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Aqueous OH Kinetics of Aliphatic Carboxylic Acids: New Data and Updated Structure-Activity Relationship
Priyanka Jain1, Bartłomiej Witkowski1, Jakub Szlęk2,3
1Faculty of Chemistry, University of Warsaw, Al. Żwirki i Wigury 101, 02-089 Warsaw, Poland.
The Journal of Physical Chemistry. A
|March 31, 2026
Summary
This study quantifies hydroxyl radical (OH) reaction rates for many carboxylic acids in water. An improved model accurately predicts these rates, enhancing atmospheric chemistry understanding.
Area of Science:
- Atmospheric Chemistry
- Chemical Kinetics
- Environmental Science
Background:
- Hydroxyl radical (OH) reactions are crucial in atmospheric multiphase chemistry.
- Kinetics of OH reactions with carboxylic acids and their conjugate bases are not well understood.
Purpose of the Study:
- To measure aqueous-phase rate coefficients for various C4-C10 monocarboxylic acids with OH radicals.
- To develop an improved structure-activity relationship model for OH reactions with organic acids.
Main Methods:
- Relative rate technique was employed to measure rate coefficients for 22 monocarboxylic acids between 278 K and 323 K.
- Data were combined with literature values to create a comprehensive kinetic dataset.
- Activation parameters were compiled and analyzed for systematic correlations.
Main Results:
- A dataset of 112 rate coefficients for 61 carboxylates and 51 undissociated acids was compiled.
- Systematic correlations between activation parameters and molecular structures were identified.
- An improved group-contribution structure-activity relationship model was developed, showing higher accuracy in predicting measured rates.
Conclusions:
- The improved model highlights the importance of acidic hydrogen abstraction and single-electron transfer pathways.
- The model's limitations with highly oxygenated and poly(carboxylic) acids suggest modifications are needed for group-contribution models in aqueous kinetics.
- Findings advance the understanding of OH reactions with water-soluble organic compounds in the atmosphere.
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