Phase‐Transfer Agents as Catalysts for a Nucleophilic Substitution Reaction in Microemulsions

Häger, Maria; Holmberg, Krister

doi:10.1002/chem.200306048

Cited by 21 publications

(16 citation statements)

References 18 publications

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“…Typical examples of their use include phase-transfer catalysts, [7] oxidant solubilizers, [8] membrane transport agents, [9] sequestering reagents, [10] ra-…”

Section: Introductionmentioning

confidence: 99%

A Strategy for Controlling the Central Torsion Angle in Biphenyl‐Based Molecular‐Scale Bridges

et al. 2005

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The synthesis of a series of crown ether ligands (C4-C6) based upon the 2,2Ј-biphenyl unit is described. In the series, the length of the polyether chain connecting the two oxygen atoms increases progressively. These polyethers are moderately fluorescent in acetonitrile solution, but this emission is partially quenched upon the addition of various alkali metal cations. Spectrofluorimetric titrations performed with MClO 4 (M = Li + , Na + ) or KPF 6 show that binding to crown ethers C4-C6 involves the formation of a 1:1 cation/ligand complex.

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“…Typical examples of their use include phase-transfer catalysts, [7] oxidant solubilizers, [8] membrane transport agents, [9] sequestering reagents, [10] ra-…”

Section: Introductionmentioning

confidence: 99%

A Strategy for Controlling the Central Torsion Angle in Biphenyl‐Based Molecular‐Scale Bridges

et al. 2005

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“…Considering the model S N 2 reaction between 4-tert-butylbenzyl bromide and potassium iodide the situation can be different. [27] They found that the conversion within a twophase system with addition of a PTA is just as fast as in a microemulsion system with PTA. In this case the total interfacial area does not determine the reaction rate and one may assume a fast and efficient extraction equilibrium, whereby the "chemical" reaction itself is the rate determining step.…”

Section: Discussion Epoxidation Of Trans-chalcone (I)mentioning

confidence: 99%

Dramatic Enhancement of Enone Epoxidation Rates in Nonionic Microemulsions

Wielpütz

Sottmann

Strey

et al. 2006

Chemistry A European J

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The ability of microemulsions to dissolve polar and non-polar components with a huge internal interface can overcome the reagent incompatibilities frequently encountered in organic reactions. We investigated model epoxidation reactions of alpha,beta-unsaturated enones and alkaline hydrogen peroxide in different nonionic microemulsions, both in the presence and absence of a phase-transfer agent (PTA). The obtained reaction profiles were compared with those for the corresponding surfactant-free two-phase systems. In addition, we defined a time constant tau as a measure for the rate of turnover. The epoxidation of trans-chalcone using an n-alkyl-polyoxyethylene surfactant based microemulsion was fastest in the system with the PTA (tau=66 min) and slightly slower without the PTA (tau=77 min). It was still slower in the two-phase system with a PTA (tau=114 min) and extremely sluggish without a phase-transfer agent. With n-alkyl beta-D-glucopyranoside as the surfactant the conversion was twice as fast than in the former microemulsion systems, but the PTA did not accelerate the reaction further (tau=35 and 33 min). The epoxidation of vitamin K(3), the second model system, was extremely accelerated. It proceeded a factor of approximately 35 faster in the microemulsion (tau=1.44 min) than in the corresponding two-phase system (tau=57 min).

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“…[41] The microemulsion was based on a chlorinated hydrocarbon and a sugar surfactant, octyl glucoside, which means that there were no counterions competing with the nucleophile at the oil-water interface. A quaternary ammonium salt, tetrabutylammonium hydrogen sulfate, was used as phase-transfer catalyst, both in an amount equimolar to the iodide and in a catalytic amount.…”

Section: Combining the Microemulsion Approach With Phase-transfer Catmentioning

confidence: 99%

Organic Reactions in Microemulsions

Holmberg

2007

Eur J Org Chem

Self Cite

102

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Microemulsions, i.e., thermodynamically stable, one‐phase mixtures of oil, water and surfactants, are useful as reaction media as a way to overcome the reactant incompatibility problem that one frequently encounters in organic synthesis. The use of a microemulsion can be seen as an alternative to phase‐transfer catalysis, i.e., use of a two‐phase system with added phase‐transfer agent. The microemulsion approach and phase‐transfer catalysis can also be combined, i.e., the reaction can be performed in a microemulsion in the presence of a small amount of a phase‐transfer agent. A very high reaction rate may then be obtained. The reaction rate in a microemulsion is often influenced by the charge at the interface and this charge depends on the surfactant used. For instance, reactions involving negatively charged species will be accelerated by the use of a cationic surfactant. This effect is analogous to micellar catalysis and may be termed microemulsion catalysis. The acceleration is more pronounced when the surfactant counterion is small and weakly polarizable. Microemulsions can also be used to induce regiospecificity of organic reactions. Organic molecules with one more polar and one less polar end will accumulate at the oil‐water interface of microemulsions. They will orient at the interface so that the polar part of the molecule extends into the water domain and the nonpolar part extends into the hydrocarbon domain. A water‐soluble reagent will react from the “water side”, i.e., attack the polar part of the amphiphilic molecule, and a reagent soluble in hydrocarbon will react at the other end of the amphiphilic molecule. This review demonstrates that microemulsions can be a useful for (i) overcoming reactant incompatibility, (ii) speeding up reactions of one polar and one apolar reactant (microemulsion catalysis), and (iii) inducing regiospecificity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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Phase‐Transfer Agents as Catalysts for a Nucleophilic Substitution Reaction in Microemulsions

Cited by 21 publications

References 18 publications

A Strategy for Controlling the Central Torsion Angle in Biphenyl‐Based Molecular‐Scale Bridges

A Strategy for Controlling the Central Torsion Angle in Biphenyl‐Based Molecular‐Scale Bridges

Dramatic Enhancement of Enone Epoxidation Rates in Nonionic Microemulsions

Organic Reactions in Microemulsions

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