Chlorinated Phenols Research Articles

Simultaneous and Practical Difluoromethylation of Triclosan, 2,4,6-Trichlorophenol and Pentachlorophenol in Soils for their Qualitative Detection by Electron Ionization GC-MS

The extremely rapid (30 seconds) and practical derivatization of three environmentally relevant chlorinated phenols (CPs): triclosan, 2,4,6-trichlorophenol and pentachlorophenol for their qualitative detection by GC-MS is presented. The method involves the use of the eco-friendly difluoromethylating agent diethyl (bromodifluoromethyl) phosphonate (DBDFP) and results in the efficient tagging of the hydroxyl group in the phenols with the difluoromethyl (CF2H) moiety. Moreover, the protocol is carried out at ambient temperature and thus eliminates the heating involved with more conventional methods such as silylation. Another important facet of the derivatization is its biphasic nature, allowing for the specific tagging of phenolic species that are present in water or in an organic matrix. The derivatization yields difluoromethylated ether versions of the phenols with enhanced detectability by EI-GC-MS and as a way of demonstrating the robustness of the protocol, the three CPs were derivatized and unequivocally identified when spiked in three different types of soils: Virginia type A soil, Ottawa Sand and Nebraska EPA soil at a 1 μg g-1 concentration each. The protocol offers a fast way of derivatizing these types of phenols since no prior, separate sample preparation or extraction steps are needed.

Regiodivergent Chlorination of Phenols Controlled by a Lewis Base Catalyst

Regiodivergent Chlorination of Phenols Controlled by a Lewis Base Catalyst

Chlorination Revisited: Does Cl– Serve as a Catalyst in the Chlorination of Phenols?

The aqueous chlorination of (chloro)phenols is one of the best-studied reactions in the environmental literature. Previous researchers have attributed these reactions to two chlorine species: HOCl (at circum-neutral and high pH) and H2OCl+ (at low pH). In this study, we seek to examine the roles that two largely overlooked chlorine species, Cl2 and Cl2O, may play in the chlorination of (chloro)phenols. Solution pH, chloride concentration, and chlorine dose were systematically varied in order to assess the importance of different chlorine species as chlorinating agents. Our findings indicate that chlorination rates at pH < 6 increase substantially when chloride is present, attributed to the formation of Cl2. At pH 6.0 and a chlorine dose representative of drinking water treatment, Cl2O is predicted to have at best a minor impact on chlorination reactions, whereas Cl2 may contribute more than 80% to the overall chlorination rate depending on the (chloro)phenol identity and chloride concentration. While it is not possible to preclude H2OCl+ as a chlorinating agent, we were able to model our low-pH data by considering Cl2 only. Even traces of chloride can generate sufficient Cl2 to influence chlorination kinetics, highlighting the role of chloride as a catalyst in chlorination reactions.

The Catalyst-Controlled Regiodivergent Chlorination of Phenols.

Different catalysts are demonstrated to overcome or augment a substrate's innate regioselectivity. Nagasawa's bis-thiourea catalyst was found to overcome the innate para-selectivity of electrophilic phenol chlorination, yielding ortho-chlorinated phenols that are not readily obtainable via canonical electrophilic chlorinations. Conversely, a phosphine sulfide derived from 2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) was found to enhance the innate para-preference of phenol chlorination.

Preparation of Pd-Fe/graphene catalysts by photocatalytic reduction with enhanced electrochemical oxidation-reduction properties for chlorophenols

A convenient method based on photocatalytic reduction was used to prepare graphene-supported Pd, Fe, and bimetallic Pd-Fe nanoparticle (NP) catalysts under mild conditions. The obtained catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Their potential application to the electrocatalytic degradation of chlorinated phenols (CPs) was investigated by cyclic voltammetry (CV) and chronoamperometry. The graphene-supported bimetallic Pd-Fe NP catalyst (Pd0.5Fe0.5/graphene) exhibited the optimal surface performance and contained highly abundant and widespread Pd-Fe NPs of approximately 6.75±0.05nm in size. It exhibited higher electrocatalytic activity for dechlorination of CPs attributed to its higher hydrogen adsorption peak current of 0.117mA than that of the Pd/graphene catalyst, with a 1% weight ratio of Pd (Pd1.0/graphene catalyst), and the Fe/graphene catalyst, with a 1% weight ratio of Fe (Fe1.0/graphene catalyst). The highest reductive peak current (0.038mA) was obtained at −0.347V when using the Pd0.5Fe0.5/graphene catalyst, indicating that the Pd0.5Fe0.5/graphene catalyst has the highest electrocatalytic activity for accelerating the two-electron reduction of O2 to H2O2. In addition, the electrocatalytic activity was enhanced when feeding with O2 and at pH 12.8. The electrochemical reductive reaction of O2 is typically a diffusion-controlled electrochemical process. The calculated values of k representing the mass transfer rate were in the order Pd0.5Fe0.5/graphene (0.379)>Pd1.0/graphene (0.178)>Fe1.0/graphene (0.175). The reduction peak currents for four CPs decreased in the order 3-chlorophenol (0.0214mA)>2,4,5-trichlorophenol (0.0190mA)>2,4-dichlorophenol (0.0188mA)>4-chlorophenol (0.0178mA), indicating that the Pd0.5Fe0.5/graphene electrode would show the most powerful indirect electro-oxidation for 3-CP degradation in comparison with the other CPs. Therefore, the Pd0.5Fe0.5/graphene catalyst exhibits a higher electrocatalytic activity than the Pd1.0/graphene catalyst and Fe1.0/graphene catalyst for the reductive dechlorination and indirect electrochemical oxidation of CPs.

Gas Phase Thermal Oxidation of Endosulfan and Formation of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans.

This paper investigates the thermal decomposition of technical endosulfan under oxidative conditions and the subsequent formation of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/F, dioxins), and their precursors. Both quantum chemical calculations and laboratory experiments were employed to investigate the pathways of oxidation of endosulfan. The laboratory scale apparatus used consists of a tubular reactor and product collection system and analysis train. The results report the effect of temperature (523-923 K) and O2 concentration on PCDD/F formation in a N2 bath gas at a residence time of 5 s. The decomposition of endosulfan produces two types of PCDD/F precursors, involving all chlorinated benzenes (CBz) and chlorinated phenols (CPh). Oxidation of endosulfan favors the formation of PCDF over PCDD. Octachlorodibenzofuran is the most abundant homologue group detected in all experiments. The maximum emission factor for PCDD/F was observed at 923 K and O2 content of 6% and corresponds to 64 ng TEQ-WHO2005 per mg of endosulfan and a total dioxin concentration of 1131 ng/mg of endosulfan.

Testing the Possibility of Photochemical Synthesis of Chlorinated Phenols, Benzenes and Biphenyl: Pre-study Guide for Standards Synthesis

Since deuterium 2H (D) is an isotope of hydrogen 1H, the testing of the possibility of photochemical synthesis of marked chlorinated phenol, biphenyl and benzene using normal solvents was studied. The irradiation of full chlorinated compounds dissolved in normal solvents such as MeOH or n-hexane has led to a reaction substitution in which a chlorine atom was substituted by hydrogen atom forming less grade chlorinated chlorophenols, biphenyls and benzenes. The quantum yields of pentachlorophenol, decachlorobiphenyl and hexachlorobenzene under irradiation using polychromatic light were calculated and found to be 5.7 x 10-3, 1.6 x 10-2 and 1.2 x 10-2 Mol·Einstein-1, respectively. Depending on this study the production of marked chlorinated or non-chlorinated compounds using deuterated appropriate solvents such as MeOH d4 or n-hexane d14 is possible. However, more efforts should be made towards chromatographically separation of synthesized standards and byproducts in order to make the use of these marked compounds as standards in residue analysis feasible.

Testing the Possibility of Photochemical Synthesis of Chlorinated Phenols, Benzenes and Biphenyl: Pre-study Guide for Standards Synthesis

Since deuterium 2H (D) is an isotope of hydrogen 1H, the testing of the possibility of photochemical synthesis of marked chlorinated phenol, biphenyl and benzene using normal solvents was studied. The irradiation of full chlorinated compounds dissolved in normal solvents such as MeOH or n-hexane has led to a reaction substitution in which a chlorine atom was substituted by hydrogen atom forming less grade chlorinated chlorophenols, biphenyls and benzenes. The quantum yields of pentachlorophenol, decachlorobiphenyl and hexachlorobenzene under irradiation using polychromatic light were calculated and found to be 5.7 x 10-3, 1.6 x 10-2 and 1.2 x 10-2 Mol·Einstein-1, respectively. Depending on this study the production of marked chlorinated or non-chlorinated compounds using deuterated appropriate solvents such as MeOH d4 or n-hexane d14 is possible. However, more efforts should be made towards chromatographically separation of synthesized standards and byproducts in order to make the use of these marked compounds as standards in residue analysis feasible.

Evaluation of flow-rate dynamics in the simultaneous photocatalytic treatment of multichlorinated substituted phenols in continuous-flow systems.

The project investigated the simultaneous degradation of chlorophenols dissolved in aqueous systems. The photocatalysis advanced oxidation process was the technology applied to achieve treatment. Chemical behavioural tracking was performed using the chloride dehalogenation sequence dynamics. The study recorded reductive dehalogenation chemical transformation kinetics of multi-substituted chlorinated phenolics in continuous flow reactor systems. This was performed by manipulation of liquid flow-rates in the photocatalytic oxidations process using suspended and immobilised catalyst applications. A modified Langmuir-Hinshelwood kinetic model was proposed that explained the oxidation transformational behaviour of the dehalogenation process derived intermediates. Complementary photocatalytic performance matrices were established for each flow regime; model parameters were calculated and estimated for behavioural profiles of all compounds under scrutiny.

ChemInform Abstract: Aromatic Monochlorination Photosensitized by DDQ with Hydrogen Chloride under Visible‐Light Irradiation.

Photochlorination of aromatic substrates by hydrogen chloride with 2,3-dichloro-5,6-cyano-p-benzoquinone (DDQ) occurs efficiently to produce the corresponding monochlorinated products selectively under visible-light irradiation. The yields for the chlorination of phenol were 70 % and 18 % for p- and o-chlorophenol, respectively, without formation of further chlorinated products. The photoinduced chlorination is initiated by electron transfer from Cl(-) to the triplet excited state of DDQ. The radical intermediates involved in the photochemical reaction have been detected by time-resolved transient absorption measurements.

Synergetic inhibition of PCDD/F formation from pentachlorophenol by mixtures of urea and calcium oxide

Chlorophenols are structurally similar to PCDD/Fs and have been considered as highly potential precursors for PCDD/Fs formation. The suppressing effects of PCDD/F formation from pentachlorophenol (PCP) were investigated on various mass ratios of CaO and urea. The total concentration of 2,3,7,8-PCDD/Fs, mostly dominated by OCDD, was determined to be 48.58–10186ng/mg in inhibitor-reaction systems, being much lower than that in blank reaction system (75654ng/mg). Interestingly, compared with pure CaO and urea reaction system, the concentration and TEQ of formed 2,3,7,8-PCDD/Fs in mixed urea/CaO reaction system were lower, especially with 5–20% urea reaction systems being respectively at decrease by 96.5-99.4% and 99.2-99.7%. The suppression efficiency of TEQ in 5–20% urea reaction systems could be always approximately 100% under 250–350°C. These results suggested that mixed inhibitors, especially 5–20% urea inhibitors, have a synergetic inhibition effect for PCDD/Fs formation from PCP. Mixed inhibitor generated several intermediates, involving CO2, H2O, NH3, Ca(OH)2, CaCO3, HNCO, biuret and ammelide. The complex between PCP and Ca, N-doped species, lower chlorinated phenols and benzenediol, and organic acids were also determined. Synergetic inhibition mechanism may be attributed to accelerated facilitation of acid-base reaction and N doping. The decomposition of PCP itself also contributes to prevent PCDD/Fs formation.

Transformation of avobenzone in conditions of aquatic chlorination and UV-irradiation

Emerging contaminants represent a wide group of the most different compounds. They appear in the environment at trace levels due to human activity. Most of these compounds are not yet regulated. Sunscreen UV-filters play an important role among these emerging contaminants. In the present research the reactions of 4-tert-butyl-4’-methoxydibenzoylmethane (avobenzone), the most common UV filter in the formulation of sunscreens, were studied under the combined influence of active chlorine and UV-irradiation. Twenty five compounds were identified by GC/MS as transformation products of avobenzone in reactions of aquatic UV-irradiation and chlorination with sodium hypochlorite. A complete scheme of transformation of avobenzone covering all the semivolatile products is proposed. The identification of the two primary chlorination products (2-chloro-1-(4-tert-butylphenyl)-3-(4-methoxyphenyl)-1,3-propanedione and 2,2-dichloro-1-(4-tert-butylphenyl)-3-(4-methoxyphenyl)-1,3-propanedione) was confirmed by their synthesis and GC/MS and NMR analysis. Although the toxicities of the majority of these products remain unknown substituted chlorinated phenols and acetophenones are known to be rather toxic. Combined action of active chlorine and UV-irradiation results in the formation of some products (chloroanhydrides, chlorophenols) not forming in conditions of separate application of these disinfection methods. Therefore caring for people «well-being» it is of great importance to apply the most appropriate disinfection method. Since the primary transformation products partially resist powerful UV-C irradiation they may be treated as stable and persistent pollutants.

Influence of chlorine substitution on adsorption of gaseous chlorinated phenolics on multi-walled carbon nanotubes embedded in SiO2

Multi-walled carbon nanotubes (MWCNTs) embedded in SiO2 particles were prepared through the floating-catalyst chemical vapor deposition method. The parameters reaction time and flow rate of the carbon source (CH4) were studied to obtain optimum conditions for MWCNT synthesis. The obtained MWCNTs were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy to confirm their morphology and crystallinity. The optimum conditions were a CH4 flow rate of 100 ml/min in a H2–Ar mixture at a flow rate of 500 ml/min and a reaction time of 20 min. Under these conditions, MWCNTs with average outer and inner diameters of around 50 and 10 nm, respectively, were obtained. SiO2 particles with embedded MWCNTs were studied for their adsorption of gaseous chlorinated phenolic compounds (CPCs), with emphasis on the effect of number of chlorine substituents. The CPC compounds of 2-chlorophenol (CP) and 2,4-dichlorophenol (DCP) were compared against phenol (P). Adsorption of P and CPCs on the particles fit well the Langmuir isotherm. The adsorption capacities of P, CP, and DCP on SiO2 particles with embedded MWCNTs were found to be 3.12, 13.83, and 44.25 mg/g, respectively. Desorption activation energy was determined by thermogravimetric analysis. Chlorine substitution on P changed the adsorption process from physical to chemical adsorption. The particles showed high potential for use as a pre-concentration unit for solid-phase microextraction.

Aromatic Monochlorination Photosensitized by DDQ with Hydrogen Chloride under Visible-Light Irradiation.

Photochlorination of aromatic substrates by hydrogen chloride with 2,3-dichloro-5,6-cyano-p-benzoquinone (DDQ) occurs efficiently to produce the corresponding monochlorinated products selectively under visible-light irradiation. The yields for the chlorination of phenol were 70 % and 18 % for p- and o-chlorophenol, respectively, without formation of further chlorinated products. The photoinduced chlorination is initiated by electron transfer from Cl(-) to the triplet excited state of DDQ. The radical intermediates involved in the photochemical reaction have been detected by time-resolved transient absorption measurements.

Dechlorination of chlorinated phenols by subnanoscale Pd0/Fe0 intercalated in smectite: pathway, reactivity, and selectivity

Smectite clay was employed as templated matrix to prepare subnanoscale Pd0/Fe0 particles, and their components as well as intercalated architectures were well characterized by X-ray energy dispersive spectroscopy (X-EDS) and X-ray diffraction (XRD). Furthermore, as-prepared Pd0/Fe0 subnanoscale nanoparticles were evaluated for their dechlorination effect using chlorinated phenols as model molecules. As a result, pentachlorophenol (PCP) is selectively transformed to phenol in a stepwise dechlorination pathway within 6h, and the dechlorination rate constants show linearly relationship with contents of Pd as its loadings <0.065%. Comparing with PCP, other chlorinated phenols display similar degradation pattern but within much shorter time frame. The dechlorination rate of chlorinated phenols increases with decreasing in number of -Cl attached to aromatic ring, which can be predicted by the total charge of the aromatic ring, exhibiting an inversely linear relationship with the dechlorination rates. While the selectivity of dechlorination depends on the charges associated with the individual aromatic carbon. Chloro-functional groups at the ortho-position are easier to be dechlorinated than that at meta- and para- positions yielding primarily 3,4,5-TCP as intermediate from PCP, further to phenol. The effective dechlorination warrants their potential utilizations in development of in-situ remediation technologies for organic pollutants in contaminated water.

Investigation of photo-assisted and crude peroxidase mediated transformations of chlorinated phenols (CPs) from spiked and industrial wastewaters: identification of reaction products.

This work focused on photo-assisted crude peroxidase mediated transformations of chlorinated phenols (CPs) from spiked and industrial wastewaters and the identification of reaction products formed. Garden radish Raphanus sativus was the source of crude peroxidase. No chlorine bearing compounds were detected by gas chromatography-high resolution mass spectrometry analysis. Under identical test conditions, the concentrations of 4-chlorophenol and 2,4-dichlorophenol were demoted to zero from 514 mg/L, 652 mg/L and that of 2,4,6-trichlorophenol and pentachlorophenol were reduced to 18 mg/L and 37 mg/L from 790 mg/L and 1066 mg/L, respectively (high-pressure liquid chromatography analysis). Chloride ion release profiles also showed a progressively increasing trend. A neat chemical oxygen demand removal to the extent of 63-79% was achieved in the case of spiked wastewater sample and to the extent of 77% for industrial wastewaters. A hypothesis reaction scheme was also suggested to comprehend the mechanism of degradation reactions.

Adsorption of chlorinated phenols on multiwalled carbon nanotubes

This work studies the adsorption of four chlorinated phenols (2,4-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,5-tetrachlorophenol and pentachlorophenol) in aqueous solutions on multiwalled carbon nanotubes (MWCNT).

Salting‐out assisted liquid–liquid extraction coupled to dispersive liquid–liquid microextraction for the determination of chlorophenols in wine by high‐performance liquid chromatography

A novel procedure of sample preparation combined with high-performance liquid chromatography with diode array detection is introduced for the analysis of highly chlorinated phenols (trichlorophenols, tetrachlorophenols, and pentachlorophenol) in wine. The main features of the proposed method are (i) low-toxicity diethyl carbonate as extraction solvent to selectively extract the analytes without matrix effect, (ii) the combination of salting-out assisted liquid-liquid extraction and dispersive liquid-liquid microextraction to achieve an enrichment factor of 334-361, and (iii) the extract is analyzed by high-performance liquid chromatography to avoid derivatization. Under the optimum conditions, correlation coefficients (r) were >0.997 for calibration curves in the range 1-80 ng/mL, detection limits and quantification limits ranged from 0.19 to 0.67 and 0.63 to 2.23 ng/mL, respectively, and relative standard deviation was <8%. The method was applied for the determination of chlorophenols in real wines, with recovery rates in the range 82-104%.

Comparison of cyclic and polymeric disulfides as catalysts for the regioselective chlorination of phenols

Two cyclic and two polymeric disulfides have been synthesized and established to be useful catalysts for the chlorination of m-xylenol, o-cresol, m-cresol and phenol using freshly distilled sulfuryl chloride in the presence of aluminum or ferric chloride as a co-catalyst at room temperature. The yields of p-isomers and para/ortho ratios were higher compared to cases where no catalyst was used with most catalysts for most phenols even when a very low concentration of disulfide was used.

Effect of sodium dodecyl benzene sulfonate on the process of Fenton degradation of 4-chlorophenol

The Fenton process has been shown to be very successful in removing highly toxic chlorinated phenols from water. However, the influence of other constituents in industrial wastewater, such as sodium dodecyl benzene sulfonate (SDBS) surfactants should be intensively researched. In this study, the effects of SDBS on the kinetics of 4-chlorophenol (4-CP) degradation undergoing Fenton process have been studied. Results showed that 4-CP degradation ratio decreased as SDBS concentration increased. The 4-CP degradation ratio declined from 98.3 to 84.5% when the SDBS concentration increased from 0 to 2.0 mmol L−1 after 10 min reaction. This experimental result was attributed to the hydration between 4-CP and SDBS and the consumption of hydroxyl radicals (⋅OH) by surfactants. The SDBS had amphiphilic structure in water environment with hydrophilic and hydrophobic entities. It could interact with 4-CP functional groups via hydrophilic groups (benzene sulfonate) by hydration in the aqueous phase. The kinetics modeling indicates that the 4-CP degradation reaction followed the pseudo-first-order reaction for 4-CP concentration. The SDBS also had affirmative effects on the hydrophilic and organic acid intermediate organic matter mineralization. The SDBS existence could reduce the maximum concentrations of intermediate products. For example, the organic acids intermediate maleic acid concentration was descend from 2.59 to 0.21 mmol L−1 when the SDBS concentration increased from 0 to 2.0 mmol L−1. In a word, the surfactants SDBS can reduce the 4-CP degradation ratio and encourage the intermediate products mineralization.