Electrochemical destruction of chlorophenoxy herbicides by anodic oxidation and electro-Fenton using a boron-doped diamond electrode

The degradation of herbicides 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in aqueous medium of pH 3.0 has been comparatively studied by anodic oxidation and electro-Fenton using a boron-doped diamond (BDD) anode. All solutions are totally mineralized by electro-Fenton, even at low current, being the process more efficient with 1 mM Fe²⁺ as catalyst. This is due to the production of large amounts of oxidant hydroxyl radical (OH) on the BDD surface by water oxidation and from Fenton’s reaction between added Fe²⁺ and H₂O₂ electrogenerated at the O₂-diffusion cathode. The herbicide solutions are also completely depolluted by anodic oxidation. Although a quicker degradation is found at the first stages of electro-Fenton, similar times are required for achieving overall mineralization in both methods. The decay kinetics of all herbicides always follows a pseudo first-order reaction. Reversed-phase chromatography allows detecting 4-chlorophenol, 4-chloro-o-cresol, 2,4-dichlorophenol and 2,4,5-trichlorophenol as primary aromatic intermediates of 4-CPA, MCPA, 2,4-D and 2,4,5-T, respectively. Dechlorination of these products gives Cl⁻, which is slowly oxidized on BDD. Ion-exclusion chromatography reveals the presence of persistent oxalic acid in electro-Fenton by formation of Fe³⁺-oxalato complexes, which are slowly destroyed by OH adsorbed on BDD. In anodic oxidation, oxalic acid is mineralized practically at the same rate as generated.     

Electrochemical degradation of 2,4,5-trichlorophenoxyacetic acid in aqueous medium by peroxi-coagulation. Effect of pH and UV light

Acidic aqueous solutions with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) concentrations up to 270 ppm in the pH range 2.0-6.0 at 35 °C can be rapidly degraded by peroxi-coagulation using an Fe anode and an O₂-diffusion cathode. 2,4,5-T and its products are then efficiently oxidized with OH radicals produced from Fenton's reaction between Fe²⁺ and H₂O₂ generated by the electrodes. Under pH regulation at low currents, more than 90% of organics are destroyed at pH 3.0, although its optimum pH is 4.0. Higher degradations are reached without pH regulation. Solutions with 2,4,5-T concentration ≤200 ppm are more rapidly depolluted under UV irradiation, because of the production of more OH from photo-Fenton reaction. Coagulation of products with the Fe(OH)₃ precipitate formed predominates when pH is regulated to 2.0 and 3.0 in the absence of UV light, whereas parallel mineralization is favored without pH regulation and under UV irradiation. The 2,4,5-T decay follows a pseudo first-order reaction, with the same rate constant in the presence and absence of UV light. 2,4,5-trichlorophenol, 2,5-dichlorohydroquinone, 4,6-dichlororesorcinol and 2,5-dihydroxy-p-benzoquinone have been identified and quantified as aromatic intermediates by reverse-phase chromatography. Chloride ions are released from the oxidation of these chlorinated products. The evolution of generated carboxylic acids, such as glycolic, glyoxylic, formic, malic, maleic, fumaric and oxalic, has been followed by ion-exclusion chromatography. The great stability of oxalic acid and its complexes with Fe³⁺ at pH regulated to 3.0 can explain that concentrated solutions can not be completely degraded.     

Immobilization of TiO2 on an ITO substrate to facilitate the photoelectrochemical degradation of an organic dye pollutant

In this study, we developed an immobilized TiO₂ semiconductor on an ITO glass substrate (TiO₂/ITO) and investigated its photocatalytic and electrochemical performance. The TiO₂/ITO samples were prepared via a spin-coating process followed by calcination and were used for the photocatalytic or electrochemical degradation of an organic dye pollutant. The measured photocatalytic performance was comparable to that reported in previous publications; however, a remarkable result was obtained in our electrochemical system. The formation of hydroxyl radicals (OH) strongly dominated the electrochemical system, which resulted in outstanding degradation performance. Therefore, we propose a commercializable photoelectrochemical system that can maximize the degradation of pollutants in wastewater treatment plants.     

Influence of hydrogen bonding upon the TiO2 photooxidation of isopropanol and acetone in aqueous solution

This study investigates the aqueous photocatalytic degradation of small polar organic compounds (SPOCs) that bear hydrogen-bonding capabilities but do not readily adsorb to the TiO₂ catalyst. The effect of pH on the TiO₂ surface hydroxyl speciation and surface acid/base equilibria was used to elucidate the possible role of hydrogen-bonding interactions in the degradation of acetone and isopropanol in aqueous TiO₂ photocatalytic systems. The kinetic parameters describing the decomposition of these two model compounds were obtained by gas chromatographic analysis of their photoreaction systems and interpreted on the grounds of the Brönsted acid/base properties of the TiO₂ surface speciation and solute hydrogen-bonding numerical scales. The results showed that the fastest initial degradation rates of acetone and isopropanol occurred in a pH range where the optimal conditions for adsorption through hydrogen bonding to the TiO₂ surface and optimum concentration of hydroxyl radicals (OH) coincide. The fastest degradation constants were observed at pH 6.04 and 8.61 for acetone and isopropanol, respectively. The hypothesis of hydrogen bonding to surface hydroxyl groups presented in this study challenges the common assumption that these model compounds do not adsorb to surface sites, and that their oxidative pathways of degradation only occur via homogeneous-phase reaction with free OH radicals.     

Photocatalytic mineralization of phenol catalyzed by pure and mixed phase hydrothermal titanium dioxide

The photocatalytic mineralization of phenol catalyzed by pure (anatase, rutile) and mixed phase hydrothermal TiO₂ was studied in aqueous solution employing different oxidative agents, H₂O₂ and O₂. In the case of H₂O₂, rutile particles, having large dimensions and high aspect ratio (size: 30–70 nm × 150–350 nm), display the highest catalytic activity due to their low tendency to recombine electrons and holes generated by UV irradiation. By using water dissolved gaseous O₂, the catalytic TiO₂ activity generally decreases and rutile displays the lowest efficacy. In fact, oxygen preferentially chemisorbs at the surface of the nanosized particles of anatase (5–15 nm) and acts as effective electron scavenger, inhibiting the electron-hole recombination. The number of electron and hole traps (Ti³⁺, O₂⁻ and O⁻) and the rate of formation of the short-lived hydroxyl radicals OH under UV irradiation, were evaluated by electron paramagnetic resonance (EPR). A correlation was suggested among the amount of the charge carrier centers, the rate of formation of OH radicals and the catalyst photoactivity. This confirms that the photocatalytic properties depend on the possibility that electrons and holes separately interact with the oxidative agents at the TiO₂ surface, inducing the formation of OH radicals.     

Electrochemical oxidation of aliphatic hydrocarbons promoted by inorganic radicals. I. OH radicals

The OH initiated oxidation of aliphatic hydrocarbons by the simultaneous electrochemical reduction of O₂ and of Fe(III) at controlled potential was investigated in the liquid phase over a Fe(III) concentration range 0.5–5 mM. OH radicals were generated by the reaction: Fe(II)+H₂O₂Fe(III)+^.OH+OH^– The compounds studied were the linear alkane hydrocarbons from C₅ to C₁₀ and 3-methyl pentane. The results showed that the ketones are the only reaction products and that the yields decrease with increasing number of carbonium atoms of the hydrocarbon. Decreasing yields were also observed with increasing Fe(III) concentration.     

The mechanism of the reaction of graphite oxide to reduced graphene oxide under ultraviolet irradiation

Under ultraviolet (UV) irradiation, the formation and reduction mechanism of reduced graphene oxide (rGO) layers prepared from graphite oxide (GO) sheets have been investigated. The effects of hydroxyl free radicals (HO), hydroxide ions (OH⁻) or hydrazine molecules (N₂H₄) are considered. It has been demonstrated that the HO radicals, UV-induced from H₂O₂ molecules in aqueous solution, cannot reduce GO into rGO, but to some extent oxidize and damage the GO structure, simultaneously accompanied by a slight increase of acidity, possibly because of a release of H⁺ from H₂O₂ and GO during the reaction. The existence of OH⁻ ions or N₂H₄ instead of H₂O₂ molecules enables GO sheets to be quickly reduced into rGO due to the effect of photo-induced electrons on the GO sheets. The electrons are photogenerated mainly from OH⁻ or N₂H₄ in a GO aqueous dispersion. Because GO in diluted N₂H₄ aqueous solution can be photo-reduced almost completely within half an hour at room temperature, it is inferred that many more electrons are generated from N₂H₄ than from OH⁻.     

Oxidation of herbicides by in situ synthesized hydrogen peroxide and fenton’s reagent in an electrochemical flow reactor: study of the degradation of 2,4-dichlorophenoxyacetic acid

This paper reports an investigation of H₂O₂ electrogeneration in a flow electrochemical reactor with RVC cathode, and the optimization of the O₂ reduction rate relative to cell potential. A study of the simultaneous oxidation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by the in situ electrogenerated H₂O₂ is also reported. Experiments were performed in 0.3 M K₂SO₄ at pH 10 and 2.5. Maximum hydrogen peroxide generation rate was reached at −1.6 V versus Pt for both acidic and alkaline solutions. Then, 100 mg L⁻¹ of 2,4-D was added to the solution. 2,4-D, its aromatic intermediates such as chlorophenols, chlororesorcinol and chlorinated quinone, as well as TOC were removed at different rates depending on pH, the use of UV radiation and addition of Fe(II). The acidic medium favored the hydroxylation reaction, and first order apparent rate constants for TOC removal ranged from 10⁻⁵ to 10⁻⁴ s⁻¹. In the presence of UV and iron, more than 90% of TOC was removed. This value indicates that some of the intermediates derived from 2,4-D decomposition remained in solution, mainly as more biodegradable light aliphatic compounds.     

Combination of Ozone with Activated Carbon as an Alternative to Conventional Advanced Oxidation Processes

The objective of this study was to compare the efficiency of O₃/granular activated carbon (GAC) to enhance ozone transformation into ·OH radicals, with the common advanced oxidation processes (O₃/OH^?, O₃/H₂O₂). The results obtained with model systems under the given experimental conditions showed that the system O₃/OH^? (pH 9) and O₃/H₂O₂ (pH 7, [H₂O₂] = 1·10^?5 M) are more efficient than O₃/GAC (pH 7, [GAC] = 0.5 g/L) to enhance ozone transformation into ·OH radicals. However, in Lake Zurich water the O₃/GAC process has a similar efficiency as O₃/H₂O₂ for ozone transformation into ·OH radicals. The results also show that the presence of GAC during Lake Zurich water ozonation leads to (i) removal of hydrophilic and hydrophobic micropollutants, (ii) reduction of the concentration of CO₃ ^2?/HCO₃ ^?, and (iii) decrease of the concentration of dissolved organic carbon (DOC) present in the system.     

The influence of various factors on aqueous ozone decomposition by granular activated carbons and the development of a mechanistic approach

The decomposition of aqueous ozone in the presence of various granular activated carbons (GAC) was studied. The variables investigated were GAC dose, presence of tert-butyl alcohol (TBA), aqueous pH as well as textural and chemistry surface properties of GAC. All the GAC tested enhanced the rate of ozone decomposition to some extent. From the analysis of experimental results it was deduced that ozone transformation into HO radicals mainly occurred in the liquid bulk through a radical chain reaction initiated by OH⁻ and ions. Hydroperoxide ions arise from the formation of H₂O₂ on surface active sites of GAC and its further dissociation. No direct relationship between textural properties of GAC and the rate of ozone decomposition was found. However, a multiple regression analysis of data revealed that basic and hydroxyl surface oxygen groups (SOG) of GAC favor the kinetics of the ozone decomposition process. It is thought that these groups are the active sites for ozone transformation into H₂O₂. Repeated used of GAC in ozonation experiments resulted in loss of basic and hydroxyl SOG with formation of carboxyl, carbonyl and lactone-type groups. Then, pre-ozonation of GAC reduces its ability to enhance the aqueous ozone transformation into hydroxyl radicals.     

Anodic oxidation and electro-Fenton treatment of rotenone

Rotenone, a widely used botanical insecticide submitted to strong restrictions regarding its environmental hazards, was studied as a target compound for electro-Fenton (EF) treatment in aqueous-acetonitrile mixture (70:30) of pH 3.0. In this system, the degradation of organic pollutants occurs by attack of hydroxyl radicals (OH) which are produced from the reaction of added ferrous catalyst (Fe²⁺) and hydrogen peroxide (H₂O₂) electrogenerated by oxygen reduction at carbon felt cathode. The degradative efficiency of EF system was comparatively studied versus anodic oxidation method (AO) in absence and presence of H₂O₂. It was found that only EF is sufficiently powerful to induce fast and efficient mineralization of rotenone and its degradation intermediates.The mineralization of rotenone was found to depend largely on organic solvent type, metal ion catalyst, applied current and initial rotenone concentration. The best operative conditions are achieved using aqueous-acetonitrile mixture of pH 3.0 in the presence of 0.2 mM Fe²⁺ catalyst with a current intensity of 100 mA. Under these optimized conditions, 30 min were sufficient to completely degrade rotenone in 100 mL of a 20 mg L⁻¹ solution. A nearly complete mineralization (∼96% of COD removal) was achieved after 8 h treatment.Rotenone removal kinetic was found to obey the pseudo-first order model and the absolute second order rate constant (k_Rot = 2.49 × 10⁹ M⁻¹ s⁻¹) for the reaction between the substrate and OH was derived.HPLC-MS and HPLC-DAD analysis were applied to identify and follow the evolution of rotenone oxidation products. Three stable aromatic intermediates were observed and two of these were identified as 12aβ-hydroxyrotenone and hydroquinone. Subsequent attack of these intermediates by OH radicals leads to the formation of aliphatic carboxylic acids such as succinic, acetic, oxalic and formic, quantified by ion-exclusion chromatography.     

A new flow reactor for the treatment of polluted water with microwave and ultrasound

Microwave (MW) and high‐intensity ultrasound (US) provide innovative techniques for the degradation of persistent organic pollutants (POPs). When Fenton's reagent is used to treat industrial wastes, organic pollutants are degraded by highly reactive hydroxyl radicals (HO·) that can oxidize almost any organic compound to carbon dioxide and water. These reactions, when carried out under US or MW, are faster and much more efficient. The present work assesses the combined effect of US and MW using a new flow reactor developed in our laboratory. In this 5 L pilot reactor the liquid was pumped in parallel through a modified domestic MW oven and through a cell where it was irradiated with two US generators working at 20 and 300 kHz, while MW irradiation took place in a modified domestic oven. We studied the degradation of 2,4‐dibromophenol (0.1 g L^?1 in water) by Fenton's reagent, assessing the contribution of each energy source to the overall effect, and found that MW and US‐300 kHz played the main role. A modest amount of oxidant (6 mL 30% H₂O₂ per 1 L of polluted water) sufficed to achieve complete degradation within 6 h, at which time organic compounds were no longer detectable. Even if no Fenton's reagent was added, about one half of the pollutant was degraded after 3 h irradiation. Copyright © 2007 Society of Chemical Industry     

Photophysical and photocatalytic properties of nanosized copper-doped titania sol–gel catalysts

The effect of doping the TiO₂ lattice with copper was studied. TiO₂–Cu semiconductors (0.1, 0.5, 1.0 and 5.0 Cu wt.%) were synthesized by the sol–gel method by incorporating Cu (NO₃)₂ into the titanium alkoxide solution. In the samples thermally treated at 500 °C, mesoporous materials (9.5–12 nm) with specific surface areas of 90–52 m²/g were obtained. The X-ray diffraction (XRD) patterns of the annealed samples present anatase as the sole nanocrystalline phase (28 nm). The UV–vis diffuse reflectance spectra of the Cu-doped samples show a shift in the band gap to lower energy levels. The X-ray photoelectron spectroscopy (XPS) reveals a reduction in the oxidation state of the copper precursor, Cu(II), stabilizing Cu(0) and Cu(I) in the annealed solids. The photocatalytic test for the 2,4-dichlorophenoxyacetic acid degradation showed high efficiency and mineralization up to 92% (total organic carbon, TOC) in the Cu-doped sol–gel materials. The enhancement of the photocatalytic activity was discussed as an effect due to the Cu content as well as to the formation of stable Cu(I) in the Cu-doped TiO₂ semiconductors.     

Mechanistic investigation of the conductive ceramic Ebonex as an anode material

Ebonex^® is a conductive and corrosion-resistant ceramic with the approximate composition Ti₄O₇. Anodic and/or cathodic polarization of a pair of Ebonex electrodes changed their surface composition, as shown by the development of a potential difference between them. In consequence, the activity of an Ebonex anode with respect to oxidation of an organic substrate depends on its past history. The anodic oxidation of p-nitrosodimethylaniline, which has been used as a model compound for the detection and quantitation of hydroxyl radicals, was studied in order to determine whether hydroxyl radicals are produced upon anodic polarization of Ebonex. The results were ambiguous, because direct oxidation of this substrate and oxidation of water to hydroxyl radicals occur at similar potentials. p-Benzoquinone (BQ) was found to be a more satisfactory mechanistic probe because it is resistant to direct oxidation. The rates of both disappearance and overall mineralization of BQ at Ebonex were intermediate between the corresponding rates at boron-doped diamond (BDD) and Ti/IrO₂-Ta₂O₅ anodes, which promote one-electron and two-electron oxidations respectively. However, it is not yet clear whether mineralization is initiated by hydroxyl radicals formed in lower yield than at ‘active’ materials such as BDD, or whether oxidation involves less reactive intermediates such as HO₂ radicals.     

Electronic and electrochemical properties of cationic complexes [Fe(R-Sal)2Trien] in solution: Evidence of formation of phenoxyl radicals upon oxidation

Electronic and electrochemical properties of four ferric [Fe(R-Sal)₂Trien]⁺ complexes with R = 5-OMe, 5-Cl, 5-Br and 3,5-Cl₂ were studied. The occurrence of thermally-induced spin equilibria in solution was demonstrated by optical spectroscopy. Electrochemical properties of these complexes revealed interesting behaviour in oxidation, and the formation of phenoxyl radicals within these compounds was evidenced by spectro-electrolysis.     

Degradation of 4,6-dinitro-o-cresol from water by anodic oxidation with a boron-doped diamond electrode

Anodic oxidation of 4,6-dinitro-o-cresol (DNOC) has been studied in a cell of 100 ml with a boron-doped diamond anode and a graphite cathode, both of 3-cm² area. Solutions containing up to approximately 240 mg l⁻¹ of compound in the pH range 2.0-12.0 have been treated at 100, 300 and 450 mA between 15 and 50 °C. Total mineralization is always achieved due to the great amount of hydroxyl radical (OH) produced as oxidant on the anode surface. Total organic carbon is more rapidly removed in acid medium, being the optimum pH 3.0. The degradation rate increases when temperature, current and DNOC concentration increase. However, at 100 mA depollution becomes more effective from 71 mg l⁻¹ of initial pollutant. A pseudo first-order kinetics for DNOC decay is always found by reversed-phase chromatography, with a rate constant practically independent of pH, as expected if the same electroactive species is oxidized in all media. Ion-exclusion chromatography allowed the detection of oxalic acid as the ultimate carboxylic acid. The mineralization process leads to the complete release of NO₃⁻ ions from the destruction of nitroderivative intermediates. These products are oxidized simultaneously with accumulated oxalic acid up to the end of electrolyses. Comparative treatment of the same solutions with a Pt anode yields a quite poor depollution because of the generation of much lower amounts of reactive OH on its surface.     

Biodegradation of 2,4-dichlorophenoxy acetic acid (2,4-d) by pseudomonas cepacia: Stoichiometric study

Pseudomonas cepacia biodegraded 2,4-dichlorophenoxyacetic acid (2,4-D) according to the following stoichiometric equation: C₈ H₆ Cl₂ O₃ + c₁ O₂ + c₂ NH₃ → c₃ CH_x N_z O_y + c₄ CO₂ + c₅ H₂ O + c₆ Cl_? + c₇ REIM where CH_x N_z O_y represents the bacterial cells and REIM is the residual extracellular intermediate metabolites. The stoichiometric coefficients c₁ to c₇ were determined from C, N, O, H and Cl balances together with the experimental data on the biodegradation of ¹⁴ C-carboxy-labeled-2,4-D and ¹⁴ C-ring-uniformly-labeled-2,4-D. The stoichiometric equation obtained predicted satisfactorily the total oxygen consumption for and the total heat production from the biodegradation of 2,4-D for a wide range of initial concentrations from 80 to 500 mg/L.     

Electrochemical waste water treatment: Electrooxidation of acetaminophen

Oxidation of acetaminophen at boron-doped diamond (BDD) and at Ti/SnO₂ anodes in a plug-flow divided electrochemical reactor led to electrochemical combustion, whereas at Ti/IrO₂ benzoquinone was the exclusive product except at very long electrolysis times. The difference is explicable in terms of the different mechanisms of oxidation: direct oxidation at the anode for Ti/IrO₂ vs. indirect oxidation involving electrogenerated hydroxyl radicals at BDD and Ti/SnO₂. At BDD, at which the efficiency of degradation of acetaminophen was greatest, the rate of electrolysis at constant concentration was linearly dependent on the current, and at constant current linearly dependent on the concentration. Current efficiencies for mineralization up to 26% were achieved without optimization of the cell design.     

Selective chlorination of 4-chlorotoluene to 2,4-dichlorotoluene over zeolite catalysts

The performance of various zeolites in the liquid phase chlorination of 4-chlorotoluene (4-CT) with gaseous chlorine at a moderate temperature and normal pressure has been examined. A comparison under the same conditions with Lewis acid catalyst FeCl₃, is also carried out. It is found that zeolite K-L exhibits higher selectivity for 2,4-dichlorotoluene (2,4-DCT/3,4-DCT = 3.54) compared to the other zeolites studied and also FeCl₃ catalyst (2,4-DCT/3,4-DCT = 3.18), while the rate of 4-CT conversion (75.8 mmol g^–1 h^–1) is found to be comparable on K-L and FeCl₃ catalysts. The highest rate of 4-CT conversion, among the catalysts studied is obtained over K-beta (101.4 mmol g^–1 h^–1). FeCl₃ catalyst produces higher amounts of tri- and tetra-substituted products due to its non-shape-selective character. Mainly the side-chain chlorinated product (,4-dichlorotoluene) is obtained over K-X, amorphous SiO₂ and in the absence of catalyst. Solvents influence the rate of 4-CT conversion as well as the 2,4-DCT/3,4-DCT isomer ratio. 1,2-dichloroethane appears to be the best solvent in enhancing the 2,4-DCT/3,4-DCT isomer ratio when the reaction temperature is raised from 313 to 353 K.     

Electro-Fenton degradation of antimicrobials triclosan and triclocarban

The antimicrobials triclosan (2,4,4′-trichloro-2′-hydroxydiphenyl ether) and triclocarban (N-(4-chlorophenyl)-N′-(3,4-dichlorophenyl)urea) have been degraded by four electro-Fenton systems using undivided electrolytic cells with a Pt or boron-doped diamond (BDD) anode and a carbon felt or O₂ diffusion cathode. The main oxidant is hydroxyl radical (OH) produced both on the anode surface from water oxidation and in the medium by Fenton's reaction, which takes place between electrogenerated H₂O₂ and Fe²⁺ coming from cathodic reduction of O₂ and Fe³⁺, respectively. Triclosan from saturated aqueous solutions of pH 3.0 is completely removed in all cells, decreasing its decay rate in the order: Pt/carbon felt > BDD/carbon felt > Pt/O₂ diffusion > BDD/O₂ diffusion, in agreement with their OH generation ability from Fenton's reaction. Glyoxylic, maleic and oxalic acids are identified as aliphatic intermediates. Complexes between oxalic acid and iron ions persist largely in solution, although Fe²⁺-oxalato complexes are mineralized by OH in the medium and Fe³⁺-oxalato complexes are destroyed by OH on BDD. Analogous treatments of more concentrated triclosan solutions using a 20:80 (v/v) acetonitrile/water mixture as solvent evidence the role of hydroxyl radicals along the degradation. In this hydroorganic medium hydroxylated derivatives such as 2,4-dichlorophenol, 4-chlorocatechol, chlorohydroquinone and chloro-p-benzoquinone, and carboxylic acids such as maleic, oxalic, formic and acetic acids are detected as products. Complete destruction of iron-oxalato complexes and released Cl⁻ ion involves some oxidizing species coming from parallel acetonitrile oxidation. The same electro-Fenton systems also yield the overall removal of triclocarban in acetonitrile/water mixtures, giving rise to urea, hydroquinone, chlorohydroquinone, 1-chloro-4-nitrobenzene and 1,2-dichloro-4-nitrobenzene as primary intermediates.