Supporting_Information_pdf – Supplemental material for CuO-catalyzed oxidation of aryl acetates with aqueous tert-butyl hydroperoxide for the synthesis of α-ketoesters

Supplemental material, Supporting_Information_pdf for CuO-catalyzed oxidation of aryl acetates with aqueous tert-butyl hydroperoxide for the synthesis of α-ketoesters by Jin Jiang in Journal of Chemical Research</p

Oxidation of Triclosan by Permanganate (Mn(VII)): Importance of Ligands and In Situ Formed Manganese Oxides

Experiments were conducted to examine permanganate (Mn(VII); KMnO4) oxidation of the widely used biocide triclosan (one phenolic derivative) in aqueous solution at pH values of 5−9. Under slightly acidic conditions, the reactions displayed autocatalysis, suggesting the catalytic role of in situ formed MnO2. This was further supported by the promoting effects of the addition of preformed MnO2 colloids on Mn(VII) oxidations of triclosan and two other selected phenolics (i.e., phenol and 2,4-dichlorophenol), as well as p-nitrophenol which otherwise showed negligible reactivity toward Mn(VII) and MnO2 colloids, respectively. Surprisingly, phosphate buffer significantly enhanced Mn(VII) oxidation of triclosan, as well as phenol and 2,4-dichlorophenol over a wide pH range. Further, several other selected ligands (i.e., pyrophosphate, EDTA, and humic acid) also exerted oxidation enhancement, supporting a scenario where highly active aqueous manganese intermediates (Mn(INT)aq) formed in situ upon Mn(VII) reduction might be stabilized to a certain extent in the presence of ligands and subsequently involved in further oxidation of target phenolics, whereas without stabilizing agents Mn(INT)aq autodecomposes or disproportionates spontaneously. The effectiveness of Mn(VII) for the oxidative removal of triclosan in natural water and wastewater was confirmed. Their background matrices were also found to accelerate Mn(VII) oxidation of phenolics

Oxidation of Sulfoxides and Arsenic(III) in Corrosion of Nanoscale Zero Valent Iron by Oxygen: Evidence against Ferryl Ions (Fe(IV)) as Active Intermediates in Fenton Reaction

Previous studies have shown that the corrosion of zerovalent iron (ZVI) by oxygen (O2) via the Fenton reaction can lead to the oxidation of various organic and inorganic compounds. However, the nature of the oxidants involved (i.e., ferryl ion (Fe(IV)) versus hydroxyl radical (HO•)) is still a controversial issue. In this work, we reevaluated the relative importance of these oxidants and their role in As(III) oxidation during the corrosion of nanoscale ZVI (nZVI) in air-saturated water. It was shown that Fe(IV) species could react with sulfoxides (e.g., dimethyl sulfoxide, methyl phenyl sulfoxide, and methyl p-tolyl sulfoxide) through a 2-electron transfer step producing corresponding sulfones, which markedly differed from their HO•-involved products. When using these sulfoxides as probe compounds, the formation of oxidation products indicative of HO• but no generation of sulfone products supporting Fe(IV) participation were observed in the nZVI/O2 system over a wide pH range. As(III) could be completely or partially oxidized by nZVI in air-saturated water. Addition of scavengers for solution-phase HO• and/or Fe(IV) quenched As(III) oxidation at acidic pH but had little effect as solution pH increased, highlighting the importance of the heterogeneous iron surface reactions for As(III) oxidation at circumneutral pH

Adsorptive Fractionation of Humic Acid at Air−Water Interfaces

By using a simple bubble column, the adsorption behavior of a commercial soil-humic acid (CHA) at air−water interfaces was investigated. At pH 4.0, the concentrations of the CHA exhibited clear gradients in the bubble column, and increased significantly along the column height; smaller concentration gradients were also observed at pH 6.0. These concentration profiles demonstrate the surface activity of humic acid and pH-dependent affinity toward air−water interfaces. Taking advantage of the bubble column method, we interestingly found that the adsorptive fractionation of the CHA at air−water interfaces did occur. The components with higher molecular weight and stronger UV absorptivity showed greater affinity toward air−water interfaces, despite that the fractionation pattern was reduced to a certain extent as solution pH increased. The organic carbon-normalized pyrene partition coefficient KOC values deviated from the corresponding values of original bulk solutions at both pH 4.0 and 6.0, and increased along the height of the column. Our results demonstrate the usefulness of the simple bubble column, and suggest that the adsorptive fractionation of humic acid at air−water interfaces might have implications for some natural environments and engineered systems where air−water interfaces exist extensively

Role of Ligands in Permanganate Oxidation of Organics

We previously demonstrated that several ligands such as phosphate, pyrophosphate, EDTA, and humic acid could significantly enhance permanganate oxidation of triclosan (one phenolic biocide), which was explained by the contribution of ligand-stabilized reactive manganese intermediates in situ formed upon permanganate reduction. To further understand the underlying mechanism, we comparatively investigated the influence of ligands on permanganate oxidation of bisphenol A (BPA, one phenolic endocrine-disrupting chemical), carbamazepine (CBZ, a pharmaceutical containing the olefinic group), and methyl p-tolyl sulfoxide (TMSO, a typical oxygen-atom acceptor). Selected ligands exerted oxidation enhancement for BPA but had negligible influence for CBZ and TMSO. This was mainly attributed to the effects of identified Mn(III) complexes, which would otherwise disproportionate spontaneously in the absence of ligands. The one-electron oxidant Mn(III) species exhibited no reactivity toward CBZ and TMSO for which the two-electron oxygen donation may be the primary oxidation mechanism but readily oxidized BPA. The latter case was a function of pH, the complexing ligand, and the molar [Mn(III)]:[ligand] ratio, generally consistent with the patterns of ligand-affected permanganate oxidation. Moreover, the combination of the one-electron reduction of Mn(III) (Mn(III) + e− →Mn(II)) and the Mn(VII)/Mn(II) reaction in excess ligands (Mn(VII) + 4Mn(II) →ligands 5Mn(III)) suggested a catalytic role of the Mn(III)/Mn(II) pair in permanganate oxidation of some phenolics in the presence of ligands

Oxidation of Phenolic Endocrine Disrupting Chemicals by Potassium Permanganate in Synthetic and Real Waters

In this study, five selected environmentally relevant phenolic endocrine disrupting chemicals (EDCs), estrone, 17β-estradiol, estriol, 17α-ethinylestradiol, and 4-<i>n</i>-nonylphenol, were shown to exhibit similarly appreciable reactivity toward potassium permanganate [Mn­(VII)] with a second-order rate constant at near neutral pH comparable to those of ferrate­(VI) and chlorine but much lower than that of ozone. In comparison with these oxidants, however, Mn­(VII) was much more effective for the oxidative removal of these EDCs in real waters, mainly due to the relatively high stability of Mn­(VII) therein. Mn­(VII) concentrations at low micromolar range were determined by an ABTS [2,2-azino-bis­(3-ethylbenzothiazoline)-6-sulfonic acid diammonium] spectrophotometric method based on the stoichiometric reaction of Mn­(VII) with ABTS [Mn^VII + 5ABTS → Mn^II + 5ABTS^•+] forming a stable green radical cation (ABTS^•+). Identification of oxidation products suggested the initial attack of Mn­(VII) at the hydroxyl group in the aromatic ring of EDCs, leading to a series of quinone-like and ring-opening products. The background matrices of real waters as well as selected model ligands including phosphate, pyrophosphate, NTA, and humic acid were found to accelerate the oxidation dynamics of these EDCs by Mn­(VII). This was explained by the effect of in situ formed dissolved Mn­(III), which could readily oxidize these EDCs but would disproportionate spontaneously without stabilizing agents

New Insights into the Combination of Permanganate and Hydrogen Peroxide as a Novel Oxidation Process for Enhanced Removal of Organic Contaminants

Hydrogen peroxide (H2O2) has recently been reported as a novel activator for enhancing permanganate (Mn(VII)) oxidation, where the removal of trace organic contaminants (TrOCs) was mainly ascribed to the contribution of Mn(VI). This study reassessed the performance and mechanism of the Mn(VII)/H2O2 process for TrOC removal and identified the role of diverse potential reactive species (i.e., intermediate manganese species and radicals). The maximum removal efficiency of organics by the Mn(VII)/H2O2 process was achieved at a [H2O2]/[Mn(VII)] ratio of 1, and acidic pH conditions were conducive to the reactions. UV–vis and XPS spectra suggested the in situ formation of MnO2 in the Mn(VII)/H2O2 process. Degradation of structurally diverse TrOCs by the Mn(VII)/H2O2 process and Mn(VII)/MnO2 process exhibited similar selectivity and pH-dependence, implying that the in situ-formed MnO2 should play an important role in catalyzing Mn(VII) oxidation toward TrOCs in the Mn(VII)/H2O2 process. In addition, the degradation kinetics of TrOCs in the Mn(VII)/H2O2 process were generally higher in phosphate buffer than those in borate buffer, which was attributed to the contribution of Mn(III)–phosphate complexes. The formation of Mn(III) in the presence of ligands (e.g., phosphate, pyrophosphate) was proved via UV–vis spectra and ligand concentration experiments. Based on results from the methyl phenyl sulfoxide (PMSO) probe and metal ion effect experiments, the possible involvement of high-valent manganese species (i.e., Mn(V)/Mn(VI)) was ruled out. Moreover, the results of radical quenching experiments indicated the negligible contribution of O2•– and •OH. Findings in this study advance the mechanistic understanding of a novel oxidation process by combining Mn(VII) with H2O2 for environmental decontamination

Kinetic and Mechanistic Insights into the Oxidative Transformation of Atrazine by Aqueous Fe(IV): Comparison with Hydroxyl and Sulfate Radicals

This study explored the oxidative transformation of atrazine (ATZ) by an aqueous iron­(IV)–oxo complex (Fe­(IV)) formed through ozonation of Fe­(II) and compared it to ATZ oxidation by •OH and SO4•– generated by ultraviolet (UV) irradiation of H2O2 and peroxydisulfate (PDS), respectively. The second-order rate constant between Fe­(IV) and ATZ was estimated to be greater than (5.18 ± 0.3) × 105 M–1 s–1 at pH 3, which was markedly higher than the reactivity of Fe­(IV) toward various water matrices. Consequently, Fe­(IV) achieved the most effective selective abatement of ATZ, compared with •OH- and SO4•–-mediated processes. Moreover, in the Fe­(II)/O3 system, we identified six products of ATZ and grouped them into three types: dealkylation (desethyl-atrazine [DEA] and desisopropyl-atrazine), alkylic-oxidation (atrazine amide [CDIT] and 2-hydroxy-4-(2-hydroxy-ethylamino)-6-isopropylamino-s-triazine), and dechlorination-hydroxylation (N-(4-hydroxy-6-(isopropylamino)-1,3,5-triazin-2-yl) acetamide and deethylhydroxyatrazine) products. These products also constituted the primary outcomes of ATZ in the UV/H2O2 and UV/PDS systems. Mechanism analysis revealed that Fe­(IV) and SO4•– triggered the dealkylation of ATZ by electron transfer, whereas •OH initiated dealkylation by H-atom abstraction, which resulted in the reactive oxidant nature-dependent distribution of specific ATZ oxidation products. Specifically, the [CDIT]/[DEA] ratio was quantified as 0.2, 0.7, and 2.3 in Fe­(IV)-, •OH-, and SO4•–-mediated oxidation processes, respectively. Accordingly, this ratio was developed as a sensitive internal probe for evaluating the relative contribution of Fe­(IV) and •OH/SO4•– during ATZ oxidative abatement

Oxidation of Phenolic Endocrine Disrupting Chemicals by Potassium Permanganate in Synthetic and Real Waters

In this study, five selected environmentally relevant phenolic endocrine disrupting chemicals (EDCs), estrone, 17β-estradiol, estriol, 17α-ethinylestradiol, and 4-<i>n</i>-nonylphenol, were shown to exhibit similarly appreciable reactivity toward potassium permanganate [Mn­(VII)] with a second-order rate constant at near neutral pH comparable to those of ferrate­(VI) and chlorine but much lower than that of ozone. In comparison with these oxidants, however, Mn­(VII) was much more effective for the oxidative removal of these EDCs in real waters, mainly due to the relatively high stability of Mn­(VII) therein. Mn­(VII) concentrations at low micromolar range were determined by an ABTS [2,2-azino-bis­(3-ethylbenzothiazoline)-6-sulfonic acid diammonium] spectrophotometric method based on the stoichiometric reaction of Mn­(VII) with ABTS [Mn^VII + 5ABTS → Mn^II + 5ABTS^•+] forming a stable green radical cation (ABTS^•+). Identification of oxidation products suggested the initial attack of Mn­(VII) at the hydroxyl group in the aromatic ring of EDCs, leading to a series of quinone-like and ring-opening products. The background matrices of real waters as well as selected model ligands including phosphate, pyrophosphate, NTA, and humic acid were found to accelerate the oxidation dynamics of these EDCs by Mn­(VII). This was explained by the effect of in situ formed dissolved Mn­(III), which could readily oxidize these EDCs but would disproportionate spontaneously without stabilizing agents