A quantum chemical approach to the water assisted neutral hydrolysis of ethyl acetate and its derivatives

Schmeer, Georg; Sturm, Peter

doi:10.1039/a808558g

Cited by 31 publications

(33 citation statements)

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“…22 For a two-step gas-phase hydrolysis of ethyl acetate with n = 2 (Scheme 2), 6-31+G* calculations afford a free energy barrier of 64.3 kcal/mol. 21 In the B3LYP/6-31G*/ SCRF calculations of Yamabe et al on the aqueous hydrolysis of ethyl acetate in the presence of different numbers of active water molecules, 23 the concerted (one-step) free energy barrier ranges between 42.9 and 47.9 kcal/mol, much higher than the experimental DG { of Skrabal and Zahorka. 16 A two-step mechanism with k -1 & k 2 gives free energy barriers close to the experimental DG { , the reaction via a fourwater molecule complex being favoured.…”

Section: Neutral Ester Hydrolysismentioning

confidence: 98%

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The neutral hydrolysis of methyl acetate — Part 2. Is there a tetrahedral intermediate?

et al. 2009

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A computational strategy that reproduces the experimental rates of hydration of formaldehyde, acetaldehyde, acetone, and cyclohexanone and the rates of acetic acid and 2-hydroxypyridine-catalyzed hydration of acetone has been extended to the results of the neutral hydrolysis of methyl acetate reported in Part 1. Calculations have been performed for one-step and two-step mechanisms, with cooperative assistance from one to three additional water molecules in the presence and absence of the acetic acid product. The calculations predict that, for the neutral reaction, a one-step mechanism will be favoured if tetrahedral intermediates have a short lifetime and do not interconvert prior to breakdown (case A), and a two-step mechanism will be operative if tetrahedral intermediates are allowed to interconvert prior to breakdown (case B). The experimental results are consistent with the predictions of case A. In the presence of acetic acid, case A predicts that the acid will contribute only 1.6% to the overall rate, a negligible acceleration over the noncatalytic process, and case B predicts general acid catalysis to be an order of magnitude greater than the experimental result. It is concluded that the neutral hydrolysis of methyl acetate is mainly a cooperative one-step process, and that general acid catalysis by the acetic acid product does not occur.Key words: cooperative mechanism, one-step mechanism, tetrahedral intermediate. Résumé :Une stratégie théorique permettant de reproduire les vitesses expérimentales d'hydratation du formaldéhyde, de l'acétaldéhyde, de l'acétone et de la cyclohexanone ainsi que les vitesses d'hydratation de l'acétone catalysée par l'acide acétique et la 2-hydroxypyridine a été étendue aux résultats de l'hydrolyse neutre de l'acétate de méthyle rapportée dans la partie 1. Les calculs ont été effectués pour les mécanismes à une et à deux étapes, avec l'assistance coopérative d'une, deux ou trois molécules d'eau, en présence et en absence d'acide acétique produit. Les calculs permettent de prédire que, pour la réaction neutre, le mécanisme en une étape sera favorisé si les intermédiaires tétraédriques sont de courte vie et qu'ils ne donnent pas lieu à une interconversion avec leur rupture (cas A) et un mécanisme en deux étapes qui opérera si les intermé-diaires peuvent subir une interconversion avant leur rupture (cas B). Les résultats expérimentaux sont en accord avec les prédictions du cas A. En présence d'acide acétique, le cas A prédit que l'acide ne contribuera qu'à 1,6% de la vitesse globale, une accélération négligeable par rapport au processus non catalytique; le cas B prédit une catalyse acide générale qui serait d'un ordre de grandeur plus important que le résultat expérimental. On peut donc en conclure que l'hydrolyse neutre de l'acétate de méthyle est principalement en processus coopératif en une étape et que la catalyse par l'acide acétique produit n'a pas lieu.Mots-clés:mécanisme coopératif, mécanisme en une étape, intermédiaire tétraédrique.[Traduit par la Rédaction]

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Section: Neutral Ester Hydrolysismentioning

confidence: 98%

“…At 298 K (Table1, entry 1) the hydrolysis of ethyl acetate proceeds with a first-order rate constant of 2.47 Â 10 -10 s -1 (DG { = 30.6 kcal/mol 21 ).…”

Section: Neutral Ester Hydrolysismentioning

confidence: 99%

The neutral hydrolysis of methyl acetate — Part 2. Is there a tetrahedral intermediate?

et al. 2009

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“…Previously, the same group modified the polymer consistent force field (PCFF) by optimizing the parameters for the torsion potentials of the ester groups [56,57] Schmeer et al, on the other hand, reported results on the neutral hydrolysis of esters, using a quantum chemical approach in the gas phase. [58] In the following MD-and quantum mechanical investigations are described, which were performed for the same polymers. [59,60] The simulation conditions were similar to those of other typical recent MD-studies on amorphous polymers, i.e., model systems composed of 5000-10000 atoms, characteristic model dimensions of about 4-5 nm (bulk models) and simulation times up to a few ns.…”

Section: Molecular Modelling Approachmentioning

confidence: 99%

Knowledge‐Based Approach towards Hydrolytic Degradation of Polymer‐Based Biomaterials

et al. 2009

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The concept of hydrolytically degradable biomaterials was developed to enable the design of temporary implants that substitute or fulfill a certain function as long as required to support (wound) healing processes or to control the release of drugs. Examples are surgical implants, e.g., sutures, or implantable drug depots for treatment of cancer. In both cases degradability can help to avoid a second surgical procedure for explanation. Although degradable surgical sutures are established in the clinical practice for more than 30 years, still more than 40% of surgical sutures applied in clinics today are nondegradable.1 A major limitation of the established degradable suture materials is the fact that their degradation behavior cannot reliably be predicted by applying existing experimental methodologies. Similar concerns also apply to other degradable implants. Therefore, a knowledge-based approach is clearly needed to overcome the described problems and to enable the tailored design of biodegradable polymer materials. In this Progress Report we describe two methods (as examples for tools for this fundamental approach): molecular modeling combining atomistic bulk interface models with quantum chemical studies and experimental investigations of macromolecule degradation in monolayers on Langmuir-Blodgett (LB) troughs. Finally, an outlook on related future research strategies is provided.

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“…The hydration of carbonyl compounds has a long standing interest, both experimentally [7][8][9][10] and theoretically. [11][12][13][14][15][16][17][18][19][20][21][22] In most reactions of carbonyl compounds, such as aldehydes, ketones, esters, amides, the carboxylic acids, and their derivatives, the initial hydration or the nucleophilic addition of water at the carbonyl group, leading to a tetrahedral intermediate, is the rate-determining step. For example, the neutral hydrolyses of carboxylic acid derivatives normally proceed through the addition-elimination mechanism, [9] in which the hydration of the carbonyl group to yield a tetrahedral intermediate is the key step for hydrolysis.…”

mentioning

confidence: 99%

“…[11][12][13][14][15][16][17][18][19][20][21][22] In most reactions of carbonyl compounds, such as aldehydes, ketones, esters, amides, the carboxylic acids, and their derivatives, the initial hydration or the nucleophilic addition of water at the carbonyl group, leading to a tetrahedral intermediate, is the rate-determining step. For example, the neutral hydrolyses of carboxylic acid derivatives normally proceed through the addition-elimination mechanism, [9] in which the hydration of the carbonyl group to yield a tetrahedral intermediate is the key step for hydrolysis.For the hydration of carbonyl compounds, all the previous ab-initio calculations proposed a concerted mechanism for the rate-determining hydration step, [11][12][13][14][15][16][17][18][19][20] including the nucleophilic attack of one water molecule onto the carbonyl carbon atom coupled with the concerted proton transfer to the carbonyl oxygen atom assisted by one or more water molecules as shown in Scheme 1. However, most of the calculated Gibbs free energies of activation (DG°) for the concerted mechanism exceed the experimental value considerably, [23] although calculations with a relatively small basis set happen to predict activation energies comparable to the experimental value.…”

mentioning

confidence: 99%

Hydration of Carbonyl Groups: The Labile H₃O⁺ Ion as an Intermediate Modulated by the Surrounding Water Molecules

Wang

Cao

2011

Angew Chem Int Ed

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Water plays a quite important role in chemical and biological processes, such as acid-base reactions, [1,2] proton transfer in membrane proteins, [3][4][5] keto-enol tautomerization, [6] and the hydration of carbonyl compounds. The hydration of carbonyl compounds has a long standing interest, both experimentally [7][8][9][10] and theoretically. [11][12][13][14][15][16][17][18][19][20][21][22] In most reactions of carbonyl compounds, such as aldehydes, ketones, esters, amides, the carboxylic acids, and their derivatives, the initial hydration or the nucleophilic addition of water at the carbonyl group, leading to a tetrahedral intermediate, is the rate-determining step. For example, the neutral hydrolyses of carboxylic acid derivatives normally proceed through the addition-elimination mechanism, [9] in which the hydration of the carbonyl group to yield a tetrahedral intermediate is the key step for hydrolysis.For the hydration of carbonyl compounds, all the previous ab-initio calculations proposed a concerted mechanism for the rate-determining hydration step, [11][12][13][14][15][16][17][18][19][20] including the nucleophilic attack of one water molecule onto the carbonyl carbon atom coupled with the concerted proton transfer to the carbonyl oxygen atom assisted by one or more water molecules as shown in Scheme 1. However, most of the calculated Gibbs free energies of activation (DG°) for the concerted mechanism exceed the experimental value considerably, [23] although calculations with a relatively small basis set happen to predict activation energies comparable to the experimental value. This unexpected agreement between theory and experiment can be ascribed to use of relatively small basis set (see below). In a recent study the initial water autoionization was assumed to be involved in the hydrolysis of esters, [23] and the predicted Gibbs activation energies by molecular dynamics (MD) simulations for the key steps are comparable to DG°of 23.8 kcal mol À1 for the water autoionization, [24] in agreement with the experimental value of 26.1 kcal mol À1 .[25] However, in this mechanism the water autoionization as the rate-determining step is a prerequisite to hydrolysis, implying that the Gibbs free energies of activation (DG°) are little changed for different esters.Nevertheless, the experimental rate constants for the hydration of esters can vary by 10 7 fold, which approximately corresponds to an activation energy difference of 10 kcal mol À1 . Experimental studies by Bell et al. suggested that the hydration of the carbonyl group may proceed through a stepwise transfer of three protons in a cyclic array of three water molecules, [26] and that an intermediate Eigen ion (H 3 O + ) [27] is most likely involved in hydration. However, to date, there is no computational evidence for H 3 O + as the key intermediate. This situation may arise from the use of inappropriate cluster models for hydrated species in previous computational studies. Theoretical calculations on the Gibbs free energy of hydration for the proton sh...

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A quantum chemical approach to the water assisted neutral hydrolysis of ethyl acetate and its derivatives

Cited by 31 publications

References 13 publications

The neutral hydrolysis of methyl acetate — Part 2. Is there a tetrahedral intermediate?

The neutral hydrolysis of methyl acetate — Part 2. Is there a tetrahedral intermediate?

Knowledge‐Based Approach towards Hydrolytic Degradation of Polymer‐Based Biomaterials

Hydration of Carbonyl Groups: The Labile H₃O⁺ Ion as an Intermediate Modulated by the Surrounding Water Molecules

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A quantum chemical approach to the water assisted neutral hydrolysis of ethyl acetate and its derivatives

Cited by 31 publications

References 13 publications

The neutral hydrolysis of methyl acetate — Part 2. Is there a tetrahedral intermediate?

The neutral hydrolysis of methyl acetate — Part 2. Is there a tetrahedral intermediate?

Knowledge‐Based Approach towards Hydrolytic Degradation of Polymer‐Based Biomaterials

Hydration of Carbonyl Groups: The Labile H3O+ Ion as an Intermediate Modulated by the Surrounding Water Molecules

Contact Info

Product

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Hydration of Carbonyl Groups: The Labile H₃O⁺ Ion as an Intermediate Modulated by the Surrounding Water Molecules