Effective Phase-transfer Catalyst Research Articles

Metal-Organic Framework Nanoparticles with Universal Dispersibility through Crown Ether Surface Coordination for Phase-Transfer Catalysis and Separation Membranes.

Dispersing metal-organic framework (MOF) solids in stable colloids is crucial for their availability and processibility. Herein, we report a crown ether surface coordination approach for functionalizing the surface-exposed metal sites of MOF particles with amphiphilic carboxylated crown ether (CEC). The surface-bound crown ethers significantly improve MOF solvation without compromising the accessible voids. We demonstrate that CEC-coated MOFs exhibit exceptional colloidal dispersibility and stability in 11 distinct solvents and six polymer matrices with a wide range of polarities. The MOF-CEC can be instantaneously suspended in immiscible two-phase solvents as an effective phase-transfer catalyst and can form various uniform membranes with enhanced adsorption and separation performance, illustrating the effectiveness of crown ether coating.

Polymer-Supported Poly(Ethylene Glycol) as a Phase-Transfer Catalyst for Cross-Aldol Condensation of Isobutyroaldehyde and Formaldehyde.

Immobilized poly(ethylene glycol) (PEG 600-PS) was used as an effective phase-transfer catalyst for the synthesis of hydroxypivaldehyde from isobutyraldehyde (IBA) and formaldehyde in the presence of an inorganic base. Studies on the influence of the parameters on the course of the reaction in a batch reactor showed that the use of the PEG 600-PS catalyst allowed one to obtain HPA with high efficiency (IBA conversion >96%, selectivity >98%) in a relatively short time and under mild conditions (2 h, 40 °C). The developed method enables easy separation of the post-reaction mixture by simple phase separation, and the immobilized catalyst can be separated by filtration and then used five times without a loss in its activity. The high activity and stability of the catalyst was also confirmed in a test carried out in a flow reactor.

Multigram synthesis of N-alkyl bis-ureas for asymmetric hydrogen bonding phase-transfer catalysis.

Fluorine is a key element present in ~35% of agrochemicals and 25% of marketed pharmaceutical drugs. The availability of reliable synthetic protocols to prepare catalysts that allow the efficient incorporation of fluorine in organic molecules is therefore essential for broad applicability. Herein, we report a protocol for the multigram synthesis of two representative enantiopure N-alkyl bis-urea organocatalysts derived from (S)-(-)-1,1'-binaphthyl-2,2'-diamine ((S)-BINAM). These tridentate hydrogen bond donors are highly effective phase-transfer catalysts for solubilizing safe and inexpensive metal alkali fluorides (KF and CsF) in organic solvents for enantioselective nucleophilic fluorinations. The first catalyst, characterized by N-isopropyl substitution, was obtained by using a two-step sequence consisting of reductive amination followed by urea coupling from commercially available starting materials (14 g, 48% yield and 5-d total synthesis time). The second catalyst, featuring N-ethyl alkylation and meta-terphenyl substituents, was accessed via a novel, scalable, convergent route that concluded with the coupling between N-ethylated (S)-BINAM and a preformed isocyanate (52 g and 52% overall yield). On this scale, the synthesis requires ~10 d. This can be reduced to 5 d by performing some steps in parallel. Compared to the previous synthetic route, this protocol avoids the final chromatographic purification and produces the desired catalysts in very high purity and improved yield.

Carbohydrate-Based Azacrown Ethers in Asymmetric Syntheses

Carbohydrate-based crown ethers represent a special group of chiral phase transfer catalysts. Several derivatives of these macrocycles have been synthesized in our research group. Among these compounds, monoaza-15-crown-5 lariat ethers proved to be effective phase transfer and enantioselective catalysts in certain reactions. Those chiral azacrown ethers incorporating various carbohydrate moieties in the macrocyclic structure are reviewed, which generated asymmetric induction in reactions, such as Michael addition, epoxidation of enones, Darzens condensation and Michael-initiated ring-closure (MIRC) reaction. Effects on the catalytic activity of the structural changes are the focus.

Potent Ferroptosis Inhibitors Can Catalyze the Cross-Dismutation of Phospholipid-Derived Peroxyl Radicals and Hydroperoxyl Radicals

Nitroxides were recently shown to catalyze the cross-dismutation of alkylperoxyl and hydroperoxyl radicals, making them uniquely effective radical-trapping antioxidants (RTAs) in unsaturated hydrocarbons where both species are formed. Given the abundance of unsaturated lipids in biological membranes, the continuous generation of hydroperoxyl (superoxide) as a byproduct of aerobic respiration, and the demonstrated cytoprotective properties of some nitroxides, we probed if cross-dismutation operates in phospholipid bilayers and cell culture. Interestingly, only nitroxides that were efficiently converted to amines in situ were effective, with their activity paralleling the stability of the incipient aminyl radicals. The ether-linked diarylamine phenoxazine, one of the most potent RTAs known, was particularly effective as a cross-dismutation catalyst. In contrast, phenolic RTAs such as α-tocopherol (α-TOH), the most potent form of vitamin E, were found to be inefficient due to the preference for the combination of hydroperoxyl and phenoxyl radicals over H-atom transfer between them. Experiments carried out in mouse embryonic fibroblasts corroborated these findings. Cells cotreated with phenoxazine (or its nitroxide) and a superoxide source were better protected from ferroptosis than those treated with phenoxazine (or its nitroxide) alone. No such synergy was observed for cells treated with α-TOH. Live cell imaging established that cytoprotection was associated with suppression of (phospho)lipid peroxidation. These results highlight the remarkable capacity for select amines to act as effective phase-transfer catalysts for a reducing equivalent (an H atom), such that a water-soluble "reactive oxygen species" can be used to quench a lipid-soluble one.

Preparation of-hydroxyphenylacetic acid with cyclodextrins as an effectivephase-transfer catalyst and its reaction mechanism

An effective procedure for the synthesis of $\alpha $-hydroxyphenylacetic acid with cyclodextrin (CD) catalysts was developed. The phase-transfer catalyst types, catalyst loadings, reaction times, reaction temperatures, and substrate molar ratios were investigated to optimize the reaction conditions. In addition, the factors that affect the reaction were studied, and the relationship between benzaldehyde and $\beta $-cyclodextrin ($\beta $-CD) was analyzed through 2D-ROESY. The equilibrium constant when $\beta $-CD was used as the catalyst was calculated. The results indicated that $\beta $-CD is the optimal catalyst for the reported reaction (yield: 69.08%). Furthermore, the mechanism underlying the reported reaction was proposed.

Isoindolinones as Michael Donors under Phase Transfer Catalysis: Enantioselective Synthesis of Phthalimidines Containing a Tetrasubstituted Carbon Stereocenter.

Readily available chiral ammonium salts derived from cinchona alkaloids have proven to be effective phase transfer catalysts in the asymmetric Michael reaction of 3-substituted isoindolinones. This protocol provides a convenient method for the construction of valuable asymmetric 3,3-disubstituted isoindolinones in high yields and moderate to good enantioselectivity. Diastereoselectivity was also investigated in the construction of contiguous tertiary and quaternary stereocenters. The use of acrolein as Michael acceptor led to an interesting tricyclic derivative, a pyrroloisoindolinone analogue, via a tandem conjugated addition/cyclization reaction.

Improving oxidation stability of sunflower biodiesel by partial hydrogenation using a special catalyst

AbstractThe aim of this study was to increase the oxidation stability of biodiesel from sunflower‐oil by partial‐hydrogenation. Activated carbon, which was obtained from viscum album L., was used as a new and effective original phase transfer catalyst during partial hydrogenation. Temperature, pressure, and catalyst/biodiesel ratios were selected as the experimental parameters and their effects on the oxidation stability were investigated by using the 23 factorial design. A first‐order model was obtained using analysis of variance. The physical properties such as density, viscosity, pour point, and cloud point of sunflower biodiesel samples were determined using the standard methods. The oxidative stability (induction period, IP) values were found experimentally by the Rancimat method and cis and trans‐configurations of the biodiesel samples were characterized by Fourier transform infrared (FTIR) spectra before and after hydrogenation. Partially hydrogenated biodiesels were found to have better oxidative stability, and lower pour point and cloud point properties compared to non‐hydrogenated sunflower biodiesel. It can be stated that kinematic viscosities and the densities of the partial hydrogenated biodiesels did not change significantly.

Investigation on the Acylation of Heterocyclic Alcoholate Anions with O,O-Dialkyl Phosphorochloridothioate in Water Solvent

The acylation of some heterocyclic alcoholate anions with O,O-dialkyl phosphorochloridothioate has been investigated. Higher yields and fewer byproducts were achieved in water at 50 °C by employing an effective phase-transfer catalyst (PTC) (benzyl triethylammonium chloride [BTEAC]), acylation catalyst (AC) (4-dimethylaminopyridine), and surfactant (sodium dodecyl sulfate), under weakly basic (pH 9.5∼10) conditions. This reaction can also be applied to synthesize other insecticides with excellent yields.

Greener and facile aqueous regioselective synthesis of vicinal azidoalcohols using silica-bound 3-((polyethyleneglycol)ethyl)-8-methyl-1H-imidazol-3-ium bromide as a recyclable catalyst

An environmentally benign, aqueous synthesis of vicinal azidoalcohols by the regioselective nucleophilic ring opening of epoxides with azide anion using silica-bound 3-((polyethyleneglycol)ethyl)-8-methyl-1H-imidazol-3-ium bromide as an effective heterogeneous phase transfer catalyst is described. Short reaction time, simple work-up procedure, high yield, reusability, and use of an eco-friendly catalyst are some of the striking features of the present protocol.

Fast and effective reduction of nitroarenes by sodium dithionite under PTC conditions: application in solid-phase synthesis

Herein, conditions for the fast and effective reduction of aromatic nitro groups bound to hydrophobic polystyrene-based Wang and Ring resins utilizing sodium dithionite in dichloromethane–water under PTC conditions are reported. Tetrabutylammonium hydrogen sulfate (TBAHS) was found to be an effective phase-transfer catalyst for this reaction. This method allows for the reduction of nitro groups to amino groups under mild conditions with complete conversion and is tolerant of other functional groups. This method is a superior alternative to tin(II) chloride-based reduction, which is known for its shortcomings.

Novel bis-piperidinium and bis-pyrrolidinium compounds as versatile phase-transfer catalysts

Syntheses and applications of new bis-piperidinium and bis-pyrrolidinium compounds as effective two-center phase-transfer catalysts are presented. Applications of these catalysts have been explored in etherification and N-alkylation reactions, and comparisons between these catalysts and traditional phase-transfer catalysts such as cetyltrimethylammonium bromide (CTAB) and 1-ethyl-3-methylimidazolium chloride (emim + Cl - ) are presented.

Chemical attachment of dibromocarbene to carbon nanotubes

Dibromocarbene-modified multi-walled carbon nanotubes were prepared and characterized. The presence of different phase transfer catalyst has some effects on the modification, and benzyltriethylammonium chloride is a more effective phase transfer catalyst in the cycloaddition of dibromocarbene to multi-walled carbon nanotubes. The tube structure of functionalized multi-walled carbon nanotubes is well kept and amorphous carbon was removed from multi-walled carbon nanotube samples through repeating water/chloroform washing. Cycloadditon of dibromocarbene to multi-walled carbon nanotubes did not affect their defect sites, which are still well kept for further modification.

Two Highly Effective Phase-Transfer Catalysts for the Enantioselective Synthesis of ?-Amino Acid Derivatives

In this paper we review our recent studies into the phase-transfer catalysed asymmetric alkylation of glycine imines using quaternary ammonium salt catalysts derived from dihydrocinchonidine and ?-methylnaphthylamine.

Recent Advances in Asymmetric Phase‐Transfer Catalysis

The use of chiral nonracemic onium salts and crown ethers as effective phase-transfer catalysts have been studied intensively primarily for enantioselective carbon-carbon or carbon-heteroatom bond-forming reactions under mild biphasic conditions. An essential issue for optimal asymmetric catalysis is the rational design of catalysts for targeted reaction, which allows generation of a well-defined chiral ion pair that reacts with electrophiles in a highly efficient and stereoselective manner. This concept, together with the synthetic versatility of phase-transfer catalysis, provides a reliable and general strategy for the practical asymmetric synthesis of highly valuable organic compounds.

Highly Enantioselective Epoxidation of 2‐Methylnaphthoquinone (Vitamin K3) Mediated by New Cinchona Alkaloid Phase‐Transfer Catalysts

In the area of catalytic asymmetric epoxidation, the highly enantioselective transformation of cyclic enones and quinones is an extremely challenging target. With the aim to develop new and highly effective phase-transfer catalysts for this purpose, we conducted a systematic structural variation of PTCs based on quinine and quinidine. In the total of 15 new quaternary ammonium PTCs, modifications included, for example, the exchange of the quinine methoxy group for a free hydroxyl or other alkoxy substituents, and the introduction of additional elements of chirality through alkylation of the alkaloid quinuclidine nitrogen atom by chiral electrophiles. For example, the well-established 9- anthracenylmethyl group was exchanged for a "chiral" anthracene in the form of 9-chloromethyl-[(1,8-S;4,5-R)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene. The asymmetric epoxidation of vitamin K(3) was used as the test reaction for our novel PTCs. The readily available PTC 10 (derived from quinine in three convenient and high-yielding steps) proved to be the most enantioselective catalyst for this purpose known to date: At a catalyst loading of only 2.50 mol %, the quinone epoxide was obtained in 76 % yield and with 85 % ee (previously: < or =34 % ee), using commercial bleach (aqueous sodium hypochlorite) as the oxidant. To rationalize the sense of induction effected by our novel phase-transfer catalysts, a computational analysis of steric interactions in the intermediate chlorooxy enolate-PTC ion pair was conducted. Based on this analysis, the sense of induction for all 15 novel PTCs could be consistently explained.

Advantage of in situ generation of N-arylsulfonyl imines from α-amide sulfones in the phase-transfer-catalyzed asymmetric Strecker reaction

Highly efficient, catalytic enantioselective synthesis of N-arylsulfonyl α-amino nitriles from the corresponding α-amido sulfones has been achieved under toluene–aqueous potassium cyanide biphasic conditions using chiral quaternary ammonium iodide ( R, R, R)- 1 as an effective phase-transfer catalyst. This Strecker synthesis involving the in situ generation of the reactive N-sulfonyl imines is advantageous for the cyanation of the substrates having primary and secondary alkyl substituents.

Cycloalkylation reactions of fatty amines with α,ω-dihaloalkanes: Role of bis-quaternary ammonium salts as phase-transfer catalysts

Bis-quaternary salts are effective phase-transfer catalysts in the cycloalkylation phase reactions of amines. The catalytic activity of these quats is similar to that of conventional quaternary ammonium catalysts, such as benzyltriethylammonium chloride and tetraethylammonium bromide. Bis-quaternary ammonium surfactants have attracted great interest. They are constituted of two hydrophilic groups per molecular unit, separated by a spacer. This is quite different from the catalytic behavior for the conventional surfactant, which leads to a more selective alkylation. Phase-transfer catalysis and micellar phase-transfer catalysis are two well-known methods of promoting reactions mainly between lipophilic and hydrophilic reactants. An intramolecular cycloalkylation of fatty amines, C 12 H 25 NH 2 and C 16 H 33 NH 2 , with several α,ω-dihaloalkanes, viz., 1,2-dibromoethane C 2 H 4 Br 2 , trans -1,4-dichloro-2-butene C 4 H 6 Cl 2 , 1,6-dibromohexane Br(CH 2 ) 6 Br, under PTC conditions are reported. In particular, the cycloalkylation of amine with an excess of α,ω-dihaloalkane has been studied in the presence of 1.9 × 10 −6 mol% bis-quaternary dihalide surfactants (I and II) as PT catalysts and sodium hydroxide (25%) as a base, at 50–60 °C. The reaction was completed in less than 4 h selectively yielding the desired cycloadduct. The structures of the synthesized cycloadducts formed were evidenced by elemental analyses, IR and 1 H NMR spectral analyses.

A green procedure for the synthesis of cinnamate esters using Aliquat®336

As an effective solid-liquid phase-transfer catalyst as well as an ionic liquid medium Aliquat® 336 has been applied in the synthesis of cinnamate esters under mild green chemistry procedures involving microwave irradiation.

The Synthesis and Applications of Asymmetric Phase‐Transfer Catalysts Derived from Isomannide and Isosorbide.

AbstractFor Abstract see ChemInform Abstract in Full Text.