Acid-catalyzed hydrolysis kinetics of organic hydroperoxides: Computational strategy and structure-activity relationship

Abstract

Organic hydroperoxides (ROOHs) are key components of atmospheric aerosols. Determining the acid-catalyzed hydrolysis rate constants (kA) of ROOHs is crucial for assessing their atmospheric fate and environmental impacts. However, available kA values are limited due to the difficulty in obtaining authentic ROOH standards. Herein, we addressed this limitation by developing a computational strategy and probing the structure-activity relationship of kA values. We screened the protonated water cluster (H+(H2O)n) model, a critical prerequisite for density functional theory (DFT) calculations of kA, by comparing experimental kA values of four ROOHs with DFT-calculated values using H+(H2O)n (n=1, 2, 3, 4) models. Results show that the H+(H2O)2 model reliably predicts kA values with DFT method. Further investigation of 53 additional ROOHs including 45 model compounds and 8 atmospherically relevant species reveals that substituents at the Cα (the carbon atom directly bonded to the -OOH group) site, including -NH2, -N(CH3)2, -OH, -OCH3, -CH = CH2, -SH, and -PH2, can facilitate acid-catalyzed hydrolysis. Notably, the -NH2 and -N(CH3)2 substituents exhibit stronger facilitating effect than the well-documented -OH and -OCH3 substituents. Additionally, we clarified that not all nitrogen- or oxygen-containing substituents equally enhance kA, as their efficacy depends on the substituents attached to the O or N atoms. This study provides a reliable computational strategy and essential guidelines for predicting kA values of ROOHs, enabling more accurate simulations in atmospheric chemistry models.