Chlorophenol Isomers Research Articles

A PdPt nanoparticle-decorated thiol-functionalized MOF with high peroxidase-like activity for colorimetric sensing of D-glucose and chlorophenol isomers.

The peroxidase (POD)-like catalytic activity of various nanozymes was extensively applied in many significant fields. In this study, a thiol-functionalized MOF-loaded PdPt nanocomposite (UiO-66-(SH)2@PdPt) was fabricated, which possesses superior and selective POD-like activity with strong affinity towards H2O2 and 3,3',5,5'-tetramethylbenzidine under mild conditions. The POD-like property of UiO-66-(SH)2@PdPt was used to sensitively detect the concentration of D-glucose under near-neutral (pH = 6.5) conditions. The detection limit of D-glucose was as low as 2.7 μM, and the linear range of D-glucose was 5-700 μM. In addition, UiO-66-(SH)2@PdPt could accelerate the oxidative coupling chromogenic reaction of chlorophenol (CP) and 4-aminoantipyrine (4-AAP) in the presence of H2O2. Based on this phenomenon, a simple and visualized sensing array for the identification of chlorophenol contaminant isomers was further constructed to finally achieve the effective differentiation of three monochlorophenol isomers and six dichlorophenol isomers. Furthermore, a colorimetric detection method for 2-chlorophenol and 2,4-dichlorophenol was established. This work provides an effective means to improve the catalytic activity and selectivity of nanozymes by introducing an ideal carrier, which will be of significant value for the design of efficient nanozymes.

Purification of Chlorophenol Isomers by Stripping Crystallization Combining Melt Crystallization and Vaporization.

Stripping crystallization (SC) was introduced in this work to purify p-chlorophenol from the p-chlorophenol-rich liquid mixture and to purify m-chlorophenol from the m-chlorophenol-rich liquid mixture, respectively. Essentially, SC combines melt crystallization and vaporization to produce the solid product and the vapor from a liquid mixture via a series of three-phase transformations at reduced pressures during the cooling process. At the end of the SC, only the solid product remained while the liquid mixture was almost eliminated and the produced vapor was removed. A set of differential equations based on the mass and energy balances were proposed to determine the incremental variations of the amounts of remaining liquid, produced solid and produced vapor during the batch SC process. The experimental yield and product purity of the final product obtained from the batch SC experiments were compared with those predicted by the model.

Fabrication of spherical silica amino-functionalized microporous organic network composites for high performance liquid chromatography

Microporous organic networks (MONs) are a potential class of microporous materials in analytical chemistry. As great efforts have been made in sample pretreatment and gas chromatography, the application of MONs in high performance liquid chromatography (HPLC) has largely lagged and has never been investigated. In addition, directly packing of MONs into columns for HPLC is impractical due to the high column pressure and low column efficiency resulted from the sub-micron sized and irregular MONs. To solve these issues and uncover the possibility of MONs in HPLC, here we report the fabrication of spherical silica amino-functionalized MON (SiO2@MON-NH2) composite as a novel stationary phase for HPLC. Neutral, acidic and alkaline probes were evaluated on SiO2@MON-NH2 packed column. A column efficiency of 21,246 plates per meter was obtained for n-propylbenzene. The results revealed the hydrophobic interaction was the main separation mechanism on SiO2@MON-NH2 packed column. Baseline separation of benzenediol, dichlorophenol, chlorophenol and phenylenediamine position isomers, deoxynucleosides and nucleosides was also achieved on SiO2@MON-NH2 packed column. The relative standard deviations of retention time, peak height and peak area for the studied position isomers, deoxynucleosides and nucleosides were 0.2–0.7%, 0.3–3.7% and 1.7–3.5%, respectively. The SiO2@MON-NH2 packed column also offered better resolution for dichlorophenol isomers, deoxynucleosides and nucleosides than SiO2–NH2 and commercial C18 columns. These results revealed the potential of MONs in HPLC and also provided a new way for the use of nano-sized or irregular MONs in HPLC.

The Effect of a Polar Solvent on the ππ*-Bands of Chlorophenol Isomers

The optical absorption spectra of para-, meta-, and ortho-chlorophenol in the gas phase and in a polar solvent (methanol) are recorded. It is shown that the bathochromic shifts of the first and second ππ* absorption bands in a methanol solution compared to their positions in the gas phase are caused by the formation of a hydrogen bond between chlorophenol and methanol molecules and by the effect of solvent on the formed hydrogen complex. The result was obtained by calculating electronic spectra by the TDDFT B3LYP/6-311++G(d,p) method with the use of the polarizable continuum model.

The Preparation of Pd/Foam-Ni Electrode and Its Electrocatalytic Hydrodechlorination for Monochlorophenol Isomers

Noble metal palladium modified foamed nickel electrode (Pd/foam-Ni) was prepared by electrodeposition method. The fabricated electrode showed better catalytic performance than the Pd/foam-Ni prepared by conventional electroless deposition. The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Electrocatalytic activity of the Pd/Ni was studied for the hydrodechlorination of monochlorophenol isomers. The Pd/Ni exhibited good catalytic activity for 3-chlorophenol (3-CP). Complete decomposition of chlorophenol isomers could be achieved within 2 h, and the hydrodechlorination process conformed to the pseudo-first-order kinetic model. It showed a supreme stability after recycling for 5 times. The Pd/Ni exhibited a promising application prospect with high effectiveness and low Pd loading.

Adsorption of Phenol and Chlorophenol Mixtures on Silicalite-1 Determined by GC-MS Method

A method is presented in which gas chromatography coupled with mass spectrometry (GC-MS) allows quantitative simultaneous detection of mixtures of phenol (Ph), 2-chlorophenol (2-CPh), 3-cholorphenol (3-CPh), and 4-cholorophenol (4-CPh) in aqueous mixtures after being adsorbed on silicalita-1, utilizing selected-ion monitoring (SIM) and full-scan modes mass selective detection. GCMS with SIM at m/z = 64 and m/z = 128 showed good detection selectivity for mixtures of Ph, 2-CPh and 3-CPh (M1), and 2-CPh and 4-CPh (M2). Silicalita-1 was obtained from an amorphous organo-alumino-silicic gel from rice husk, an abundant and low cost agricultural waste residue that is readily available in large quantities. This product was used as a sorbent for solid phase extraction of organic analytes from aqueous solutions. The adsorption of the three chlorophenol isomers, ortho-, meta-, and para-, by silicalite-1 has been studied independently, showing that meta- and para-chlorophenol isomers are adsorbed more than ortho-chlorophenol. However the adsorption behavior of mixtures of these isomers was not reported. In this work, it was found that when the ortho-isomer is mixed either with meta or para-chlorophenol, considerable differences were observed in the adsorption process; in the studied mixture, the ortho-isomer was adsorbed more than the meta-and para-chlorophenol.

Investigation of steric effect in the formation of hydrogen-bonded complexes of isomeric chlorophenols with N,N-dimethylaniline

In order to study the steric effect in the formation hydrogen bonded complexes two systems were chosen. The formation of hydrogen bonded complexes of N,N-dimethylaniline (DMA) with o-chlorophenol (o-CP) as well as m-chlorophenol (m-CP) in tetrahydrofuran medium is established by ultrasonic and UV spectral methods. Ultrasonic velocity (u), density (ρ) and viscosity (η) are measured for the two systems in the concentration range 0.01M–0.1M and acoustical and excess thermo acoustical properties are computed. The trend in the acoustical and excess parameters with concentration in both the ternary systems establishes the formation of hydrogen bonded complexes between tertiary amine (DMA) and the two chlorophenols. The formation constants (K) of the hydrogen bonded complexes are reported and compared with those obtained by UV spectral method. It may be pointed out that trend in K values obtained by acoustical method is the same as that obtained by optical method. Experimentally obtained K values are correlated with the molecular properties of chlorophenols computed using B3LYP/6-311++G(d,p) basis set. The geometry, bond characteristics and interaction energies of the hydrogen bonded complexes were investigated through quantum chemical calculations. The computed values of molecular properties explain the trend in the experimental ‘K’ values of the two complexes. It is found that complex of ortho-Chlorophenol (o-CP) with DMA is thermodynamically less stable than the DMA-meta-Chlorophenol (m-CP) complex indicating the steric influence of chloro substituent near the site of complex formation.

Mechanism of Intrinsic Chemiluminescence Production from the Degradation of Persistent Chlorinated Phenols by the Fenton System: A Structure-Activity Relationship Study and the Critical Role of Quinoid and Semiquinone Radical Intermediates.

We found recently that intrinsic chemiluminescence (CL) could be produced by all 19 chlorophenolic persistent organic pollutants during environmentally friendly advanced oxidation processes. However, the underlying mechanism for the structure-activity relationship (SAR, i.e., the chemical structures and the CL generation) remains unclear. In this study, we found that, for all 19 chlorophenol congeners tested, the CL increased with an increasing number of chlorine atoms in general; and for chlorophenol isomers (such as the 6 trichlorophenols), the CL decreased in the order of meta- > ortho-/para-Cl-substituents with respect to the -OH group of chlorophenols. Further studies showed that not only chlorinated quinoid intermediates but also, more interestingly, chlorinated semiquinone radicals were produced during the degradation of trichlorophenols by the Fenton reagent; and the type and yield of which were determined by the directing effects, hydrogen bonding, and steric hindrance effect of the OH- and/or Cl-substitution groups. More importantly, a good correlation was observed between the formation of these quinoid intermediates and CL generation, which could fully explain the above SAR findings. This represents the first report on the structure-activity relationship study and the critical role of quinoid and semiquinone radical intermediates, which may have broad chemical and environmental implications for future studies on remediation of other halogenated persistent organic pollutants by advanced oxidation processes.

Precursor anion states in dissociative electron attachment to chlorophenol isomers.

We report a theoretical study on low-energy (<10 eV) elastic electron scattering from chlorophenol isomers, namely, para-chlorophenol (pCP), meta-chlorophenol (mCP), and ortho-chlorophenol (oCP). The calculations were performed with the Schwinger multichannel method with pseudopotentials, and analysis of the computed integral cross sections and virtual orbitals revealed one σCCl (∗), one σOH (∗), and three π(∗) shape resonances. We show that electron capture into the two lower lying π(∗) orbitals initiates dissociative processes that lead to the elimination of the chloride ion, accounting for the two overlapping peaks where this fragment was observed. Despite the relatively small differences on the energetics of the π(∗) resonances, a major isomeric effect was found on their corresponding autodetachment lifetimes, which accounts for the observed increasing cross sections in the progression pCP < mCP < oCP. In particular, dissociation from the π1 (∗) anion of pCP is largely suppressed because of the unfavorable mixing with the σCCl (∗) state. We found the intramolecular hydrogen bond present in oCP to have the opposite effects of stabilizing the σCCl (∗) resonance and destabilizing the σOH (∗) resonance. We also suggest that the hydrogen abstraction observed in chlorophenols and phenol actually takes place by a mechanism in which the incoming electron is directly attached to the dissociative σOH (∗) orbital.

Silicalite-1, an adsorbent for 2-, 3-, and 4-chlorophenols

The adsorption of the three chlorophenol isomers, ortho, meta and para, by silicalite-1 has been studied at 30 °C, below the solubility (at the same temperature) in water. Large differences, up to 30 times, have been observed between the adsorption of the para- vs. the ortho-isomer. The difference of behavior observed between the isomers is assigned to the tendency to self-organization of the para-isomer. It seems probable that the adsorption sites are at the intersection channels. From a technical point of view, silicalite-1 seems a competitive adsorbent for p-chlorophenol.

Identification of excited singlet states of chlorophenol isomers

The UV spectra of optical absorption of para-, meta-, and ortho-chlorophenol are recorded in the gas phase. The bands of UV spectra are assigned to the electronic transitions of molecules to definite excited singlet states on the basis of calculations by the TDDFT B3LYP/6-311++G(d, p) method. In each case the electron configuration making the predominant contribution to the particular singlet state is determined. The energies of singlet electronic transitions are shown to depend on the energy spacing between the molecular orbitals involved in these transitions.

Solar driven production of toxic halogenated and nitroaromatic compounds in natural seawater

Natural seawater (NSW) sampled in March and June 2007 in the Gulf of Trieste, Italy, has been spiked with phenol and irradiated in a device simulating solar light spectrum and intensity. Opposite to the case of artificial seawater, for which phenol is slightly degraded by direct photolysis, in NSW the phenol degradation mediated by natural photosensitizers occurs, forming several secondary pollutants, including hydroxyderivatives (1,4-benzoquinone, resorcinol), three chlorophenol isomers, 2,3-dichlorophenol, 2- and 4-bromophenol, 2- and 4-nitrophenol, and several condensed products (2 and 4-phenoxyphenol, 2,2′-, 4,4′- and 2,4-bisphenol). These compounds are toxic to bacteria and other living organisms. Ecotoxicologic effect has been evaluated by using the Vibrio Fischeri luminescent bacteria assay. This technique uses marine organisms, and it is therefore well suited for the study on marine samples. A correlation exists between the intermediates evolution and the toxicity profile, as the largest toxicity is observed when compounds with the lower EC50 (halophenols, phenoxyphenols) are formed at higher concentration.

Effect of ortho-chlorine substitution on the partition behavior of chlorophenols

Chlorophenol isomers are known to possess substantially different octanol/water and octane/water partition constants depending on whether the chlorine substituents are in the ortho or meta/ para position. Here we show that the same is also true for environmental partition processes such as water/air and humic acid/air partitioning. Quantitative structure property relationships (QSPR) such as those in the widely used EPI-suite or SPARC fail to correctly predict this influence of the substituent position on the compound’s partitioning. Only a more sophisticated quantum chemical software, called COSMOtherm, correctly reproduced these effects. Based on this and earlier experiences we conclude that COSMOtherm may be a better tool for screening large sets of chemicals for which no experimental data on their partitioning yet exist.

Definitive evidence for the existence of isomeric chlorophenyl radicals (C 6H 4Cl [rad]) from charge inversion mass spectrometry and DFT calculations

Free radical species are much more reactive than stable molecules, and so usually exist only as transient intermediates in chemical reactions. Charge inversion mass spectrometry using alkali metal targets is an effective method for determining the structure and dissociation processes of radicals, and can also enable differentiation between isomeric forms of compounds whose parent ions have similar mass spectra and similar collisionally activated dissociation spectra, such as the isomers of dichlorobenzene and chlorophenol. The charge inversion process using alkali metal targets proceeds via near-resonant neutralization, followed by spontaneous dissociation of the excited neutrals, and then endothermic negative ion formation. In the normalized charge inversion spectra of ortho-, meta-, and para-dichlorobenzene (C 6H 4Cl 2) measured in this work, the intensities of the peaks associated with chlorine anions (Cl −) are almost same for each of the isomers, whereas the intensities of the peaks associated with the chlorophenyl anions (C 6H 4Cl −) display a strong dependence on the isomeric structure of the parent compound. The similarities of the Cl − ion peak intensities indicate that neutralization cross-sections and branching ratios to produce Cl radicals are the same for each of the isomeric precursor C 6H 4Cl 2 + ions. The strong isomer-dependence of the peak intensities of C 6H 4Cl − anions suggests that the chlorophenyl radicals (C 6H 4Cl ) formed from C 6H 4Cl 2 by loss of Cl do not undergo isomerization, and that the electron transfer cross-sections to form the negative ions are strongly isomer-dependent. Density functional theory (DFT) calculations on the o-, m-, and p-C 6H 4Cl radicals show that the barriers to isomerization are in excess of 2.8 eV, and these high isomerization barriers are believed to be the reason for the absence of isomerization among the C 6H 4Cl radicals during the charge inversion process. Calculated adiabatic electron affinities and vertical electron affinities both show differences for the o-, m-, and p-isomers, but the trend in the magnitude of the electron affinities has an inverse relation to the peak intensities of the isomeric C 6H 4Cl − ions in the charge inversion spectra. It is, therefore, assumed that the cross-sections for negative ion formation are influenced by many factors other than the electron affinity, such as the relatively large geometrical distortion in the chlorophenyl radicals predicted in this work. The good agreement between the experimental results and the theoretical predictions obtained in this work provides compelling evidence for the existence of isomeric C 6H 4Cl radicals that do not undergo isomerization during charge inversion mass spectrometry.

Degradation of 2,4-dichlorophenol by using glow discharge electrolysis

Degradation of 2,4-dichlorophenol (2,4-DCP) in aqueous by glow discharge electrolysis (GDE) has been investigated. Ultraviolet (UV) absorption spectra, atomic force microscopy (AFM), high performance liquid chromatography (HPLC) and gas chromatogram–mass spectrum (GC/MS) are used to monitor the degradation process and to identify the major oxidation intermediate products. It has been found that 2,4-DCP undergoes a series of intermediate step, which leads to form a number of intermediate products, mainly isomeric chlorophenols and aliphatic acids. These products are further oxidized, eventually, mineralized into CO 2 and Cl −. A degradation pathway for 2,4-DCP is proposed on the basis of detection of intermediate compounds.

Comparison of dissociation mechanism between collisionally activated dissociation and charge inversion using alkali metal targets for chlorophenol isomers

Chlorinated aromatic compounds are well-known environmental pollutants whose toxicities depend dramatically on the chlorine substitution pattern, making differentiation of chlorophenol isomers important for environmental analysis. Collisionally activated dissociation (CAD) spectra and charge inversion spectra of ortho-, meta-, and para-chlorophenols (ClC 6H 4OH) and their partially deuterated forms (ClC 6H 4OD) were measured using alkali metal targets. The peaks associated with C 6H 4O + and C 5H 5Cl + ions observed in the CAD spectra result from the loss of HCl and CO fragments, respectively, after the re-arrangement of the hydroxyl hydrogen atom. The peaks associated with C 6H 4OH − and ClC 6H 4O − ions observed in the charge inversion spectra result from Cl loss and from hydroxyl bond dissociation, respectively. Isomeric differentiation is possible based on the clear differences observed in the relative intensities of these pairs of peaks. Although the intensities of the peaks associated with C 6H 4O + relative to those of C 5H 5Cl + in the CAD spectra are independent of the target species, the intensities of the peaks associated with C 6H 4OH − relative to those of ClC 6H 4O − in the charge inversion spectra are target dependent. The isomeric dependence of the positive ion distribution patterns in the CAD spectra is proposed to be due to the differences in the rate of the hydrogen atom re-arrangement process. In contrast, the isomeric dependence of the negative ion distribution patterns in the charge inversion spectra is attributed to differences in the bond strength involved in the direct dissociation process in the neutral intermediate species.

Semivolatile and volatile compounds from the pyrolysis and combustion of polyvinyl chloride

Emissions evolved from the pyrolysis and combustion of polyvinyl chloride (PVC) were studied at four different temperatures (500, 700, 850 and 1000 °C) in a horizontal laboratory tubular quartz reactor in order to analyse the influence of both temperature and reaction atmosphere on the final products from thermal and oxidative reactions. It was observed that the CO 2/CO ratio increased with temperature. Methane was the only light hydrocarbon whose yield increased with temperature up to 1000 °C. Benzene was rather stable at high temperatures, but in general, combustion at temperatures above 500 °C was enough to destroy light hydrocarbons. Semivolatile hydrocarbons were collected in XAD-2 resin and more than 160 compounds were detected. Trends on polyaromatic hydrocarbon (PAH) yields showed that most had a maximum at 850 °C in pyrolysis, but naphthalene at 700 °C. Formation of chlorinated aromatics was detected. A detailed analysis of all isomers of chlorobenzenes and chlorophenols was performed. Both of them reached higher total yields in combustion runs, the first ones having a maximum at 700 °C and the latter at 500 °C. Pyrolysis and combustion runs at 850 °C were conducted to study the formation of polychlorodibenzo- p-dioxins (PCDDs) and polychlorodibenzofurans (PCDFs). There was more than 20-fold increase in total yields from pyrolysis to combustion, and PCDF yields represented in each case about 10 times PCDD yields.

Chemometric approach in optimization of micellar liquid chromatographic separation of some halogenated phenols

Simultaneous optimization of separation quality and analysis time of the micellar liquid chromatography of nine chlorophenol isomers was investigated. The effect on retention of three experimental parameters was studied using multivariate analysis. The factors studied were the concentration of sodium dodecyl sulfate, propanol content and pH of the mobile phase. The experiments were performed according to the face-centred cube central composite design and the inverse form of the experimental retention times for analytes were fitted to the polynomial models. The results of the analysis of variance showed that the models obtained explain greater than 99% of the variance observed in the chromatograms. Good predictive ability of the models was verified as high values of the statistics R 2 and F were obtained for the linear relationship between predicted cross-validated and experimental values of the dependent variable. The study showed that the use of Pareto-optimality method, an approach from multi-criteria decision-making, allows the selection of the best possible combinations of separation and analysis time in micellar liquid chromatography of chlorophenols.

The site-selective functionalization of halogen-bearing phenols: an exercise in diversity-oriented organometallic synthesis

The organometallic approach to diversity-oriented organic synthesis was subjected to a further test, this time in the phenol series. The model compounds selected were 2,3,6-trifluorophenol, the three isomers of (trifluoromethoxy)phenol and the three isomers of chlorophenol. A combination of optionally site selective metalations and protective group-controlled metalations enabled the selective generation of several isomeric intermediates in each case and their subsequent conversion into functionalized derivatives, in particular hydroxybenzoic acids.

Multi-criteria decision making in micellar liquid chromatographic separation of chlorophenols.

Simultaneous optimization of separation quality and analysis time of the micellar liquid chromatography of nine chlorophenol isomers was investigated. The effect on retention of three experimental parameters was studied using multivariate analysis. The factors studied were the concentration of sodium dodecyl sulfate, propanol content, and pH of the mobile phase. The experiments were performed according to the face-centered cube central composite design and the inverse form of the experimental retention times of analytes was fitted to polynomial models. The results of the analysis of variance showed that the models obtained explain over 99% of the variance observed in the chromatograms. The good predictive ability of the models was verified by high correlation coefficient (R2 > 0.99) and F ratio values for the plots of predicted cross-validated versus experimental retention times. The study showed that the use of the Pareto-Optimality method, an approach from multi-criteria decision making, allows selection of the best possible combinations of separation quality and analysis time in micellar liquid chromatography of chlorophenols.