Kinetics of ionization of 1,3-indandione in methyl sulfoxide-water mixtures. Solvent effect on intrinsic rates and Broensted coefficients

Bernasconi, Claude F.; Paschalis, P.

doi:10.1021/ja00271a027

Cited by 54 publications

(26 citation statements)

References 1 publication

(1 reference statement)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For a given ApK + log (p/q) value (ApK = p K t H -p K i and p and q are the usual statistical factors used for Brijnsted plots), phenols appear to be more efficient oxygen-acid catalysts than carboxylic acids. This behaviour is qualitatively the same as that found in the study of reactions [ l ] in 50% H 2 0 -50% DMSO ( 3 , and in the study of the ionization of acetylacetone and 1,3-indandione in various H20-DMSO mixtures ( 18,19). A noteworthy feature of Fig.…”

Section: No2-n02h O-supporting

confidence: 87%

“…That the RSP fails to account for the situation observed is not surprising since it is now well known that reactions which involve resonance stabilized carbanions, and which are therefore subject to large transition state imbalances, cannot be treated by common formalisms (7,9,11,18,19,24). In particular, it has been shown that the effect of a solvent change on the intrinsic rate constant ko for the deprotonation of a carbon acid (or reprotonation of the corresponding carbanion) is closely related to specific stabilizing or destabilizing factors of reactants and products (1 1, 18,19,25).…”

Section: No2-n02h O-mentioning

confidence: 99%

“…In particular, it has been shown that the effect of a solvent change on the intrinsic rate constant ko for the deprotonation of a carbon acid (or reprotonation of the corresponding carbanion) is closely related to specific stabilizing or destabilizing factors of reactants and products (1 1, 18,19,25). For reactions involving an anionic base B-like those of eq.…”

Section: No2-n02h O-mentioning

confidence: 99%

“…[I], for example, solvation of the base is a reactant stabilizing factor while solvation of the resulting carbanion C-is a product stabilizing factor and, to a first approximation, the changes in ko can be described by eq. [12] (1 1, 18,19). Sl y: ? and are the solvent activity coefficients of the base B-and the carbanion C-, respectively, for the transfer from a solvent S, to a solvent S2, a!-and a:-measure the progress of desolvation of B-and of solvation of C-at the transition state, respectively, while P is the measured Bronsted p value for deprotonation of the carbon acid by various [12] 6 log S'k% = (cis--P) log s l y 3 + ( a 5 -P)(-log concentrated solution of 2 is required.…”

Section: No2-n02h O-mentioning

confidence: 99%

See 3 more Smart Citations

Transient nitronic acid formation in the protonation of the carbanion of 2,2′,4,4′-tetranitrodiphenylmethane in acidic methanol

Terrier¹,

Chatrousse²,

Schaal³

et al. 1987

Can. J. Chem.

View full text Add to dashboard Cite

. Can. J. Chem. 65, 1980Chem. 65, (1987.Rates of deprotonation of 2,2',4,4'-tetranitrodiphenylmethane (1) by a variety of bases B and of protonation of the resulting carbanion (2) by the conjugated acids BH in methanol have been measured at 20°C. The Bronsted aBH coefficients for protonation of 2 by phenol and carboxylic acid buffers are equal to 0.58 and 0.43, respectively, as compared with aBH values of 0.59 and 0.52 res ectively, for the same reactions in 50% H 2 0 -50% DMSO. On the other hand, a comparison of the intrinsic .rate constants k: (in the Marcus sense) in the two solvents reveals that the effect of going from 50% H 2 0 -50% DMSO to methanol is to lower ktaH for the phenol reactions by a factor of 2 but to increase k$'OoH for carboxylic acid reactions by a factor of 5. It is shown that the solvent effects on a B H and k:H can all be understood in the context of the Principle of Imperfect Synchronisation (PIS) recently proposed by Bernasconi. In addition, a fast equilibrium protonation of the carbanion 2 is found to precede its conversion to 1 at low pH, i.e., pH < 5. The resulting protonated species is suggested to be the nitronic acid 2,H arising from fast protonation of a para NOz group of 2. The pK: value associated with the ionization of 2,H is -4.25. Chem. 65, 1980Chem. 65, (1987.Les vitesses de dtprotonation du tetranitro-2,2',4,4' diphCnylmCthane (1) par diverses bases B-ainsi que les vitesses de protonation du carbanion correspondant (2) par les acides conjugues BH ant et6 mesurees a t = 20°C dans le mCthanol. Les Despite the absence of an electron-withdrawing group directly bonded to the exocyclic ionizable carbon, 2,2',4,4'-tetranitrodiphenylmethane 1 has a noteworthy acidity in methanol (1).The p~p O H value for formation of the very stable carbanion 2 is 15.30 at 20°C, i.e., 2 is half-formed in a potassium methoxide solution -0.03 M.We have taken advantage of the stability of 2 to c a n y out a comprehensive kinetic study of the reactions shown in eq. [I] over the pH range of 3-14.86 at 20°C in methanol. k F o H , k p O , and k; are the rate constants for deprotonation of 1 by methanol, methoxide ion, and any buffer base, respectively, while k", k q o H , and k!f;' refer to the rates of reprotonation of the carbanion 2 by the solvated proton, methanol, and any buffer acid, respectively. Our results allow the determination of the intrinsic reactivity of 1 in methanol and reveal the existence of a fast equilibrium between 2 and a new species in the most acidic solutions (pH < 5). This species is postulated as a nitronic acid resulting from the protonation of a NO2 group of 2. The dependence of the protonation rates of 2 upon the acidity and the nature of the protonating agent is also discussed. ResultsRates of proton transfer in methanol were measured using buffer solutions or dilute C H 3 0 K o r benzene sulfonic acid solutions, always under pseudo-first-order conditions. The For personal use only.

show abstract

Section: No2-n02h O-supporting

confidence: 87%

Section: No2-n02h O-mentioning

confidence: 99%

Section: No2-n02h O-mentioning

confidence: 99%

Section: No2-n02h O-mentioning

confidence: 99%

See 2 more Smart Citations

Transient nitronic acid formation in the protonation of the carbanion of 2,2′,4,4′-tetranitrodiphenylmethane in acidic methanol

Terrier¹,

Chatrousse²,

Schaal³

et al. 1987

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…This would explain why our data for nicotinic and isonicotinic acids cannot be satisfactorily analysed on the basis of the NH+/N acidity behaviour of the common pyridinium cation. Interestingly, the log value of the solvent activity coefficients y, for the transfer of acetic acid from water to 90% Me,SO has been measured: log y, = -1,5 (41). Such a value supports theidea that the solvent change must affect the roleofthe COOH group.…”

Section: Resultsmentioning

confidence: 63%

Solvent effect on preferred protonation sites in nicotinate and isonicotinate anions

Hallé¹,

Lelièvre²,

Terrier³

1996

Can. J. Chem.

View full text Add to dashboard Cite

Potentiometric determinations of the two successive acidities of nicotinic and isonicotinic acids (AH,') have been carried out in aqueous dimethyl sulfoxide mixtures containing up to 95% Me2S0 by volume. In both systems, the results reveal that the addition of Me,SO induces a proton transfer from the pyridinium ring to the carboxylate group, the tautomeric equilibrium between the neutral forms of the two acids being displaced toward the zwitterionic form (AH') in aqueous solution, but toward the molecular form (AH0) in Me,SO. An analysis of the data by means of Hammett relationships previously established for benzoi'c acids over the whole range of H,O/Me,SO mixtures allowed the four microscopic acidity constants as well as the tautomeric equilibrium constant KT pertaining to the complete ionization scheme of the two acids to be determined. At 20°C, there are equal populations of the tautomeric AH0 and AH' species in the mixtures containing 38 and 47% Me,SO for the nicotinic and isonicotinic systems, respectively. Hammett relationships describing the ionization behaviour of a number of substituted pyridinium cations in H,O/Me,SO mixtures are also discussed. Possible reasons accounting for the peculiar effects exerted by the NH,, CONH,, and COOH substituents on the process are suggested.Key words: nicotinic and isonicotinic acids, substituted pyridines, acidities, tautomeric equilibrium, protonation sites, water -dimethyl sulfoxide mixtures.Resume : Les deux aciditts successives des acides nicotinique et isonicotinique (AH,' ) ont Cte determinees par potentiometrie dans des milieux eau-dimCthylsulfoxyde contenant jusqu'a 95% de Me,SO en volume. L'addition de Me,SO provoque le transfert protonique du cycle pyridinium vers le groupement carboxylate, de sorte que la forme zwitterionique AH*, trks majoritaire dans I'eau, ckde progressivement la place B la forme molCculaire AH0 qui devient unique dans le dimethylsulfoxyde. Le traitement des resultats, h I'aide des relations de Hammett d'energie libre prealablement Ctablies pour les acides benzo'iques dans les mtlanges H,O/Me,SO, permet les determinations des quatre constantes microscopiques et de la constante de tautomtrie KT decrivant le schema des ionisations successives de ces deux diacides. A 20°C, on a CgalitC entre les populations des formes zwitterionique (AH') et molCculaire (AH0) dans 1es milieux contenant respectivement 38% (acide nicotinique) et 47% (acide isonicotinique) de MezSO en masse. Les relations de Hammett d'Cnergie libre, dtcrivant l'ionisation d'un grand nombre de pyridines substituCes dans IesmClanges H20/Me,S0, sont discuttes. Les effets particuliers observes pour les substituants NH,, CONH, et COOH sont analysts.

show abstract

Effect of solvent composition on the acidity of phenols in dimethyl sulfoxide-water mixtures

Tarkka

Xie

et al. 1998

J. Phys. Org. Chem.

View full text Add to dashboard Cite

The effect of solvent composition on the acidity of substituted phenols in DMSO-H 2 O systems was examined. It is shown that in DMSO-H 2 O mixtures with up to 35 mol% DMSO there is a linear relationship between the pK a values of monosubstituted phenols in the binary solvent mixtures of different compositions and the corresponding pK a values in water. This leads to an equation relating the slope and intercept terms, pK a (DMSO-H 2 O) = slope[pK a (H 2 O)] intercept. The basis of this relationship in the Kirkwood-Westheimer equation is examined. The significance of a possible 'supersolvent' is discussed. The applicability of the relationships derived herein to other rate-equilibria relationships and solvent mixtures is considered.

show abstract

Kinetics of ionization of 1,3-indandione in methyl sulfoxide-water mixtures. Solvent effect on intrinsic rates and Broensted coefficients

Cited by 54 publications

References 1 publication

Transient nitronic acid formation in the protonation of the carbanion of 2,2′,4,4′-tetranitrodiphenylmethane in acidic methanol

Transient nitronic acid formation in the protonation of the carbanion of 2,2′,4,4′-tetranitrodiphenylmethane in acidic methanol

Solvent effect on preferred protonation sites in nicotinate and isonicotinate anions

Effect of solvent composition on the acidity of phenols in dimethyl sulfoxide-water mixtures

Contact Info

Product

Resources

About