Liquid-liquid Phase-transfer Catalysis Research Articles

Selective Oxidation of Lauryl Alcohol to Lauraldehyde under Liquid-Liquid Phase Transfer Catalysis (LL-PTC) with Potassium Chromate as the Oxidizing Agent

In the present research, the selective oxidation of lauryl alcohol to lauraldehyde was studied under liquid-liquid phase transfer conditions using potassium chromate (K2CrO4) as an oxidizing agent and tetrabutyl ammonium bromide (TBAB) as the phase transfer catalyst. Chromium (VI) reagents are used in these oxidations since the alcohols are selectively oxidized to the aldehydes without any over-oxidation. In non-aqueous solutions the oxidation by chromium (VI) does not go to completion as the intermediate partially oxidized material containing chromium must be hydrolysed for oxidation to continue. Liquid-Liquid Phase Transfer Catalysis (LL-PTC) involves the transfer of one reactant from the aqueous phase to the organic phase with the help of small quantities of a phase transfer catalyst which is usually quaternary ammonium or phosphonium salt. It was observed that no over-oxidation products such as lauric acid and high molecular weight esters of lauryl alcohol were formed under the reaction conditions used. The effect of various reaction parameters such as the speed of agitation, temperature, the concentration of lauryl alcohol, the concentration of potassium chromateand phase transfer catalyst loading were studied. A reaction mechanism involving the formation of chromate ester in the organic phase has been proposed and a kinetic model has been developed based on the experimental results obtained.

Synthesis and reactivity of platinum(II) triphenylphosphino complexes with aromatic aldoximes

trans-[Pt(μ-Cl)Cl(PPh3)]2 reacted with arylaldoximes in 1,2-dichloroethane to afford [PtCl2(PPh3){N(OH)CHAr}] (Ar=3,4-dimethoxyphenyl, 1-naphthyl, 9-anthryl) where aldoxime ligands are N-coordinated to platinum. The obtained complexes are soluble in chlorinated solvents, where they afford equilibrium mixtures of cis,trans and/or (E),(Z) isomers. Equilibria in solution were studied by 31P-NMR spectroscopy and solid state structural data were obtained by single crystal X ray diffraction studies. The reactivity of [PtCl2(PPh3){N(OH)CHAr}] complexes with basic aqueous solutions was studied, under liquid-liquid phase transfer catalysis conditions. The outcome of the reaction depends on the stereochemistry of the precursors: cis,(Z)-isomers promptly undergo cyclization to the corresponding dinuclear derivatives [Pt{μ-(κ2-N,O)}-{N(O)CHAr}Cl(PPh3)]2, where two aldoximate ligands symmetrically bridge two metal centers.

Efficient synthesis of functional long-chain alkyl disulfides under liquid-liquid phase-transfer catalysis: The analysis of chemical equilibrium and phase-transfer mechanism

Functional long-chain alkyl disulfides were herein synthesized under liquid-liquid phase-transfer catalysis. The component of final products could be mainly controlled by feeding molar ratio of S/Na2S which factually dominated a chemical equilibrium among monosulfide, disulfide and trisulfide anions. The binding capability of sulfur anions with dimethyldidodecylammonium cation increases in the order of monosulfide<disulfide<trisulfide. Both the binding capability and the concentration of these sulfur anions determine which anion will be phase-transferred and generate corresponding products in phase-transfer reaction. Such method can be used to directly synthesize functional long-chain alkyl disulfides of high purity.

Kinetic study on the synthesis of 1,4-dithiane under ultrasound and multi-site phase-transfer catalyst in liquid-liquid PTC condition

In this work, the simple, efficient and convenient method to synthesis of 1,4-dithiane from 1,2-dibromoethane and sodium sulfide under heterogeneous liquid-liquid phase-transfer catalysis (LL-PTC) condition in the presence of ultrasound irradiation (40 kHz, 300W) and multi-site phase-transfer catalyst was reported. The multi-site phase-transfer catalyst namely 1,4-dibenzyl-1,4-diazoniabicyclo[2.2.2]octanium dibromide (MPTC) was successfully prepared and used as a superior catalyst for this synthesis. The combination of both ultrasound and multi-site phase-transfer catalyst are resulted in enhanced reaction rate and efficiency than the individual operations. The reaction was carried out under pseudo-first order condition. The kinetic aspects such as the effect of agitation speeds, ultrasound frequencies, different phase transfer catalysts, various organic solvent, volume of hexane, the amount of prepared MPTC, various temperature, the amount of water, the concentration of 1,2-dibromoethane, on the conversion of 1,2-dibromoethane and the apparent rate constant (K app ) were investigated in detail. The suitable mechanism has been proposed for reaction system.

Anion exchange cycle of catalyst in liquid–liquid phase-transfer catalysis reaction: Novel autocatalysis

Abstract Novel autocatalytic process under liquid–liquid phase-transfer catalysis (LL-PTC) condition was found, which was induced by the anion exchange of catalyst. Induction period existed in Horner–Wadsworth–Emmons reaction under LL-PTC conditions and was not caused by the equilibrium of reactants or the saturation of the intermediate. Introduction of the more hydrophilic anion to PTC system could increase the initial reaction rate and decrease the induction time, especially for diethyl phosphate anion (another product of the bond-forming reaction, PO−). Furthermore, the generation of ion-pair (PTC+PO−) in the biphasic system was certified by extraction experiments. PTC+PO− showed a higher catalytic activity (more than 2-fold) and a higher distribution coefficient from the interfacial region to the organic phase (2.7-fold) than the initial catalyst. Accordingly, the interfacial mechanism including the instinct catalytic cycle and the autocatalytic cycle was proposed, which were induced by the initial catalyst and PTC+PO−, respectively. Subsequently the dependence of instinct catalytic activity and autocatalytic activity on reaction parameters was compared.

ChemInform Abstract: Phase Transfer Catalysis: Some Recent Applications in Organic Synthesis

Abstract A survey dealing with the use of anhydrous potassium carbonate as an efficient base for promoting organic reactions under solid–liquid phase transfer catalysis (SL-PTC) conditions is reported. In particular, the generation in situ of trifluoro- and trichloroacetamidide, and reactions of these azaanions with 2-bromocarboxylic esters and epoxides, affording protected α-amino acids and β-amido alcohols, respectively, are described. The reduction of allylic nitroderivatives with CS 2 to oximes or nitriles under SL- and liquid–liquid PTC (LL-PTC) is also presented. Finally, new preparation methods and a study of the reactivity of quaternary onium fluorides, hydrogendifluorides and dihydrogentrifluorides, together with the use of dihydrogentrifluorides as hydrofluorinating agents under SL-PTC conditions, are reported.

ChemInform Abstract: Phase Transfer Catalyzed Synthesis of Amides and Esters of 2,4-Dichlorophenoxyacetic Acid.

Abstract A convenient procedure is reported for the preparation of amides and esters via the reaction of 2,4-dichlorophenoxyacetyl chloride with amines or phenols under the condition of liquid-liquid phase transfer catalysis using polyethylene gtycol-600 as the catalyst. The products have been characterised on the basis of analytical and spectral (IR and H-NMR) data.

Ionic Liquids as Phase-Transfer Catalysts: Etherification Reaction of 1-Octanol with 1-Chlorobutane

Various ionic liquids have been examined along with some traditional phase-transfer catalysts, such as Aliquat reagents, in a standard liquid−liquid phase-transfer catalysis (LLPTC) reaction. A standard O-alkylation LLPTC reaction was chosen because of its relatively high yields and low incident of reaction side products. As expected, quaternary tetraalkyl ammonium catalysts all resulted in high conversion to product. Aliquat HTA-1, a high temperature phase-transfer catalyst normally used in nonaqueous reactions, resulted in yields only slightly higher than the noncatalyzed reaction. Substituted pyrrolidinium salts had relatively good catalytic activity, while substituted pyridinium and imidazolium catalysts showed either very little or no catalytic activity. Catalysts with fixed cationic charges resulted in high conversion for the etherification reactions; however, compounds with an aromatic π-bonding system were not suitable as phase-transfer catalysts.

Role of Third Phase in Intensification of Reaction Rates and Selectivity: Phase-Transfer Catalyzed Synthesis of Benzyl Phenyl Ether

In the current work, the merits of the creation of a third phase in a typical biphasic reaction have been illustrated. The advantages of liquid-liquid-liquid phase-transfer catalysis (L-L-L PTC) have been brought out over liquid-liquid phase-transfer catalysis (L-L PTC) by considering the etherification of phenol by benzyl chloride to benzyl phenyl ether. L-L-L PTC is a novel strategy for waste reduction and improving profitability, in which a catalyst-rich middle phase is formed between the other two phases, wherein the main reaction takes place and intensifies the rates of reaction as well as offers better selectivity including catalyst reusability, unlike in the L-L PTC. The etherification of phenol with benzyl chloride under L-L PTC is accompanied by side reactions that lower the selectivity, and the catalyst cannot be recovered but wasted as an effluent, causing a load on the environment. However, the transformation of L-L PTC into L-L-L PTC leads to 100% conversion of the limiting reactant benzyl chloride with 100% selectivity to benzyl phenyl ether. The catalyst-rich phase is recovered and reused to some extent. This also helps in waste minimization, which is a major theme of green chemistry. The current work deals with the effects of different kinetic and processes parameters on enhancement in rates and selectivities in L-L-L PTC over L-L PTC. A mathematical model is also developed.

Catalytic Benzoylation of 4-Chloro-3-methylphenol Sodium Salt in Third-Liquid Phase under Conditions of Phase-Transfer Catalysis

In the present study, the benzoylation of 4-chloro-3-methylphenol sodium salt to synthesize 4-chloro-3-methylphenyl benzoate by triliquid phase-transfer catalysis (TL-PTC) was investigated. The third-liquid phase (catalyst phase) can be formed from benzyl tri-n-butylammonium bromide (QBr) reacted with sodium 4-chloro-3-methylphenoxide in the aqueous phase by extra addition of NaCl or NaBr using heptane as the solvent. Before the reaction, about 89% of the catalyst can be concentrated within 1.5 cm 3 of third-liquid phase to make a high catalyst concentration of 1.13 mol/L, which embraces 99.5% of benzyl tri-n-butylammonium 4-chloro-3-methylphenoxide (catalytic intermediate QOR) in the third-liquid phase. The product yield based on benzoyl chloride (limiting reactant) is 98.7% in 30 min of reaction at 20 °C. The reaction rate is strongly dependent on the stirring speed, showing that the interfacial reaction is important. The variations of compositions in the third-liquid phase during the reaction are analyzed. The molar ratio of QOR to Q + in the third-liquid phase remains almost constant after 2 min of reaction, and QOR is not found in the organic phase. The main reaction region locates in the third-liquid phase. The experimental results can be well correlated by pseudo-first-order kinetics. A comparison of product yield under triliquid and liquid-liquid PTC systems shows that TL-PTC offers an effective method for ester synthesis.

PHASE-TRANSFER CATALYZED BENZOYLATION OF 4-CHLORO-3-METHYLPHENOL SODIUM SALT IN LIQUID-LIQUID SYSTEM

The reaction of sodium 4-chloro-3-methylphenoxide (ArONa) and benzoyl chloride (ROCl) to synthesize 4-chloro-3-methylphenyl benzoate (ArOOR) was investigated by liquid-liquid phase-transfer catalysis in the present study. The catalytic intermediate was synthesized and its behaviors during the reaction were explored. The product yield was above 97.2% within 0.5 h of reaction at 10°C and 100 rpm using tetrabutylammonium bromide as the catalyst. The benzoylation reaction was governed by the interfacial reaction and the intrinsic reaction in the bulk phase. During the reaction, a fraction (0.55–0.65) of the catalyst was observed in the form of catalytic intermediate, tetrabutylammonium 4-chloro-3-methylphenoxide (ArOQ), and its concentration would be near constant after 6 min of induction period. A reaction mechanism and pseudo-first-order kinetics were proposed to describe this phase-transfer catalyzed benzoylation successfully. Extra additions of NaCl and NaBr in the aqueous phase would increase the concentration of ArOQ in the organic phase to enhance the overall reaction, while a poison effect was observed for extra addition of NaI. A more hydrophilic catalyst, tetrabutylammonium hydrogen sulfate, was also favorable to conduct this type of interfacial intrinsic reaction with the apparent activation energy 7.13 kcal/mol.

Colorful Chemical Demonstrations on the Extraction of Anionic Species from Water into Ether Mediated by Tricaprylylmethylammonium Chloride (Aliquat 336), a Liquid–Liquid Phase-Transfer Agent

Liquid–liquid phase transfer catalysis (LLPTC) plays an ever-increasing role in academic research and in the large scale industrial production of chemicals. This method involves a biphasic medium composed of water and an organic solvent in which the LLPT-catalyst plays a critical role in the transport of some water-soluble reagents (e.g., nucleophiles or bases) from water into the organic layer. This article provides a list of easy to perform and relatively safe experiments that may be used to demonstrate the extraction of some colorful water-soluble reagents by Aliquat 336 into ether. This demonstrative process serves to simulate the preliminary extractive step of an ionic species in LLPT-catalyzed reactions and introduce various undergraduate chemistry concepts and principles to students.

ANALYSIS OF FACTORS AFFECTING THE SYNTHESIS OF ALLYL PHENYL ETHER BY TRI-LIQUID-PHASE CATALYSIS

In order to improve the selectivity of allyl phenyl ether (ROPh), the main product, in the etherification of allyl bromide (RBr) and sodium phenolate (NaOPh) with tetra-n-butylammonium bromide (QBr) as a phase-transfer catalyst, the technique of tri-liquid-phase phase-transfer catalysis, instead of the liquid-liquid one, was employed. The reaction was performed in a batch reactor, and the factors affecting the conversion and selectivity were investigated. The possibility of reusing the phase-transfer catalyst was also evaluated. Experimental results indicate that the addition of a small amount of Na2CO3 will benefit the formation of a third liquid phase and enhances both the conversion of RBr and the overall yield of ROPh. Both the conversion and the overall yield are maximal when the mole fraction of QBr in the mixture of NaOPh and QBr is about 0.3. A high reaction temperature enhances the conversion and the overall yield. Under optimal conditions, complete conversion and near 100% yield can be obtained within 10 minutes. Although the reaction rate by the tri-liquid-phase catalysis is slightly lower than that observed with the same amount of catalyst by conventional liquid-liquid phase-transfer catalysis, the selectivity of ROPh is higher and the catalyst can be easily reused by the reuse of the third liquid phase without any loss of its catalytic activity in the former case. Because the reuse of catalyst was found to be feasible, the production of ROPh with a continuous-flow reactor becomes possible.

A Novel Synthesis of Cyclic Polythioethers Using Liquid-Liquid Phase-Transfer Catalysis

The synthesis of cyclic polythioethers has been achieved by the reactions of dithiols with alkyl dihalides. Thiols are not only hard to handle owing to their unpleasant smell, but also they are easily oxidizable, thus it is not easy to obtain various dithiols. However, we have developed a procedure for the preparation cyclic polythioethers by the reaction of dithioiminium salts with alkyl dihalides using phase-transfer catalyst without the use of dithiols, and have examined the ion recognition of these compounds.

The Influence of the Molar Ratio SPCl 3 : Phenol on the Formation of the Disubstituted Secondary Products in the Liquid-Liquid PTC Synthesis of Arylthiophosphoric Acid Dichlorides

The Influence of the Molar Ratio SPCl 3 : Phenol on the Formation of the Disubstituted Secondary Products in the Liquid-Liquid PTC Synthesis of Arylthiophosphoric Acid Dichlorides

Selective Preparation of Key Intermediates for the Synthesis of Gemini Surfactants by Phase-Transfer Catalysis

A comparison of liquid-liquid and solid-liquid PTC for the selective synthesis of diglycidyl ether from protected pentaerythritol and epichlorohydrin is presented. Solid-liquid PTC was found to be more useful than liquid-liquid PTC because the use of water or other solvents can be avoided and higher yields and selectivity are achieved. It was proved that etherification takes place in the solid phase-organic phase system even in the absence of the phase-transfer catalyst. However, the use of tetrabutylammonium bisulfate as catalyst is essential due to its crucial effect on the enhancement of the rate of etherification and on the improvement of the selectivity to diglycidyl ether, which is higher than 98%.

On the Investigation of a Phase-Transfer Catalysis Reaction in an Oscillatory Baffled Reactor

A liquid-liquid phase-transfer catalysis (PTC) system investigated in this work consists of two immiscible liquid phases, n-butyl bromide (BuBr, with toluene as an organic solvent) and sodium phenolate (NaOPh, dissolved in water), each containing a reagent. To initiate the reaction between reagents a phase-transfer mechanism is required, which is accomplished through the use of a phase-transfer catalyst (PT-Cat). The PT-Cat transfers one reagent from one phase to the other, whereupon the other reagent can react with the catalyst-reagent transient. In our work two types of PT-Cat, i.e., benzyltributylammonium chloride (BTAC) and tetrabutylammonium bromide (TBAB), were used. The PTC reaction is performed in both an oscillatory baffled reactor (OBR) and a stirred tank reactor (STR). In this paper we report our experimental results of reaction rates in the two reactors for a range of operating conditions. Our preliminary results indicate that the OBR has the capability of enhancing reaction rates above those observed in the STR.

INFLUENCE OF THE REACTION CONDITIONS IN THE N-ALKYLATION OF ACRIDONE-2-CARBOXYLIC ACIDS

The synthesis and a study about the influence of the solvent in the alkylation reaction of 2-Carboxy-6-chloro-9(10H) acridone (3b) and 2-Carboxy-6-chloro-7-nitro-9(10H) acridone (3a) was done, obtaining the N-ethyl ester derivative of the alkylated products. Using the liquid-liquid phase transfer catalysis only the N-alkylated derivative was obtained in both cases with an improved yield.

ChemInform Abstract: A Practical Olefin Hydroboration under Liquid‐Liquid Phase Transfer Catalysis Conditions.

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ChemInform Abstract: Phase-Transfer Catalyzed Syntheses of Diaryl 1,2-Phenylene Dioxydiacetates and N-Aryl-5-(2-chlorophenyl)-2-furamides.

Abstract A series of diaryl 1,2-phenylene dioxydiacetates and N-aryl-5-(2-chlorophenyl)-2-furamides are synthesized in good to excellent yields under the conditions of liquid-liquid phase transfer catalysis using polyethylene glycol-400 as the catalyst.