Decomposition of multifunctionalized α-alkoxyalkyl-hydroperoxides derived from the reactions of Criegee intermediates with diols in liquid phases

The oxidation of volatile organic compounds in the atmosphere produces organic hydroperoxides (ROOHs) that typically possess not only -OOH but also other functionalities such as -OH and -C(=O). Because of their high hydrophilicity and low volatility, such multifunctionalized ROOHs are expected to be taken up in atmospheric condensed phases such as aerosols and fog/cloud droplets. However, the characteristics of ROOHs that control their fates and lifetimes in liquid phases are poorly understood. Here, we report a study of the liquid-phase decomposition kinetics of multifunctionalized alpha-alkoxyalkyl-hydroperoxides (alpha-AHs) that possessed an ether, a carbonyl, a hydroperoxide, and two hydroxy groups. These ROOHs were synthesized by ozonolysis of alpha-terpineol in water in the presence of 1,3-propanediol, 1,4-butanediol, or 1,5-pentanediol. Their decomposition products were detected as chloride anion adducts by electrospray mass spectrometry as a function of reaction time. Experiments using (H2O)-O-18 and D2O revealed that hemiacetal species were alpha-AH decomposition products that further transformed into other products. The result that the rate coefficients (k) of the decomposition of C-15 alpha-AHs increased exponentially from pH 5.0 to 3.9 was consistent with an H+-catalyzed decomposition mechanism. The temperature dependence of k and an Arrhenius plot yielded activation energies (E-a) of 15.7 +/- 0.8, 15.0 +/- 2.4, and 15.9 +/- 0.3 kcal mol(-1) for the decomposition of alpha-AHs derived from the reaction of alpha-terpineol CIs with 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol, respectively. The determined E-a values were compared with those of related ROOHs. We found that alkyl chain length is not a critical factor for the decomposition mechanism, whereas the presence of additional -OH groups would modulate the reaction barriers to decomposition via the formation of hydrogen-bonding with surrounding water molecules. The derived E-a values for the decomposition of the multifunctionalized, terpenoid-derived alpha-AHs will facilitate atmospheric modeling by serving as representative values for ROOHs in atmospheric condensed phases.

Automated summary

This study investigates the liquid-phase decomposition kinetics of multifunctionalized alpha-alkoxyalkyl-hydroperoxides (alpha-AHs). The results reveal that hemiacetal species are the main decomposition products and the reaction rate is influenced by pH and temperature.