Electrolyte effects upon acid-catalyzed ester hydrolyses

Bunton, Clifford A.; Crabtree, James H.; Robinson, L. M.

doi:10.1021/ja01007a027

Cited by 38 publications

(19 citation statements)

References 4 publications

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“…This water inolecule is then rendered more active by the presence of the NO,-group. Such a possibility is not inconsistent with the specific salt effects reported by Bunton and co-workers (28,29) and provides a guide to the probable reason that evidence for ion-pair return from the solvent-separated ionpair is not observed in solvents of fair nucleophilicity. Both of the foregoing arguments weigh against the ion-pair return hypothesis as a logical possibility to account for the large negative values of ACpS reported here but provide no clear alternative.…”

supporting

confidence: 61%

The hydrolysis of 1- and 2-adamantyl nitrate in water: limiting values of ΔCp^≠ for displacement of the nitrate ion in water

Koshy¹,

Mohanty²,

Robertson³

1977

Can. J. Chem.

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Values of AC,* have been obtained for the hydrolysis of 1-and 2-adamantyl nitrate in water and of 1-adamantyl nitrate in 0.2 111~1 fraction ethanol-water and acetonitrile-hater. The limiting value of AC,= for displacement of the NO,-ions in water is more negative than -130 cal mol-' deg-'. Much less negative values in mixed solvents show that the large negative values obtained for hydrolysis in water derive in some manner from the structural properties of water. The mechanistic in~plications of these facts are discussed. Chem. 55, 1314Chem. 55, (1977.On a obtenu des valeurs de AC,' pour l'hydrolyse des nitrates d'adarnantyle-1 et -2 dans I'eau et du nitrate d'adamantyle-1 dans des melanges Cthanol-eau et acitonitrile-eau de 0.2 fraction n~olaire. La valeur lirnite de AC,, = pour le dCp1acement des ions NO3-dans l'eau est plus negative que -130 cal n~o l -' deg-'. Des valeurs beallcoup plus negatives dans les solvants mixtes nlontrent que les valeurs tres negatives obtenues pour l'hydrolyse dans l'eau proviennent d'une maniere q~ielconque des proprietks structurales de I'eau. On discute des il~lplications n~Ccanistiques de ces faits.[Traduit par le jour~lal]In this paper we examine the mechanistic structure of the reactant, the group being disimplications of the values of AC,= derived from placed, and the nucieophilic and ionizing the hydrolysis of the I -and 2-adarnantyl properties of the solvent. The latter consideranitrates in water and in mixed solvents. In tion, though long recognized (9); is not always solvolytic displacement reactions, the adamantyl observed. Water is a unique solvent in this structure ensures the absence of rear-side respect. Because of the tendency to form nucleophilic interaction ( I ) and since participation by H or Me is unllkely (2), displacement from the adamantyl structure makes certain that the niechanis~n is SN1 (3-5), Lim (6), or kc (7), as one chooses. Because the 2-adamantyl structure thus eliminates the possibility of 'border-line mechanism' and mixed kinetics (ref. 5, pp. 320-321) mhich had been recognized in earl~er discussions of displacement from secondary carbons, the 2-adamantyl structure was proposed by Schleyer et 01. as a limiting transient structures about weakly polar solutes (10) and the fi~rther characteristic that these structures are sensitive to temperature and to the develop~nent of charge on the anion, me are provided, through AC,* values. with a 'handle' for evaluating the degree of charge development at the transition state (1 1).Very early 111 studying their proposed SY1/S,2 mechanistic classification of ~lucleophilic displacement reactions, Hughes and lngold recognized the need for a range of charge development standard for evaluating the mechanism for at the transition state and for the possibility of displacen~ent from secondary carbons (2).'shielding' and mixed kinetics (5). This logical The mechanism of such solvolytic SN dis-extension of the simplistic SN1/SN2 mechanistic placements is recognized to depend on the classification was provided with a...

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supporting

confidence: 61%

The hydrolysis of 1- and 2-adamantyl nitrate in water: limiting values of ΔCp^≠ for displacement of the nitrate ion in water

Koshy¹,

Mohanty²,

Robertson³

1977

Can. J. Chem.

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“…[10] with eq. [5] now leads to eqs. [11] and [12] as the relationships for k f and k r in terms of the elementary rate constants in the mechanism of Scheme 1.…”

Section: Discussionmentioning

confidence: 98%

“…These effects were explained qualitatively in terms of the change in the activity of the water, changes in the activity coefficients of the different solutes involved in the equilibrium, and the formation of ion pairs. The effects are especially large in the case of perchlorate, an electrolyte regarded as inert in many contexts, but with an appreciable effect upon the ionization of neutral substrates where a delocalized positive charge is developed in a carbon residue in the transition state (5). Wyatt (6) proposed a value of 1.3 dm 3 mol -1 for the equilibrium constant for the formation of the ion pair TMT + ClO 4 -from dissociated ions in aqueous solution in order to bring the derived H R values for aqueous perchloric acid onto the same water activity scale as that for aqueous sulfuric acid.…”

mentioning

confidence: 99%

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

Crugeiras¹,

Maskill²

1999

Can. J. Chem.

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We have studied the equilibration shown in eq. [3] of 4,4′-dimethoxytrityl alcohol in aqueous perchloric and nitric acids containing low proportions of acetonitrile using stopped-flow kinetics techniques. The rate constants for the overall progress to equilibrium, k obs , have been resolved into forward and reverse components using the equilibrium UV absorbance and a value for the molar absorptivity of the 4,4′-dimethoxytrityl carbenium ion determined in concentrated aqueous perchloric acid. The forward reaction (rate constant k f ) is first order in both the alcohol and the acid concentrations; the reverse reaction (rate constant k r ) is pseudo first order with respect to the carbocation. At constant hydronium ion concentration, the forward rate constant increases linearly with the concentration of electrolyte, whereas the reverse rate constant decreases. These effects depend upon the nature of the anion, but not the cation, and are not ionic strength effects. At constant anion concentrations, k f in both acids, and k r in perchloric acid, are independent of hydronium ion concentration; however, k r decreases with increasing hydronium ion concentration at constant nitrate concentration. At nonconstant ionic strength, changes in k f and k r observed in increasing concentrations of perchloric acid are attributable wholly to changes in perchlorate concentration. A mechanism is proposed which involves pre-equilibrium protonation of the alcohol, heterolysis of the protonated alcohol to give a 4,4′-dimethoxytrityl carbenium ion -water ion-molecule pair, then conversion of this into a dissociated carbenium ion in equilibrium with ion pairs. To account for the strong effects of perchlorate and nitrate upon the forward rate constants, it is proposed that these anions provide additional reaction channels from the ion-molecule pair. However, we find no evidence of acid catalysis in the reaction of the ion-molecule pair (in contrast to our finding for the reaction of the corresponding ion-molecule pair formed from dimethoxytritylamine in acidic media). Some of the elementary rate and equilibrium constants of the proposed mechanism have been evaluated.

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“…Also for the hydrolysis of 1b , 1c , this order varied in a similar way, as expected. Bunton and his coworkers have suggested that such an order is characteristic of a bimolecular (A2) mechanism, because the transition state of the positive character is being preferentially stabilized by small anions of high charge density such as Cl − . On the contrary, the transition states of the unimolecular A1 mechanism are preferred for stabilization by anions of low charge density such as ClO 4 − , so the order of the A1 reaction is HClO 4 > H 2 SO 4 > HCl.…”

Section: Resultsmentioning

confidence: 99%

“…White solid (395 mg, 74%); mp 192–193 (Lit . 199–200) °C; Rf (75% ether/benzene): 0.48; IR (KBr) (ν max , cm −1 ): 3270 (N‐H), 3060 (Ar.…”

Section: Methodsmentioning

confidence: 99%

Acid‐catalyzed hydrolysis of 5‐substituted‐1H,3H‐2,1,3‐benzothiadiazole 2,2‐dioxides (5‐substituted benzosulfamides): kinetic behavior and mechanistic interpretations

Ertürk

Bekdemi̇r

2015

J of Physical Organic Chem

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The acid-catalyzed hydrolysis of a series of 5-substituted-1H,3H-2,1,3-benzothiadiazole 2,2-dioxides has been investigated in aqueous solutions of sulfuric, perchloric, and hydrochloric acid at 85.0 ± 0.05°C. Analysis of the kinetic data by the excess acidity method, Arrhenius parameters, the order of the catalytic effects of strong acids, the kinetic deuterium isotope effect, and the substituent effect have indicated that the hydrolysis of 5-substituted benzosulfamides 1a-d occur with a mechanistic switchover from A2 to A1 in the studied range: an A2 mechanism in low acidity regions and an A1 mechanism in high acid concentrations.

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Electrolyte effects upon acid-catalyzed ester hydrolyses

Cited by 38 publications

References 4 publications

The hydrolysis of 1- and 2-adamantyl nitrate in water: limiting values of ΔCp^≠ for displacement of the nitrate ion in water

The hydrolysis of 1- and 2-adamantyl nitrate in water: limiting values of ΔCp^≠ for displacement of the nitrate ion in water

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

Acid‐catalyzed hydrolysis of 5‐substituted‐1H,3H‐2,1,3‐benzothiadiazole 2,2‐dioxides (5‐substituted benzosulfamides): kinetic behavior and mechanistic interpretations

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Electrolyte effects upon acid-catalyzed ester hydrolyses

Cited by 38 publications

References 4 publications

The hydrolysis of 1- and 2-adamantyl nitrate in water: limiting values of ΔCp≠ for displacement of the nitrate ion in water

The hydrolysis of 1- and 2-adamantyl nitrate in water: limiting values of ΔCp≠ for displacement of the nitrate ion in water

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

Acid‐catalyzed hydrolysis of 5‐substituted‐1H,3H‐2,1,3‐benzothiadiazole 2,2‐dioxides (5‐substituted benzosulfamides): kinetic behavior and mechanistic interpretations

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The hydrolysis of 1- and 2-adamantyl nitrate in water: limiting values of ΔCp^≠ for displacement of the nitrate ion in water

The hydrolysis of 1- and 2-adamantyl nitrate in water: limiting values of ΔCp^≠ for displacement of the nitrate ion in water