Neutral hydrolysis of p-nitrophenyl dichloroacetate in highly aqueous tert-butyl alcohol. Effects due to solvent structural integrity

Engberse.Jf,; Engberts, Jan B. F. N.

doi:10.1021/ja00811a051

Cited by 16 publications

(7 citation statements)

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“…Previous studies have shown that the hydrolysis of activated esters structurally similar to 1a − d , but also of similar activated amides, is retarded by most hydrophobic cosolutes. ,,− In the present study, these rate retardations are interpreted using both a thermodynamic model and a kinetic model…”

Section: Introductionmentioning

confidence: 81%

Kinetic Evidence for Hydrophobically Stabilized Encounter Complexes Formed by Hydrophobic Esters in Aqueous Solutions Containing Monohydric Alcohols

et al. 2001

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Kinetic evidence for hydrophobically stabilized encounter complexes formed by hydrophobic esters in aqueous solutions containing monohydric alcohols Buurma, N.J.; Pastorello, L.; Blandamer, M.J; Engberts, J.B.F.N. Abstract: The pH-independent hydrolysis of four esters, p-methoxyphenyl 2,2-dichloroethanoate (1a), p-methoxyphenyl 2,2-dichloropropanoate (1b), p-methoxyphenyl 2,2-dichlorobutanoate (1c), and p-methoxyphenyl 2,2-dichloropentanoate (1d), in dilute aqueous solution has been studied as a function of the molality of added cosolutes ethanol, 1-propanol, and 1-butanol. The rate constants for the neutral hydrolysis decrease with increasing cosolute concentration. These kinetic medium effects respond to both the hydrophobicity of the ester and of the monohydric alcohol. The observed rate effects were analyzed using both a thermodynamic and a kinetic model. The kinetic model suggests a molecular picture of a hydrophobically stabilized encounter complex, with equilibrium constants K ec often smaller than unity, in which the cosolute blocks the reaction center of the hydrolytic ester for attack by water. The formation of these encounter complexes leads to a dominant initial-state stabilization as follows from the thermodynamic model. Decreases in both apparent enthalpies and entropies of activation for these hydrolysis reactions correspond to unfavorable enthalpies and favorable entropies of complexation, which confirms that the encounter complexes are stabilized by hydrophobic interactions. IntroductionHydrophobic interactions are important noncovalent driving forces for inter-and intramolecular binding and assembly processes in aqueous chemistry and biochemistry. 1 These interactions vary from relatively weak pairwise intermolecular contacts to cooperative bulk association processes. The driving force for these hydrophobic interactions usually originates from a delicate balance between enthalpic and entropic effects, largely due to changes in hydration of the interacting solutes. Both experimental 2 and computational studies 3 have contributed to our present understanding of these rather complex phenomena.In addition to chemical equilibria, hydrophobic interactions often play a key role in chemical reactions 4 and catalytic processes. 5 The pH-independent hydrolysis of activated esters, p-methoxyphenyl 2,2-dichloroalkanoates 1a-d, in the presence of hydrophobic cosolutes, was chosen for detailed analysis. The hydrolyses of 1a-d proceed via the mechanism shown in Scheme 1. 6,7 All these reactions are water-catalyzed between pH 2.0 and 5.5. The reactions proceed via a dipolar activated complex in which two water molecules, one of which, acting as a general base, are involved with three protons in flight.Detailed computer simulations, using both quantum and classical dynamics, revealed that proton tunneling is involved in the rate-determining step, 8 the water molecules involved in the activated complex being therefore subject to severe orientational requirements. Consistent with these views, strongly negati...

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Section: Introductionmentioning

confidence: 81%

Kinetic Evidence for Hydrophobically Stabilized Encounter Complexes Formed by Hydrophobic Esters in Aqueous Solutions Containing Monohydric Alcohols

et al. 2001

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“…In this case, n equals two. 9 The corresponding equilibrium relation in terms of chemical potentials is;…”

Section: Thermodynamic Analysis Of Kinetic Datamentioning

confidence: 99%

Kinetics of hydrolysis of 4-methoxyphenyl-2,2-dichloroethanoate in binary water–cosolvent mixtures; the role of solvent activity and solute–solute interactions

2005

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Rate constants are reported for the pH-independent hydrolysis of 4-methoxyphenyl-2,2-dichloroethanoate in aqueous solution as a function of the concentration of added cyanomethane (acetonitrile), polyethylene glycol (PEG 400) and tetrahydrofuran (THF). The concentration of water was varied between ca. 25 and 55.5 M. It was found that the variation in water activity yields only a minor contribution to the observed variation in rate constants. Interestingly, for both cyanomethane and PEG 400 log(k) varies approximately linearly with the molar concentration of water. Medium effects in highly aqueous solutions ([H(2)O] > 50 M) of ethanol, 1-propanol, 2-propanol, 1-butanol and 2-methyl-2-propanol have also been determined. Unexpectedly, in this concentration range the alcohols induce significantly smaller effects per unit volume than cyanomethane. The present results are discussed in terms of pairwise interaction parameters. Isobaric activation parameters have been determined and reveal remarkable differences in the nature of the induced medium effects.

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“…The kinetics of the pH‐independent hydrolysis of activated esters has been investigated by the El Seoud group in water–acetonitrile mixtures and by Engberts group in a range of aqueous binary mixtures at low organic co‐solvent content . In the present work, the pH‐independent hydrolysis of 4‐MPDA was studied in mixtures of water and various co‐solvents, including methanol, ethanol, acetonitrile, DMSO, and 1,4‐dioxane.…”

Section: Resultsmentioning

confidence: 98%

Reaction kinetics and solubility in water-organic binary solutions are governed by similar solvation equilibria

Salmar

Vaalma

Tenno

et al. 2015

J. Phys. Org. Chem.

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aThe solvation effects observed in water-organic solutions were studied by combining data for reaction kinetics and dissolution equilibria by means of a linear free-energy (similarity) analysis. Kinetic data for the pH-independent hydrolysis of (4-methoxyphenyl)-2,2-dichloroacetate measured in this work and solubility data for naphthalene, and other substrates of low polarity, in aqueous binary mixtures of methanol, ethanol, acetonitrile, dimethyl sulfoxide (DMSO), and 1,4-dioxane were used. Linear similarity relationships were discovered for these data over the full range of solvent compositions studied. To gain insight into the similarities observed between these different phenomena, molecular dynamics simulations were carried out for naphthalene and an ester in water-acetonitrile solutions. The results revealed considerable preferential solvation of these substrates by the co-solvent. Linear relationships between the experimental data and the mole fractions of acetonitrile in the solvation shells of substrates were found. Surprisingly, a linear relationship was found between the mole fractions of acetonitrile in the solvation shells of the ester and naphthalene. This linearity indicated that a similar solvation mechanism governs even such different phenomena as dissolution and reaction kinetics. The relationships between the experimental data and the results of the molecular dynamics calculations found in this work explained the solvent effect observed in water-organic solutions on the molecular level.

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Neutral hydrolysis of p-nitrophenyl dichloroacetate in highly aqueous tert-butyl alcohol. Effects due to solvent structural integrity

Cited by 16 publications

References 1 publication

Kinetic Evidence for Hydrophobically Stabilized Encounter Complexes Formed by Hydrophobic Esters in Aqueous Solutions Containing Monohydric Alcohols

Kinetic Evidence for Hydrophobically Stabilized Encounter Complexes Formed by Hydrophobic Esters in Aqueous Solutions Containing Monohydric Alcohols

Kinetics of hydrolysis of 4-methoxyphenyl-2,2-dichloroethanoate in binary water–cosolvent mixtures; the role of solvent activity and solute–solute interactions

Reaction kinetics and solubility in water-organic binary solutions are governed by similar solvation equilibria

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