Distribution of amines in water/AOT/n-hexane reverse micelles: influence of the amine chemical structure

Zingaretti, Lilian; Correa, N. Mariano; Boscatto, Liliana; Chiacchiera, Stella Maris; Durantini, Edgardo N.; Bertolotti, Sonia G.; Rivarola, Claudia R.; Silber, Juana J.

doi:10.1016/j.jcis.2004.12.057

Cited by 29 publications

(25 citation statements)

References 38 publications

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“…When no À OH is present, the phenols exist solely in the form of nonionized species. As we have previously demonstrated, [44][45][46][47] the AOT SO 3 À head is a very good hydrogen-bond acceptor, thus the different phenols should be located at the AOT RM interface and interact through hydrogen bonding with the surfactant. This interaction prevails over that of water molecules for the AOT polar head group at any water content.…”

Section: Resultsmentioning

confidence: 97%

“…Also, we have previously shown that hydrogen-bonding interactions are a powerful driving force for different solutes to reside at the AOT RM interface. [44][45][46][47] In studies performed by Magid et al, [40] pure water was used to prepare the RMs, thus there was no doubt that phenols were in their acidic form, as confirmed from their absorption spectra. [40,41] Interestingly, Menger and Saito have shown that, at pH 8.5, judging from the lack of the band of the ionized species, no p-nitrophenolate was present in the pool of AOT RMs [41] despite the fact that the pK a of p-nitrophenol (p-NPh) in water is 7.14.…”

Section: Introductionmentioning

confidence: 99%

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Inhibited Phenol Ionization in Reverse Micelles: Confinement Effect at the Nanometer Scale

et al. 2011

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We found that the absorption spectra of 2-acetylphenol (2-HAP), 4-acetylphenol (4-HAP), and p-nitrophenol (p-NPh) in water/sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT)/n-heptane reverse micelles (RMs) at various W(0) (W(0) = [H(2)O]/[surfactant]) values studied changed with time if (-)OH ions were present in the RM water pool. There is an evolution of ionized phenol (phenolate) bands to nonionized phenol absorption bands with time and this process is faster at low W(0) values and with phenols with higher bulk water pK(a) values. That is, in bulk water and at the hydroxide anion concentration used, only phenolate species are observed, whereas in AOT RMs at this fixed hydroxide anion concentration, ionized phenols convert into nonionized phenol species over time. Furthermore, we demonstrate that, independent of the (-)OH concentration used to prepare the AOT RMs, the nonionized phenols are the more stable species in the RM media. We explain our results by considering that strong hydrogen-bonding interactions between phenols and the AOT polar head groups result in the existence of only nonionized phenols at the AOT RM interface. The situation is quite different when the phenols are dissolved in cationic benzyl-n-hexadecyldimethylammonium chloride RMs. Therein, only phenolates species are present at the (-)OH concentrations used. The results clearly demonstrate that the classical definition of pH does not apply in a confined environment, such as in the interior of RMs and challenge the general idea that pH can be determined inside RMs.

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Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Inhibited Phenol Ionization in Reverse Micelles: Confinement Effect at the Nanometer Scale

et al. 2011

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“…Numerous kinetic investigations over a large area of different reactions have been reported previously using UV analysis. [35][36][37][38][39][40][41][42][43][44][45][46] In order to gain further insight into the reaction mechanism, a kinetic study of the reactions was undertaken by the UV spectrophotometric technique. First, it was necessary to find the appropriate wavelength in order to follow the kinetic study of the reaction.…”

Section: Kinetic Studiesmentioning

confidence: 99%

Synthesis of stable phosphorus ylides from 3, 5-dimethylpyrazole and kinetic investigation of the reactions by UV spectrophotometry

Habibi‐Khorassani¹,

Maghsoodlou²,

Nassiri³

et al. 2007

Arkivoc

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Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reactions between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of a NH-acid, such as 3,5-dimethylpyrazole. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. To determine the kinetic parameters of the reactions, they were monitored by UV spectrophotometery. The second order fits were drawn and the values of the second order rate constant (k 2 ) were calculated automatically using standard equations within the program. At the temperature range studied, the dependence of the second order rate constant (Ln k 2 ) on reciprocal temperature was in good agreement with the Arrhenius equation. This provided the relevant plots to calculate the activation energy of all reactions. Furthermore, useful information was obtained from studies of the effect of solvent, structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates) and also concentration of reactants on the rate of reactions. The proposed mechanism was confirmed according to the obtained results and steady state approximation and first step (k 2 ) of reaction was recognized as a rate-determining step on the basis of experimental data.

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“…To know the location of molecular probes in the aggregates, can give information about their residing place in biological systems. 6 We have previously studied the properties of a series of nitroanilines, 17 diphenylamines, 18 carotenoids 19 and amines 20 in reverse micelles of AOT in n-hexane or n-heptane at different W 0 .…”

Section: Introductionmentioning

confidence: 99%

“…Taking into account the studies in pure solvents 17 such a red shift can be partly interpreted owing to the greater polarity of the micelle interface with regard to the organic solvent 12 but also because the hydrogen bond acceptor ability of the polar heads of the surfactant. [17][18][19][20] Thus, in this system, o-NA is acting as hydrogen bond donor through the NH 2 group. Figures 2 and 3 show typical spectra of o-NA in n-heptane/AOT nonaqueous reverse micelles as a function of AOT concentration at W S = 2, for GY and DMA respectively.…”

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confidence: 99%

Binding of o-nitroaniline to nonaqueous AOT reverse micelles

Falcone¹,

Silber²,

Biasutti³

et al. 2011

Arkivoc

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Distribution of amines in water/AOT/n-hexane reverse micelles: influence of the amine chemical structure

Cited by 29 publications

References 38 publications

Inhibited Phenol Ionization in Reverse Micelles: Confinement Effect at the Nanometer Scale

Inhibited Phenol Ionization in Reverse Micelles: Confinement Effect at the Nanometer Scale

Synthesis of stable phosphorus ylides from 3, 5-dimethylpyrazole and kinetic investigation of the reactions by UV spectrophotometry

Binding of o-nitroaniline to nonaqueous AOT reverse micelles

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