Base-catalyzed Isotopic Exchange of Molecular Hydrogen. II. Rate Dependence on Basicity in the Dimethyl Sulfoxide–Water System

Symons, E. A.; Buncel, Erwin

doi:10.1139/v73-251

Cited by 15 publications

(3 citation statements)

References 22 publications

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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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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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“…This value compares with the range of smaller slopes, 0.23-0.36, seen for exchange of D2 in the same solvent system. 19 The detritiation of Me2SO itself produced a slope of 0.94. 20 For detritiation of another haloform, chloroform, log k was plotted against .…”

Section: Cf3d Cf3h(t) Isotope Exchange (A) Acidity Functionmentioning

confidence: 98%

Hydrogen isotope exchange between fluoroform (CF3H) and water. 2. Catalysis by hydroxide ion in the presence of added dimethyl sulfoxide

Symons¹,

Clermont²,

Coderre³

1981

J. Am. Chem. Soc.

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“…Another illustration of the use of models to interpret transition state transfer functions is found in the isotopic exchange between molecular hydrogen (deuterium) and a hydroxylic solvent under base catalysis (34)(35)(36)(37)(38). A variety of mechanisms have been proposed for this deceptively simple reaction (39), but only those consistent with the transfer function data in DMSO/water systems need to be considered further.…”

Section: Transfer Functions and Transition Statesmentioning

confidence: 99%

Solvent effects on rates and equilibria: A practical approach

Buncel¹,

Wilson²

1980

J. Chem. Educ.

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Base-catalyzed Isotopic Exchange of Molecular Hydrogen. II. Rate Dependence on Basicity in the Dimethyl Sulfoxide–Water System

Cited by 15 publications

References 22 publications

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

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

Hydrogen isotope exchange between fluoroform (CF3H) and water. 2. Catalysis by hydroxide ion in the presence of added dimethyl sulfoxide

Solvent effects on rates and equilibria: A practical approach

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