Initial-state and transition-state solvent effects on reaction rates and the use of thermodynamic transfer functions

Buncel, Erwin; Wilson, H.K.

doi:10.1021/ar50133a007

Cited by 58 publications

(27 citation statements)

References 74 publications

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“…For the reaction catalyzed by p-toluenesulfonic acid, the term loglo(falkenefBH+)/(f* fn) in eqn. (11) increases with increasing acid concentration. The increase of the term which contains the activity coefficients can be explained by the relatively large salting-in effect of the p-toluenesulfonate ion on non-electrolytes of the Hammett indicator type [ 151.…”

Section: Rate Constantsmentioning

confidence: 87%

Effect of solvent on the hydration of 2-methyl-propene in solutions of p-toluenesulfonic acid and poly(styrenesulfonic acid)

Meuldijk

Joosten

Stamhuis

1986

Journal of Molecular Catalysis

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Section: Rate Constantsmentioning

confidence: 87%

Effect of solvent on the hydration of 2-methyl-propene in solutions of p-toluenesulfonic acid and poly(styrenesulfonic acid)

Meuldijk

Joosten

Stamhuis

1986

Journal of Molecular Catalysis

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“…Metal ion catalysis of the reaction will be observed when the difference in free energy between AM* and Af (6Gf) is greater than the difference in free energy between EtOM and M+ + EtO-(6G0). That is, when the transition state is stabilized to a greater extent than the ground state of the nucleophile (16,17). This situation will occur when association of the metal ion with the transition state ( K 3 is greater than its association with ethoxide ion (K&.…”

Section: Kdmentioning

confidence: 99%

Metal ion catalysis in nucleophilic displacement reactions at carbon, phosphorus, and sulfur centers. I. Catalysis by metal ions in the reaction of p-nitrophenyl diphenylphosphinate with ethoxide

Dunn¹,

Buncel²

1989

Can. J. Chem.

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The effect of macrocvclic crown ether and cryptand complexing agents on the rate of the nucleo~hilic displacement reaction of p-nitrophenyl diphenyiphosphinate by alkali-Aetal ethokdes i n ethanol at 25OC has been s'tudied b; spectrophotometric techniques. For the reactions of potassium ethoxide, sodium ethoxide, and lithium ethoxide, the observed rate constant increased in the order KOEt < NaOEt < L~O E~. Crown ether and cryptand cation-complexing agents have a retarding effect on the rate.Increasing the ratio of complexing agent to base results in a decrease in kobs to a minimum value corresponding to the rate of reaction of free ethoxide ion. In complementary experiments, alkali metal ions were added to these reaction systems in the form of unreactive salts, causing an increase in reaction rate. The kinetic data were analysed in terms of ion-pairing treatments, which allowed evaluation of rate coefficients due to free ethoxide ions and metal ion -ethoxide ion pairs. Possible roles of the metal cations are discussed in terms of ground state and transition state stabilization. Evaluation of the equilibrium constants for association of the metal ion with ground state (K,) and the transition state (K&) shows that catalysis occurs as a result of enhanced association between the metal ion and the transition state, with Kgvalues increasing in the order K+ < Na+ < Li+. A model is proposed in which transition state stabilization arises largely from chelation of the solvated metal ion to two charged oxygen centers. This appears to be the first reported instance of catalysis by alkali metal cations in nucleophilic displacement at phosphoryl centers.

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“…The magnitude of such rate enhancement can, however, vary greatly depending on the system involved. Thus whereas a number of processes in which proton transfer from substrate to base is rate-determining exhibit rate enhancements of 101° or more when the medium is changed from aqueous (or alcoholic) to --99mol% DMSO (33)(34)(35)(36)(37)(38), exchange of D2 in the DMSO-H20-OHp system is accelerated only by -lo4 when the medium is changed from purely aqueous to 99.5% DMSO (39,40).…”

Section: Mediutn Dependence Of Proton Exchangementioning

confidence: 99%

Hydrogen exchange studies. XIV. Kinetics and mechanism of base-catalyzed hydrogen exchange in 1,3-dinitrobenzene in aqueous dimethylformamide and relationship with σ-complex formation

Buncel¹,

Zabel²

1981

Can. J. Chem.

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ERWIN BUNCEL and ALLEN W. ZABEL. Can. J . Chem. 59, 3177 (1981). Kinetic data have been evaluated for hydrogen exchange in 1,3-dinitrobenzene (DNB), occurring at the 2-position, in dimethylformamide (DMF) -D,O mixtures containing deuteroxide ion. The pseudo first order rate constants for exchange, k,,,. show inverse dependence on the initial DNB concentration, which can be quantitatively related to the extent of o-complex formation in these systems. The profile fork,,,, as function of medium compositio~l exhibits a maximum at ca. 70 mol% DMF, and E ,~, for o-complex formation reaches a plateau at about the same medium composition. The equilibrium constants for o-complex formation, K,, are used to calculate the free. or uncomplexed, deuteroxide ion concentrations, which then allow one to calculate k 2 . the second order rate constants for exchange. The k, values show a uniformly increasing tendency with increased DMF content. Correlations with medium basicity are examined, and the nature of the log k, and log K, vs. H-plots afford insight into the origin of the medium dependence of proton exchange. The results of the present study are consistent with the cr-complex being an unreactive form of the substrate towards exchange, which occurs via uncomplexed DNB present in small concentration. The study also rules out the possibility that the colored species present in these systems is the carbanion formed on deprotonation of DNB.ERWIN BUNCEL et ALLEN W . ZABEL. Can. J. Chem. 59. 3177 (1981). O n a evalue les donnees cinetiques de l'echange d'hydrogene se produisant en position 2 du dinitro-1,3 benzene (DNB) dans des melanges de dimethylformamide (DMF) -D,O contenant I'ion deuteroxyde. L a constante de vitesse d e pseudo ordre un de l'echange k,,,, revele un effet inverse de la concentration initiale de DNB qui peut etre relie quantitativement aux taux deformation du complexe o dans ces systemes. 1.e profil de k,,, en fonction de la composition du milieu montre un maximum pour environ 70 molR de DMF et le E, , , de la formation du complexeo atteint un plateau pour environ la meme composition du milieu. On a utilise la constante d'equilibre d e la formation du complexe o K,, pour calculer les concentrations de I'ion deuteroxyde libre. ou non complexe qui permettent de calculer k, la constante d e vitesse d'ordre deux de I'echange. Les valeurs de k2 montrent une tendance d'augmentation uniforme avec la teneur en DMF. On a examine les correlations avec la basicite du milieu; la nature des courbes de log k, et log K, en fonction de H-fournit des renseignements sur I'origine de l'effet du milieu lors de I'echange de proton. Les resultats de la presente etude sont en accord avec un complexe o qui ne donnerait pas de reaction d'echange celui-ci se produisant par I'intermediaire du DNB non complexe present a une concentration faible. L'etude ecarte egalement la possibilite que l'espece coloree presente dans ces systemes soit le carbanion forme par la protonation du DNB.[Traduit par le journal]

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Initial-state and transition-state solvent effects on reaction rates and the use of thermodynamic transfer functions

Cited by 58 publications

References 74 publications

Effect of solvent on the hydration of 2-methyl-propene in solutions of p-toluenesulfonic acid and poly(styrenesulfonic acid)

Effect of solvent on the hydration of 2-methyl-propene in solutions of p-toluenesulfonic acid and poly(styrenesulfonic acid)

Metal ion catalysis in nucleophilic displacement reactions at carbon, phosphorus, and sulfur centers. I. Catalysis by metal ions in the reaction of p-nitrophenyl diphenylphosphinate with ethoxide

Hydrogen exchange studies. XIV. Kinetics and mechanism of base-catalyzed hydrogen exchange in 1,3-dinitrobenzene in aqueous dimethylformamide and relationship with σ-complex formation

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