Acidity Functions for Strongly Basic Solutions

Bowden, Keith

doi:10.1021/cr60240a001

Cited by 129 publications

(85 citation statements)

References 26 publications

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“…Also this will allow us to draw more valid comparisons with other systems. A measure of medium basicity which is generally used is that given by the H-acidity function (43)(44)(45)(46). We have previously evaluated an H-scale for the DMF-H20-OH-system, based on the deprotonation of very weak acid indicators (47), and in Table 5 we have listed the appropriate H-values corresponding to the given solvent compositions.…”

Section: Complexing On Exchange Rates As Function Of Medium Compositionmentioning

confidence: 99%

“…The plot of log kOb, vs. H-showed an initial linear portion (slope 0.73) but then levelled off at an H-value corresponding to practically complete The suggestion by Crampton and Gold (24) that the o-complex could act as a catalyst in exchange is pertinent also to our study. It would then follow that the o-complex could also contribute to the basicity of the medium, which would serve to justify our current use of the H function in its normally accepted sense (43)(44)(45)(46). Thus whereas H-values are taken to refer to constant hydroxide ( d e~t e r o x i d e )~ ion concentration (0.01 M), in the present system the free O D concentration is continually diminishing as a result of o-complex formation.…”

Section: Cotnparison Btqith Other Systemsmentioning

confidence: 99%

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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: Complexing On Exchange Rates As Function Of Medium Compositionmentioning

confidence: 99%

Section: Cotnparison Btqith Other Systemsmentioning

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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“…For binary solvent systems consisting of dipolar aprotic-protic solvent mixtures, such as the DMSO-water case of the present study, tlie medium basicity at constant stoicliionietric hydroxide ion concentration does not remain constant but increases dramatically as the proportion of the protic component decreases (29,30). Tlie increased basicity is generally ascribed (29)(30)(31)(32) ROH-) and is given by J-= -log a,+ f Ro,,-/a,,20 f ,. It is seen that the two fi~nctions are related by the expression :…”

Section: Rate Depetidence On Acidity Fimctiotismentioning

confidence: 81%

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

Symons¹,

Buncel²

1973

Can. J. Chem.

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Isotopic exchange of D, has been determined in mixtures of dimethyl sulfoxide and water under catalysis by hydroxide ion. The rate of exchange increases by ca. lo4 as the medium composition is changed from 0% DMSO to 99.6% DMSO at 65 "C. The unusually low sensitivity to medium basicity is reflected in abnormally low slope values for the plots of log k,,, us. H-or J -. When [Me4NOH] is varied at a given medium composition, the apparent order with respect to [Me4NOH] is greater than unity.These results are discussed in terms of (1) rate determining proton transfer from D, to OH-with formation of hydride ion; (2)

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“…2-Aminopyrimidine, a cyclic amidine that exists in tautomeric forms, is a very poor nucleophilic reagent, a highly deactivated aniline with acidic properties. [29][30][31] The acidity of 2-aminopyrimidine is increased by the aza substitution, compared with aniline and aminopyridines, due to the electronic effects exerted by the ring nitrogen atoms. We consider that initial nucleophilic attack of the amino group on the carbonyl of the acid chloride first affords the expected amide.…”

Section: Resultsmentioning

confidence: 99%

Insights into the N,N-diacylation reaction of 2-aminopyrimidines and deactivated anilines: an alternative N-monoacylation reaction

Théodorou¹,

Gogou²,

Giannousi³

et al. 2013

Arkivoc

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During the N-benzoylation reaction for the synthesis of N-substituted aminopyrimidines, an undesired N,N-diacylation reaction took place. The extension of this N-acylation reaction to a series of several 2-aminopyrimidines, aminopyrazines and highly deactivated anilines produced analogous results. The possible mechanism responsible for that behavior is investigated and an advantageous alternative procedure for the clean formation of the desired amides is suggested.

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Acidity Functions for Strongly Basic Solutions

Cited by 129 publications

References 26 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

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

Insights into the N,N-diacylation reaction of 2-aminopyrimidines and deactivated anilines: an alternative N-monoacylation reaction

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