Chlorophenols, oxidation

Effect of pH on chlorophenol oxidation rates at various pH values. (Data from Benitez, F.J. et at., Chemosphere, 41, 1271-1277,2000.)... 

Li R, Savage PE, Szmukler D. 2-Chlorophenol oxidation in supercritical water global kinetics and reaction products. AIChE J 1993 39(1) 178 187. 

A hr dm 3. Recently, the electrochemical incineration of p-benzoquinone in acetate buffer has been reported by Houk et al. [54]. The cell was similar to that above cited for 4-chlorophenol oxidation (see Sec. III.B), with a Ti or Pt anode coated with a film of the oxides of Ti, Ru, Sn, and Sb. These anodes are stable but somewhat less efficient than an Fe(III)-doped Pb02 film coated on Ti employed in a previous work [55], The COD of 50 mL of 100 ppm / -benzoquinone decreased from an initial value of 190 to 2 ppm during 64 hr of electrolysis at 1 A. The major intermediate products identified were hydroquinone and aliphatic acids including maleic, succinic, malonic, and acetic acids. The suggested reaction sequence is given in Fig. 13, where succinic acid is obtained from a cathodic reduction of maleic acid, which is formed from the breakdown of the dihydroxylated derivative generated by an attack of adsorbed hydroxyl radicals onto p-benzoquinone. Further mineralization of succinic acid occurs via its consecutive oxidation to malonic and acetic acids. 

Boudenne, J. L. and Cerclier, O. (1999) Performance of carbon black-slurry electrodes for 4-chlorophenol oxidation. Water Res. 33,494-504. 

The effect of pH on 4-chlorophenol oxidation is shown in Figure 4. The results show that oxidation is favored under both acidic and basic conditions. This fact implies that different reaction mechanisms may be operative and that photocatalytic oxidation is affected by both H+ and OH- ions. At high pH, the number of hydroxyl ions on the TiO surface increases because of the abundance of OH- ions, thereby increasing the population of -OH radicals. Hickling and Hill (25) suggested that, at high pH, the adsorbed OH- group can be readily converted to OH radical upon irradiation. 

Chlorophenol oxidation to benzoquinone is accomplished by separating the reaction mixture into two flows, one aqueous and the other organic with the... 

Prepared by condensing p-chlorophenol with phlhalic anhydride in sulphuric acid solution in the presence of boric acid. The chlorine atom is replaced by hydroxyl during the condensation. It can also be prepared by oxidation of anthraquinone or 1-hydroxyanthraquinone by means of sulphuric acid in the presence of mercury(ll) sulphate and boric acid. 

Low molecular weight poly(l,3-phenylene oxide) [25190-64-1] has been prepared from the sodium salt of y -chlorophenol with copper as a catalyst... 

All the chlorophenols can be separated usiag C g-grafted siUca columns. In NH2 grafted columns, the elution depends on the An electrochemical detector ia oxidation mode, more sensitive than uv detectors, is generally used to detect very low quantities, especially ia analy2iag 2,4,5-trichlorophenol. 

For selective estimation of phenols pollution of environment such chromatographic methods as gas chromatography with flame-ionization detector (ISO method 8165) and high performance liquid chromatography with UV-detector (EPA method 625) is recommended. For determination of phenol, cresols, chlorophenols in environmental samples application of HPLC with amperometric detector is perspective. Phenols and chlorophenols can be easy oxidized and determined with high sensitivity on carbon-glass electrode. 

Quinizarin has been prepared by heating /)-chlorophenol, phthalic anhydride, and sulfuric acid by heating hydroquinone with phthalic anhydride - by heating hydroquinone, phthalic anhydride and c.i>. sulfuric acid by oxidizing anthraquinone... 

Clofibrate causes a necrotizing myopathy, particularly in patients with renal failure, nephrotic syndrome or hypothyroidism. The myopathy is painful and myokymia of unknown origin is sometimes present. The mechanism of damage is not known, but p-chlorophenol is a major metabolite of clofibrate and p-chlorophe-nol is a particularly potent uncoupler of cellular oxidative phosphorylation and disrupts the fluidity of lipid membranes. Muscle damage is repaired rapidly on the cessation of treatment. 

The results for the hydrolysis of chlorobenzene, o-chlorotoluene and p-chloroanisole in presence of cuprous oxide at different temperatures (Fig. 14) show a good selectivity for the reaction of the chlorobenzene. But, the p-chloroanisole is also transformed by a secondary demethylation reaction into the corresponding p-chlorophenolate. 

Pera-Titus M, Garcia-Molina V, Banos MA et al (2004) Degradation of chlorophenols by means of advanced oxidation processes a general review. Appl Catal B 47 219-256... 

Uniformly labeled 2,4-dichlorophenol- C (purchased from New England Nuclear Corp, Boston, Mass.) was used in the tracer preparation. This provided a label at all carbon positions in the dibenzo-dioxin structure. 2,7-Dichlorodibenzo-p-dioxin- C after initial cleanup by fractional sublimation, contained approximately 5% of an impurity, detected by thin layer chromatography (TLC) which gave mass peaks at 288, 290, 292, and 294 in the mass spectrometer, consistent with a trichloro-hydroxydiphenyl oxide. This is probably the initial condensation product of the Ullman reaction and is most likely 2-(2,4-dichlorophenoxy)-4-chlorophenol. It was removed easily by extractions with aqueous... 

Evans CS, B Dellinger (2005a) Mechanisms of dioxin formation from the high temperature oxidation of 2-chlorophenol. Environ Sci Technol 39 122-127. 

Salicylate is an intermediate in the metabolism of PAHs including naphthalene and phen-anthrene, and its degradation involves oxidation to catechol. The hydroxylase (monooxygenase) has been extensively studied (references in White-Stevens and Kamin 1972) and in the presence of an analog that does not serve as a substrate, NADH is oxidized with the production of H2O2 (White-Stevens and Kamin 1972). This uncoupling is characteristic of flavoenzymes and is exemplified also by the chlorophenol hydroxylase from an Azotobacter sp. that is noted later. 

Mutations at the active site of CYPlOl (cytochrome P450j,j jj) from a strain of Pseudomonas putida made possible the monooxygenation of chlorinated benzenes with less than three substituents to chlorophenols, with concomitant NIH shifts for 1,3-dichlorobenzene (Jones et al. 2001). Further mutations made it possible to oxidize even pentachlorobenzene and hexachlorobenzene to pentachlorophenol (Chen et al. 2002). Integration of the genes encoding cytochrome PTSO. into Sphingobium chlorophenolicum enabled this strain to partially transform hexachlorobenzene to pentachlorophenol (Yan et al. 2006). 

A facultatively anaerobic organism designated Anaeromyxobacter dehalogenans (Sanford et al. 2002) was capable of dechlorinating ortho-chlorinated phenols using acetate as electron donor—2-chlorophenol was reduced to phenol and 2,6-dichlorophenol to 2-chloro-phenol (Cole et al. 1994). A strain of Desulfovibrio dechloracetivorans was also able to couple the dechlorination of ortho-substituted chlorophenols to the oxidation of acetate, fumarate, lactate, and propionate (Sun et al. 2000). 

A spore-forming strain of Desulfitobacterium chlororespirans was able to couple the dechlorination of 3-chloro-4-hydroxybenzoate to the oxidation of lactate to acetate, pyruvate, or formate (Sanford et al. 1996). Whereas 2,4,6-trichlorophenol and 2,4,6-tribro-mophenol supported growth with the production of 4-chlorophenol and 4-bromophenol, neither 2-bromophenol nor 2-iodophenol was able to do so. The membrane-bound dehalogenase contains cobalamin, iron, and acid-labile sulfur, and is apparently specific for ortho-substituted phenols (Krasotkina et al. 2001). 

Sun B, JR Cole, RA Sanford, JM Tiedje (2000) Isolation and characterization of Desulfobvibrio dechlorace-tivorans sp. nov., a marine dechlorinating hacterium growing hy coupling the oxidation of acetate to the reductive dechlorination of 2-chlorophenol. Appl Environ Microbiol 66 2408-2413. 

Cravotto G, Binello A, Di Carlo S, Orio L, Zhi-Lin Wu, Ondmschka B (2010) Oxidative degradation of chlorophenol derivatives promoted by microwaves or power ultrasound a mechanism investigation. Environ Sci Poll Res 17(3) 674-687... 

Chaliha S, Bhattacharyya KG (2008) Using Mn(II) - MCM41 as an environment - friendly catalyst to oxidize phenol, 2-chlorophenol and 2-nitrophenol in aqueous solution. Ind Eng Chem Res 47 1370-1379... 

Cao, G., Li, Y., Zhang, Q., and Wang, H. (2010) Synthesis and characterization ofLa203/Ti02 F and the visible light photocatalytic oxidation of 4-chlorophenol. Journal of Hazardous materials, 178 (1-3), 440-449. 

A large quantity (700 kg) of the chlorophenol, left in contact with cone, sodium hydroxide solution for 3 days, decomposed, attaining red heat and evolving fumes which ignited explosively. Although this could not be reproduced under laboratory conditions, it is believed that exothermic hydrolysis to the hydroquinone (possibly with subsequent aerobic oxidation to the quinone) occurred, the high viscosity of... 

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