Speed Limits for Acid–Base Chemistry in Aqueous Solutions
Mateusz L. Donten,
Joost VandeVondele,
Peter Hamm
Affiliations
Mateusz L. Donten
SCS-Metrohm Foundation Award for best oral presentation University of Zurich Institute of Physical Chemistry Winterthurerstrasse 190 CH-8057 Zurich, Switzerland
Joost VandeVondele
University of Zurich Institute of Physical Chemistry Winterthurerstrasse 190 CH-8057 Zurich, Switzerland
Peter Hamm
University of Zurich Institute of Physical Chemistry Winterthurerstrasse 190 CH-8057 Zurich, Switzerland [email protected]
Proton transfer reactions, including acid–base recombination, are commonly considered to occur 'nearly instantaneously'. However, their actual time scales may stretch far into the microsecond range, as acid–base reactions are diffusion controlled and the concentrations are low near neutral pH. The interplay of competing bases in the pH relaxation is illustrated using a model acid–base system consisting of o-nitrobenzaldehyde (oNBA) as a proton cage and acetate ions and hydroxyl ions as bases. The kinetically controlled behavior leads to highly counterintuitive states, i.e. acetate ions are transiently protonated for hundreds of nanoseconds despite the presence of a much stronger base OH–.
