Skip to main content
NCBI home page
ACS AuthorChoice logoLink to ACS AuthorChoice
. 2023 May 8;57(47):18950–18959. doi: 10.1021/acs.est.3c00788

Hydrogen Peroxide Formation during Ozonation of Olefins and Phenol: Mechanistic Insights from Oxygen Isotope Signatures

Joanna Houska †,‡, Laura Stocco †,‡, Thomas B Hofstetter †,§,*, Urs von Gunten †,‡,§,*
PMCID: PMC10690717  PMID: 37155568

Abstract

graphic file with name es3c00788_0006.jpg

Mitigation of undesired byproducts from ozonation of dissolved organic matter (DOM) such as aldehydes and ketones is currently hampered by limited knowledge of their precursors and formation pathways. Here, the stable oxygen isotope composition of H2O2 formed simultaneously with these byproducts was studied to determine if it can reveal this missing information. A newly developed procedure, which quantitatively transforms H2O2 to O2 for subsequent 18O/16O ratio analysis, was used to determine the δ18O of H2O2 generated from ozonated model compounds (olefins and phenol, pH 3–8). A constant enrichment of 18O in H2O2 with a δ18O value of ∼59‰ implies that 16O–16O bonds are cleaved preferentially in the intermediate Criegee ozonide, which is commonly formed from olefins. H2O2 from the ozonation of acrylic acid and phenol at pH 7 resulted in lower 18O enrichment (δ18O = 47–49‰). For acrylic acid, enhancement of one of the two pathways followed by a carbonyl–H2O2 equilibrium was responsible for the smaller δ18O of H2O2. During phenol ozonation at pH 7, various competing reactions leading to H2O2 via an intermediate ozone adduct are hypothesized to cause lower δ18O in H2O2. These insights provide a first step toward supporting pH-dependent H2O2 precursor elucidation in DOM.

Keywords: ozonation, hydrogen peroxide, reaction mechanisms, olefins, phenol, oxygen isotopes, isotope ratio mass spectrometry

Short abstract

Oxygen isotope signatures in H2O2 provide novel mechanistic insights into its formation upon ozonation of olefins and phenol.

Introduction

Hydrogen peroxide (H2O2) is a common reactive oxygen species in natural and technical aquatic systems and in living organisms.1−4 During oxidative water treatment with ozone (O3), H2O2 is a secondary oxidant species which is formed via various reactions such as ozone self-decay and oxidation of organic compounds.5−10 One of the main formation pathways for H2O2 is the Criegee mechanism (Figure 1), where the sum of organic peroxides and H2O2 is formed with up to 100% yield (in % of consumed O3) along with potentially toxic aldehydes and ketones.10−12 Most of them are expected to be degraded during biological post-treatment.13

Figure 1.

Figure 1

Open in a new tab

Criegee mechanism of a disubstituted olefin (−R1 and −R2) via the Criegee ozonide and the formation of two carbonyl compounds, an α-hydroxyalkylhydroperoxide and finally H2O2, which are in equilibrium. The oxygen atoms are colored based on their origin (red from O3 and blue from H2O).

Aldehydes and ketones are formed from both phenols and olefins, but the H2O2 yields for phenols (∼18% at pH 7 and ∼36% at pH 35) are generally much lower.8,14 For the ozonation of olefins, the stoichiometric formation of H2O2 is typically not pH-dependent.10 The pH dependence of the H2O2 yields from phenol could be related to multiple reaction pathways. H2O2 formation from phenol ozonation at pH 3 is mainly accompanied by the formation of organic acids, which points to a Criegee-type mechanism that proceeds in analogy to that shown in Figure 1.5 However, at pH 7, H2O2 formation is attributed to a combination of benzoquinone and organic acid formation, which involves reactions other than the Criegee mechanism.

Phenolic sites in dissolved organic matter (DOM) are generally considered the main oxidant-reactive groups, but olefinic moieties are also present at lower concentrations.15−17 Consequently, the formation of H2O2 upon ozonation of DOM is difficult to rationalize and the contribution of oxidant-reactive sites therein as well as the underlying formation pathways are not sufficiently understood. A previous study showed that both olefins and phenols form similar aldehydes and ketones during ozonation, but the two types of precursors from DOM can only be distinguished in rare cases.12 Since the same precursors lead to the formation of H2O2, a similar knowledge gap exists for H2O2.

Compound-specific isotope analysis (CSIA) offers complementary avenues to elucidate reaction mechanisms of organic chemicals during water treatment based on the evaluation of the natural abundance of the stable isotope composition of reaction products.18−21 Previous studies have used CSIA to study the formation of N-nitrosamines upon chloramination of various N-containing precursor compounds22−24 and have found that sequences of reactions and their isotope effects can lead to characteristic isotopic compositions. Upon chloramination, 13C/12C and 15N/14N ratios in N-nitrosamines are indicative of a specific formation pathway. Likewise, the observations of distinct 13C/12C ratios in chloroform formation during chlorination of DOM allowed distinguishing between resorcinol- and phenol-type precursors.25

Based on these findings, it is posited that the measurement of 18O/16O ratios of H2O2 generated in ozonation processes could reveal mechanistic information on the aforementioned reactions. The observation of different pathways to H2O2 from olefins and phenols and the different pH-dependent molar H2O2 yields5,10 may lead to pathway-dependent changes in δ18O of H2O2. As exemplified in Figure 1, the ozonation of olefins results in the transfer of only two of three O atoms of O3 to H2O2. A discrimination between reactions of heavy and light O atoms in O3 isotopologue intermediates that lead to H2O2 and other O-containing products can be expected. Therefore, partitioning of O atoms between H2O2 and other O-containing products could additionally contribute to fractionation in O isotopes in H2O2. However, O isotope fractionation of H2O2 has never been studied in the context of oxidative water treatment, partly because methods for δ18O quantification of H2O2 and O3 in aqueous matrices are unavailable.

Because the functioning of isotope ratio mass spectrometers requires the conversion of analytes into small analyte gases,26 H2O2 is oxidized to O2 for measurement of 18O/16O.27−29 This conversion has been achieved by three different methods: (i) conversion by catalase (H2O2 → 1/2 O2 + H2O),23,28,30,31 (ii) oxidation by permanganate in acidic solution (2 MnO4– + 6 H+ + 5 H2O2 → 2 Mn2+ + 8 H2O + 5 O2),32,27 or (iii) oxidation by HOCl (HO2– + HOCl → H2O + Cl– + O2).30 The first method using catalase has been applied to determine the hydrogen and oxygen isotope composition of commercial H2O2,28 but only 50% of the H2O2 is transformed to O2, making it less favorable for experiments with low H2O2 yields. The second method using permanganate has been applied for determining δ18O in rainwater samples27 and in H2O2 self-decomposition experiments,29 but its application is hampered by the need of extensive extraction and purification procedures requiring several liters of sample. Moreover, it is unclear whether organic peroxides, which are in equilibrium with H2O2 (Figure 1), are also transformed to O2. The third approach using HOCl, by contrast, is particularly promising for the mechanistic evaluation of ozonation reactions in the laboratory because H2O2 is quantitatively transformed to O2 in a fast reaction with HOCl (k = 4.4. × 107 M−1 s−1). O2 can subsequently be quantified by detecting the phosphorescence of 1O2 at 1270 nm.5 This method can also be applied to distinguish H2O2 from organic peroxides.

The goal of this study was to explore the utility of stable isotope-based approaches for the elucidation of the mechanisms of H2O2 formation during ozonation of olefinic and phenolic moieties. To this end, the two main objectives were (1) the development and implementation of an analytical procedure for the quantification of 18O/16O ratios in H2O2 through its conversion to O2 with the ensuing O isotope ratio measurements by established methods33−35 and (2) the assessment of O isotope fractionation of H2O2 formed through well-defined ozone reactions via Criegee intermediates to H2O2 for cinnamic acid14 and sorbic acid and more complex reactions pertinent to the formation of H2O2 from the ozonation of phenols5,36,37 and acrylic acid.6

Materials and Methods

Chemicals

All information related to reagents and solutions is provided in Section S1 in the Supporting Information.

Experimental Conditions of Ozonation Reactions

Generation of Ozone Stock Solutions

Ozone (O3) stock solutions (1.6–1.9 mM) were obtained by a previously published procedure (Section S1).10

Ozonation of Model Compounds

Model compound solutions (phenol/phenolate, sorbic acid/sorbate, acrylic acid/acrylate, and cinnamic acid/cinnamate) were ozonated at pH 3 and 7 (10 mM phosphate buffer) in 100 mL serum bottles in the presence of DMSO (1–40 mM) with molar model compound-to-ozone ratios in the range of 3–5 (for concentrations see Table S1). DMSO was added as a hydroxyl radical (•OH) scavenger, to suppress •OH reactions, which enables one to study the reactions of model compounds with ozone selectively. DMSO was selected because it has much lower yields of H2O2 from the reaction with •OH compared to the typically used tert-butanol. During ozonation, tert-butanol yields up to 30% H2O28,38 while H2O2 yields from DMSO are below 1%.39 The required DMSO concentration was estimated by calculating the scavenging efficiency (>95%), taking into account the apparent second-order rate constants for the reactions of model compounds and DMSO with ozone and •OH at pH 3 and 7, respectively (Table S1).10 Experiments at pH 3 and 7 allowed studying of the pH dependences of product formation.

Quantification of H2O2

The H2O2 concentrations of stock solutions were determined spectrophotometrically at 240 nm (ε = 40 M–1 cm–1)40 and in samples by the Allen's reagent method and via singlet oxygen (1O2) phosphorescence measurements depending on the selected model compound (see below).

In the Allen's reagent method, peroxides are quantified by a molybdate-catalyzed reaction with iodide to yield I3– (351 nm, ε = 25700 M–1 cm–1).41 Based on iodide oxidation kinetics, this method can distinguish between different species (i.e., H2O2 and performic acid, measured after 1 min) and slower-reacting organic peroxides (measured after 20 min).8,42,43 The samples were collected in disposable semimicrocuvettes (PMMA, Brand, Germany) and measured on a UV spectrophotometer (Cary 100, Varian, USA) prior to and after 1 min and after 20 min of initiating the reaction. The LOD and LOQ are 0.4 and 1.1 μM H2O2, respectively. This method was only applied if organic peroxides were expected to be formed. In all other experiments, the 1O2 phosphorescence method was applied, in which H2O2 is quantified by 1O2 measurement (1270 nm, near-infrared photomultiplier tube (NIR-PMT)) produced during the reaction of HO2– with HOCl.5,7,30 The detailed procedure for this method is provided in Section S2. For reproducible results, the equilibrium between organic peroxides vs H2O2 and the corresponding aldehydes must not be disturbed from the withdrawal of H2O2 during the transformation. Results from experiments with acrylic acid confirmed that the 1O2 method can successfully quantify H2O2 in the presence of organic peroxides (Table S3).

Method for the Quantification of 18O/16O Ratios in H2O2

Oxygen isotope signatures of H2O2 (δ18O) were determined after its conversion to molecular O2 using the procedure outlined in Figure S1. The 18O/16O ratio of the resulting O2 was subsequently measured by gas chromatography isotope ratio mass spectrometry (GC/IRMS system consisting of a GC coupled via a Conflo IV interface to a Delta V Plus isotope ratio mass spectrometer) according to established procedures.33−35 Aqueous samples were treated in three principal, consecutive steps which included (a) the removal of residual dissolved O2 from the aqueous solution, (b) the conversion of H2O2 to O2, and (c) the transfer of gaseous samples into the GC/IRMS system with subsequent isotope ratio measurements. Details of the H2O2-to-O2-conversion procedure, its validation, and the consequences for accurate and sensitive determination of 18O/16O in H2O2 are described in Sections S3 and S4.

Briefly, after completion of ozonation experiments, the pH of the H2O2-containing solution in 100 mL serum bottles was adjusted to pH 3 with H3PO4 for stabilization and the sample purged with N2 (99.999%) for 10–15 min. The oxygen-free solutions were then redistributed into 20 mL crimp vials in an anoxic glovebox (O2 <0.1 ppm, UNIlab 2000, MBraun), leaving a maximum headspace of 400 μL. The headspace was used for addition of 50–200 μL of HOCl (1.5–1.7 M) once the reactors were removed from the glovebox and the injection of the same volume of ascorbic acid (2 M) immediately after HOCl addition, to quench residual HOCl. If the pH of the reacted solutions was <7, 9–20 μL of 5 M NaOH was added to adjust the pH to 7.0 for the conversion of H2O2 (Section S4.2). After conversion of H2O2 to O2, the extraction of O2 into the 3 mL N2-containing headspace was achieved by shaking the vials for 30 min at 200 rpm on an orbital shaker.33−35 δ18O values were obtained from 18O/16O ratio measurements of O2. As is detailed in Section S4, this value corresponds to the δ18O value of H2O2 due to complete H2O2-to-O2 conversion for H2O2 concentrations ≥3 μM (Figure S8) and ≥12 μM (Figure S9), depending on the absence and presence of DMSO and phosphate buffer, respectively (Section S4).

Evaluation of 18O/16O ratio measurements of O2 followed peak integration and blank correction procedures as described in detail previously33,34 and in Section S3.4.

Several factors such as time (i.e., for purging, on the stability of the involved species), pH, H2O2 disproportionation, side reactions, or purging have the potential to influence the H2O2 and O2 concentrations and δ18O values. No major influence was expected from these factors, which are discussed in detail in Section S4.

Determination of δ18O Value of O3

δ18O of O3 was determined indirectly in a mass-balance approach through measurements of O isotope ratios of O2 by GC/IRMS. Given that O3 typically coexists with residual O2 in aqueous solutions, δ18O values of O3 (δ18OO3) were derived from the comparison of δ18O from solution type (i) containing both O3 and O2 (δ18OO3+O2) with δ18O of solution type (ii) where O3 was removed and only the residual O2 (δ18OO2) remained.

Solutions of type (i) were O3 stock solutions in which O3 was converted into O2 by inducing an O3 decay chain reaction at pH 12 (eqs S1–S6), and the total O2 content was processed as described above and in Section S3. In solutions of type (ii), O3 was removed from stock solutions through the reaction of O3 with cinnamic acid. The remaining O2 was analyzed for 18O/16O ratios. The δ18O value of O3 was obtained in a mass balance calculation from eq 1 (see eqs S7–S12 for details).

graphic file with name es3c00788_m001.jpg 1

Note that the estimate for δ18O of O3 relies on the accurate quantification of O3 and O2 concentrations which are needed to calculate the fractional concentration (fO3 and fO2). O3 concentrations were determined as described in Section S1, and O2 concentrations in the O3 stock solutions were derived through estimates of O3 and O2 partial pressures in the ozone-containing oxygen gas as detailed in Section S5 (eqs S7–S12).

Quantification of Model Compounds and Byproducts

Concentrations of phenol, cinnamic acid, benzaldehyde, and sorbic acid were measured by high-performance liquid chromatography coupled to a diode array detector (HPLC-DAD, Ultimate 3000, Thermo Scientific, Switzerland). Concentrations of acrylic acid were measured by ion chromatography (Dionex Integrion) with an IonPac AS19-4 μm column with an –OH gradient and conductivity detection. Instrumental details, measurement ranges, and dilution factors are summarized in Table S2.

Results and Discussion

Formation of H2O2 and Organic Peroxides from the Reactions of Ozone with Olefins and Phenol

The yields of H2O2 and organic peroxides were determined using the two methods described in the section on quantification of H2O2, and the results are discussed below before discussing the resulting O isotopic signatures.

The yields of H2O2 and organic peroxides (as % O3 consumed) at pH 3 and 7 of the four selected model compounds vary significantly (Figure 3a and Table S3). The H2O2 yields for cinnamic acid (90 ± 5%, Figure 3a and Table S3) were similar to those in a previous study.14 For sorbic acid a H2O2 yield of close to 100% was also observed in this study. At pH 7, the H2O2 yields when using the ozonation of acrylic acid, a compound known to form organic peroxides, were comparable for the 1O2 method and the Allen's method with 52 ± 4% and 40.11 ± 0.01%, respectively (% of consumed O3). Slight differences in the yields might come from differences in time elapsed between the reactions and the H2O2 measurement, because H2O2 is in equilibrium with an organic peroxide. In a previous study, 58% H2O2 (pH 7) was reported for this reaction system6 and thus the value from 1O2 measurement is consistent. Notably, the total peroxide yield (H2O2 and organic peroxides) determined by the Allen's method was 78–80% for acrylic acid (Table S3). This can be explained by the slow reaction of hydroxymethylhydroperoxide in the Allen's method with incomplete reaction even after 20 min.6,10,13 Overall, H2O2 concentrations can be reliably determined for ozonated model compounds by the 1O2 method, and therefore this was applied for phenol, because the Allen's method cannot be applied due to interferences of phenol transformation products.5 The H2O2 yield (per mole of consumed O3) of phenols was on average 17 ± 1% at pH 7 and increased to 33 ± 2% at pH 3 (Figure 3c). These yields are comparable to those in previous studies (13–18% at pH 7 and 36% at pH 3).5,36,37 H2O2 yields from the reaction of ozone with phenol for pH 3–4.5 and 8 are provided in Table S4. Residual model compound concentrations upon ozonation are shown in Figures S10–S13. The molar consumption of model compounds per mole of O3 is between 1.09 and 0.94 for sorbic acid/sorbate and acrylic acid/acrylate, respectively (Figures S11 and S12), which is expected based on the Criegee mechanism. For phenol/phenolate, the range is between 0.49 and 0.53 (Figure S13), close to reported values.5,37

Figure 3.

Figure 3

Open in a new tab

Reactions of ozone with phenol and olefinic model compounds. (a) H2O2 yields and (b) oxygen isotopic signatures of H2O2 formed from the reactions of ozone with phenol and olefinic model compounds at pH 3 (empty symbols) and 7 (filled symbols) and of O3 (dark red solid and dotted lines (standard deviation)). Please note the split axis between 5‰ and 40‰. (c) δ18O of H2O2 from ozonation of phenol (filled circles) and H2O2 yields (squares) for ozonation experiments at pH 3, 3.5, 3.85, 4.3, 7, and 8 (10 mM phosphate buffer). The pH is adjusted to pH 3 after ozonation to preserve H2O2 and adjusted to pH 7 for reproducible H2O2 to O2 turnover by HOCl. The number of replicates in all cases was ≥2 (see Table S5). Detailed information about ozonation of each compound is provided in Section S4.5.

Validation of the Experimental Procedure for δ18O Determination in H2O2

The reproducibility, accuracy, and precision of the experimental procedure for quantification of δ18O values in H2O2 were examined in three steps. First, the quantitative conversion of H2O2 to O2 was tested for the typical range of H2O2 concentrations in the experiments (≤120 μM). Second, the linear range and method detection limits (MDLs) for 18O/16O ratio measurements in O2 from the oxidation of H2O2 with HOCl were identified for experimental conditions representing typical concentrations used during olefin ozonation necessary to maintain a molar olefin excess relative to O3 and allow sufficient scavenging by DMSO (Table S1, Section S2). Finally, the procedure was validated by quantifying δ18O values of H2O2 from the well-characterized ozonation of cinnamic acid to benzaldehyde, glyoxylate, and H2O2.

Figure S2b shows that the conversion of H2O2 to O2 through addition of HOCl was close to stoichiometric with O2 yields of 90 ± 10% (Figure S2c) for H2O2 concentrations between 0 and 120 μM in ultrapurified water. Blank concentrations of dissolved oxygen were typically below 3 μM (Figure S2a) and were accounted for in background subtraction procedures in a stable O isotope analysis (Section S3.4). The efficient transformation to O2 led to an MDL for δ18O values of H2O2 in aqueous solution of 3 μM (Figure S8). Identical δ18O values were determined for the H2O2 concentration range up to 120 μM (Figure S8). The presence of 10 mM phosphate buffer and 5 mM of DMSO resulted in larger variations of 18O/16O ratio measurements of O2 and in a slightly elevated MDL of 12 μM (Figure S9). This MDL is consistent with those determined previously for δ18O of O2 in smaller sample volumes (10 mL vs 20 mL).33,34

Average δ18O values in H2O2 standards amounted to 21.9 ± 0.7‰ (n = 17, Figure S8b) in ultrapurified water. In a typical sample matrix, the δ18O values of these H2O2 standards were 22.2 ± 1.0‰ (n = 20) and thus identical within uncertainty (Figure S9b). All measured values coincide with the range of measured δ18O of H2O2 standards examined previously of 21.4–25.8‰.27,44 These O isotope signatures are confined to an amazingly narrow range of approximately 5‰, presumably because commercially available H2O2 is almost exclusively produced by the anthraquinone process.45 The agreement of the measurement with previous data for δ18O of H2O2 further underscores the accuracy of the presented analytical procedure.

The analytical procedure to determine O isotopes of H2O2 was applied to the reaction of ozone with cinnamate (Figure 2). Cinnamate was ozonated at three ozone doses (20, 40, and 100 μM), with an excess of olefinic compound to achieve stoichiometric H2O2 formation. These conditions corresponded to molar O3:olefin ratios of 0.1–0.5. Per mole of consumed cinnamate, 0.87 ± 0.03 mol of H2O2 and 0.92 ± 0.02 mol of benzaldehyde were obtained, in agreement with a previous study (Figure 2a).14 A correlation of applied ozone doses with cinnamate, benzaldehyde, and H2O2 formation is shown in Figure 2a. A similar correlation was obtained for measured H2O2 and O2 concentrations after addition of HOCl to the samples from cinnamate ozonation (Figure 2b).

Figure 2.

Figure 2

Open in a new tab

(top) Reaction of cinnamate with O3 leads to benzaldehyde, glyoxylate and H2O2 which can be transformed to O2 with the described chlorine-based procedure (indicated in red). (a) Formation of benzaldehyde (slope of 0.92 ± 0.02, R2 = 0.996, empty circles) and H2O2 (slope of 0.87 ± 0.03, R2 = 0.997, filled circles) as a function of increasing ozone doses. (b) Relationship between O2 formation and H2O2 (R2 = 0.997, transformed by HOCl). (c) Corresponding δ18O values as a function of increasing molar O3:cinnamate ratios. Lines in (a) and (b) indicate a 1:1 formation. The horizontal line in (c) indicates an average value of 61.3 ± 1.9%. Experimental conditions: 200 μM cinnamic acid, 10 mM phosphate buffer at pH 7, 5 mM DMSO, and O3 concentrations of 0, 20, 40, and 100 μM. Error bars indicate duplicate and triplicate measurements in (a) and (c), respectively.

The average δ18O values of H2O2 from ozonation of cinnamate was 61.3 ± 1.9‰ (Figure 2c). The three δ18O values of H2O2 are identical within measurement uncertainties. The large standard deviation of the δ18O value from experiments at low molar O3:cinnamate ratios was attributed to O2 concentrations approaching the MDL. Overall, the δ18O value is substantially higher than that of O3 (5 ± 1‰, Section S5) indicating an enrichment of 18O in H2O2. This phenomenon will be discussed in detail below.

Based on the validation of the analytical procedure with H2O2 standard solutions (Figures S8 and S9), it was concluded that δ18O can be determined reliably in experiments for the reaction of cinnamate with ozone (Figure 2c). The same analytical approach was applied to the model compounds sorbic acid, acrylic acid, and phenol (see below).

Oxygen Isotopic Signatures of H2O2 Formed from Reactions of Ozone with Olefins and Phenol

The H2O2 yields (Figure 3a) and δ18O values of H2O2 formed in ozonation reactions of three olefins, acrylic acid, sorbic acid, and cinnamic acid, as well as phenol were evaluated at pH 3 and 7. A substantial O isotope fractionation between ozone (5 ± 1‰) and H2O2 was observed in all experiments, with 18O preferentially accumulating in H2O2. Figure 3b shows that the ozonation of all compounds at pH 3 (empty symbols) and of two olefins at pH 7 (filled symbols) resulted in identical O isotopic signatures of approximately 59‰ (average δ18O of 58.6 ± 2.6‰). For sorbic acid and cinnamic acid, which exhibited an H2O2 yield close to 100% (Figure 3a), the δ18O values were pH-independent. By contrast, for ozonation of phenol and acrylic acid an identical δ18O value of H2O2 was only observed at pH 3.0.

At pH 7, the δ18O values of H2O2 from phenol and acrylic acid ozonation were 48.8 ± 2.8‰ and 47.1 ± 4.3‰, respectively. The δ18O value of H2O2 from the ozonation experiments with phenol was also evaluated at intermediate pH values as shown in Figure 3c. Between pH 3.5 and 4.3, δ18O of H2O2 gradually decreased from approximately 59‰ to 49‰ before reaching a constant value up to pH 8.0. For pH > 3.5, δ18O of H2O2 correlated with the moderate decrease of H2O2 yield from 0.25 to 0.20 (Table S4). Only at pH 3.0 did this correlation of δ18O of H2O2 with its yield become invalid.

H2O2 Formation from Cinnamate and Sorbate: Baseline Case

During ozonation of the olefins cinnamic and sorbic acid (in molar excess to ozone), O3 is transformed stoichiometrically to H2O2 and the corresponding carbonyl compounds (Figures 1 and 2). Therefore, the isotopically heavier H2O2 (∼59‰) compared to O3 (5 ± 1‰) (Figure 3b) has to result from the abundance of the different 16O- and 18O-containing species and the reactions with which heavy and light O atoms are transferred to H2O2. Figure 4 illustrates this phenomenon conceptually by considering that O3 not only consists of 16O and 18O (isotopologues 16O3 vs 16O218O) but also that the 18O isotopologue of O3 consists of two isotopomers where 18O can be located at the central or edge O atom (16O18O16O, 16O16O18O). In case (i), from the Criegee reaction of 16O3, only isotopically light H2O2 is formed. In case (ii), for 16O18O16O, all the 18O will be transferred to H2O2. In case (iii), for 16O16O18O the efficiency of the 18O transfer to H2O2 is determined by the frequency of cleaving bonds between 16O–16O relative to 16O–18O.

Figure 4.

Figure 4

Open in a new tab

Ozonation of olefins by the Criegee mechanism. Isotopologues and isotopomers of O3, the Criegee ozonide and the ensuing formation of carbonyl compound and H2O2. Preferential bond cleavage of 16O–16O bonds in the Criegee ozonide leads to an enrichment of 18O in H2O2 compared to O3. Due to their low abundance, multiply substituted heavy O3 was not taken into account. Cases (i–iii) designate the reactions of the different isotopologues and isotopomers. Black products are preferentially formed compared to gray products.

The observation of 18O-enriched H2O2 is consistent with the notion that bond dissociation energies are smaller for bonds containing light isotopes.46 The ozonide bond thus breaks preferentially between 16O–16O atoms (Figure 4, case (iii)), resulting in a larger share of 18O from the 18O-containing ozonide being transferred to H2O2 compared to O3, while a higher fraction of 16O is recovered in the formed carbonyl groups. Note that no further O–O bond cleavage occurs in the path to H2O2. This behavior of preferential reactions of bonds containing light isotopes corresponds to a normal kinetic isotope effect (KIE > 1) and suggests that the cleavage of the O–O bond in the ozonide is the source of O isotope fractionation. However, specific information about the magnitude of O–O bond cleavage isotope effects in ozonide intermediates and of the following reactions leading to H2O2 formation are not available. Here, this normal KIE was observed for the ozonation of all model compounds, but the extent of 18O fractionation between O3 and H2O2 was different for phenol and acrylic acid at pH 7 as compared to all other cases (Figure 3b). Based on these findings, it is hypothesized that the ozonation of acrylic acid and phenol deviates from the baseline case. In these cases, possibly reaction steps other than those of the Criegee mechanism lead to a smaller enrichment of 18O in H2O2.

H2O2 Formation from Ozonation of Acrylic Acid

The ozonation of acrylic acid deviates from the baseline case in that the δ18O of H2O2 is less than 59‰ at high pH (Figure 3b) and the H2O2 yields are significantly less than 100% (Figure 3a). The reaction mechanism for the ozonation of acrylic acid is shown in Figure 5a with a pH-dependent branching (formation of products 4 and 7).6 In the upper pathway, glyoxylic acid (4) is formed alongside hydroxymethylhydroperoxide (5), which is in equilibrium with formaldehyde (6) and H2O2. In the lower pathway (red dotted arrow) the Criegee-type zwitterion undergoes decarboxylation, leading to 2-hydroperoxyacetaldehyde (7) as the organic peroxide species. Glycolaldehyde (10) and H2O2 are then formed by hydrolysis of the dioxetane (8).6

Figure 5.

Figure 5

Open in a new tab

Mechanisms for the reactions of ozone with (a) acrylic acid and (b) phenol. Green arrows indicate Criegee-type pathways. Red dotted arrows indicate other pathways.

The pH dependence of the two pathways was previously determined by measuring the formaldehyde yield (6) as a function of the pH.6 A formaldehyde fraction of 0.72 at pH 2 and 0.52 at pH 7 indicates that the decarboxylation pathway becomes more important at higher pH. However, the present study shows that the yields of H2O2 were similar at both pH values (52%, Figure 3a) and are consistent with previous H2O2 measurements for pH 7 (58% yield).6 The finding of greater 18O enrichment in H2O2 at lower pH (Figure 3b) implies that the decay of the Criegee ozonide cannot be solely responsible for the observed 18O enrichment. Both mechanisms proceed through the same Criegee ozonide and the same ensuing zwitterion. The main differences between the two mechanisms are the yields of the carbonyl-containing products formaldehyde (6) and glycolaldehyde (10). These compounds are in equilibrium with the corresponding organic peroxides 5 and 9, which together with H2O2 make up 100% of the consumed ozone.6 Organic peroxides thus not only account for the 48% share of O3 atoms that did not wind up in H2O2 (Table S3) but could also determine the δ18O of H2O2 through an O isotope fractionation pertinent to the equilibrium between organic peroxides and aldehydes/H2O2 (5 ⇄ 6 + H2O2, 9 ⇄ 10 + H2O2, Figure 5a). The correlation of lower δ18O of H2O2 with higher pH and an increased contribution of the decarboxylation pathway suggest that the smaller O isotope fractionation could arise from the equilibrium 9 ⇄ 10 + H2O2. The enthalpy of formation of RH2C–OOH bonds varies as a function of R.8 It increases from R = H to R = CH3 from −139 to −175.4 kJ/mol. Therefore, it can be expected that the C–OOH bond is stronger for glycolaldehyde (containing an ethyl group) than for formaldehyde (containing a methyl group), which would lead to a preferential bonding of the 18OOH and therefore a lower δ18O in the H2O2 in equilibrium at pH 7 compared to pH 3. It is interesting to note that the reaction 5 ⇄ 6 + H2O2 leads to an isotopic composition similar to that for H2O2 formed during the stoichiometric ozonation of cinnamate or sorbate, where no organic peroxides accumulate. At this point, there is not sufficient information to explain this observation.

H2O2 Formation from Ozonation of Phenol

At pH 7, the H2O2 yield from ozonation of phenol is much lower at 17% (Figure 3a) and the δ18O of H2O2 (∼49‰) deviates significantly from the baseline case (59‰) at pH 3 (Figure 3b). In contrast to acrylic acid (similar δ18O of H2O2 at pH 7), where the mechanism at both pH values proceeds through the same Criegee ozonide and the ensuing zwitterion, phenol can react with ozone via a monodentate (11 → 12) or bidentate (11 → 13) attack or an outer sphere electron transfer (11 → 14) (Figure 5b). The formed ozone adduct 12 can react further via different pathways: release of an ozonide radical anion (O3•–) (14), hydrogen peroxide (pKa(H2O2) = 11.847) (15), hydroperoxyl radical (pKa (HO2•−) = 4.848) (16), and singlet oxygen (1O2) (17).5,7,10,36,37

Apart from the Criegee-type mechanisms (reaction products from ozonation of 19, Figure 5b), H2O2 can also be formed from 12 (Figure 5b) by a direct rearrangement with heterolytic bond cleavage of the O–O bond, leading to H2O2 and benzoquinone (12 → 15) or homolytic bond cleavage of the O–O bond (12 → 16) which leads to benzoquinone and/or H2O2 by various ensuing reactions ((i)–(iv) in Figure 5b).5,36 Overall, reactions with phenols (equilibrium of phenol (11a) and phenolate (11b), pKa 9.9) offer not only multiple pathways to H2O2 in a sequence of pH-dependent reactions but also pathways which compete with H2O2 formation.

At pH 3, about 90% of the ozone reactions occur with phenol and only 10% with phenolate, whereas the fraction of the phenolate reactions increases dramatically with increasing pH (>99% at pH 7, Figure S15). Estimations of Gibbs free energies show that for neutral phenol, the bidentate addition of O3 (11a → 13) is thermodynamically favored.5 For phenolate, the monodentate attack and a rearrangement of a bidentate form to the noncyclic form are both favored (11b → 12 and 12 → 13, respectively).5 Consequently, there is a distinction of predominance of the pathways at different pH values potentially leading to differences in δ18O of H2O2.

At pH 3, 2 mole of ozone are consumed per mole of phenol (Figure S13). Consequently, further reactions with transformation products are expected, such as with muconic acid, which has an apparent second-order rate constant for the reaction with ozone that is one order of magnitude higher than for phenol at pH 3 (k = 1.3 × 104 M–1 s–1 (muconic acid) vs k = 1.5 × 103 M–1 s–1 (phenol)).6,49 Under these conditions the higher H2O2 yields (33%) compared to pH 7 (17%) is caused by H2O2 formation by a Criegee-type mechanism from muconic acid (19). Potential H2O2 formation with concomitant benzoquinone formation is only minor (15% benzoquinone yield at pH 3 in % of consumed O35). Thus, it is posited that H2O2 formation at pH 3 is mainly based on Criegee-type reactions leading to a δ18O of H2O2 similar to that for the baseline case.

With increasing pH, the H2O2 yields and the determined δ18O of the formed H2O2 clearly decrease (Figure 3c) with an inflection point at around pH 3.85. At this pH, phenol and phenolate exhibit the same kinetic contribution to the oxidation of total phenol by ozone with the same apparent second-order rate constants (Figure 3c and Figure S15).10

At pH 7, H2O2 is mainly formed by concomitant benzoquinone formation (30% benzoquinone yield at pH 7 in % of consumed O35), where higher benzoquinone yields compared to H2O2 may arise from ensuing reactions ((i) and (iv) in Figure 5b). The lower yields of H2O2 at pH 7 (17%) compared to pH 3 (33%) might be caused by competing ozone reactions without H2O2 formation, which may also influence the δ18O of H2O2. A case in point is the loss of 1O2 from the ozone adduct (12 → 17, Figure 5b). 1O2 yields at pH 7 are around 5–6%, while 1O2 was not detected at pH 3.36 In addition, pathway 12 → 14 is more pronounced at pH 7 than at pH 3, which can be concluded from the corresponding •OH yields (pH 3 (∼20%), pH 7 (∼30%)).36

The transfer of oxygen atoms from O3 to H2O2 and other reactive oxygen species from the ozone adduct 12 substantially differs from the baseline case, which involves the Criegee ozonide (Figure 4). Figure S14 shows the fate of the different ozone adduct isotopologues and isotopomers. For the Criegee ozonide isotopologues, a preferential bond cleavage of 16O–16O leads to the transfer of all 18O atoms to H2O2 (Figure 4). During ozonation of phenolate, only three out of four ozone adduct isotopologues and isotopomers transfer 18O to H2O2 and other reactive oxygen species (Figure S14a–c). The ozone adduct isotopomer (Figure 14d) with a C–18O bond will lead to a loss of 18O to the oxygen-containing aromatic products. Consequently, less 18O is transferred to H2O2 and other reactive oxygen species compared to the baseline case, which can explain the lower δ18O of H2O2. Furthermore, competing pathways enhance this effect as 18O can be lost, which is then no longer available for H2O2 formation. For example, electron transfer (12 → 14) leads to a loss of 18O to O3•– for all heavy isotopomers ((i), Figure S14a–d) and thus is not available for H2O2 formation, leading to an even lower δ18O of H2O2 compared to the baseline case.

Overall, comparing the different pathways that contribute to the H2O2 budget at pH 3 and 7, it can be concluded that Criegee-type reactions are more pronounced at pH 3 and mostly control the observed δ18O of H2O2 of ∼59‰. The agreement of this value with H2O2 from olefin ozonation might be fortuitous. At pH 7, H2O2 is mainly formed via benzoquinone formation. However, the competing ozone-consuming reactions electron transfer (12 → 14, which leads to •OH formation) and the loss of 1O2 (12 → 17) lead to lower H2O2 yields. Overall, the lower δ18O of H2O2 of ∼49‰ at pH 7, compared to the baseline case (Figure 4), is governed by (1) a lower expected δ18O of H2O2 from the benzoquinone formation pathway (Figure S14), (2) formation of 1O2 (12 → 17), and (3) consumption of ozone without H2O2 formation and loss of 18O by the electron transfer process (12 → 14).

Implications

A novel method for the measurement of the oxygen isotope composition of H2O2 has been developed. This method was applied to investigate the oxygen isotopic composition of H2O2 formed during ozonation of olefins and phenol. It was found that δ18O of H2O2 is significantly higher (>40‰) than in ozone for all precursors. Whereas for ozonation at pH 3 the δ18O of H2O2 was the same for all precursors, at pH 7, the δ18O of H2O2 was 10‰ lower for ozonation of acrylic acid and phenol. This observation opens a potential option for pH-dependent H2O2 precursor elucidation in more complex compound mixtures such as dissolved organic matter (DOM). It is expected that olefins with an acrylic acid type ozonation chemistry are rare in such matrices and that the ozone chemistry is mainly determined by phenols and olefins reacting by a standard Criegee mechanism. Under these conditions, the pH-dependent concentration and δ18O of H2O2 could potentially yield information on the respective precursors, which are also important for the formation of undesired carbonyl compounds.12 However, to use O isotope fractionation trends in this manner, a more extensive and more rigorous assessment of ozonation of various olefins and substituted phenols and mixtures thereof in terms of pH-dependent H2O2 yields and δ18O of H2O2 needs to be performed. Additionally, the ozonation of standard DOM samples and DOM from environmental water samples should be explored to assess the feasibility of the proposed approach. A similar conceptual approach has been successfully applied to elucidate precursors of chloroform formation during chlorination of model compounds and real water samples.25 Furthermore, there are many reactions in environmental (bio)chemistry where H2O2 is involved and the novel method for O isotope analysis reported here could be applied to gain more mechanistic insights into processes involving reactive oxygen species.1,3,4,50

Acknowledgments

The project was financially supported by the Swiss National Science Foundation (SNSF) project no. 181975. We acknowledge Numa Pfenninger for assistance with the glovebox, Charlotte Bopp and Jakov Bolotin for support with analytical instrumentation, and Sarah Pati for helpful discussions. Charlotte Bopp is also acknowledged for her invaluable comments on the manuscript.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.3c00788.

  • Reagents, solutions, and instrumental details, overview of measurement of model compounds, analytical approach for the determination of δ18O in H2O2, application of isotopic H2O2 characterization to ozonation experiments, approach for the derivation of δ18O in O3, and background information to explain isotopic signatures (PDF)

The authors declare no competing financial interest.

Supplementary Material

es3c00788_si_001.pdf (1.4MB, pdf)

References

  1. Cooper W. J.; Zika R. G. Photochemical Formation of Hydrogen Peroxide in Surface and Ground Waters Exposed to Sunlight. Science (1979) 1983, 220 (4598), 711–712. 10.1126/science.220.4598.711. [DOI] [PubMed] [Google Scholar]
  2. Kok G. L. Measurements of Hydrogen Peroxide in Rainwater. Atmospheric Environment (1967) 1980, 14 (6), 653–656. 10.1016/0004-6981(80)90048-7. [DOI] [Google Scholar]
  3. Winterbourn C. C. The Biological Chemistry of Hydrogen Peroxide. Methods in Enzymology 2013, 528, 3–25. 10.1016/B978-0-12-405881-1.00001-X. [DOI] [PubMed] [Google Scholar]
  4. Sies H. Role of Metabolic H2O2 Generation: Redox Signaling and Oxidative Stress. J. Biol. Chem. 2014, 8735–8741. 10.1074/jbc.R113.544635. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Tentscher P. R.; Bourgin M.; von Gunten U. Ozonation of Para -Substituted Phenolic Compounds Yields p -Benzoquinones, Other Cyclic α,β-Unsaturated Ketones, and Substituted Catechols. Environ. Sci. Technol. 2018, 52 (8), 4763–4773. 10.1021/acs.est.8b00011. [DOI] [PubMed] [Google Scholar]
  6. Leitzke A.; von Sonntag C. Ozonolysis of Unsaturated Acids in Aqueous Solution: Acrylic, Methacrylic, Maleic, Fumaric and Muconic Acids. Ozone Sci. Eng. 2009, 31 (4), 301–308. 10.1080/01919510903041354. [DOI] [Google Scholar]
  7. Muñoz F.; Mvula E.; Braslavsky S. E.; von Sonntag C. Singlet Dioxygen Formation in Ozone Reactions in Aqueous Solution. Journal of the Chemical Society, Perkin Transactions 2 2001, 0 (7), 1109–1116. 10.1039/b101230o. [DOI] [Google Scholar]
  8. Flyunt R.; Leitzke A.; Mark G.; Mvula E.; Reisz E.; Schick R.; von Sonntag C. Determination of •OH, O2•−, and Hydroperoxide Yields in Ozone Reactions in Aqueous Solution. J. Phys. Chem. B 2003, 107 (30), 7242–7253. 10.1021/jp022455b. [DOI] [Google Scholar]
  9. Buffle M.-O.; Schumacher J.; Meylan S.; Jekel M.; von Gunten U. Ozonation and Advanced Oxidation of Wastewater: Effect of O3 Dose, PH, DOM and HO•-Scavengers on Ozone Decomposition and HO• Generation. Ozone Sci. Eng. 2006, 28 (4), 247–259. 10.1080/01919510600718825. [DOI] [Google Scholar]
  10. von Sonntag C.; von Gunten U.. Chemistry of Ozone in Water and Wastewater Treatment-From Basic Principles to Applications; IWA publishing: 2012. [Google Scholar]
  11. Lim S.; Shi J. L.; von Gunten U.; McCurry D. L. Ozonation of Organic Compounds in Water and Wastewater: A Critical Review. Water Res. 2022, 118053. 10.1016/j.watres.2022.118053. [DOI] [PubMed] [Google Scholar]
  12. Houska J.; Manasfi T.; Gebhardt I.; von Gunten U. Ozonation of Lake Water and Wastewater: Identification of Carbonous and Nitrogenous Carbonyl- Containing Oxidation Byproducts by Non-Target Screening. Water Res. 2023, 232, 119484. 10.1016/j.watres.2022.119484. [DOI] [PubMed] [Google Scholar]
  13. Manasfi T.; Houska J.; Gebhardt I.; von Gunten U. Non-Target Screening Method for the Identification and Quantification of Carbonyl Compounds in Ozonated Lake Waters and Wastewaters. Water Res. 2023, 119751. 10.1016/j.watres.2023.119751. [DOI] [PubMed] [Google Scholar]
  14. Leitzke A.; Reisz E.; Flyunt R.; von Sonntag C. The Reactions of Ozone with Cinnamic Acids: Formation and Decay of 2-Hydroperoxy-2-Hydroxyacetic Acid. Journal of the Chemical Society, Perkin Transactions 2 2001, 0 (5), 793–797. 10.1039/b009327k. [DOI] [Google Scholar]
  15. Önnby L.; Salhi E.; McKay G.; Rosario-Ortiz F. L.; von Gunten U. Ozone and Chlorine Reactions with Dissolved Organic Matter - Assessment of Oxidant-Reactive Moieties by Optical Measurements and the Electron Donating Capacities. Water Res. 2018, 144, 64–75. 10.1016/j.watres.2018.06.059. [DOI] [PubMed] [Google Scholar]
  16. Wenk J.; Aeschbacher M.; Salhi E.; Canonica S.; von Gunten U.; Sander M. Chemical Oxidation of Dissolved Organic Matter by Chlorine Dioxide, Chlorine, And Ozone: Effects on Its Optical and Antioxidant Properties. Environ. Sci. Technol. 2013, 47 (19), 11147–11156. 10.1021/es402516b. [DOI] [PubMed] [Google Scholar]
  17. Houska J.; Salhi E.; Walpen N.; von Gunten U. Oxidant-Reactive Carbonous Moieties in Dissolved Organic Matter: Selective Quantification by Oxidative Titration Using Chlorine Dioxide and Ozone. Water Res. 2021, 207, 117790. 10.1016/j.watres.2021.117790. [DOI] [PubMed] [Google Scholar]
  18. Terhalle J.; Nikutta S. E.; Krzeciesa D. L.; Lutze H. V.; Jochmann M. A.; Schmidt T. C. Linking Reaction Rate Constants and Isotope Fractionation of Ozonation Reactions Using Phenols as Probes. Water Res. 2022, 210, 117931. 10.1016/j.watres.2021.117931. [DOI] [PubMed] [Google Scholar]
  19. Willach S.; Lutze H. V.; Somnitz H.; Terhalle J.; Stojanovic N.; Lüling M.; Jochmann M. A.; Hofstetter T. B.; Schmidt T. C. Carbon Isotope Fractionation of Substituted Benzene Analogs during Oxidation with Ozone and Hydroxyl Radicals: How Should Experimental Data Be Interpreted?. Environ. Sci. Technol. 2020, 54 (11), 6713–6722. 10.1021/acs.est.0c00620. [DOI] [PubMed] [Google Scholar]
  20. Willach S.; Lutze H. V.; Eckey K.; Löppenberg K.; Lüling M.; Terhalle J.; Wolbert J. B.; Jochmann M. A.; Karst U.; Schmidt T. C. Degradation of Sulfamethoxazole Using Ozone and Chlorine Dioxide - Compound-Specific Stable Isotope Analysis, Transformation Product Analysis and Mechanistic Aspects. Water Res. 2017, 122, 280–289. 10.1016/j.watres.2017.06.001. [DOI] [PubMed] [Google Scholar]
  21. Maier M. P.; Prasse C.; Pati S. G.; Nitsche S.; Li Z.; Radke M.; Meyer A.; Hofstetter T. B.; Ternes T. A.; Elsner M. Exploring Trends of C and N Isotope Fractionation to Trace Transformation Reactions of Diclofenac in Natural and Engineered Systems. Environ. Sci. Technol. 2016, 50 (20), 10933–10942. 10.1021/acs.est.6b02104. [DOI] [PubMed] [Google Scholar]
  22. Spahr S.; von Gunten U.; Hofstetter T. B. Carbon, Hydrogen, and Nitrogen Isotope Fractionation Trends in N-Nitrosodimethylamine Reflect the Formation Pathway during Chloramination of Tertiary Amines. Environ. Sci. Technol. 2017, 51 (22), 13170–13179. 10.1021/acs.est.7b03919. [DOI] [PubMed] [Google Scholar]
  23. Spahr S.; Cirpka O. A.; von Gunten U.; Hofstetter T. B. Formation of N-Nitrosodimethylamine during Chloramination of Secondary and Tertiary Amines: Role of Molecular Oxygen and Radical Intermediates. Environ. Sci. Technol. 2017, 51 (1), 280–290. 10.1021/acs.est.6b04780. [DOI] [PubMed] [Google Scholar]
  24. Spahr S.; Bolotin J.; Schleucher J.; Ehlers I.; von Gunten U.; Hofstetter T. B. Compound-Specific Carbon, Nitrogen, and Hydrogen Isotope Analysis of N-Nitrosodimethylamine in Aqueous Solutions. Anal. Chem. 2015, 87 (5), 2916–2924. 10.1021/ac5044169. [DOI] [PubMed] [Google Scholar]
  25. Arnold W. A.; Bolotin J.; von Gunten U.; Hofstetter T. B. Evaluation of Functional Groups Responsible for Chloroform Formation during Water Chlorination Using Compound Specific Isotope Analysis. Environ. Sci. Technol. 2008, 42 (21), 7778–7785. 10.1021/es800399a. [DOI] [PubMed] [Google Scholar]
  26. Sessions A. L. Isotope-Ratio Detection for Gas Chromatography. J. Sep Sci. 2006, 29 (12), 1946–1961. 10.1002/jssc.200600002. [DOI] [PubMed] [Google Scholar]
  27. Savarino J.; Thiemens M. H. Analytical Procedure to Determine Both Δ18O and Δ17O of H2O2 in Natural Water and First Measurements. Atmos. Environ. 1999, 33 (22), 3683–3690. 10.1016/S1352-2310(99)00122-3. [DOI] [Google Scholar]
  28. Barnette J. E.; Lott M. J.; Howa J. D.; Podlesak D. W.; Ehleringer J. R. Hydrogen and Oxygen Isotope Values in Hydrogen Peroxide. Rapid Commun. Mass Spectrom. 2011, 25 (10), 1422–1428. 10.1002/rcm.5004. [DOI] [PubMed] [Google Scholar]
  29. Guo H.; Yu X.; Lin M. Kinetic Isotope Effects in H2O2 Self-Decomposition: Implications for Triple Oxygen Isotope Systematics of Secondary Minerals in the Solar System. Earth Planet Sci. Lett. 2022, 594, 117722. 10.1016/j.epsl.2022.117722. [DOI] [Google Scholar]
  30. Held A. M.; Halko D. J.; Hurst J. K. Mechanisms of Chlorine Oxidation of Hydrogen Peroxide. J. Am. Chem. Soc. 1978, 100 (18), 5732–5740. 10.1021/ja00486a025. [DOI] [Google Scholar]
  31. Wingo W. J.; Emerson G. M. Calibration of Oxygen Polarographs by Catalase-Catalyzed Decomposition of Hydrogen Peroxide. Anal. Chem. 1975, 47 (2), 351–352. 10.1021/ac60352a009. [DOI] [Google Scholar]
  32. Baertschi P. Zur Frage Der Herkunft Des Sauerstoffs Bei Der Oxydation von Wasserstoffperoxyd Durch Permanganat. Experientia 1951, 7 (6), 215–216. 10.1007/BF02138996. [DOI] [PubMed] [Google Scholar]
  33. Bopp C. E.; Bolotin J.; Pati S. G.; Hofstetter T. B. Managing Argon Interference during Measurements of 18O/16O Ratios in O2 by Continuous-Flow Isotope Ratio Mass Spectrometry. Anal Bioanal Chem. 2022, 414 (20), 6177–6186. 10.1007/s00216-022-04184-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Pati S. G.; Bolotin J.; Brennwald M. S.; Kohler H.-P. E.; Werner R. A.; Hofstetter T. B. Measurement of Oxygen Isotope Ratios (18O/ 16O) of Aqueous O2 in Small Samples by Gas Chromatography/Isotope Ratio Mass Spectrometry. Rapid Commun. Mass Spectrom. 2016, 30 (6), 684–690. 10.1002/rcm.7481. [DOI] [PubMed] [Google Scholar]
  35. Pati S. G.; Kohler H.-P. E.; Hofstetter T. B. Characterization of Substrate, Cosubstrate, and Product Isotope Effects Associated With Enzymatic Oxygenations of Organic Compounds Based on Compound-Specific Isotope Analysis. Methods Enzymol 2017, 596, 291–329. 10.1016/bs.mie.2017.06.044. [DOI] [PubMed] [Google Scholar]
  36. Mvula E.; von Sonntag C. Ozonolysis of Phenols in Aqueous Solution. Org. Biomol Chem. 2003, 1 (10), 1749. 10.1039/b301824p. [DOI] [PubMed] [Google Scholar]
  37. Ramseier M. K.; von Gunten U. Mechanisms of Phenol Ozonation-Kinetics of Formation of Primary and Secondary Reaction Products. Ozone Sci. Eng. 2009, 31 (3), 201–215. 10.1080/01919510902740477. [DOI] [Google Scholar]
  38. Acero J. L.; von Gunten U. Influence of Carbonate on the Ozone/Hydrogen Peroxide Based Advanced Oxidation Process for Drinking Water Treatment. Ozone Sci. Eng. 2000, 22 (3), 305–328. 10.1080/01919510008547213. [DOI] [Google Scholar]
  39. Yurkova I. L.; Schuchmann H. P.; Von Sonntag C. Production of OH Radicals in the Autoxidation of the Fe(II)-EDTA System. Journal of the Chemical Society. Perkin Transactions 2 1999, (10), 2049–2052. 10.1039/a904739e. [DOI] [Google Scholar]
  40. Bader H.; Sturzenegger V.; Hoigné J. Photometric Method for the Determination of Low Concentrations of Hydrogen Peroxide by the Peroxidase Catalyzed Oxidation of N,N-Diethyl-p-Phenylenediamine (DPD). Water Res. 1988, 22 (9), 1109–1115. 10.1016/0043-1354(88)90005-X. [DOI] [Google Scholar]
  41. Bichsel Y.; von Gunten U. Determination of Iodide and Iodate by Ion Chromatography with Postcolumn Reaction and UV/Visible Detection. Anal. Chem. 1999, 71 (1), 34–38. 10.1021/ac980658j. [DOI] [PubMed] [Google Scholar]
  42. Allen A. O.; Hochanadel C. J.; Ghormley J. A.; Davis T. W. Decomposition of Water and Aqueous Solutions under Mixed Fast Neutron and Gamma Radiation. J. Phys. Chem. 1952, 56 (5), 575–586. 10.1021/j150497a007. [DOI] [Google Scholar]
  43. Stemmler K.; von Gunten U. OH Radical-Initiated Oxidation of Organic Compounds in Atmospheric Water Phases: Part 2. Reactions of Peroxyl Radicals with Transition Metals. Atmos. Environ. 2000, 34 (25), 4253–4264. 10.1016/S1352-2310(00)00219-3. [DOI] [Google Scholar]
  44. Velivetskaya T. A.; Ignatiev A. v.; Budnitskiy S. Y.; Yakovenko V. v.; Vysotskiy S. v. Mass-Independent Fractionation of Oxygen Isotopes during H2O2 Formation by Gas-Phase Discharge from Water Vapour. Geochim. Cosmochim. Acta 2016, 193, 54–65. 10.1016/j.gca.2016.08.008. [DOI] [Google Scholar]
  45. Campos-Martin J. M.; Blanco-Brieva G.; Fierro J. L. G. Hydrogen Peroxide Synthesis: An Outlook beyond the Anthraquinone Process. Angewandte Chemie - International ed. 2006, 45, 6962–6984. 10.1002/anie.200503779. [DOI] [PubMed] [Google Scholar]
  46. Willi A. V.Isotopeneffekte Bei Chemischen Reaktionen; Thieme: 1983. [Google Scholar]
  47. Sein M. M.; Zedda M.; Tuerk J.; Schmidt T. C.; Golloch A.; von Sonntag C. Oxidation of Diclofenac with Ozone in Aqueous Solution. Environ. Sci. Technol. 2008, 42 (17), 6656–6662. 10.1021/es8008612. [DOI] [PubMed] [Google Scholar]
  48. Bielski B. H. J.; Cabelli D. E.; Arudi R. L.; Ross A. B. Reactivity of HO2/O−2 Radicals in Aqueous Solution. J. Phys. Chem. Ref. Data 1985, 14 (4), 1041–1100. 10.1063/1.555739. [DOI] [Google Scholar]
  49. Hoigné J.; Bader H. Rate Constants of Reactions of Ozone with Organic and Inorganic Compounds in Water—II: Dissociating Organic Compounds. Water Res. 1983, 17 (2), 185–194. 10.1016/0043-1354(83)90099-4. [DOI] [Google Scholar]
  50. Bopp C. E.; Bernet N. M.; Kohler H. P. E.; Hofstetter T. B. Elucidating the Role of O2 Uncoupling in the Oxidative Biodegradation of Organic Contaminants by Rieske Non-Heme Iron Dioxygenases. ACS Environmental Au 2022, 2 (5), 428–440. 10.1021/acsenvironau.2c00023. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

es3c00788_si_001.pdf (1.4MB, pdf)

Articles from Environmental Science & Technology are provided here courtesy of American Chemical Society

RESOURCES