Ionization Constants of Aqueous Glycolic Acid at Temperatures up to 250 ∘C Using Hydrothermal pH Indicators and UV-Visible Spectroscopy

Acridinium Ion Ionization at Elevated Temperatures and Pressures to 200 °C and 2000 bar

“…More dilute (∼0.3 to 0.5 mmol•kg −1 ) acridine stock solutions prepared with acetic acid appeared to be stable, and no precipitates were observed in solutions stored for up to a month. Spectra of solutions in which the pH was adjusted with hydrochloric and acetic acid, or acetate and sodium hydroxide, showed no change over 30 min at any studied temperature and pressure, which is consistent with the observation of Ryan et al [10] and in contrast to the observation of Bulemela et al [14] who reported that absorbance of acridine decreased by 0.9 % per minute at both at 25 and 250°C. These differences might be caused by oxidation processes in nondeoxygenated aqueous acridine solutions, as suggested was by Lee et al [8,9].…”

Standard Partial Molar Volumes of Aqueous Glycolic Acid and Tartaric Acid from 25 to 350 °C: Evidence of a Negative Krichevskii Parameter for a Neutral Organic Solute

“…Because the neutral species of carboxylic acids ionize in water, a small correction to remove the contribution of the ionized species was made using Young's rule 4,16 The degree of ionization, α, for glycolic and tartaric acids was calculated from extrapolated ionization constants reported by Shock and Xie and Tremaine, respectively. Shock's values have been confirmed in our laboratory by direct measurements up to 250 °C . Values for V φ (RCOO - ,aq + H + ,aq) were calculated from recently measured values of V φ (RCOO - ,aq + Na + ,aq) for both acids. , The magnitude of the correction is less than 0.5 cm 3 ·mol -1 for HGly(aq) and 1.1 cm 3 ·mol -1 for H 2 Tar(aq) at the highest temperature studied.…”

“…Shock's values have been confirmed in our laboratory by direct measurements up to 250 °C. 15 Values for V φ (RCOO -,aq + H + ,aq) were calculated from recently measured values of V φ (RCOO -,aq + Na + ,aq) for both acids. 16,24 The magnitude of the correction is less than 0.5 cm 3 ‚mol -1 for HGly(aq) and 1.1 cm 3 ‚mol -1 for H 2 Tar(aq) at the highest temperature studied.…”

“…The sources of chemicals and methods of preparing solutions were discussed in our previous papers. , High-temperature volumetric measurements were made in a vibrating-tube densitometer, constructed according to the design of Albert and Wood, as modified by Corti et al A detailed description of the densitometer and the experimental procedures has been given by Xiao et al and Clarke and Tremaine . The densitometer was calibrated daily with pure water and standard solutions of 1.0000 mol·kg -1 NaCl(aq), using the reference values compiled by Hill and Archer, respectively.…”

“…Glycolic acid (HGly), HOCH 2 COOH, and tartaric acid (H 2 Tar), HOOCCH(OH)CH(OH)COOH, are of interest in this context because they are small molecules with extreme hydrogen bonding, having one −OH group and one −COOH group on each alkyl carbon. In earlier papers, , we reported the ionization constant of glycolic acid and the apparent molar volumes of tartaric acid and its sodium salt at temperatures up to 250 °C, as part of a larger study to examine the effect of hydrogen-bonding functional groups on the standard partial molar volumes of organic acids, bases, and zwitterions at elevated temperatures. In this work, the measurements have been extended to temperatures of 350 °C and pressures of 20 MPa in an attempt to observe whether these hydroxy-carboxylic acids display positive or negative Krichevskii behavior.…”