A substitution reaction in an oil-in-water microemulsion catalyzed by a phase transfer catalyst

Häger, Maria; Holmberg, Krister

doi:10.1016/s0040-4039(99)02261-3

Cited by 32 publications

(17 citation statements)

References 4 publications

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“…The reaction in the microemulsion was much faster than the reaction in the two-phase system when an equimolar amount of PTA was present in both systems. [8] In that reaction system, the extraction constant was considerably lower than in the present system due to two contributing factors. Firstly, the solvent was trichloroethylene, which is less polar than dichoromethane.…”

Section: Full Papercontrasting

confidence: 50%

“…There are only a few reports in the literature on the use of PTAs in combination with microemulsions and none of these have dealt with the issue in a systematic way. [8][9] However, the effect of PTAs in micelles and macroemulsions have been studied in some detail by Battal and co-workers. [10][11] We here show that PTC can indeed be used to accelerate microemulsionbased reactions and we believe that the results presented offer great promise for use of the combined approach in preparative organic chemistry.…”

Section: Full Papermentioning

confidence: 99%

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

Häger¹,

Holmberg²

2004

Chemistry A European J

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The reaction between 4-tert-butylbenzyl bromide and potassium iodide was carried out in microemulsions based on different nonionic surfactants, and the reaction rates were compared with those obtained in two-phase systems with added phase-transfer agent, either a quaternary ammonium salt or a crown ether. The reactions were relatively fast in the microemulsions and extremely sluggish in the two-phase systems without additional phase-transfer agent. Addition of a phase-transfer agent did not accelerate the reaction when a hydrocarbon was used as organic solvent, neither in the two-phase system nor in the microemulsion. When a chlorinated hydrocarbon was used as solvent, phase-transfer catalysis became effective and the rate obtained in the two-phase system with an equimolar amount of phase-transfer agent added was higher than that obtained in the microemulsion. When a catalytic amount of phase-transfer agent was used, the rate in the two-phase system was about the same as the rate obtained in the microemulsion without the phase-transfer agent. The combined approach, that is, use of a microemulsion as the reaction medium and addition of a phase-transfer agent, gave the highest reaction rate. The quaternary ammonium salt (tetrabutylammonium hydrogen sulfate) was a more efficient catalyst in the microemulsion system than the crown ether ([18]crown-6).

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Section: Full Papercontrasting

confidence: 50%

Section: Full Papermentioning

confidence: 99%

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

Häger¹,

Holmberg²

2004

Chemistry A European J

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“…For some reactions the reactivity in a microemulsion is of the same order as that in a two-phase system with added phase transfer agent [3] but in other instances the reaction is considerably faster in a microemulsion. [4,5] It will be demonstrated in the section "Combining the microemulsion approach with phase-transfer catalysis" that very high reactivity can be obtained by combining the two approaches.…”

Section: Overcoming Reactant Incompatibilitymentioning

confidence: 99%

“…In an attempt to combine the two methods and take advantage of both the high reactivity of a poorly solvated anion in phasetransfer catalysis and the very large oil-water interface of a microemulsion, ring-opening of a lipophilic epoxide was carried out in a microemulsion in the presence of a conventional Q salt, tetrabutylammonium hydrogen sulfate. [5] Reactions were also performed in a two-phase system with and without added Q salt. It was found that the rate of the Q salt-catalyzed system is increased further when the reaction is carried out in a microemulsion instead of an oilwater two-phase system.…”

Section: Combining the Microemulsion Approach With Phase-transfer Catmentioning

confidence: 99%

Organic Reactions in Microemulsions

Holmberg

2007

Eur J Org Chem

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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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“…Microemulsions have been explored as media for a broad range of organic reactions and the reaction rate has been found to be high, sometimes exceeding that obtained by phase transfer catalysis [8]. It has also been found that the microemulsion approach and phase transfer catalysis can be combined, giving rise to very high reactivity [9,10].…”

Section: Introductionmentioning

confidence: 99%