Acid–Base and Thermodynamic Properties ofd-Gluconic Acid and Its Interaction with Sn²⁺and Zn²⁺

Abstract

In this paper, new potentiometric, calorimetric, and voltammetric measurements are reported to model the behavior of D-gluconic acid in aqueous NaCl (aq) and NaNO 3(aq) ionic media at different ionic strengths and temperatures (283.15 ≤ T/K ≤ 318.15) also in the presence of Sn 2+ and Zn 2+ . The protonation constants of D-gluconic acid (Gluc − in its deprotonated form) in NaCl (aq) and NaNO 3(aq) are very similar. The dependence on ionic strength of the protonation constant was modeled by means of the extended Debye−Huckel type equation, the Specific ion Interaction Theory (SIT) and a weak interaction model. At infinite dilution and T = 298.15 K, the thermodynamic parameters for the proton binding reaction, determined by direct calorimetric titrations and temperature gradients of protonation constants, are log K H0 = 3.709 ± 0.004, ΔG 0 = −21.18 ± 0.01 kJ mol −1 , ΔH 0 = −4.56 ± 0.04 kJ mol −1 , and TΔS 0 = 16.6 ± 0.1 kJ mol −1 , indicating that the reaction is exothermic and entropic in nature. Potentiometric and voltammetric measurements on the Sn 2+ and Zn 2+ /Gluc − systems allowed us to determine the MGluc + species for both systems at different ionic strengths, together with the Sn(Gluc) 2 and Sn(OH)Gluc species. The values of the formation constant of the SnGluc + species are higher than the corresponding ZnGluc + . During the experiments, the precipitation of insoluble species was evidenced at pH ≥ 4.0 for Sn 2+ /Gluc − and pH ≥ 7.0 for Zn 2+ /Gluc − . The stoichiometry of the precipitates was established by means of thermogravimetric analysis, and the solubility of the two salts, Sn(OH)Gluc (s) and Zn(Gluc) 2(s) , was determined in pure water, in NaCl and in NaNO 3 aqueous media. In pure water, the total solubility is S T = 0.262 ± 0.001 and 0.082 ± 0.006 mol kg −1 for the ZnGluc 2 and Sn(OH)Gluc, respectively. Calorimetric measurements were performed to determine the enthalpy changes of the gluconate protonation and Sn 2+ complex formation constants at different ionic strengths. The effect of two anions, as fluoride and citrate, on the stability of the Sn 2+ / Gluc − species was studied by means of potentiometric measurements at I = 0.15 and 1.02 mol kg −1 , and it was found that the formation of mixed complexes is thermodynamically favored.

Complex equilibria in strongly alkaline aqueous solutions containing Ca(II), Nd(III) and gluconate ions

“…(albeit that may be different for another background electrolyte) 42 . Their results are in good agreement with the published data of Bretti et al, who determined the pKa at various ionic strengths and temperatures and reported a pKa value of 3.763 at 4.4 M ionic strength (NaCl) 43 . At pH > 6 only the deprotonated Glucis present in solution, and at pH = 11 hydroxyl groups start to deprotonate, and the Gluc 2form dominates acid-base equilibria over pH = 13 36 .…”

“…At pH > 6 only the deprotonated Glucis present in solution, and at pH = 11 hydroxyl groups start to deprotonate, and the Gluc 2form dominates acid-base equilibria over pH = 13 36 . 43 1.021 M NaNO3 3.363 43 4.436 M NaCl 3.763 43 Zhang et al observed that chemical shifts on the 13 C NMR spectra of Glucshow a tendency similar to an inflection point at pH = 13. They speculated that this could occur because a second deprotonation takes place and Gluc 2forms by deprotonation of an alcoholic hydroxyl group.…”

Electrochemical Synthesis of Bismuth Particles: Tuning Particle Shape through Substrate Type within a Narrow Potential Window

“…As aforementioned, gluconate mainly exists as gluconic acid in the bath. The complexing capacity of gluconic acid is much lower than that of the gluconate anion [ 18 ]. As a result, gluconic acid acts as a throwing power additive rather than as a complexing agent.…”