interface, shedding new light on the dynamics of bioenergetics and phase-transfer catalysis systems as well as on previous SECM studies of liquid/liquid interfaces.

Synthesis and Cytotoxicity of Silicon and GermaniumContaining Pyridine Oxime O‐Ethers

Silicon and germanium containing pyridine aldoxime, ketoxime and amidoxime O-ethers have been prepared using phase transfer catalytic systems oxime alkyl halide solid KOH 18-crown-6 benzene and oxime alkyl halide solid K2CO3 or Cs2CO3 18-crown-6 toluene. Cytotoxic activity of silicon and germanium containing pyridine oxime O-ethers was tested in vitro on two monolayer tumor cell lines: MG- 22A (mouse hepatoma) and HT-1080 (human fibrosarcoma). O-[3-Yriethylsilylpropyl]- and O-[3-(1-methyl- 1-silacyclopentyl)propyl] oximes of pyridine aldehydes and ketones exhibit high cytotoxicity. Presence of methyl group in the pyridine ring considerably decreased activity of amidoxime O-ethers. Oxime ethers containing two elements are essentially inactive. For 2-acetylpyridine oxime ethers the activity increases in order of alkyl substituents: Et3GeCH2CH2SiMe2CH2 < Et3SiCH2CH2CH2 < (CH2)4SiCH2CH2CH2. Cytotoxicity of ketoxime O-ethers is considerably lower in comparison with aldoxime O-ethers.

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.

Trimethylsilylcyanation of heteroaromatic ketones in the CsF/18-crown-6/benzene phase-transfer catalytic system

The trimethylsilylcyanation of heteroaromatic ketones in the Me3SiCN/CsF/18-crown-6/benzene phasetransfer catalytic system has been studied. The reaction products have been isolated selectively in yields of up to 95%.

Attempting to grade phase transfer catalysts

Electrical potential oscillations across liquid–liquid interfaces in phase transfer catalytic systems were studied. The possibility of using the amplitudes of these oscillations as a criterion for grading the catalysts in order of their efficacies for a reaction was suggested. Gradation in the efficacies of the catalysts derived on the basis of the gradation in the amplitudes in the reactions of nucleophilic nature was shown to be in agreement with the gradation in the partition coefficients of the nucleophiles in the presence of the phase transfer catalysts. Copyright © 1999 John Wiley & Sons, Ltd.

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.

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.

Relation between Third-Phase Properties and Rate of Dehydrohalogenation of 2-Bromooctane in Phase Transfer Catalytic System.

The purpose of this paper is to investigate the relationship between the properties and catalytic activity of the third phase in a phase transfer catalytic system. The conditions of formation of the third phase are investigated by changing the kind of phase transfer catalyst (PTC), organic solvents, and concentration of potassium hydroxide in the aqueous phase. When tetrabutylammonium bromide, (Bu) 4 NBr, is used as the phase transfer catalyst, the third phase is formed with both dodecane and toluene as organic solvents. On the other hand, when tetrahexylammonium bromide, (Hex) 4 NBr, is used as the phase transfer catalyst, the third phase forms with dodecane but not with toluene. The volume of the third phase, the base strength, the concentration of catalyst, water, and organic solvent in the third phase were measured. Solidification phenomena are observed for some cases of higher KOH concentrations in the aqueous phase. Dehydrohalogenation of 2-bromooctane in the organic phase was carried out in a batch reactor with the potassium hydroxide solution in the aqueous phase. The observed reaction rate constant (k obs ), which is determined from the first order kinetics, increases remarkably with the increase in concentration of KOH in the aqueous phase (ξ KOH ) for the condition of third phase formation. However, for the solidification condition, the reaction rate drops sharply because only the external surface of the solid is effective for the reaction. The distribution coefficient of reactant between the organic phase and the third phase, (K A ) and the reaction rate constant in the third phase (k third ) can be related to the concentration of water in the third phase (C H2 O) independent of the catalysts and organic solvents. Since PTC exists in the third phase, it can be reused without any loss of catalytic activity.

Chlorination of pyridylacetylenes in the phase transfer catalytic system CCl4/KOH/18-crown-6

Chlorination of pyridylacetylenes in the phase transfer catalytic system CCl4/KOH/18-crown-6

Mathematical modeling of solid-liquid phase-transfer catalysis

Use of phase-transfer catalysis (PTC) has been quite common in organic synthesis in the last two decades. However, there are very few publications on the modeling of PTC systems, particularly solid-liquid systems. The present research suggests a systematic procedure for modeling these reactions, which includes reaction both in the liquid and solid phases. The equations describing these models provide a rational basis for the scale-up of PTC reactions.

Third-phase catalytic activity of halogen exchange reactions in phase transfer catalytic system

The purpose of this study was to clarify the cause of high catalytic activity of a third phase in a phase transfer catalysis system. The halogen substitution reaction between benzyl chloride in an organic phase and potassium bromide (KBr) in an aqueous phase was carried out. The conditions of formation of the third phase were searched by changing the kinds of phase transfer catalysts, organic solvents and the concentration of KBr in an aqueous phase. When tetrabutylammonium bromide was used as a phase transfer catalyst, a third phase was formed with both dodecane and toluene as organic solvents. On the other hand, when tetrapentylammonium bromide was used as a catalyst, a third phase was formed with dodecane but not with toluene. The distributions of catalysts, benzyl bromide and Br − among phases were measured. Based on the results, the place where the reaction occurred could be classified into three types, that is, in an organic phase (type I), at the interface between an organic phase and an aqueous phase (type II) and in a third phase (type III). The reaction rate of type III was the largest because of high concentration of both reactants in a third phase. The reaction rate varied with the kinds of third phase significantly. This variation could be explained by a difference in the concentration of benzyl chloride in the third phase. The rate constant of the first-order kinetics was, however, independent of the kinds of third phase. This value agreed with that of an organic phase of type I. Repeated use of a third phase was also studied to apply phase transfer catalysts to industrial purpose. After the reaction was completed, an organic phase containing a product was removed and a new organic phase containing a reactant was charged. By repeating this operation, the third phase could be reused without any loss of its catalytic activity.

ChemInform Abstract: A New Methodology for Obtaining α‐Oxo Ester Equivalents: Sulfanylation of α‐Sulfonyl Carboxylic Esters in a Solid/Liquid Phase Transfer Catalytic System.

AbstractChemInform 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.

A New Methodology for Obtaining α-Oxo Ester Equivalents: Sulfanylation of α-Sulfonyl Carboxylic Esters in a Solid/Liquid Phase Transfer Catalytic System

A new, convenient procedure for the synthesis of a wide range of α-methylsulfanyl-α-phenylsulfonyl carboxylic esters has been developed and their facile conversion to the corresponding α-oxo esters demonstrated.

Catalytic epoxidation by heteropolyoxoperoxo complexes: from novel precursors or catalysts to a mechanistic approach

In the course of systematic investigations, both the ‘H 2WO 4/H 2O 2-H 2O/H 3PO 4’ and ‘ H 3[ PW 12 O 40] · yH 2 O/ H 2 O 2- H 2 O/ H 3 PO 4’ systems are found to show several 31P and 183W NMR signals which can be assigned to new phosphatoox-operoxotungstate species, [PW x O y ] z− ( x = 1–4). It is clear that in the oxidations, the Keggin heteropolyanion is only a precursor to the true catalyst. The addition of Q +Cl − (an appropriate onium salt) to these systems leads to the isolation of pure crystalline salts: Q 3[PO 4{WO(O 2) 2} 4], 1, and Q 2[HPO 4{WO(O 2) 2} 2], 2. The solid state structure of [( n-C 4H 9) 4N] 2[HPO 4{WO(O 2) 2} 2] is known. Synthesis and structural investigation of complexes with other assembling anions were also reported. Some of these complexes are: Q 3[PO 4{MoO(O 2) 2} 4], 3, Q 2[SO 4{MoO(O 2) 2} 2], 4, Q 3[AsO 4{WO(O 2) 2} 4], 5, Q 2[HAsO 4{WO(O 2) 2} 2], 6, Q 2[CH 3AsO 3{WO(O 2) 2} 2] · H 2O, 7, 2Q 3[(HSO 4)(SO 4){W 3O 6(O 2) 3}] · 7H 2O, 8, Q 2[W 4O 6(O 2) 6(CH 3OH) 2(CH 3O) 2], 9, etc. Some of these polyanions ( 1 to 7) have one or two neutral [M 2O 2(μ-O 2) 2(O 2) 2] moieties with one bridging and one non-bridging peroxo group on each W (or Mo) center. Infrared and/or Raman and 31P and 183W NMR spectra show that the structures of the anions are conserved in organic solvents at room temperature. There is also clear evidence for the formation of [(PO 4){Mo 4− x W x O 20}] 3− in the reaction of [PMo 4O 24] 3− and [PW 4O 24] 3−; novel mixed compounds can be isolated. The salts with the [M 2O 2(μ-O 2) 2(O 2) 2] moiety, in particular with M = W, are among the most efficient for the transfer of ‘active oxygen’ to olefinic substrates. ( R)-(+)-limonene is stoichiometrically epoxidized; only half the peroxide oxygen is transferred to the olefinic substrate at room temperature. The results show an effect of the assembling ligand in stoichiometric systems and in phase transfer catalytic systems. Extended Hückel molecular orbital calculations have been used to support an active oxygen-to-olefin transfer mechanism. The best mechanistic model involves direct interaction of one olefinic carbon atom with an oxygen atom of the peroxo groups without binding of the alkene to the transition metal center.

Solvent and salt effects on the formation of third liquid phase and the reaction mechanisms in the phase transfer catalysis system—Reaction between N-butyl bromide and sodium phenolate

The effects of solvents and salts (including base) on the formation of a third liquid phase, distribution of catalyst, reaction mechanism and reaction rate in the reaction between n-butyl bromide and sodium phenolate (NaOPh) with tetrabutylammonium bromide (QBr) as a phase transfer catalyst were investigated. The organic solvents used include chlorobenzene, toluene and hexane while sodium bromide and sodium hydroxide were tested in the study of salt effects. The effect of NaOPh concentration was also investigated. The results reveal that the kind of solvent and the amount of NaOH added are two important factors influencing the formation of a third liquid phase, the distribution of catalyst and the reaction rate. It is found that NaBr and NaOH can force QBr (or QOH) out from the aqueous phase to the organic phase or to form a third liquid phase depending on whether the organic solvent is polar or nonpolar. NaOH also has the ability to extract reversely QOPh from the organic phase or the third liquid phase to the aqueous phase. In some cases, however, a third liquid phase will appear when a large amount of NaOH is added. Based on the experimental findings, three types of reaction schemes are proposed for such complicated phase transfer catalysis systems.

Peroxide synthesis from alkyl halides, alcohols and alkenes

New and improved methods of peroxide synthesis have been developed along with advances in peroxide analyses. Hydroperoxides were obtained by one of three methods: i) perhydrolysis of alkyl mercury tetrafluoroborates (RHgBF4); ii) perhydrolysis of alkyl trifluoromethanesulfonates (triflates, ROSO2CF3); and iii) photooxygenation of unsaturated fatty esters (methyl oleate) with sensitizer in a phase transfer catalysis (PTC) system. Dialkyl peroxides also were prepared by three methods: hydroperoxidation of the mercury and triflate intermediates and an innovation of the reaction of superoxide anion with alkyl halides in a PTC system. Chromatographic—gas‐liquid chromatography (GLC) and high‐performance liquid chromatography (HPLC)—methods were examined in detail for compositional analysis of hydroperoxides and dialkyl peroxides in reaction mixtures and for purity determinations. Dialkyl peroxides were further analyzed by an improved rapid iodometric method by using strong non‐oxidizing acid (HCLO4) and iron catalysis.

Triazolines XVIII.1Nickel Peroxide Oxidation of 4,5-Dihydro-1H-1,2,3-triazoles Bearing Sterically Crowdedortho-Substituted 5-Phenyl Groups

Nickel peroxide functions as an efficient oxidizing agent, superior to permanganate (phase-transfer catalytic system), in the oxidative dehydrogenation of 4,5-dihydro-1H-1,2,3-triazoles 1a-1, bearing sterically crowded ortho-substituted 5-phenyl groups, to 1H-1,2,3-triazoles 2a-1

Kinetics of phase-transfer etherification reactions of p-chloronitrobenzene by alkoxides

The substitution reaction of chloride by alkoxide anions in p-chloronitrobenzene in a Phase-transfer catalytic system has been studied and successfully performed in high yield and without the occurrence of side reactions. The effect of several parameters has been experimentally, investigated. In particular, the poisoning effect of the chloride anion produced throughout the reaction is studied and a practical answer to successfully overcome this problem and increase yields is presented. A kinetic model based on the collected data is proposed.