Dichloride Anion Radical Research Articles

Chlorination mechanism of benzene series in aqueous system under the combined action of Cl- and multiple free radicals

In this study, non-targeted analysis revealed that the Fe2+/perodisulfate/Cl- system degraded aniline (AN) and nitrobenzene (NB), yielding 7 types and 4 types of aromatic chlorides, respectively. In order to explore their chlorination mechanism and the influence of different functional groups, various reactions (radical adduct formation (RAF), hydrogen atom abstraction (HAA) and single electron transfer (SET)) of benzene series with various functional group with sulfate radical (SO4·-), hydroxyl radical (·OH), chlorine radical (·Cl) and dichloride anion radicals (Cl2·-) were explored by Gibbs free energy (ΔG), and the subsequent reactions of SET and HAA products (organic free radical) were innovatively explored by ΔG. This study revealed that the reaction between benzene compounds containing electron-donating groups and ·Cl was dominated by HAA rather than RAF; the reaction between benzene compounds containing electron-withdrawing groups and ·Cl was dominated by RAF. Aromatic compounds containing electron-donating groups can undergo SET reaction and generate aromatic chlorides in the presence of O2 and Cl-. Combined with the product analysis, it was found that the HAA reaction of aromatic compounds will lead to the obvious formation of biphenyl compounds and aromatic chlorides in the presence of Cl-. Compared with the conditions of RAF of ·Cl and chlorination of SET products, the chlorination reaction between HAA products and Cl- is ubiquitous, which is more likely to be the key to the formation of aromatic chlorides in mixed systems. This study provides a theoretical basis for further study on the formation risk of chlorinated products in advanced oxidation process.

Oxidation of simulated wastewater by Fe2+-catalyzed system: The selective reactivity of chlorine radicals and the oxidation pathway of aromatic amines

Aromatic amines (AAs), a characteristic pollutant with electron-donating groups in textile industry, having high reactivity with reactive chlorine free radicals, is probably the precursor of chlorinated aromatic products in advanced oxidation treatment. In this study, Fe2+/peroxydisulfate (PDS)/Cl- and Fe2+/H2O2/Cl-systems were used to treat four kinds of AAs (5-Nitro-o-toluidine (NT), 4-Aminoazobenzol (AAB), O-Aminoazotoluene (OAAT), 4,4′-Methylene-bis(2-chloroaniline) (MBCA)) in simulated wastewater, and the selectivity of various reactive species to AAs, the oxidation law and pathway of AAs were explored. The results showed that dichloride anion radical (Cl2·-) could effectively oxidize four AAs, and chlorine radical (·Cl) was strongly reactive to AAB and MBCA, especially MBCA. The largest f – (Fukui function) of MBCA is 0.0822, which is the lowest of the four AAs, so ·Cl might be more sensitive to electrophilic point than hydroxyl radical (·OH). The oxidation pathway of NT and MBCA showed that ·Cl mainly played the role of electron transfer to AAs instead of generating chlorinated products, but the addition of ·OH to –NH2 generated aromatic nitro compounds with higher toxicity than NT and MBCA. Therefore, the electron transfer of ·Cl and Cl2·- could not only improve the removal of AAs but also reduce the generation of toxic products. This study found that the reactivity of reactive chlorine free radicals was not necessarily related to chlorination, which provided a theoretical basis for the further studies into the formation mechanism of chlorination products.

Formation and transformation of reactive species in the Fe2+/peroxydisulfate/Cl− system

The influence of Cl− on the formation mechanism of active components is often neglected in the Fe2+/peroxydisulfate (PDS) system containing a large amount of ferryl ion reactive specie (Fe(Ⅳ)). In the current investigation, the effects of Cl− concentration on the removal of methyl phenyl sulfoxide (PMSO), the formation of methyl phenyl sulfone (PMSO2), the transformation of reactive species and oxidation products were investigated under different reaction conditions that included Fe2+ dosage, PDS dosage, and pH0. The results showed that Cl− complexing Fe2+ increased the formation path of sulfate radical (SO4·−) in the Fe2+/PDS system. Fe2+ dosage and pH0 value affected the content and morphology of Fe2+-Cl− complex, thus affecting the composition of reactive species. According to the experiment of free radical steady-state concentration, it was found that low concentration of Cl− reacted with SO4·− and increased the steady-state concentration of chlorine radicals (8.09 × 10−13 M [·Cl]ss at 1.41 mM Cl−), while at high concentration of Cl−, the contents of SO4·−, hydroxyl radical (·OH) and dichloride anion radicals (Cl2·−) increased and the contents of Fe(Ⅳ) and ·Cl decreased. ·Cl had strong reactivity with PMSO, and PMSO and its oxidation products were chlorinated under the combined action of ·Cl and Cl2·−. This work reveals the reaction mechanism and environmental application risks of Fe2+/PDS technology and lays the groundwork for subsequent industrial application of Fe2+/PDS system.

Treatment of simulated textile sludge using the Fenton/Cl− system: The roles of chlorine radicals and superoxide anions on PAHs removal

The main content of this work is to investigate the removal of polycyclic aromatic hydrocarbons (PAHs: phenanthrene, anthracene, and fluoranthene) from simulated sludge solid phase employing an Fenton/Cl− system under various Cl− contents and pH values. The steady-state concentrations of the hydroxyl, chlorine, and dichloride anion radicals ([·OH]ss, [·Cl]ss, and [Cl2·-]ss) in heterogeneous system were first measured using tert-butanol, nitrobenzene, and benzoic acid. The outcomes exhibited that increasing the Cl− content from 50 to 2000 mg/L (pH = 3.0) or raising the pH from 3.0 to 5.0 (1000 mg/L Cl−) caused [·OH]ss to continuously decrease and [Cl2·-]ss and the concentration of superoxide anions (HO2·/O2·-) to continuously increase. When the pH was 3.0 and the Cl− concentration was 1000 mg/L, [·Cl]ss had a maximum value of 9.27 × 10−14 M. Combining the results of PAH removal, radical quenching, and product analysis, it was found that ·Cl in the Fenton/Cl− system promoted the oxidative degradation of phenanthrene without forming chlorination byproducts. Furthermore, HO2·/O2·- was helpful in removing anthracene and fluoranthene. Under the environment of high Cl− content (≥1000 mg/L), PAHs could be removed more effectively by using HO2·/O2·-. This investigation underpins further study on the regulation of reactive species and the efficient degradation of target organic matter in Fenton/Cl− system, and provides a basis for studying the formation of chlorinated or toxic byproducts in the process of treating textile dyeing sludge by Fenton.

Comparison of the Fe2+/H2O2 and Fe2+/PMS systems in simulated sludge: Removal of PAHs, migration of elements and formation of chlorination by-products

In this study, polycyclic aromatic hydrocarbons (PAHs) at practical concentrations in the simulated sludge treated by the Fe2+/H2O2 and Fe2+/peroxymonosulfate (PMS) systems were evaluated in terms of the PAHs (phenanthrene, anthracene, fluoranthene) removal, element migration, Cl− effect, and chlorination by-product formation. The results indicated that according to the removal rate of PAHs, the optimal dosage of the Fe2+/PMS system (∑PAHs removal rate was 64.66 ± 2.82 %) was 1/30 of that for the Fe2+/H2O2 system (∑PAHs removal rate was 78.63 ± 0.38 %). The elemental contents in the simulated sludge were mainly affected by the extent of advanced oxidation and the amount of generated iron flocs. By studying the PAHs removal, free chlorine formation, total organochlorine content, and PAHs products in Fe2+/H2O2/Cl- and Fe2+/PMS/Cl- systems, it was found that chlorine radicals (·Cl) had high reactivity with phenanthrene and fluoranthene, whereas dichloride anion radicals (Cl2·-) exhibited the opposite behavior. Furthermore, PAHs were oxidized by ·Cl and hydroxyl radical in the Fe2+/H2O2/Cl- system, whereas PAHs and their products were chlorinated by free chlorine and ·Cl in the Fe2+/PMS/Cl- system to six chlorinated by-products such as Cl-PAHs (9-Cl-phenanthrene, 2-Cl-anthracene, 9,10-Cl2-anthracene, 3-Cl-fluoranthene). These results provide some useful suggestions for the safe advanced oxidation process treatment of textile dyeing sludge.

Temperature dependence of the rate constant for hydrogen atom reaction with Cl 2 −• in water by pulse radiolysis of aqueous HCl solution

Abstract The temperature dependence of the rate constant for the reaction of dichloride anion radical ( Cl 2 - • ) with atomic hydrogen (H•) in water up to 75 °C has been determined by pulse radiolysis of deaerated 0.1 M HCl solution. The room temperature value is (6.1±0.6)×109 M−1 s−1. The activation energy of (13.2±0.6) kJ mol−1 is less than 16.7 kJ mol−1, expected for the diffusion-controlled reaction. Based on the temperature dependence of the rate constant for the reactions H•+ Cl 2 - • and H•+Cl2, derived in this work, and on that reported earlier ( Szala-Bilnik et al., 2014 ) for Cl 2 - • + Cl 2 - • , we show that a value of (10±2) M−1 s−1 determined by Hartig and Getoff (1982) for k (H•+H2O) in water at 25 °C is overestimated by at least two orders of magnitude.

Photoinduced orientational order of dichloride anion radicals

The photo-orientation of dichloride anion radicals (Cl2−·) in a glassy solution of 5 M LiCl is discussed. The quantitative characteristics of orientation of paramagnetic molecules were determined using the anisotropy of optical absorption and the angular dependence of the EPR spectrum. The orientational distribution function of ordered anion radicals was determined by joint computer modeling of the EPR spectrum recorded at different directions of the symmetry axis of a sample relative to the magnetic field of a spectrometer. It was found that the value of the order parameter (−0.1 ± 0.01), calculated from the orientational distribution function coincides with the value obtained under the measurements of the linear dichroism in the range of the detection error (−0.12 ± 0.01).

Electric charge distribution in proteins and ionic strength dependence of reaction rate.

The ionic strength dependence of the reaction rate between protein and dichloride anion radical has been investigated by flash photolysis of aqueous chloride-containing lysozyme, ribonuclease A, or insulin. The rate constant for the reaction of lysozyme or ribonuclease A with dichloride anion radicals decreases with increasing ionic strength, while it increases for insulin. The dependence was found to obey an equation derived from the theory of Debye and Hückel or the equation of Wherland and Gray for lysozyme within experimental errors. For ribonuclease A, however, it deviates largely from these equations. In the case of insulin a moderate deviation was observed. The different behavior in the ionic strength dependence is discussed in terms of the electric charge distribution in the protein molecules.

Comparison of Reactivities of Dibromide Anion Radical and Dichloride Anion Radical in Neutral Aqueous Solution

Abstract Rate constants of reactions of dibromide anion radical with some aliphatic dipeptides or unsaturated compounds including pyrimidine bases have been determined by flash photolysis. Difference in activation energy between, dibromide and dichloride anion radicals has been estimated by comparing rate constants obtained for common substrates.

Rates of reactions of some aqueous free radicals with platinum-ammine complexes using pulse radiolysis

The fast reaction technique of pulse radiolysis in conjunction with UV- visible absorption detection was used to determine the rate of reactions of hydrated electron, hydrogen atom, hydroxyl radical and dichloride anion radical with tetraammineplatinum(II) perchlorate and with trans- dihydroxotetraammineplatinum(IV) perchlorate complexes. Generally these reactions proceed at near diffusion-controlled rates. The second-order rate constant for the reaction of e aq − , H, OH and Cl 2 − radical with the Pt(II) complex are (1.9±0.1)·1010 M−1·s−1, (2.8±0.3)·1010 M−1·s−1, (6.6±0.4)·109 M−1·s−1 and (9±1)·109 M−1·s−1, respectively. The rate constant for the reaction of e aq − with the Pt(IV) complex is (4.9±0.3)·1010 M−1·s−1, however, H atom and OH radical reactions proceed at relatively slower rates.

A pulse radiolysis study of tetraammineplatinum(II) complex ion in aqueous chloride media

The reaction of dichloride anion radical with tetraammineplatinum(II) ion has been studied in aqueous, acidic solution using the fast-reaction technique of pulse radiolysis in conjunction with UV-visible absorption detection. The second-order rate constant for the reaction of Cl . 2 radical with the platinum(II) complex is calculated to be (9±1) × 10 9 dm 3·mol -1·s -1, and the reaction leads to products which absorb strongly in the region of 250–350 nm. Very similar spectral features arise from the reaction of hydroxyl radical and Pt(NH 3) 2+ 4 in the presence of low concentrations of free chloride ion. The transients are proposed to be platinum(III) chloro species, and the interrelationships between the species are discussed.

Determination of Rate Constants for Reactions of Bichloride Anion Radical with Some Dipeptides in Aqueous Solution of KCl and K2S2O8 by Flash Photolysis

Abstract Determination of rate constants for reactions of dichloride anion radical was conducted by conventional flash photolysis of aqueous solutions of KCl and K2S2O8, where no participation of HOCL−· is expected in decay kinetics of dichloride anion radical. The optimum conditions found for the determination are 0.1 mol dm−3 KCl and 10−4 mol dm−3 K2S2O8. Under the present experimental conditions, S2O82− serves to convert chloride ion to dichloride anion radical through reaction with hydrated electron produced by photolysis of chloride ion. For glycyltryptophan, the competition method was employed, because its transient absorption overlaps the absorption due to dichloride anion radical. The rate constants determined are almost the same as those obtained in N2O-saturated aqueous solution of KCl (1 mol dm−3). The reactivity of dipeptides toward dichloride anion radical is discussed.

Reactions of Dichloride Anion Radical with Nucleosides, Nucleotides, and Polynucleotides

Abstract Rate constants for reactions of dichloride anion radical with nucleosides, nucleotides, and polynucleotides were determined in neutral aqueous solutions of potassium chloride by the conventional flash photolysis. The reactivities of these compounds toward the anion radical are in the order: bases>nucleosides>nucleotides>polynucleotides. This trend is similar to that observed with the corresponding reactions with hydroxyl radical. A comparison of the reactivities of nucleosides, nucleotides, and polynucleotides toward dichloride anion radical with those toward hydroxyl radical has revealed that the reactivities of these compounds are governed mainly by their base moiety. This trend in the reactivities is discussed in terms of steric effect.

Transient Intermediate Produced from 5-Aminouracil in Reaction with Dichloride Anion Radical

Abstract A transient absorption, which is relatively long-lived, was found in a flash photolysis of aqueous potassium chloride containing 5-aminouracil. The transient absorption with a peak at about 335 nm was assigned to an intermediate produced from 5-aminouracil through a one-electron oxidation by dichloride anion radical. For the intermediate, a possible structure is proposed to explain its long life-time. On the basis of the transient absorption, a determination of the rate constant for the reaction of 5-aminouracil with dichloride anion radical was carried out by use of a competition kinetics. The value of (2.9±0.2)×108 dm3 mol−1 s−1 was obtained as the rate constant on the basis of rate constants of several reference compounds. By comparing the values obtained by the competition method with those estimated by a direct analysis of the decay rate of dichloride anion radical, the validity of the competition method was examined.

Reactions of dichloride anion radicals with pyrimidine and its derivatives.

Rate constants for the reactions of dichloride anion radicals with pyrimidine and its derivatives were determined by a conventional flash photolysis. Kinetic treatment was carried out by assuming that second-order self decay of the anion radicals and the reaction with a substrate proceed simultaneously. Values of the rate constants were found within 1.1 × 107 to 4.1 × 109 M-1 s-1; the lowest reactivity was observed for pyrimidine and the highest for 2, 4, 6triaminopyrimidine. Comparison of the rate constants with those for hydroxyl radicals suggests that the dichloride anion radicals undergo a different reaction with pyrimidine bases from that of the hydroxyl radicals. A transient absorption due to an intermediate produced in the reaction with the anion radicals was observed for 5-aminouracil. This is only a case where relatively long-lived absorption was observed. The absorption was used to determine the rate constants for the reactions with the anion radicals.

Reactions of dichloride anion radicals with aliphatic peptides in aqueous solutions.

Rate constants for the reactions of dichloride anion radicals with aliphatic peptides were determined by a conventional flash photolysis of 1 M solutions of potassium chloride containing aliphatic peptides. The rate constants were found to increase with increasing number of C-H bond. Partial rate constants were assigned to each C-H bond of the aliphatic peptides, as estimated for the reactions of hydroxyl radicals with the same substrates. Trend in the partial rate constants and the effect of a protonated amino group on the reactivity indicate a reaction mechanism, hydrogen atom abstraction, similar to hydroxyl radicals.

Some reactions of the dichloride anion radical

Measurements by pulse radiolysis give rate constants for the reaction Cl 2 − + HO 2 of k=(1.0±0.1)×10 9 dm 3 mol −1 s −1, for Cl 2 −+ Cl 2 − (at ionic strength 0.2 mol dm −3) of 2 k=(4.0±0.4) ×10 9 dm 4 mol −1 s −1 and for Cl 2+ H of k=(7±1)×10 9 dm 3 mol −1 s −1.