A study in preferential solvation using a solvatochromic pyridinium betaine and its relationship with reaction rates in mixed solvents

Dawber, J. Graham; Ward, J.R.; Williams, Richard A.

doi:10.1039/f19888400713

Cited by 144 publications

(77 citation statements)

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“…The effects of preferential solvation E T (30) , which is sensitive to solvent-solvent interaction, on the rate of nucleophilic substitution reaction involving anions in binary mixed solvents have been examined [25][26][27][28].…”

Section: The Correlation Of Rate Constant Values K a With Preferentiamentioning

confidence: 99%

“…In binary solvent mixtures, the solvent-solvent interactions dominate the solute-solvent interactions since the solvent is present in large excess compared with the solute [25]. These solvent-solvent interactions may be due to either hydrogen bond formation or polarizability effects that would affect the property under consideration.…”

Section: The Correlation Of Rate Constant Values K a With Preferentiamentioning

confidence: 99%

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Effect of acetonitrile–water mixtures on the reaction of dinitrochlorobenzene and dinitrochlorobenzotrifluoride with hydroxide ion

El‐Mallah

Senior

Nabil

et al. 2010

Int J of Chemical Kinetics

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The kinetics of alkaline hydrolysis of 2-chloro-3,5-dinitrobenzotrifluoride 1 and 1-chloro-2,4-dinitrobenzene 2 were studied in various acetonitrile-water (AN-H 2 O) mixtures (10-90% w/w) at different temperatures. Thermodynamic parameters H # and S # show great variation, whereas G # appears to vary little with the solvent composition presumably due to compensating variations. The results are discussed in terms of the solvent parameters such as preferential solvation, dielectric constant, polarity/polarizability, and hydrogen bond donor and acceptor parameters. It has been found that the factors controlling the reaction rates are the desolvation of OH − , the solvophobicity of the medium, and free water molecules in rich AN mixed solvent. The data showed that the solvatochromic parameters of (AN-H 2 O) mixed solvent are destroyed in the presence of excess OH − . C

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Section: The Correlation Of Rate Constant Values K a With Preferentiamentioning

confidence: 99%

Section: The Correlation Of Rate Constant Values K a With Preferentiamentioning

confidence: 99%

Effect of acetonitrile–water mixtures on the reaction of dinitrochlorobenzene and dinitrochlorobenzotrifluoride with hydroxide ion

El‐Mallah

Senior

Nabil

et al. 2010

Int J of Chemical Kinetics

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“…This observation could not be explained on the basis of viscosity change of aqueous ethanol solution as a result of alcohol concentration change, since the viscosity reached a maximum at 50% ethanol (Marcus, 2002). Instead, the polarity change of the solution might have played a critical role in affecting the extraction, according to the theory of preferential solvation proposed by Dawber, Ward, and Williams (1988) in the study of reaction rates in mixed solvents using pyridinium betaine. The concept of an excess polarity was introduced to represent the departure of polarity from a linear relationship in a binary solvent mixture, and a positive excess polarity indicated preferential solvation of a solute by the more polar component of the solvent, whereas a negative one represented preferential solvation by the less polar component.…”

Section: Extraction Of Isoflavones From Red Clover Flowersmentioning

confidence: 97%

Recovery of isoflavones from red clover flowers by a membrane-based process

Kumar

Lamb

et al. 2006

Innovative Food Science & Emerging Technologies

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Isoflavones in red clover flowers were extracted and recovered using a new process that mainly comprised of ethanol extraction, membrane processing, micelle formation and drying. To obtain maximum isoflavone extraction an ethanol concentration between 40% and 50% in water was found to be optimal. The extracted isoflavones were processed by ultrafiltration for preliminary purification, and then concentrated by reverse osmosis. As ethanol was removed by evaporation, micelles were formed in the reverse osmosis retentate, which was dried to yield an isoflavoneenriched product. This product contained about 9% isoflavone highlighting its potential use as a direct nutraceutical supplement. Crown Copyright © 2006 Published by Elsevier Ltd. All rights reserved. Keywords: Isoflavones; Red clover flower; Extraction; Membrane and processIndustrial relevance: Isoflavones present in agricultural biomass are utilized as source of functional food supplements. Extraction and refining of isoflavones involves several steps and the process is very energy intensive. This work reports an interesting approach for extraction and refining of isoflavones by developing a new process, which is energy efficient and gives a final product, which contains sufficiently high amounts of isoflavones for consumer applications.

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“…The relative importance of a S is understandable because of the formation of hydrogen-bonds between the solvent and the probe phenolate oxygen, as shown by 1 H NMR. 21 The dependence on p* S is also expected because these probe have large dipole moments. In fact the (calculated) dipole moments, m (probe) , for six of the probes shown in Figure 1 (RB, WB, QB, MePM; MePMBr, and MePMBr 2 ) were found to correlate linearly with the regression coefficient (s)…”

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confidence: 94%

Solvation simplified

Seoud¹

2010

Quím. Nova

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Recebido em 24/5/10; aceito em 28/9/10; publicado na web em 16/11/10The effects of solvents on chemical phenomena is complex because there are various solute-solvent interaction mechanisms. Solvatochromism refers to the effects of solvents on the spectra of probes. The study of this phenomenon sheds light on the relative importance of the solvation mechanisms. Solvation in pure solvents is quantitatively analyzed in terms of a multi-parameter equation. In binary solvent mixtures, solvation is analyzed by considering the organic solvent, S, water, W, and a 1:1 hydrogen bonded species (S-W). The applications of solvatochromism to understand distinct chemical phenomena, reactivity and swelling of cellulose, is briefly discussed.Keywords: solvation ; solvatochromism; solute-solvent interactions.The need for understanding solvation is clear: most reactions are carried out in the liquid phase; the solvent is not a "spectator". It acts as a heat-and mass-transfer agent; it participates in proton transfers (for acid/base catalyzed reactions) and in the solvation of ions, dipolar species, etc. Consider the decomposition of 6-nitro-3-carboxybenzisoxazole, whose reaction scheme is depicted in Figure 1. This example is particularly illustrative of the effects of solvents on reactivity because it is a simple, spontaneous decomposition reaction. Therefore, effects of changing the solvent on the observed rate constant, k obs , can be unequivocally attributed to differences in solvation between the reactant state-where the negative charge is concentrated on the carboxylate anion-and the transition state, where the charge is dispersed over several atoms. The half-lives of this reaction in hexamethylphosphotriamide, acetonitrile, and water, are 0.001 s, 11.6 min, and one day, respectively! 1Can these large differences in k obs be correlated with solvent properties? The results of such attempt is shown in Table 1, where the subscript (S) refers to solvent, e r , E T (30), a S , b S refer to the solvent relative permittivity, its empirical polarity, hydrogen-bond donation capacity or "acidity", and hydrogen-bond acceptance capacity or "basicity", respectively (vide infra for more discussion of the last three solvent descriptors). Table 1 reveals that there is no correlation between log k obs and any single solvent property. Inclusion of a second descriptor leads to a noticeable improvement in the regression analysis; a four-descriptor equation gives the best correlation coefficient. The conclusion from Table 1 is obvious: solvent effects on chemical reactivity, and presumably other phenomena, e.g., chemical equilibria and spectroscopic data, are complex; any successful correlation with a single solvent descriptor is, most certainly, fortuitous.The following questions now arise: (i) What is the reason for this complex dependence of chemical phenomena on solvent properties?(ii) Can the relative importance of each solute-solvent interaction be identified and quantified? (iii) How can we treat solvation in solvent mixtures? The object...

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A study in preferential solvation using a solvatochromic pyridinium betaine and its relationship with reaction rates in mixed solvents

Cited by 144 publications

References 4 publications

Effect of acetonitrile–water mixtures on the reaction of dinitrochlorobenzene and dinitrochlorobenzotrifluoride with hydroxide ion

Effect of acetonitrile–water mixtures on the reaction of dinitrochlorobenzene and dinitrochlorobenzotrifluoride with hydroxide ion

Recovery of isoflavones from red clover flowers by a membrane-based process

Solvation simplified

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