Acidity and tautomerism of .beta.-keto esters and amides in aqueous solution

Bunting, John W.; Kanter, James P.

doi:10.1021/ja00078a008

Cited by 51 publications

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“…These A, , , are listed in Tables 1 and 2, and vary systematically in the order: methyl < phenyl < 3-pyridyl < 4-pyridyl < 3-(N-methyl pyridinio) < 4-(N-methyl pyridinio) for the enolates; i.e., systematically from a-f for the conjugate bases from each of 1,7, and 8. The same ordering of A, , , values was also observed (14) for the enolate conjugate bases of the corresponding P-keto esters and amides. All symmetrical enolate ions (3) have longer wavelength absorption maxima (Table 1) The acidities of the enols ( p~f )…”

Section: Resultssupporting

confidence: 76%

“…This technique, and the algebraic treatment of the kinetic data that allows the calculation of p~F , have recently been described (14) in some detail. Values of p~F are included in Tables 1 and 2.…”

Section: Resultsmentioning

confidence: 99%

“…These species include six symmetrical , ketones (la-lf; see Table l), six P-keto methyl ketones (7a-I 7f; see Tables 1 and 2; note that l a = 7a), and six P-keto phenyl ketones (8a-8f; note that 8a = 76 and 8b = 16). Useful linear free energy relationships are established between values for the various classes of P-diketones and the corresponding P-keto esters and arnides (14). We have also found that the en01 contents of P-keto esters and amides are not, in 0 0 0 0…”

Section: Introduction [I] Keq = [H' ] [E-]/([kh] + [Eh)]mentioning

confidence: 84%

“…The spectro hotometric measurements of pK,eq and the evalu-R ation of pK, in pH-jump experiments by stopped-flow spectrophotometry closely followed the methods described in detail in our recent work (14). All experimental data are for aqueous solutions of ionic strength of 0.1 (KC1 + buffer) at 25"C, with the exception of data for dibenzoylmethane (lb) for which limited aqueous solubility required the addition of 10% acetonitrile to all aqueous solutions.…”

Section: Pk Measurementsmentioning

confidence: 99%

“…The study of unsymmetrical P-diketones introduces an additional complication, which is not relevant for symmetrical P-diketones, and is of no significance for P-keto esters or amides that we have recently examined (14). Unsymmetrical P-diketones (4) can enolize to give a pair of en01 structural isomers (5 and 6).…”

Section: Introduction [I] Keq = [H' ] [E-]/([kh] + [Eh)]mentioning

confidence: 99%

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The acidity and tautomerism of β-diketones in aqueous solution

Bunting¹,

Kanter²,

Nelander³

et al. 1995

Can. J. Chem.

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Abstract:The acidity and ket-no1 tautomerism of a series of symmetrical P-diketones (RCOCH2COR (1): R = methyl (a), phenyl (b), 3-pyridinyl (c), 4-pyridinyl(4, 3-(N-methy1)pyridinio (e), and 4-(Nrnethy1)pyridinio ( f ) ) and two series of unsymmetrical P-diketones (RCOCH2COCH, (7a-7fi and RCOCH,COC6H5 (8a4f )) have been investigated in aqueous solution at 25°C and ionic strength 0.1. Values of p K 2 were measured spectrophotometrically, and the acidities of the enols ( p m were obtained from the analysis of the pH dependence of the buffer catalysis for the general acid-catalyzed protonation of the enolate conjugate bases. These data in tum allowed the calculation of the acidities of the keto tautorners (p@) and the equilibrium constants for enolization (K, = [Enoll/ [Keto]). In general, KE is greater for the symmetrical ketones (1) than for the corresponding R-substituted unsymmetrical ketones (7 and 8). K, is much more sensitive to the nature of the R substituent in these three series of P-diketones than in the corresponding series of P-keto esters and amides. Correlations between for 8 and 7 combined with the known acidities of the corresponding P-keto esters and arnides provide the first accurate estimates of the acidities of dirnethyl malonate (pKa = 13.0) and malonarnide (pKa = 12.5) in aqueous solution.Key words: acidity, tautomerisrn, P-diketones. (8a4f)). On a rnesuri les pKaq spectrophotomCtriquement et on a dCterminC les acidids des Cnols ( p e ) par une analyse de la relation entre la dCpendance sur le pH de la catalyse du tampon sur la protonation par catalyse acide gCnCrale des bases conjuguCes Cnolates. Ces donnCes permettent ensuite de calculer les aciditCs des cCto-tautomtres et les constantes d9Cquilibre de 1'Cnolisation (KE = [Bnol:~/[~~tone]). En gCnCral, la valeur de KE est plus grande pour les cCtones symCtriques (1) que pour les cCtones non symttriques correspondantes substituies pardes groupes R (7 et 8). La valeur de KE est beaucoup plus sensible la nature du substituant R dans ces trois sCries de P-dicttones que dans les sCries correspondantes de P-cCtoamides. Des corrClations entre les valeurs des des composCs 7 et 8 cornbinCes avec les aciditCs connues des p-cktoesters et P-cCtoamides correspondants foumissent les prernisres Cvaluations prCcises des aciditks du malonate de dimCthyle (pKa = 13,O) et du malonarnide (pKa = 12,5) en solution aqueuse.

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Section: Resultssupporting

confidence: 76%

Section: Resultsmentioning

confidence: 99%

Section: Introduction [I] Keq = [H' ] [E-]/([kh] + [Eh)]mentioning

confidence: 84%

Section: Pk Measurementsmentioning

confidence: 99%

Section: Introduction [I] Keq = [H' ] [E-]/([kh] + [Eh)]mentioning

confidence: 99%

See 3 more Smart Citations

The acidity and tautomerism of β-diketones in aqueous solution

Bunting¹,

Kanter²,

Nelander³

et al. 1995

Can. J. Chem.

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Proton Transfer to and from Carbon in Model Reactions

Amyes

Richard

2006

Hydrogen‐Transfer Reactions

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The Scope and Limitations of LSER in the Study of Tautomer Ratio

Taylor

2013

Tautomerism

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A change in solvent commonly gives rise to major changes in the rates and equilibria of chemical reactions. While solvent effects have long been studied, their quantitative analysis is a relatively recent achievement. The crucial step in this development lies in the solvatochromic approach, above all associated with Taft and coworkers [1, 2], which is a multiple regression technique that relies on giving numerical values to the solvent properties concerned. In this methodology, spectroscopic shifts, mostly ultraviolet (UV) or nuclear magnetic resonance (NMR) but sometimes of other sorts, are used to generate values for each property by comparison with a standard nonpolar solvent, for example, cyclohexane, as described in the following sections. The thermodynamic status of these shifts is uncertain: they were originally supposed to be free-energy related but they are not free energies per se and some have been demonstrated [3] to represent blends of G with H. As used in linear solvation energy relationships (LSER), however (see discussion below), the values themselves are unexceptionable provided that they are proportional to the energy of the molecular property they purport to describe, and even their precise thermodynamic status is of muted importance if they are mutually orthogonal. Essentially, LSER is an empirical topic and here will be treated as such. The Taft-Kamlet LSER MethodologyThe overall LSER equation in its most comprehensive form [1] is set out as follows:where XYZ is the free energy of the process, rate, or equilibrium, in a given solvent, XYZ 0 is the value expected for the solvent cyclohexane, and the remaining terms list * This author is deceased.Tautomerism: Methods and Theories, First Edition. Edited by Liudmil Antonov.

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Acidity and tautomerism of .beta.-keto esters and amides in aqueous solution

Cited by 51 publications

References 0 publications

The acidity and tautomerism of β-diketones in aqueous solution

The acidity and tautomerism of β-diketones in aqueous solution

Proton Transfer to and from Carbon in Model Reactions

The Scope and Limitations of LSER in the Study of Tautomer Ratio

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