Transformation Of Phenol Research Articles

Phenol transformation induced by UVA photolysis of the complex FeCl2+

Here we show that the photolysis of FeCl2+ upon UV irradiation of Fe(III) at pH 0.5, yielding Cl• and then Cl 2 −• , upon further reaction with Cl−, induces phenol degradation. The photolysis of FeCl2+ can be highlighted and studied as the huge interference by FeOH2+ can be avoided under such conditions. Our data allowed the assessment of a photolysis quantum yield for FeCl2+ of 5.8 × 10−4 under UVA irradiation, much lower compared to the literature value of 0.5. The discrepancy can be explained if the photolysis process is efficient but photoformed Fe2+ and Cl• undergo recombination inside the solvent cage.

Efficacy of mediators for enhancing the laccase-catalyzed oxidation of aqueous phenol

Laccase from Trametes versicolor was characterized in terms of its catalytic stability and reactivity towards phenol as a model substrate in the absence or presence of four common redox mediators. Laccase was inactivated when incubated in the presence of mediators including 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS), violuric acid (VA), 1-hydroxybenzotriazole (HBT) and 2,2′,6,6′-tetramethylpiperidine- N-oxyl (TEMPO) at pH 6 and 25 °C. Monophasic and biphasic exponential decay expressions were successfully used to model laccase inactivation under these conditions. Phenol transformation in the absence of mediators was optimum at pH 6. The addition of HBT or VA moderately enhanced phenol transformation between pH 3 and 5. TEMPO and ABTS significantly enhanced both the extent and rates of phenol transformation, particularly at pH 6. Over the course of a reaction, some mediator species gradually transformed into compounds that were no longer active as mediators. In general, the use of mediators enhanced phenol transformation; however, in certain instances their practical application may be limited since they contribute to laccase inactivation and considerable quantities are required.

Wet milling of H-ZSM-5 zeolite and its effects on direct oxidation of benzene to phenol

Abstract The direct oxidation of benzene to phenol with N2O over ZSM-5 catalysts suffers from the problem of rapid catalyst deactivation mainly due to the secondary transformation of phenol into heavier hydrocarbon compounds leading to the catalyst coking. In order to investigate the deactivation behavior of the ZSM-5 catalysts during this reaction, a comparative study was performed over ZSM-5 catalysts having different crystal sizes. The original catalyst was milled to two different periods of time to obtain catalysts having various crystal sizes. The original and the milled catalysts were tested for the benzene to phenol reaction to get an insight into the effect of crystal size on the catalyst deactivation. There was a decrease in catalyst deactivation with a decrease in crystal size. An indirect dependence of catalyst deactivation with total acidity was observed.

Photochemincal processes involving nitrite in surface water samples

A study into nitrite photochemistry was carried out on surface (both lake and river) water samples. In the tested samples, nitrite photolysis accounted for 0–60 % of .OH photoproduction, nitrate for 0–40 %, and dissolved organic matter (DOM) photochemistry played on average the main role. In real surface waters, an effect of radiation extinction by the water column would also be observed, and is expected to inhibit nitrate photochemistry at a higher extent compared to nitrite or DOM. Nitrite showed a definite time evolution with irradiation. Photodegradation prevailed in samples with the highest initial concentrations, while photogeneration with DOM transformation was evident in the presence of undetectable initial nitrite levels. Nitrite also accounted for up to 9 % of .OH scavenging, which would produce up to 66 % of photoformed nitrogen dioxide. The remaining percentage of nitrogen dioxide generation is accounted for by nitrate photolysis. Photogenerated nitrogen dioxide could then be involved in significant processes of aromatic nitration, in particular in the transformation of phenol into nitrophenols.

Assessing the steady-state [·NO2] in environmental samples

Based on available literature data of [NO2-], steady-state [*OH], and *OH generation rate upon nitrate photolysis in environmental aqueous samples under sunlight, the steady-state [*NO2], could be calculated. Interestingly, one to two orders of magnitude more *NO2 would be formed in photochemical processes in atmospheric water droplets compared to transfer from the gas phase. The relative importance of nitrite oxidation compared to nitrate photolysis as an *NO2 source would be higher in atmospheric than in surface waters. The calculated levels of *NO2 could lead to substantial transformation of phenol into nitrophenols in both atmospheric and surface waters.

Transformation of phenol, catechol, guaiacol and syringol exposed to sodium hypochlorite

Germs, xenobiotics and organic matter that influence the colour, turbidity and organoloeptic properties of water are removed by chlorination. Unfortunately, chlorine oxidants including sodium hypochlorite, used in water treatment induce processes that partly convert the treated compounds to unwanted chlorinated derivatives. The purpose of this work was to analyse the efficiency of transformation of phenol, catechol, guaiacol and syringol exposed to sodium hypochlorite and determine the intermediates formed during oxidative conversion of these compounds. The analysis was performed in aerobic conditions, both in acidic (pH 4.0) and alkaline (pH 8.0) medium. The effectiveness of transformation was slightly higher in acidic in comparison to alkaline conditions. Some chlorophenols, such as 2-chlorophenol, 2,4-dichlorophenol, 2,4,5-trichlorophenol and pentachlorophenol were determined as the products of phenol conversion. Chlorophenols were also formed during catechol, guaiacol and syringol transformation by replacement of hydroxy and methoxy residues by chlorine atoms. Moreover, some chlorocatechols and chlorinated methoxyphenols were determined during catechol and methoxyphenols transformations. Higher concentrations of chlorinated compounds were observed in the alkaline environment during phenol transformation. Conversion of catechol and methoxyphenols generated higher amounts of chlorinated intermediates in the acidic medium. In samples carboxylic acids like acetic and formic acids were determined. The formation of these compounds was the result of the cleavage of aromatic structure of phenols.

Benzene to phenol hydroxylation with N2O over Fe-Beta and Fe-ZSM-5: Comparison of activity per Fe-site

Abstract Fe-Beta catalysts with iron content of 0.045–2.0 wt.% were studied in the benzene to phenol transformation with N2O and compared to similar Fe-ZSM-5 catalysts to understand the influence of zeolite structure on the Fe-sites activity. The Fe-containing zeolites were prepared either by a direct hydrothermal synthesis or by a post-synthesis Fe deposition followed by activation (steaming or high temperature treatment in He). Total amount of Fe(II) active sites able to form atomic oxygen (O)Fe, from N2O, was quantified by the transient response method at 523 K measuring the released N2. The fraction of the (O)Fe active in CO oxidation was determined via the amount of CO2 released. The catalyst activity in the benzene to phenol transformation over the activated isomorphously substituted Fe-Beta and Fe-ZSM-5 zeolites was directly proportional to the amount of the (O)Fe active in CO oxidation. The turnover frequency (TOF) over Fe-Beta and Fe-ZSM-5 catalysts was found to be close indicating a similarity in the structures of Fe active sites. The observed ∼2-fold difference can be attributed to the influence of the zeolite host lattices. The difference between Fe-Beta and Fe-ZSM-5 was also observed in DRIFT spectra of NO adsorbed on iron sites at room temperature. The bands of NO adsorbed on Fe-Beta and Fe-ZSM-5 were at 1873 and 1878/1891 cm−1, respectively. The areas of these bands correlate with the amount of (O)Fe active in CO oxidation. Comparison of the DRIFT spectra of adsorbed NO on the zeolites with the spectra on some iron containing compounds allowed to attribute the adsorption sites to Fe(II) sites and not to Fe(III) sites.

A novel silk fibroin‐supported iron catalyst for hydroxylation of phenol

AbstractThe aim of this study was to explore the potential use of silk fibroin (SF) as a catalyst support material for phenol hydroxylation reactions. Iron‐substituted silk fibroin fibers were prepared using formic acid at room temperature and characterized using inductively coupled plasma atomic‐emission spectrometry, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR) and optical microscopy. Measurement of an FTIR spectrum showed that the secondary structure was β‐structure before and after iron substitution. To evaluate the catalytic properties of prepared catalyst, phenol hydroxylation reaction was carried out using aqueous hydrogen peroxide as an oxidant. An excellent transformation of phenol into dihydroxybenzenes (catechol and hydroquinone) was achieved. Phenol conversions of 3.3%, 61.2%, and 80.3% were obtained at room temperature, 40 °C and 60 °C respectively. It was found that no further phenol conversion proceeded because catalysts became separated from the reaction system during the reaction. No significant leaching of the iron was detected. Catalyst could be reused several times without a significant change in activity. Parent silk fibroin fibers without iron were inactive. Copyright © 2006 Society of Chemical Industry

A pseudo‐steady state model of the kinetics of laccase‐catalysed oxidation of aqueous phenol

AbstractA model has been developed to describe the kinetics of the oxidation of phenol by oxygen using laccase (EC 1.10.3.2) from Trametes versicolor as catalyst. The model incorporates an assumption, referred to as the pseudo‐steady state assumption, that at any instant during the reaction the enzyme achieves an approximate steady state distribution of its various forms around the catalytic cycle. The model was validated by comparing model predictions with experimental observations of phenol transformation and oxygen consumption over time. Excellent agreement was found between experimental data and model predictions. The pseudo‐steady state assumption had the advantage of reducing the complexity of the model equations to be solved while simultaneously maintaining the model's predictive ability. The pseudo‐steady state model was further simplified in accordance with specific initial conditions to provide a simplified method for the estimation of the model constants. Copyright © 2006 Society of Chemical Industry

Host (nanodimensional pores of zeolite Y)–guest (tetraaza[14]annulene nickel(II) complexes, [Ni(Me 4R 2Bzo[14]tetraeneN 4)]) nanocomposite materials: Ship-in-a-bottle synthesis, characterization and liquid phase oxidation of phenol with hydrogen peroxide

Nickel(II) complexes with tetraaza[14]annulene ligands “5,7,12,14-tetramethyldibenzo-1,4,8,11-tetraazacyclotetradecine [Ni(Me 4R 2Bzo[14]tetraeneN 4)] (R = H, CH 3, Cl and NO 2) have been prepared from the one-pot template condensation reaction of substituted-1,2-phenylenediamine (4-methyl-; 4-chloro-; 4-nitro-1,2-phenylenediamine) with 2,4-pentanedione in the presence of nickel(II) ion within the nanocavity pores of zeolite-Y [Ni(Me 4R 2Bzo[14]tetraeneN 4)]@NaY”. The new materials were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV/VIS, XRD, BET and DRS). All encapsulated complexes served as catalyst for the oxidation of phenol to a mixture of catechol and hydroquinone using hydrogen peroxide as an oxidant. A suitable reaction condition has been optimized for [Ni(Me 4(NO 2) 2Bzo[14]tetraeneN 4)]@NaY by considering the effect of various parameters such as reaction time and amount of oxidant, different solvents, concentration of substrate etc., for the maximum transformation of phenol.

Uptake and transformation of phenol and chlorophenols by hairy root cultures of Daucus carota, Ipomoea batatas and Solanum aviculare

Hairy root cultures of Daucus carota L., Ipomoea batatas L. and Solanum aviculare Forst were investigated for their susceptibility to the highly toxic pollutants phenol and chlorophenols and for the involvement of inherent peroxidases in the removal of phenols from liquid media. Roots of D. carota grew normally in medium containing 1000 μmol l −1 of phenol, whilst normal growth of roots of I. batatas and S. aviculare was only possible at levels up to 500 μmol l −1. In the presence of chlorophenols, normal root growth was possible only in concentrations not exceeding 50 μmol l −1, except for I. batatas which was severely affected at all concentrations. Despite the reduction in biomass, the growth of S. aviculare cultures was sustained in medium containing up to 2000 μmol l −1 of phenol or 2-chlorophenol, and up to 500 μmol l −1 of 2,6-dichlorophenol. The amounts of phenol removed by the roots within 72 h of treatment were 72.7%, 90.7% and 98.6% of the initial concentration for D. carota, I. batatas and S. aviculare, respectively. For the removal of 2,6-dichlorophenol the values were, respectively, 83.0%, 57.7% and 73.1%. Phenols labelled with 14C were absorbed by the root tissues and condensed with highly polar cellular substances as well as being incorporated into the cell walls or membranes. The results suggest that S. aviculare, an ornamental plant, would be best suited for remediation trials under field conditions.

Cobalt-Mediated Activation of Peroxymonosulfate and Sulfate Radical Attack on Phenolic Compounds. Implications of Chloride Ions

The sulfate radical pathway of the room-temperature degradation of two phenolic compounds in water is reported in this study. The sulfate radicals were produced by the cobalt-mediated decomposition of peroxymonosulfate (Oxone) in an aqueous homogeneous system. The major intermediates formed from the transformation of 2,4-dichlorophenol were 2,4,6-trichlorophenol, 2,3,5,6-tetrachloro-1,4-benzenediol, 1,1,3,3-tetrachloroacetone, pentachloroacetone, and carbon tetrachloride. Those resulting from the transformation of phenol in the presence of chloride ion were 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 1,1,3,3-tetrachloroacetone, and pentachloroacetone. In the absence of chloride ion, phenol transformed into 2,5-cyclohexadiene-1,4-dione (quinone), 1,2-benzenediol (catechol), and 1,4-benzenediol (hydroquinone). Several parameters were varied, and their impact on the transformation of the organic compounds is also discussed. The parameters varied were the initial concentration of the organic substrate, the dose of Oxone used, the cobalt counteranion, and in particular the impact of chloride ions and the quenching agent utilized for terminating the reaction. This is one of the very few studies dealing with intermediates formed via sulfate radical attack on phenolic compounds. It is also the first studythat explores the sulfate radical mechanism of oxidation, when sulfate radicals are generated via the Co/Oxone reagent. Furthermore, it provides strong evidence on the interaction of chloride ions with sulfate radicals leading to halogenation of organics in water.

Phenol Conjugation with Peptides and Final Transformations of Conjugates in English Ryegrass Seedlings

[ 1-14C] Phenol transformation in English ryegrass (Lolium perenne L.) sterile seedlings was studied. The compound studied was assimilated by a plant through leaves as vapor. Phenol was bound with ryegrass low-molecular-weight peptides producing phenol-peptide conjugates. Conjugation with endogenous peptides is one of the main pathways of phenol detoxication in ryegrass. Nearly three fifths of phenol assimilated is conjugated with low-molecular-weight peptides. After removal of the plant from the labeled phenol-containing atmosphere, the content of conjugation products gradually decreased, followed by excretion of labeled carbon dioxide. This fact indicates that the conjugates are destructed and the carbon atoms of their radioactive component are oxidized to carbon dioxide. Almost one third of assimilated phenol is transformed via the oxidation pathway, but a small part of it is irreversibly bound with biopolymer molecules.

Cryptanaerobacter phenolicus gen. nov., sp. nov., an anaerobe that transforms phenol into benzoate via 4-hydroxybenzoate

An anaerobic bacterium that transforms phenol and 4-hydroxybenzoate (4-OHB) into benzoate, strain LR7.2T, was isolated from a culture originating from a mixture of swamp water, sewage sludge, swine waste and soil. Cells of strain LR7.2T are Gram-positive short rods (1 x 2 microm) that are electron-dense when observed by electron microscopy. The optimum pH and temperature for growth and transformation activity of 4-OHB are 7.5-8.0 and 30-37 degrees C, respectively. The bacterium does not use sulphate, thiosulphate, nitrate, nitrite, FeCl3, fumarate or arsenate as an electron acceptor. It does not normally use sulphite, although stimulation of growth and 4-OHB transformation activity at a low concentration (up to 2 mM) has been reported previously under different culture conditions. The presence of 4-OHB or phenol is essential for growth; transformation of 4-OHB or phenol into benzoate is used to produce energy for growth. Using [6D]-phenol, 4-OHB was shown to be an intermediate in the transformation of phenol into benzoate. No spore was observed. The bacterium has a DNA G+C content of 51 mol% and its major membrane fatty acid is anteiso-C(15 : 0). The 16S rRNA gene sequence of strain LR7.2T shows only 90 % similarity to its closest relative (Pelotomaculum thermopropionicum). From these results, a new taxon is proposed: Cryptanaerobacter phenolicus gen. nov., sp. nov. The type strain is LR7.2T (=ATCC BAA-820T=DSM 15808T).

Kinetic model of laccase-catalyzed oxidation of aqueous phenol

Laccase from Trametes versicolor (EC 1.10.3.2) catalyzes the oxidation of aqueous phenol by oxygen and has demonstrated good potential for applications in various industrial and environmental processes. A kinetic model of this system has been developed to facilitate a better understanding of the mechanisms and rate-limiting steps of enzyme-catalyzed transformation and to eventually assist in the choice and design of suitable reactor systems. A kinetic model was derived based on the differential and mass balance equations that describe the interactions of various forms of the enzyme with the aromatic substrate and oxygen. This model also incorporated an expression accounting for enzyme inactivation over time due to the reaction environment. The model was validated by comparing model predictions with experimental observations of phenol transformation and oxygen consumption over time at a variety of enzyme concentrations. Excellent agreement was found between experimental data and predictions of the kinetic model. Sensitivity analyses demonstrated that the reaction between oxidized-laccase and phenol was the rate-limiting step.

A kinetic study of phenol nitration and nitrosation with nitrous acid in the dark

We studied the transformation of phenol in the presence of nitrous acid in the dark. The main detected intermediates were 2-nitrophenol, 4-nitrophenol and 4- nitrosophenol. For the first time a kinetic analysis of the reaction in a pH interval relevant to environmental chemistry has been carried out. The kinetic data are consistent with phenol transformation being initiated by HNO2. The results are relevant to the chemistry of the atmosphere, where HNO2 forms upon heterogeneous conversion of · NO2, and to water treatment techniques.

Synthesis of copper-substituted aluminophosphate molecular sieves (CuAPO-11) and their catalytic behavior for phenol hydroxylation

Cu-substituted aluminophosphate molecular sieves (CuAPO-11) containing different amounts of copper were synthesized by static hydrothermal crystallization and characterized using XRD, ICP-AES, N 2-adsorption, SEM and DR UV–Vis techniques. Experimental data show that the Cu limitation in the synthesis gel used for CuAPO-11 is 0.20 in the form of CuO/Al 2O 3 molar ratio. A new Cu-containing crystal phase (denoted as CuAlPO) with a different structure from CuAPO-11 can be formed if the CuO/Al 2O 3 molar ratio in the gel is beyond the value of 0.20. To evaluate the catalytic oxidation properties of CuAPO-11 and CuAlPO, we carried out the phenol hydroxylation reaction using aqueous hydrogen peroxide (30 wt.% aqueous H 2O 2) as an oxidant; an excellent transformation of phenol into dihydroxybenzenes (catechol and hydroquinone) was achieved under benign reaction conditions.

Investigation of [Ni{Me4Bzo2[14]aneN4}]Cl2 catalyzed selective hydroxylation of phenol to catechol by H2O2 in the homogeneous medium

Abstract Chemical and electrochemical conversion of phenol to 1,2-dihydroxy benzene using H2O2 as oxidant was studied in presence of [Ni{Me4Bzo2[14]aneN4}]Cl2 as homogeneous catalyst. The reaction products were analyzed using gas chromatograph. The phenoxide salt of the complex, [Ni{Me4Bzo2[14]aneN4}](C6H5O)2 exhibits a new irreversible oxidation wave at Ep,c 0.45 V versus Ag/AgCl, which is unlike that observed in its dichloride salt with Ep,c 0.25 V, and arises due to catalyzed electro-oxidation of the phenoxide counter ions. The chemical oxidation by H2O2 was investigated in presence of different solvents and a predominant formation of catechol was observed over hydroquinone (with molar ratio 9:1). The reaction conditions were optimized, in terms of the effect of reaction temperature, amount of catalyst, H2O2 concentration, phenol concentration, nature and volume of solvent used, reaction time and pH, for the maximum transformation of phenol as well as for better selectivity towards the formation of catechol.

Enzymatic Treatment of Soils Contaminated with Phenol and Chlorophenols Using Soybean Seed Hulls

This study presents the application of soybean seed hulls for the decontamination and/or detoxification of phenol and chlorophenol polluted soils. The effect of soil was examined on both catalytic activity of soybean seed hull peroxidase (SBP) and enzymatic transformation of phenol, 2-chlorophenol, and 2,4-dichlorophenol through the polymerization reaction. The sorption of the enzyme to soil organic matter was found to account for the loss of partial catalytic activity of soybean seed hulls in a soil slurry environment. The organic matter present in loamy soils, rather than other soluble soil constituents and soil micro-organisms, is a factor in SBP inhibition by soil and the corresponding decline in treatment efficiency of phenol and chlorophenols. Under improved conditions, however, soybean seed hulls demonstrated a satisfactory ability to catalyze the polymerization reaction. Over 96% of total phenols were removed using soybean seed hulls in a soil slurry bioreactor, which demonstrates a great potential in use of soybean seed hulls, a readily available and inexpensive source of SBP, for bioremediation of soils contaminated with phenolic compounds.

Catalytic activity of chromium(III), iron(III) and bismuth(III) complexes of 1,2-bis(2-hydroxybenzamido)ethane (H2hybe) encapsulated in zeolite-Y for liquid phase hydroxylation of phenol

Iron(III), chromium(III) and bismuth(III) complexes of amidate ligand 1,2-bis(2-hydroxybenzamido)ethane (H2hybe) encapsulated in the super cages of zeolite-Y have been isolated and characterized by various physico-chemical measurements. 3D model structure generated for [Fe(hybe)·2H2O]+ suggests that zeolite-Y can accommodate these complexes in its super cages without any strain. These encapsulated complexes catalyze hydroxylation of phenol using H2O2 as oxidant to give catechol as a major and hydroquinone as a minor product. A suitable reaction condition has been optimized for [Fe(hybe)·2H2O]Cl–Y by considering the effect of various parameters such as concentration of substrate, amount of oxidant and catalysts, reaction time, temperature, and volume of solvent for the maximum hydroxylation of phenol. The results obtained over these new encapsulated catalysts showed that selectivity of the catechol formation is ca. 85%, though transformation of phenol varied in the order [Fe(hybe)·2H2O]Cl–Y (43.5%)>[Cr(hybe)·2H2O]Cl–Y (32.8%)>[Bi(hybe)·2H2O]Cl–Y (30.6%). Catalytic performance of these catalysts has been compared with different metal complexes encapsulated in zeolite-Y.