Mechanisms and Applications of Solid—Liquid Phase-Transfer Catalysis

Liotta, Charles L.; Berkner, Joachim E.; Wright, J. P.; Fair, Barbara E.

doi:10.1021/bk-1997-0659.ch003

Cited by 21 publications

(16 citation statements)

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“… 29 Solid–liquid PTC is often regarded as a green methodology, as reagents and saline products are kept in the solid state and can be readily separated by physical methods. 30 Alkylation of alcohols and other nucleophilic substrates under PTC conditions is not a novel procedure, but the potential of this methodology using DCM both as a solvent and as alkylating reagent remains almost unexplored. 31 Although DCM has been found an excellent solvent for liquid–solid PTC, 32 in the rare cases when DCM is used as an electrophile, liquid–liquid PTC methods in biphasic media (with concentrated aqueous NaOH), or highly polar solvents like N -methyl-2-pyrrolidone have been preferred.…”

Section: Results and Discussionmentioning

confidence: 99%

“…Therefore, solid–liquid PTC enhances the reactivity of solids, and at the same time improves selectivity, by reducing side processes that are common when highly reactive species are dissolved in a higher concentration (Figure ). Solid–liquid PTC is often regarded as a green methodology, as reagents and saline products are kept in the solid state and can be readily separated by physical methods . Alkylation of alcohols and other nucleophilic substrates under PTC conditions is not a novel procedure, but the potential of this methodology using DCM both as a solvent and as alkylating reagent remains almost unexplored .…”

Section: Results and Discussionmentioning

confidence: 99%

“…The mechanism responsible for the solubilization of insoluble nucleophiles depends largely on the nature of the PTC catalyst. Whereas tetraalkylammonium salts, like NBu 4 Cl, rely on the high solubility of its cation in low polarity solvents, the action of 18-crown-6 is due to the sequestration of the alkali metal cation in the cavity of the molecule. , Hence, the lower efficacy of 18-crown-6 in the reaction with NaOMe could be due to its moderate affinity for Na + (e.g., the affinity ratio K + /Na + for 18-crown-6 in the gas phase is 10:6) . It is well-known that the efficacy of complexing PTCs shows significant dependency on the size of the alkali metal .…”

Section: Results and Discussionmentioning

confidence: 99%

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NHC-CDI Betaine Adducts and Their Cationic Derivatives as Catalyst Precursors for Dichloromethane Valorization

2021

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Zwitterionic adducts of N-heterocyclic carbene and carbodiimide (NHC-CDI) are an emerging class of organic compounds with promising properties for applications in various fields. Herein, we report the use of the ICyCDI( p -Tol) betaine adduct ( 1a ) and its cationic derivatives 2a and 3a as catalyst precursors for the dichloromethane valorization via transformation into high added value products CH 2 Z 2 (Z = OR, SR or NR 2 ). This process implies selective chloride substitution of dichloromethane by a range of nucleophiles Na + Z – (preformed or generated in situ from HZ and an inorganic base) to yield formaldehyde-derived acetals, dithioacetals, or aminals with full selectivity. The reactions are conducted in a multigram-scale under very mild conditions, using dichloromethane both as a reagent and solvent, and very low catalyst loading (0.01 mol %). The CH 2 Z 2 derivatives were isolated in quantitative yields after filtration and evaporation, which facilitates recycling the dichloromethane excess. Mechanistic studies for the synthesis of methylal CH 2 (OMe) 2 rule out organocatalysis as being responsible for the CH 2 transfer, and a phase-transfer catalysis mechanism is proposed instead. Furthermore, we observed that 1a and 2a react with NaOMe to form unusual isoureate ethers, which are the actual phase-transfer catalysts, with a strong preference for sodium over other alkali metal nucleophiles.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Results and Discussionmentioning

confidence: 99%

Section: Results and Discussionmentioning

confidence: 99%

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NHC-CDI Betaine Adducts and Their Cationic Derivatives as Catalyst Precursors for Dichloromethane Valorization

2021

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“…[20] We observed similar behaviour for reactions in PFDMC, while the catalytic effect of R f -CE3 was clearly evident using thin-layer PTC conditions (entries 6 and 7), [21] where the addition of a small amount of water generates a third liquid phase coating on the surface of the solid. [22] The PTC of anion solubility in PFDMC was further extended to KOMe, and its nucleophilic aromatic substitution reaction (S N Ar) with 4-nitrochlorobenzene [Eq. (3)].…”

Section: And Clearly Defines the Formation Of A C H T U N G T R E N Nmentioning

confidence: 99%

“…This can be expected to be a long-term project, as in the case of conventional PTC. [3,22] Conclusions Polyfluorinated onium salts and macrocylic ligands with typical fluorous characteristics, and yet retaining the ability to transfer reactive anionic species from water or from a solid surface into a second liquid phase, have recently emerged on the PTC scene. Therefore, their true potential in PTC reactions has still to be discerned, and the field will be expected to continue to grow in the near future.…”

Section: And Clearly Defines the Formation Of A C H T U N G T R E N Nmentioning

confidence: 99%

Perfluorocarbon Soluble Crown Ethers as Phase Transfer Catalysts

2008

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Fluorous derivatives of dibenzo-18-crown-6 ether were readily prepared by means of metal-catalyzed cross-coupling reactions, and then successfully applied as catalysts in representative solid-liquid phase transfer catalysis (PTC) reactions, which were performed in standard organic solvents, such as chlorobenzene and toluene, and also in fluorous solvents, such as perfluoro-1,3-dimethylcyclohexane (PFDMC). It was clearly shown that properly designed fluoroponytailed crown ethers can promote the disintegration of the crystal lattice of alkali salts and transfer anions from the solid surface into an apolar, non-coordinating perfluorocarbon phase. Far from being a simple chemical curiosity, this unprecedented observation has relevant implications in the design of PTC scenarios of wide applicability. This new paradigm represents an advance in crown ether chemistry, and their use as recyclable phase transfer catalysts.

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Phase‐Transfer Catalysis

Albanese¹

2008

Kirk-Othmer Encyclopedia of Chemical Technology

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Phase‐transfer catalysis (PTC) is a powerful tool to carry out many organic reactions in a practical fashion, both in the laboratory and on the industrial scale. Significant cost savings and major process improvements can be achieved in reactions performed in water–organic solvent mixtures. Particularly striking is the possibility of replacing expensive solvents and dangerous bases that require strictly anhydrous conditions with aqueous bases and apolar, environmentally friendly, easily recyclable solvents. During the last decade notable results, both in terms of yields and stereoselectivity, were obtained in various reactions performed in the presence of chiral, nonracemic quaternary ammonium salts.

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Mechanisms and Applications of Solid—Liquid Phase-Transfer Catalysis

Cited by 21 publications

References 0 publications

NHC-CDI Betaine Adducts and Their Cationic Derivatives as Catalyst Precursors for Dichloromethane Valorization

NHC-CDI Betaine Adducts and Their Cationic Derivatives as Catalyst Precursors for Dichloromethane Valorization

Perfluorocarbon Soluble Crown Ethers as Phase Transfer Catalysts

Phase‐Transfer Catalysis

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