Effects of Metal Ions on Aqueous-Phase Decomposition of α-Hydroxyalkyl-Hydroperoxides Derived from Terpene Alcohols

Abstract

We report the results of a mass spectrometric study of the effects of atmospherically relevant metal ions on the decomposition of αhydroxyalkyl-hydroperoxides (α-HHs) derived from ozonolysis of α-terpineol in aqueous solutions. By direct mass spectrometric detection of chloride adducts of α-HHs, we assessed the temporal profiles of α-HHs and other products in the presence of metal ions. In addition, reactions between α-HHs and FeCl 2 in the presence of excess DMSO showed that the amount of hydroxyl radicals formed in a mixture of α-terpineol, O 3 , and FeCl 2 was 5.7 ± 0.8% of the amount formed in a mixture of H 2 O 2 and FeCl 2 . The first-order rate constants for the decay of α-HHs produced by ozonolysis of α-terpineol in the presence of 5 mM acetate buffer at a pH of 5.1 ± 0.1 were determined to be (4.5 ± 0.1) × 10 −4 s −1 (no metal ions), (4.7 ± 0.2) × 10 −4 s −1 (with 0.05 mM Fe 2+ ), (4.7 ± 0.1) × 10 −4 s −1 (with 0.05 mM Zn 2+ ), and (4.8 ± 0.2) × 10 −4 s −1 (with 0.05 mM Cu 2+ ). We propose that in acidic aqueous media, the reaction of α-HHs with Fe 2+ is outcompeted by H + -catalyzed decomposition of α-HHs, which produces the corresponding aldehydes and H 2 O 2 , which can in turn react with Fe 2+ to form hydroxyl radicals.

Decomposition mechanism of α-alkoxyalkyl-hydroperoxides in the liquid phase: temperature dependent kinetics and theoretical calculations

“…We recently found that the reaction of α-Tp α-HHs with Fe 2+ is outcompeted by H + -catalyzed decomposition of α-HHs at ambient concentrations of Fe 2+ and H + found in atmospheric condensed phases. 38 Further work to test the effects of structures and functionalities on the decomposition of ROOHs in the aqueous phase is underway. Our theoretical calculations imply the existence of different reaction pathways, such as water-catalyzed reactions, that could be correlated with the fates of α-AHs in ambient particles under variable relative humidity.…”

“…15 A previous iodometry analysis of a mixture of 1 mM a-Tp + 0.2 mM NaCl + 0.06 mM O 3 + 0.1 mM HCl revealed that approximately 70% of O 3 was converted into H 2 O 2 and other peroxides in water. 38 Another experimental study on the aqueous-phase decomposition of aacyloxyalkyl-hydroperoxides derived from a-pinene CIs with carboxylic acids found that H 2 O 2 is a key decomposition product. 39 Comparison of the activation energies for the decomposition of a-AHs and related ROOHs in aqueous solutions…”

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

“…Next, we performed measurements of mass spectra with the use of H 2 18 O and D 2 O. O solution, non-shifted signals at m/z 341;343 appeared initially, but they gradually shifted to m/z 343;345 (Fig. 3).…”

“…We have recently investigated the condensed-phase fates of a-hydroxyalkyl-hydroperoxides (a-HHs) and a-alkoxyalkyl-hydroperoxides (a-AHs) derived from the reaction of terpenoid-derived CIs with water and alcohols, respectively. [16][17][18][19][20][21][22][23] We have successfully detected C 11-13 a-AHs derived from the reaction of a-terpineol (a monoterpene-alcohol, a-Tp) CIs with monohydric alcohols as their chloride-adducts via on-line electrospray mass spectrometry in aqueous solutions. 23 We have found that the a-AHs decompose faster at lower pH, leading us to propose that the decompositions are catalyzed by H + .…”

“…27,28 By directly monitoring the temporal profiles of the a-AHs and their decomposition products as their chloride anion (Cl À ) adducts detected with electrospray mass spectrometry, we were able to investigate the kinetics of a-AH decomposition in aqueous solutions at different pHs and temperatures. Experiments using H 2 18 O and D 2 O solvents enabled us to identify the mechanism of decomposition of the a-AHs and a key decomposition product in an acidic aqueous medium.…”