Kinetic model for formation of DMPO-OH in water under ultrasonic irradiation using EPR spin trapping method

The rate of the formation of the 2-hydroxy-5,5-dimethyl-1-pyrrolidinyloxy (DMPO-OH) radical in water during ultrasonic irradiation was evaluated both experimentally and theoretically. The hydroxyl radical (OH radical) was indirectly detected using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as the spin trapping compound, and the generated DMPO-OH by the reaction between the OH radical and DMPO was measured by an electron paramagnetic resonance. The rate of change in the concentration of the DMPO-OH decreased with time, suggesting that not only the formation reaction of DMPO-OH but also the degradation reaction would take place by ultrasonic irradiation. The formation rate of the DMPO-OH was higher with ultrasonic power intensity and lower with reaction temperature. Based on the experimental results, a kinetic model for the formation of the DMPO-OH was proposed by considering the formation reaction, the ultrasonic degradation, and spontaneous degradation of DMPO-OH. The model well described the effect of the ultrasonic power intensity and the reaction temperature on the formation rate of DMPO-OH. The rate of the formation of the DMPO-OH was evaluated with the aid of the kinetic model.     

Kinetic model for the radical degradation of tri-halonitromethane disinfection byproducts in water

The halonitromethanes (HNMs) are byproducts of the ozonation and chlorine/chloramine treatment of drinking waters. Although typically occurring at low concentrations HNMs have high cytotoxicity and mutagenicity, and may therefore represent a significant human health hazard. In this study, we have investigated the radical based mineralization of fully-halogenated HNMs in water using the congeners bromodichloronitromethane and chlorodibromonitromethane. We have combined absolute reaction rate constants for their reactions with the hydroxyl radical and the hydrated electron as measured by electron pulse radiolysis and analytical measurements of stable product concentrations obtained by ⁶⁰Co steady-state radiolysis with a kinetic computer model that includes water radiolysis reactions and halide/nitrogen oxide radical chemistry to fully elucidate the reaction pathways of these HNMs. These results are compared to our previous similar study of the fully chlorinated HNM chloropicrin. The full optimized computer model, suitable for predicting the behavior of this class of compounds in irradiated drinking water, is provided.     

Towards a Non Empirical Kinetic Model for the Lifetime Prediction of Polyethylene Pipes Transporting Drinking Water

A kinetic model has been elaborated to predict the lifetime of polyethylene pipes transporting slightly pressurized (3–12 bars) drinking water disinfected by free radical reagents. This model is composed of three levels: i) A system of differential equations, derived from a mechanistic scheme for radical chain oxidation in the presence of free radical reagents, giving access to the spatial distribution (in the pipe wall) of oxidation products and stabilizer concentration; ii) Equations allowing to predict the profiles of average molar masses from the spatial distribution of chain scissions and crosslinking events; iii) An empirical creep equation and a failure criterion derived from regression curves obtained in pure water (without disinfectant). It is assumed that the chemical degradation modifies only the time to transition between ductile and brittle regimes of failure, and that this time is linked to the weight average molar mass according to the classical power law. By superimposing these three levels, it is possible to predict the time to failure under the coupled effects of pressure and chemical degradation. This model is successfully applied to the case of chlorine dioxide.     

Degradation of a model naphthenic acid, cyclohexanoic acid, by vacuum UV (172 nm) and UV (254 nm)/H2O2

The mechanism of hydroxyl radical initiated degradation of a typical oil sands process water (OSPW) alicyclic carboxylic acid was studied using cyclohexanoic acid (CHA) as a model compound. By use of vacuum ultraviolet irradiation (VUV, 172 nm) and ultraviolet irradiation in the presence of hydrogen peroxide UV(254 nm)/H(2)O(2), it was established that CHA undergoes degradation through a peroxyl radical. In both processes the decay of the peroxyl radical leads predominantly to the formation of 4-oxo-CHA, and minor amounts of hydroxy-CHA (detected only in UV/H(2)O(2)). In UV/H(2)O(2), additional 4-oxo-CHA may also have been formed by direct reaction of the oxyl radical with H(2)O(2). The oxyl radical can be formed during decay of the peroxyl-CHA radical or reaction of hydroxy-CHA with hydroxyl radical. Oxo- and hydroxy-CHA further degraded to various dihydroxy-CHAs. Scission of the cyclohexane ring was also observed, on the basis of the observation of acyclic byproducts including heptadioic acid and various short-chain carboxylic acids. Overall, the hydroxyl radical induced degradation of CHA proceeded through several steps, involving more than one hydroxyl radical reaction, thus efficiency of the UV/H(2)O(2) reaction will depend on the rate of generation of hydroxyl radical throughout the process. In real applications to OSPW, concentrations of H(2)O(2) will need to be carefully optimized and the environmental fate and effects of the various degradation products of naphthenic acids considered.     

Development of Flow Analytical Systems for Monitoring Thiocyanate Biodegradation in Waste Waters

ABSTRACT

Metallurgical waste waters have a very complex composition. Different reactions take place in such waters. Among them, the reaction of pyretic materials with free cyanide results in the production of thiocyanate, another hazard to the aqueous media. Biological cleanup (bioremediation) is one of the methods to eliminate SCN of waste waters and, consequently, it is necessary to develop sensitive and convenient methods for thiocyanate analysis in this bioprocess in order to assure environmental quality control.

In the work presented here different spectrophotometric flow systems based on the reaction between Fe(III) and SCN are studied to control thiocyanate in crude and biologically treated coke plant waster waters, using a conventional flow cell and a fibre optical continuous flow system. Chemical and physical parameters of the flow systems were studied. A simple, fast and sensitive continous flow system with optical fibres is proposed for monitoring thiocynate degradation in a waste water biological reactor.     

Retaining and recovering enzyme activity during degradation of TCE by methanotrophs

To determine if compounds added during trichloroethylene (TCE) degradation could reduce the loss of enzyme activity or increase enzyme recovery, different compounds serving as energy and carbon sources, pH buffers, or free radical scavengers were tested. Formate and formic acid (reducing power and a carbon source), as well as ascorbic acid and citric acid (free radical scavengers) were added during TCE degradation at a concentration of 2 mM. A saturated solution of calcium carbonate was also tested to address pH concerns. In the presence of formate and methane, only calcium carbonate and formic acid had a beneficial effect on enzyme recovery. The calcium carbonate and formic acid both reduced the loss of enzyme activity and resulted in the highest levels of enzyme activity after recovery.     

α-氰基苄基碳负离子钠盐与碳酸二乙酯的单电子转移反应动力学和机理

测定了α-氰基苄基碳负离子钠盐与碳酸二乙酯缩合反应产物的结构及其分布,反应中间体的EPR谱,反应过程中产物和溶剂的CIDNP效应和反应动力学,为这一缩合反应提出了单电子转移-负离子自由基分解-自由基偶合的非链式自由基机理     

Free-radical destruction of beta-lactam antibiotics in aqueous solution

Many pharmaceutical compounds and metabolites are being found in surface and ground waters, indicating their ineffective removal by conventional wastewater treatment technologies. Advanced oxidation/reduction processes (AO/RPs), which utilize free-radical reactions to directly degrade chemical contaminants, are alternatives to traditional water treatment. This study reports the absolute rate constants for reaction of three beta-lactam antibiotics (penicillin G, penicillin V, amoxicillin) and a model compound (+)-6-aminopenicillanic acid with the two major AO/RP reactive species: hydroxyl radical ((*)OH) and hydrated electron (e(-)aq). The bimolecular reaction rate constants (M(-1) s(-1)) for penicillin G, penicillin V, amoxicillin, and (+)-6-aminopenicillanic acid for (*)OH were (7.97 +/- 0.11) x 10(9), (8.76 +/- 0.28) x 10(9), (6.94 +/- 0.44) x 10(9), and (2.40 +/- 0.05) x 10(9) and for e(-)aq were (3.92 +/- 0.10) x 10(9), (5.76 +/- 0.24) x 10(9), (3.47 +/- 0.07) x 10(9), and (3.35 +/- 0.06) x 10(9), respectively. To provide a better understanding of the decomposition of the intermediate radicals produced by hydroxyl radical reactions, transient absorption spectra were observed from 1 to 100 micros. In addition, preliminary degradation mechanisms and major products were elucidated using (137)Cs gamma irradiation and LC-MS. These data are required for both evaluating the potential use of AO/RPs for the destruction of these compounds and studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime.     

Atmospheric aqueous-phase photoreactivity: correlation between the hydroxyl radical photoformation and pesticide degradation rate in atmospherically relevant waters

In the present study, we investigated the correlation between the hydroxyl radical formation rate (R_˙OH) and the degradation of a pesticide (mesotrione) in synthetic cloud water solutions and in two real atmospheric cloud waters collected at the top of puy de Dôme station (France). Using terephthalic acid as the hydroxyl radical chemical probe, we established the linear correlation between the photogenerated hydroxyl radical under polychromatic wavelengths and the pesticide degradation rate: (m s^?1) = (1.61 ± 0.15) × 10^?1(m s^?1). Moreover, the formation rate of hydroxyl radical in two natural cloud waters was estimated considering H₂O₂ and NO₃^? and the difference between the predicted values and those experimentally obtained could be attributed to the presence of other photochemical sources: iron‐complexes and total organic matter. The organic constituents could play a dual role of sources and scavengers of photoformed hydroxyl radicals in the aqueous phase.     

Determining calcium carbonate neutralization kinetics from experimental laboratory data

In the framework of a research aimed at estimating the performance and lifetime of porous filters filled with marble powder and used to neutralize acid waters, we propose a mathematical model for determining the calcium carbonate reaction kinetics from some experimental data. In particular we show how to determine the order of the reaction and the reaction rate when calcium carbonate is immersed in a HCl solution. These parameters are evaluated by means of a fitting procedure based on least square methods. The experiments are performed using CaCO₃ in the form of a slab and powder and measuring (by means of BET analysis) the specific reaction surface.     

The carbonate radical: its reactivity with oxygen, ammonia, amino acids, and melanins

The carbonate radical (CO 3 (*-)) is of importance in biology and chemistry. We used pulse radiolysis to generate the CO 3 (*-) radical and show there is no reaction with oxygen. However, in the presence of ammonia the CO 3 (*-) radical is removed by NO (*), which itself arises from the scavenging of NH 2 (*) by oxygen, and the mechanism of this process is reported. The CO 3 (*-) radical shows complex decay patterns in the presence of ammonia, which can be understood as a balance between the radical-radical reaction CO 3 (*-) + CO 3 (*-) and CO 3 (*-) + NH 2 (*) (the amino radical). Also, we report reactivity with glycine and alanine and with melanin models. The CO 3 (*-) reacts with both dopa-melanin (DM, a model of black eumelanin) and with cysteinyl-dopa-melanin (CDM, a model of red/blond phaeomelanin). However, the reaction rate constant is much higher with CDM than with DM.     

Contribution of the photo-Fenton reaction to hydroxyl radical formation rates in river and rain water samples.

The hydroxyl radical (OH radical) formation rates from the photo-Fenton reaction in river and rain water samples were determined by using deferoxamine mesylate (DFOM), which makes a stable and strong complex with Fe(III), resulting in a suppression of the photo-Fenton reaction. The difference between the OH radical formation rates with and without added DFOM denotes the rate from the photo-Fenton reaction. The photoformation rates from the photo-Fenton reaction were in the range of 0.7 - 45.8 x 10(-12) and 2.7 - 32.3 x 10(-12) M s(-1) in river and rain water samples, respectively. A strong positive correlation between the OH radical formation rate from the photo-Fenton reaction and the amount of fluorescent matter in river water suggests that fluorescent matter, such as humic substances, plays an important role in the photo-Fenton reaction. In rain water, direct photolysis of hydrogen peroxide was an important source of OH radicals as well as the photo-Fenton reaction. The contributions of the photo-Fenton reaction to the OH radical photoformation rates in river and rain water samples were in the ranges of 2 - 29 and 5 - 38%, respectively. Taking into account the photo-Fenton reaction, 33 - 110 (mean: 80) and 42 - 110 (mean: 84)% of OH radical sources in river and rain water samples, respectively, collected in Hiroshima prefecture were elucidated.     

Kinetics of the Production of Castor Oil Maleate through the Autocatalyzed Thermal Reaction and the Free Radical Reaction

Castor oil maleate is used in drying oils, water‐soluble paints, healthcare products, synthetic lubricants, and as a monomer in several polymers. This maleate can be produced by a direct autocatalyzed reaction between castor oil and maleic anhydride. However, the reaction rate can be increased using a free radical catalyst. In this work, the influence of the concentration of benzoyl peroxide (BPO) and temperature in the kinetics and productivity of castor oil maleate was studied. The optimal operating condition was found at 120°C, 1 mol of maleic anhydride/mol of castor oil, and 0.003 mol of BPO/mol of castor oil, yielding 90.0% of castor oil maleate in 90 min. A kinetic model was developed, and the model parameters were estimated both for the thermal autocatalyzed reaction and the free radical reaction.     

Chemical reactions occurring in the thermal treatment of PC/PMMA blends

The chemical reactions occurring in the thermal treatment of bisphenol-A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) blends have been investigated by nuclear magnetic resonance (NMR), mass spectrometry (MS), size exclusion chromatography (SEC), and thermogravimetry (TG). Our results suggest that in the melt-mixing of PC/PMMA blends, at 230°C, no exchange reactions occur and that only the depolymerization reaction of PMMA has been observed. In the presence of an ester-exchange catalyst (SnOBu₂), an exchange reaction was found to occur at 230°C, but no trace of PC/PMMA graft copolymer has been observed. Instead, an exchange reaction between the monomer methyl methacrylate (MMA), generated in the unzipping of PMMA chains, and the carbonate groups of PC has been suggested. This is due to the diffusion of MMA at the interface or even into the PC domains, where it can react with PC producing low molar mass PC oligomers bearing methacrylate and methyl carbonate chain ends and leaving the undecomposed PMMA chains unaffected. The TG curves of PC/PMMA blends prepared by mechanical mixing and by casting from THF show two separated degradation steps corresponding to that of homopolymers. This behavior is different from that of a transparent film of PC/PMMA blend, obtained by solvent casting from DCB/CHCl₃, which shows a single degradation step indicating that the degradation rate of PC is increased by the presence of PMMA in the blend. The thermal degradation products obtained by DPMS of this blend consist of methyl methacrylate (MMA), cyclic carbonates arising from the degradation of PMMA and PC, respectively, and a series of open chain bisphenol-A carbonate oligomers with methacrylate and methyl carbonate terminal groups. The presence of the latter compounds suggests a thermally activated exchange reaction occurring above 300°C between MMA and PC. The presence of bisphenol-A carbonate oligomers bearing methyl ether end groups, generated by a thermally activated decarboxylation of the methyl carbonate end groups of PC, has also been observed among the pyrolysis products. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1873–1884, 1998     

Alkoxyl- and carbon-centered radicals as primary agents for degrading non-phenolic lignin-substructure model compounds

Lignin degradation by white-rot fungi proceeds via free radical reaction catalyzed by oxidative enzymes and metabolites. Basidiomycetes called selective white-rot fungi degrade both phenolic and non-phenolic lignin substructures without penetration of extracellular enzymes into the cell wall. Extracellular lipid peroxidation has been proposed as a possible ligninolytic mechanism, and radical species degrading the recalcitrant non-phenolic lignin substructures have been discussed. Reactions between the non-phenolic lignin model compounds and radicals produced from azo compounds in air have previously been analysed, and peroxyl radical (PR) is postulated to be responsible for lignin degradation (Kapich et al., FEBS Lett., 1999, 461, 115-119). However, because the thermolysis of azo compounds in air generates both a carbon-centred radical (CR) and a peroxyl radical (PR), we re-examined the reactivity of the three radicals alkoxyl radical (AR), CR and PR towards non-phenolic monomeric and dimeric lignin model compounds. The dimeric lignin model compound is degraded by CR produced by reaction of 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), which under N(2) atmosphere cleaves the α-β bond in 1-(4-ethoxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol to yield 4-ethoxy-3-methoxybenzaldehyde. However, it is not degraded by the PR produced by reaction of Ce(4+)/tert-BuOOH. In addition, it is degraded by AR produced by reaction of Ti(3+)/tert-BuOOH. PR and AR are generated in the presence and absence of veratryl alcohol, respectively. Rapid-flow ESR analysis of the radical species demonstrates that AR but not PR reacts with the lignin model compound. Thus, AR and CR are primary agents for the degradation of non-phenolic lignin substructures.     

Microsolvation pattern of the hydrated radical anion of uracil: U-(H2O)n (n = 3-5)

The microsolvation patterns of the uracil radical anion in water clusters U-(H2O)n with n ranging from 3 to 5 were investigated by the density functional theory approach. The electron detachment energies (VDE) of the stable anionic complexes with different numbers of hydration water are predicted. The linear dependence of the VDE value of the most stable anionic complexes with respect to the hydration number suggests the importance of the clustered waters in the microsolvation of the radical anion of the nucleobases. The formation of the water clusters is found to be necessary in the most stable conformers of the tri-, tetra-, and pentahydrated radical anion of uracil. The microsolvation pattern with three or more well-separated hydration water molecules in the first hydration layer is less stable than the arrangement with the waters in tight clusters. The charge transfer between the anionic uracil and the hydration water is high. Good agreement between the experimental and the theoretical vertical detachment energy yield in this study further demonstrates the practicability of the B3LYP/DZP++ approach in the study of radical anions of the DNA subunits.     

Applications of ionizing radiation to the remediation of materials contaminated with heavy metals and polychlorinated biphenyls

We have investigated the removal from water of heavy metals and chelated heavy metal compounds using electron beam and gamma radiation. Parameter analyses include the effect of dissolved oxygen and the influence of adding various buffers and radical scavengers. Complete removal (>99%) of mercury, lead and cadmium ions, both free and chelated within EDTA, was achieved using radiation doses ranging from 3–100 kGy. We have also studied the radiation induced degradation of polychlorinated biphenyls (PCBs) in aqueous-organic and aqueous micellar systems. Rates and extent of dechlorination have been quantified in different solution matrices; reaction by-products and intermediate species have been identified; and the influences of dissolved oxygen and pH have been evaluated. The presence of a carbonate buffer was observed to significantly enhance PCB dechlorination yields by reducing concentrations of H₃O⁺. Ionizing radiation was effective in degrading PCBs in micellar solutions but scavenging of e_aq⁻ by the surfactant lowered reaction efficiencies.     

Mechanism of hydroxyl radical-induced breakdown of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-d)

Oxidative transformations by the hydroxyl radical are significant in advanced oxidation processes for the breakdown of organic pollutants, yet mechanistic details of the reactions are lacking. A combination of experimental and computational methods has been employed in this study to elucidate the reactivity of the hydroxyl radical with the widely used herbicide 2,4-D (2,4-dichlorophenoxyacetic acid). The experimental data on the reactivity of the hydroxyl radical in the degradation of the herbicide 2,4-D were obtained from gamma-radiolysis experiments with both (18)O-labeled and unlabeled water. These were complemented by computational studies of the (.)OH attack on 2,4-D and 2,4-DCP (2,4-dichlorophenol) in the gas phase and in solution. These studies firmly established the kinetically controlled attack ipso to the ether functionality as the main reaction pathway of (.)OH and 2,4-D, followed by homolytic elimination of the ether side chain. In addition, the majority of the early intermediates in the reaction between the hydroxyl radical and 2,4-DCP, the major intermediate, were identified experimentally. While the hydroxyl radical attacks 2,4-D by (.)OH-addition/elimination on the aromatic ring, the oxidative breakdown of 2,4-DCP occurs through (.)OH addition followed by either elimination of chlorine or formation of the ensuing dichlorophenoxyl radical.     

Studying the photochemical fate of methyl parathion in natural waters under tropical conditions

This article discusses the degradation of methyl parathion (MP) in natural and sterilized waters. Experiments were prepared using natural waters gathered in two aquatic systems (Rio de Janeiro State, Brazil), ultra-pure water and humic water solution under different conditions (i.e. in the presence/absence of light, sterilized/no sterilize solutions). The exposition to sunlight was carried out using experimental bottles without headspace immersed in a swimming pool for temperature control. Natural waters results showed that the degradation kinetic of MP is of first order and the half-lives for lake water experiments, under direct sunlight and shade, were 4.41 and 6.89 days, respectively. The kinetic curve for MP degradation in river waters showed that there are no differences when samples were sterilized and placed (or not) under shade conditions, and the half-lives ranged from 5.37 to 2.75 days for sterilized river water/absence of sunlight and natural/presence of sunlight, respectively. Therefore, our results showed that photolysis plays, in addition to bio- and chemical degradation, an important role in the decomposition of MP in aquatic environments.     

Do hydroxyl radical-water clusters, OH(H2O)n, n = 1-5, exist in the atmosphere?

It has been speculated that the presence of OH(H2O)n clusters in the troposphere could have significant effects on the solar absorption balance and the reactivity of the hydroxyl radical. We have used the G3 and G3B3 model chemistries to model the structures and predict the frequencies of hydroxyl radical/water clusters containing one to five water molecules. The reaction between hydroxyl radical clusters and methane was examined as a function of water cluster size to gain an understanding of how cluster size affects the hydroxyl radical reactivity.