Applicability of the <i>H</i><sub>T</sub> acidity function to the protonation of thioamides, thioureas, and thionesters

Edward, John T.; Derdall, Gary D.; Wong, Sin Cheong

doi:10.1139/v77-320

Cited by 10 publications

(4 citation statements)

References 6 publications

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“…Several studies in the past determined these pK a 's both experimentally and theoretically. For TA, Sandstrom 25 and Edward et al 26 quoted values of −1.76 and around −2.5, respectively. In the case of TU, conflicting pK a values in the literature range from −1.58 to 2.03, and Schiessl et al 23 presented evidence that −1.3 is correct for aqueous solutions.…”

Section: ■ Results and Discussionmentioning

confidence: 96%

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S-Nitrosation of Aminothiones

et al. 2015

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Nitrosation reactions span a diverse range of applications, from biochemistry to industrially important processes. This study examines nitrosation of aminothiones in acidic solutions and re-evaluates currently accepted diffusion limits and the true nature of the nitrosating agent for nitrous acid initiated reactions. Experimental measurements from stopped-flow UV/vis spectrophotometry afforded derivation of equilibrium constants and reaction enthalpies. Apparent Keq corresponds to 559-382 M(-2) for thioacetamide (TA, 15-25 °C) and 12600-5590 M(-2) for thiourea (TU, 15-35 °C), whereas the reaction enthalpies amount to -27.10 ± 0.05 kJ for TA and -29.30 ± 0.05 kJ for TU. Theoretical calculations via a thermochemical cycle agree well with reaction free energies from experiments, with errors of -2-4 kJ using solvation method SMD in conjunction with hybrid meta exchange-correlation functional M05-2X and high-accuracy multistep method CBS-QB3 for gas-phase calculations. The kinetic rates increase with acidity at activation energies of 54.9 (TA) and 66.1 kJ·mol(-1) (TU) for the same temperature range, confirming activation-controlled reactions. At pH 1 and below, the main decomposition pathway for the S-nitroso species leads to formation of nitric oxide.

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Section: ■ Results and Discussionmentioning

confidence: 96%

“…Several studies in the past determined these p K a ’s both experimentally and theoretically. For TA, Sandström and Edward et al quoted values of −1.76 and around −2.5, respectively. In the case of TU, conflicting p K a values in the literature range from −1.58 to 2.03, and Schiessl et al .…”

Section: Resultsmentioning

confidence: 97%

S-Nitrosation of Aminothiones

et al. 2015

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“…In fact, for ethyl thionbenzoate and seven substituted derivatives the maximum occurs in acid concentrations at which HT pKBH+ (43), and for thionacetamide the maximum occurs at HT = -2.5,5 close to -2.56 for pKBH+ (35).…”

Section: Results and Discussion P K I Values Of Diprotonated Cu-aminomentioning

confidence: 99%

“…A difference in hydration would also explain the different Hammett p values for the ionization of protonated thionbenzamides (-1.29: ref. 35) and benzamides (-0.92: ref. 16) and the dissociation of benzoic acids (+ 1.00).…”

Section: Results and Discussion P K I Values Of Diprotonated Cu-aminomentioning

confidence: 99%

Basicity of the thionamide group of α-aminothionamides. Attenuation of electrostatic effects by solvation

Paventi¹,

Heirtzler²,

Edward³

1986

Can. J. Chem.

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. 64,23 10 (1986). The first dissociation constants pK1 of four diprotonated cx-aminothionamides, determined spectrophotometrically, are between -8.1 to -8.8; the second dissociation constants pK2, of three of these compounds, determined titrimetrically, are between 7.3 and 7.7. Both pK1 and pK2 values are close to those calculated from current electrostatic theory for equilibria in solutions of zero ionic strength, in spite of the fact that data for pK1 values were obtained in solutions of high ionic strength. Results indicate a much larger effect of the charged ammonium group on the basicity of the thionamide group than on the basicity of the amide group. A possible explanation based on the greater hydration of the protonated amide group is advanced. MARTINO PAVENTI, FENTON HEIRTZLER et JOHN T. EDWARD. Can. J. Chem. 64, 2310Chem. 64, (1986. Utilisant des mCthodes spectrophotomCtriques on a determine les premieres constantes de dissociation (pK,) de quatre a-aminothioamides diprotones; comme Ctant entre -8,l et -8,8; faisant appel B des mCthodes titrimetriques, on a aussi determink les deuxikmes constantes de dissociation (pK2) de trois de ces composks comme etant entre 7,3 et 7,7. Les valeurs tant des pK1 que des pK2 sont proches des valeurs calculies a partir de la theorie ilectrostatique actuelle sur les Cquilibres dans des solutions de force ionique Cgale a zero, mCme si les donnees relatives aux valeurs de pKl sont obtenues dans des solutions de forces ioniques ClevCes. Les risultats indiquent que le groupement ammonium charge provoque un effet beaucoup plus important sur la basicit6 du groupement thionamide que sur la basicite du groupement amide. On propose une explication plausible qui est bas& sur une plus grande hydratation du groupement amide proton-6.[Traduit par la revue]Starting more than 60 years ago with Bjerruln ( I ) , a long succession of investigations has elaborated an electrostatic theory of substitutent effects which is gradually winning general acceptance (2-9). However, the electrostatic effect can be profoundly altered by the presence of a solvent, and although "emphasis has shifted from continuum electrostatics to interactions between specific functionalities in the ions and appropriate sites in a few solvent molecules" (lo), a discontinuous solvation model (1 1) of quantitative (as opposed to qualitative) predictive power has been slow to emerge.The older continuum solvent model was applied to electrostatic effects by Kirkwood and Westheimer (4) in 1938. As an example, we may consider the fact that the dissociation constant K2 of monoprotonated glycine 2 would be expected to be higher than KAH of the parent acid, acetic acid, because the substituted acetate ion 3 is stabilized by electrostatic interaction between NH3+ and the negatively charged carboxylate group.' On the other hand, further dissociation of 3 should be made more difficult than the dissociation of the parent methylammonium ion (KBH+) by the same electrostatic stabilization, the substituent now being C 0 2 -. Classic...

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Thiourea and Thiourea Derivatives

Mertschenk

Beck

Bauer³

2000

Ullmann's Encyclopedia of Industrial Chemistry

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Applicability of the H_T acidity function to the protonation of thioamides, thioureas, and thionesters

Cited by 10 publications

References 6 publications

S-Nitrosation of Aminothiones

S-Nitrosation of Aminothiones

Basicity of the thionamide group of α-aminothionamides. Attenuation of electrostatic effects by solvation

Thiourea and Thiourea Derivatives

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Applicability of the HT acidity function to the protonation of thioamides, thioureas, and thionesters

Cited by 10 publications

References 6 publications

S-Nitrosation of Aminothiones

S-Nitrosation of Aminothiones

Basicity of the thionamide group of α-aminothionamides. Attenuation of electrostatic effects by solvation

Thiourea and Thiourea Derivatives

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Applicability of the H_T acidity function to the protonation of thioamides, thioureas, and thionesters