Basic Remarks on Acidity

Abstract

This Review provides a unified view on Brønsted acidity. For this purpose, a brief overview of the concepts acidity, acid strengths, and pH value is given, including problems, proposed solutions, and the use of the pH /pHabsH2O scale as a unifying concept. Thereafter, some examples of the accessibility and application of unified pH values are given. The Review is rounded off with the analogy of acid-base chemistry to redox chemistry with the introduction of the unified redox scale pe . The combination of pH and pe values in the protoelectric potential map (PPM), as elaborated in ongoing studies on the thermochemistry of single ions, provides a means to classify and to compare all possible acid-base/redox reactions in a medium-independent and, thus, unified fashion.

The role of the molecular formula of ZnCl2·nH2O on its catalyst activity: a systematic study of zinc chloride hydrates in the catalytic valorisation of cellulosic biomass

“…With higher hydrates (n = 3.25-4.5), there is water present in excess of the inner coordination sphere, and available to hydrate the H + into the less active H3O + cation or even more highly hydrated species. 34,35 This hydration effect is known to suppress the Brønsted acid activity, 35 and is consistent with our experimental results. The higher acidity with lower levels of water present would be consistent with the notion of a less well hydrated hydrogen cation.…”

“…Nevertheless, discrete species of hydrated H + such as H13O6 + may not exist within these concentrated ionic solvents, unlike in dilute aqueous solutions. 34,35 H + is presumably delocalised between the water Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx (Fig. 1a), reaction of MCC favours formation of cellotriose and cellotetraose (yields up to 13 wt% and 20 wt%, respectively) up to 160 min, but at 200 min disaccharides (cellobiose and cellobiulose, 9 wt% and 8 wt% yields, respectively), monosaccharides (glucose and fructose, 22 wt% and 9 wt% yield, respectively) and furanoids (HMF, FHK and FF, yields 15, 5 and 1 mol%, respectively) predominate.…”

Glass electrode half-cells for measuring unified pH in ethanol–water mixtures

“…However, all unified acidities have been measured in non-aqueous systems only with rather special metal solidcontact glass electrode half-cells (Beliustin et al, 1992) until now. The work on unified pH started with metal solid-contact electrodes, because these electrodes performed better in water than other electrodes that were tested (Suu, 2013), and similar glass electrodes filled with mercury worked well in DMSO (Koppel et al, 1977;Kütt et al, 2008). These electrodes give stable and reproducible signals in non-aqueous solvents and their mixtures with water.…”

Generalization of Acid‐Base Diagrams Based on the Unified pH‐Scale

“…They have hitherto been limited to aqueous systems, most likely because the pH in most nonaqueous solvents has not been defined consistently so far. However, following the concept of the unified acidity scale developed by Himmel et al . it can be extended to nonaqueous systems, although one has to keep in mind that additional equilibria can play a role in nonaqueous solutions.…”