Abstract
Reduced isotropic Raman spectra of dilute sodium glycolate in aqueous solutions of NaOH (molalities ranging from 0.03 to 5.65 mol·kg−1 in OH−) have been obtained at temperatures 5, 25, and 45 °C. The Raman spectra yielded evidence of the formation of a doubly-deprotonated glycolate dianion, −O–CH2–COO− (Gly2−) from the decrease in the intensity of the hydroxyl O–H bending mode at 1365 cm−1 with increasing basicity, and the 7 cm−1 shift in the alcohol C–OH stretching mode (from 1079 to 1086 cm−1 at 5 °C). Equilibrium quotients for the second ionization constant of glycolic acid, Q2a,OH, which corresponds to the deprotonation of the glycolate hydroxyl group, were calculated from the peak area of the O–H bending mode as it decreased with higher NaOH molalities. Values for the equilibrium constant and the standard molar enthalpy of reaction at 25 °C: log K2a,OH,298 = − 1.143 ± 0.059, and ΔionH°2a,OH,298 = − 12.5 ± 1.6 kJ·mol−1, were determined by regressing the experimental equilibrium quotients to a simple extended Debye–Hückel activity coefficient model. This is the first reported spectroscopic characterization of Gly2−and the first reported values for log K2a,OH,298 and ΔionH°2a,OH,298.
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Acknowledgements
This research was supported by the Natural Science and Engineering Research Council of Canada (NSERC Grant IRCPJ 499567-15) and the University Network of Excellence in Nuclear Engineering (UNENE). The authors express their gratitude to Dr. Jenny Cox for her encouragement and insightful discussions on chemical analysis and hydrothermal geochemistry. We are also grateful to members of Prof Tremaine’s NSERC/UNENE Senior Industrial Research Chair Technical Advisory Committee, for their input on reactor chemistry and nuclear waste management for this and related projects.
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Wolf, M.W., Sasidharanpillai, S. & Tremaine, P.R. Determination of the Ionization Constant of the Hydroxyl Group of Glycolic Acid from 5 to 45 °C by Raman Spectroscopy. J Solution Chem 53, 126–143 (2024). https://doi.org/10.1007/s10953-022-01243-2
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DOI: https://doi.org/10.1007/s10953-022-01243-2