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ACID-BASE PROPERTIES OF AMINOMETHANESULPHONIC ACID N-n-PROPYL, N-n-BUTYL AND N-n-HEPTYL DERIVATIVES

By R. E. Khoma, A. N. Chebotaryov, L. T. Osadchiy, S. V. Vodzinskiy and S. V. Toporov

Abstract

Acid-base properties of aminomethanesulfonic acid N-n-propyl (n-PrAMSA), N-n-butyl (n-BuAMSA) and N-n-heptyl (n-HpAMSA) derivatives (YAMSA) in aqueous solutions at 293 – 313 K were investigated by pH measurements. The ion-molecular composition of the Y+NH2CH2SO2O- – YNHCH2SO2O- – H2O systems, dissociation concentration constants of the second dissociation step for n-PrAMSA, n-BuAMSA and n-HpAMSA (at the isoelectric point where the ionic strength is 4,94 ∙ 10–4 М) were calculated and temperature dependences of the ΔG, ΔH, and ΔS цуre determined at 293–313 K. It was shown the indicated YAMSA in aqueous solutions to exist at a ratio CNaOH/QYAMSA < 0,5, mainly in the zwitter ions form; the content of anions YNHCH2SO2O- was directly proportional to the ratio CNaOH/QYAMSA. The indicated acids lipophilicity was evaluated by the QSAR method. The correlations between experimental results and quantum-chemical calculations data were revealed. In the case of amines, for which the empirical function combining their basicity and lipophilicity (pKa +lgPow) was less than 11,08, with the increase in their pKa, the strength of the corresponding acids (pKYAMSA) decreased. The buffer action pH limits of their aqueous solutions at 298 K were determined; it was shown that using n-PrAMSA, n-BuAMSA and n-HpAMSA can maintain the acidity of the medium in the range of physiological pH values (6,8 ÷ 7,8). It is shown the enhancement of the electron-acceptor properties of the N-substituent to lead to a decrease of the temperature influence on the dissociation thermodynamic functions values of aminomethanesulfonic acids synthesized from amines, for which рKа + lgPow ≤ 11,08. With increasing of temperature, the ΔH and ΔS values of n-PrAMSA and n-BuAMSA dissociation decreased, and n-HpAMSA – on the contrary, increased, and for n-PrAMSA and n-BuAMSA at T < Textr. the reaction was endothermic, and at T > Textr. – exothermic. For the dissociation process of investigated acids, enthalpy-entropic compensation was noted with the «isothermodynamic temperature» 303 K

Topics: амінометансульфокислоти, буферні розчини, термодинаміка іонізації, ліпофільність, Chemistry, QD1-999
Publisher: Odessa I. I. Mechnikov National University
Year: 2019
OAI identifier: oai:doaj.org/article:69cceba6f244453aad36715e348ff458
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