4-chlorobenzoic Acid Research Articles

Fate of Cr(III) during Ozonation of Secondary Municipal Wastewater Effluent

ABSTRACTIn the present study, the fate of trivalent chromium (Cr(III)) during ozonation of ultrapurified water and wastewater effluent was investigated. In experiments conducted in phosphate buffered ultrapurified water, O3 alone in excess was inefficient to oxidize Cr(III) (only about 10–15% of total Cr(III) content), while in presence of the secondary oxidant, OH radical, almost all Cr(III) was oxidized to hexavalent chromium (Cr(VI)). In a wastewater effluent, spiked with Cr(III), only about 10–20% of Cr(III) was oxidized with specific ozone doses in the range 0.15–1.5 gO3/gDOC, although O3 and OH radical were both available for reaction. Cr(VI) formation was monitored in parallel with the abatement of some common micropollutants, reacting with differing apparent second-order rate constants with ozone, decreasing in the order carbamazepine>> benzotriazole> atrazine> p-chlorobenzoic acid (pCBA). Carbamazepine and benzotriazole were abated to >80% for specific O3 doses of 0.3 gO3/gDOC and 0.8 gO3/gDOC, respectively. The more ozone-resistant compounds (atrazine and pCBA) required a specific ozone dose of about 1.25 gO3/gDOC for the same relative abatement. At this specific ozone dose (i.e., 1.25 gO3/gDOC), only about 20% of Cr(III) was oxidized to Cr(VI), whereas only 10% of Cr(III) was oxidized to Cr(VI) at a more realistic specific ozone dose for enhanced wastewater treatment for micropollutant abatement (0.5 gO3/gDOC). Therefore, for typical Cr(III) levels in municipal wastewaters, effluent ozonation only leads to toxicologically insignificant Cr(VI) concentrations.

Preparation and properties of polyethylene-coated terbium complex/calcium carbonate composite fluorescent material

A reaction of terbium chloride hexahydrate and 4-chlorobenzoic acid was used to form a terbium complex on the surface of an alkaline calcium carbonate core. Different concentrations of high-density polyethylene (HDPE) toluene solution were then coated onto the prepared terbium complex/calcium carbonate composite fluorescent material (referred to as Material I), which resulted in a series of core-shell HDPE/terbium complex/calcium composite fluorescent materials (referred to as Material II). The structures of these materials were identified and analyzed using UV spectroscopy, IR spectroscopy, X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy and inductively coupled plasma-optional emission spectrometry. The thermal stability and fluorescence of these materials were also examined, and results showed that both Materials I and II were shown to have high thermal stability and high levels of fluorescence. These new types of composite fluorescent materials not only offer economic savings on expensive rare earth resources through reduced production costs, they also offer an effective alternative method for the preparation of highly fluorescent, highly temperature resistant binary terbium complexes. Further, the use of the polymer polyethylene coating on the fluorescent material significantly enhanced the emission intensity of the composite fluorescent materials and offers new possibilities for the production of high-end rare earth fluorescent materials.

Development of micellar electrokinetic chromatography method for the determination of three defined impurities in indomethacin.

A micellar electrokinetic chromatography method for the determination of indomethacin impurities (4-chlorobenzoic acid, 5-methoxy-2-methyl-3-indoleacetic acid, and 3,4-dichloroindomethacin) has been developed. A 64.5/56-cm fused silica 50μmid capillary with extended light path (150μmid) detection window was used. Internal standard was 1-naphthylacetic acid. The analytes were separated at 30kV with DAD detection at 224nm. A central composite face-centered design was applied for the optimization of the separation conditions. The effect of SDS concentration, content of methanol, concentration of phosphate buffer, and pHof the buffer were studied at three levels. The optimized background electrolyte was 20mmol/L phosphate buffer (pH7.57) containing 58mmol/L SDS and 0% MeOH. Sufficient resolution of all compounds with Rs≥3.5 was achieved within 10min. The method was validated for a range of 1.25-80μg/mL of each impurity corresponding to 0.05-3.2% relative to the concentration of indomethacin (2.5mg/mL). The calibration curves were rectilinear with correlation coefficients r2 exceeding 0.9994. The lower limit of quantification was 0.05% or 1.25μg/mL that complies with the reporting limits regarding the ICH Q3A guideline. The method was applied to purity assay of indomethacin in both bulk drug and gel.

Molecular Vise Approach to Create Metal-Binding Sites in MOFs and Detection of Biomarkers.

We report a new approach to create metal-binding site in a series of metal-organic frameworks (MOFs), where tetratopic carboxylate linker, 4',4'',4''',4''''-methanetetrayltetrabiphenyl-4-carboxylic acid, is partially replaced by a tritopic carboxylate linker, tris(4-carboxybiphenyl)amine, in combination with monotopic linkers, formic acid, trifluoroacetic acid, benzoic acid, isonicotinic acid, 4-chlorobenzoic acid, and 4-nitrobenzoic acid, respectively. The distance between these paired-up linkers can be precisely controlled, ranging from 5.4 to 10.8 Å, where a variety of metals, Mg2+ , Al3+ , Cr3+ , Mn2+ , Fe3+ , Co2+ , Ni2+ , Cu2+ , Zn2+ , Ag+ , Cd2+ and Pb2+ , can be placed in. The distribution of these metal-binding sites across a single crystal is visualized by 3D tomography of laser scanning confocal microscopy with a resolution of 10 nm. The binding affinity between the metal and its binding-site in MOF can be varied in a large range (observed binding constants, Kobs from 1.56×102 to 1.70×104 L mol-1 ), in aqueous solution. The fluorescence of these crystals can be used to detect biomarkers, such as cysteine, homocysteine and glutathione, with ultrahigh sensitivity and without the interference of urine, through the dissociation of metal ions from their binding sites.

Liquid chromatography/isotope ratio mass spectrometry analysis of halogenated benzoates for characterization of the underlying degradation reaction in Thauera chlorobenzoica CB-1T.

Halogenated benzoic acids occur in the environment due to their widespread agricultural and pharmaceutical use. Compound-specific stable isotope analysis (CSIA) has developed over the last decades for investigation of in situ transformation and reaction mechanisms of environmental pollutants amenable by gas chromatography (GC). As polar compounds are unsuitable for GC analysis we developed a method to perform liquid chromatography (LC)/CSIA for halogenated benzoates. LC/isotope ratio mass spectrometry (IRMS) utilizing a LC-Surveyor pump coupled to a MAT 253 isotope ratio mass spectrometer via a LC-Isolink interface was applied. For chromatographic separation a YMC-Triart C18 column and a potassium hydrogen phosphate buffer (150mM, pH7.0, 40°C, 200μL mL-1 ) were used, followed by wet oxidation deploying 1.5molL-1 ortho-phosphoric acid and 200g L-1 sodium peroxodisulfate at 75μL mL-1 . Separation of benzoate and halogenated benzoates could be achieved in less than 40min over a concentration range of 2 orders of magnitude. Under these conditions the dehalogenation reaction of Thauera chlorobenzoica 3CB-1T using 3-chloro-, 3-bromo- and 4-chlorobenzoic acid was investigated resulting in inverse carbon isotope fractionation for meta-substituted benzoic acids and minor normal fractionation for para-substituted benzoic acids. Together with the respective growth rates this led to the assumption that dehalogenation of para-halobenzoic acids follows a different mechanism from that of meta-halobenzoic acids. A new LC/IRMS method for the quantitative determination of halogenated benzoates was developed and used to investigate the in vivo transformation pathways of these compounds, providing some insights into degradation and removal of these widespread compounds by T. chlorobenzoica 3CB-1T .

Specific Features of Chlorinated Biphenyl Decomposition by Rhodococcus wratislaviensis Strain KT112-7 under High Salt Conditions

Rhodococcus wratislaviensis strain KT112-7 (VKM As-2623D) degraded monosubstituted 2-/4-chlorobiphenyls (94.25 mg/L) and 2,4'-dichlorobiphenyl (22.3 mg/L) when the sodium chloride content in the culture medium did not exceed 50 g/L. We have calculated the kinetic parameters of chlorobiphenyl (CB) decomposition by the КТ112-7 strain, which demonstrated decreased decomposition efficiency with increasing NaCl concentration. A linear correlation has been found between the content of saturated, unsaturated, and branched fatty acids in the cell wall of the KT112-7 strain and the NaCl content in the culture medium. The change in the content and composition of fatty acids in the cell wall apparently led to a change in the permeability of the CB cell wall. R. wratislaviensis strain KT112-7 was able to oxidize the unsubstituted ring in 2-CB and 4-CB at all studied NaCl concentrations in the medium and efficiently decomposed the chlorobenzoic acids (CBAs) that formed as a result of the oxidation. Decomposition of 2,4'-CB at low NaCl concentrations in the medium (not higher than 10 g/L) involved the oxidation of the ring substituted by chlorine in the position 4, while the presence of 20–50 g/L of NaCl led to the oxidation of the ring substituted by chlorine in the position 2. The main detected metabolite was 2-chlorobenzoic acid in the former case and 4-chlorobenzoic acid in the latter. The 4-CBA transformation proceeded via the formation of protocatechuic acid (3,4-hydroxybenzoic acid) and catechol at all of the studied sodium chloride concentrations in the medium and through another pathway involving the formation of chlorocatechol at NaCl concentrations of 30, 40, and 50 g/L.

Identification of the impurities in o-chlorophenyl cyclopentyl ketone samples by high performance liquid chromatography-hybrid ion trap/time-of-flight mass spectrometry and preparation of o-chlorophenyl cyclopentyl ketone standard

A method for the identification of relevant impurities in illegal o-chlorophenyl cyclopentyl ketone drug was developed. Identification of impurities could help regulation of this illegal drug and allow the sources of samples of the drug to be identified. An efficient and effective method for qualitatively analyzing samples using high performance liquid chromatography-hybrid ion trap/time-of-flight mass spectrometry (HPLC-IT/TOF MS) was developed. The o-chlorophenyl cyclopentyl ketone fragmentation pathway during HPLC-MSn was determined by analyzing a standard by HPLC-IT/TOF MS. The optimized HPLC-IT/TOF MS method allowed two impurities in o-chlorophenyl cyclopentyl ketone samples to be identified. According to the exact mass data of MSn and the element composition analysis, two impurities were identified as o-chlorobenzoic acid anhydride and 1,2-di-o-chlorobenzoylcyclopentene. The synthetic route of the o-chlorophenyl cyclopentyl ketone samples was proposed by analysis of these impurities. The established method made it easy to identify impurities and find the source of this illegal drug. A method for the preparation an o-chlorophenyl cyclopentyl ketone reference standard from actual samples using preparative HPLC was also developed. The mobile phase was methanol-water (85:15, v/v) and flow rate was 8 mL/min. The purity of the obtained standards, determined by analytical HPLC, was 99.53%. This method is simple, efficient, and can be used for the preparation of other illegal drugs.

Synthesis of Functionalized Triphenylenes via a Traceless Directing Group Strategy.

A novel ligand-free Pd-catalyzed cascade reaction between o-chlorobenzoic acids and cyclic diaryliodonium salts is reported. This one-pot procedure involves a carboxylic acid directed o-arylation followed by intramolecular decarboxylative annulation affording various valuable triphenylenes, which can be further transformed into diversified building blocks for material chemistry. For the first time, it was shown that an aromatic halide can react with diaryliodonium salts under the direction of carboxylic acid functionality. It was also demonstrated that the carboxylic acid could be employed as both a traceless directing group and functional handle for the atom- and step-economical one-pot double cross-coupling annulation reaction with cyclic diaryliodonium salts as the π-extending agents.

Influencing factors and kinetic studies of imidacloprid degradation by ozonation

ABSTRACTBatch kinetic tests in ozonation of imidacloprid from water were performed in this study. The pseudo-first-order rate constant of imidacloprid degradation was increased from 0.079 to 0.326 min−1 with the increasing pH from 6.02 to 8.64 at an average ozone dose of 1.149 mg L−1. When the alkalinity was increased from 0 to 250 mg L−1 NaHCO3, the pseudo-first-order rate constants decreased from 0.121 to 0.034 min−1. These results suggested that the predominant oxidant gradually switched from ozone to hydroxyl radicals () with the increase in solution pH. The secondary rate constant (10.92 ± 0.12 M−1s−1) for the reaction of imidacloprid and molecular ozone was determined at pH 2.0 and in the presence of 50 mM ter-butyl alcohol (p-chlorobenzoic acid, pCBA), respectively. An indirect competition method was used to determine the secondary rate constant for oxidation of imidacloprid in the presence of pCBA as the reference compound. The rate constants were estimated to range 2.65–3.79 M−1s−1 at pH 6.02–8.64. Results obtained from this study demonstrate that ozonation appears to be an effective method to remove imidacloprid from water.

Reoriention of diprotonated DABCO (1,4-Diazabicyclo[2.2.2]octane) cation and proton transfer in organic ferroelectric adduct DABCO-2(2-Chlorobenzoic acid)

Temperature dependences of 1H NMR as well as 35Cl NQR spin-lattice relaxation times T1 were investigated of a ferroelectric molecular adduct with Tc = 323 K, in which 1,4-diazabicyclo[2.2.2]octane (DABCO) is sandwiched between two 2-chlorobenzoic acid (2-ClBA). The NQR frequencies clearly show that proton transfer from 2-ClBA to DABCO is occurred and the molecular adduct consists of diprotonated DABCO cation and two 2-chlorobenzoate anions. The correlation time of reorientational motion of the diprotonated DABCO molecule was determined as a function of temperature. The activation energy Ea of the motion was estimated as 22 kJ mol−1 below Tc. The steep decrease of the NQR T1 with Ea = 50 kJ mol−1, observed above ca. 280 K in the ferroelectric phase, suggests a slow fluctuation of electric field gradient at chlorine nucleus.

In Silico Studies of Crystal Structure of HCV NS5B Polymerase and Inhibitor Complex

Quantum mechanics/molecular mechanics (QM/MM) and molecular dynamics simulations were performed to study the hydrogen bonding and polar interactions of an inhibitor namely 2-{[(5- bromothiophen-2-yl) sulfonyl] amino}- 4-chlorobenzoic acid with HCV NS5B polymerase. Using the initial poses, our aim is to identify the minimum energy positions and calculate binding affinities of inhibitor to HCV. Results suggest that the accuracy of binding affinity prediction can be significantly affected by the proper treatment of the hydrogen bonding and polar interactions. Using this protocol, we successfully identified important poses of low RMSD with respect to crystallographic structure from the initially docked poses. This work shows that the most important energetic component contributing to binding for this particular protein-ligand system is the conformational energy. In addition, formation of hydrogen bonds can produce favorable van der Waals interactions with some important residues. This systematic study can provide guidance for the choice of QM/MM MD methods and design of new inhibitors targeting HCV.

Low levels of iron enhance UV/H2O2 efficiency at neutral pH

While the presence of iron is generally not seen as favorable for UV-based treatment systems due to lamp fouling and decreased UV transmittance, we show that low levels of iron can lead to improvements in the abatement of chemicals in the UV-hydrogen peroxide advanced oxidation process. The oxidation potential of an iron-assisted UV/H2O2 (UV254 + H2O2 + iron) process was evaluated at neutral pH using iron levels below USEPA secondary drinking water standards (<0.3 mg/L). Para-chlorobenzoic acid (pCBA) was used as a hydroxyl radical (HO) probe to quantify HO steady state concentrations. Compounds degraded by different mechanisms including, carbamazepine (CBZ, HO oxidation) and N-nitrosodimethylamine (NDMA, direct photolysis), were used to investigate the effect of iron on compound degradation for UV/H2O2 systems. The effects of iron species (Fe2+ and Fe3+), iron concentration (0–0.3 mg/L), H2O2 concentration (0–10 mg/L) and background water matrix (low-carbon tap (LCT) and well water) on HO production and compound removal were examined. Iron-assisted UV/H2O2 efficiency was most influenced by the target chemical and the water matrix. Added iron to UV/H2O2 was shown to increase the steady-state HO concentration by approximately 25% in all well water scenarios. While CBZ removal was unchanged by iron addition, 0.3 mg/L iron improved NDMA removal rates in both LCT and well water matrices by 15.1% and 4.6% respectively. Furthermore, the combination of UV/Fe without H2O2 was also shown to enhance NDMA removal when compared to UV photolysis alone indicating the presence of degradation pathways other than HO oxidation.

A Novel Aerobic Degradation Pathway for Thiobencarb Is Initiated by the TmoAB Two-Component Flavin Mononucleotide-Dependent Monooxygenase System in Acidovorax sp. Strain T1.

Thiobencarb is a thiocarbamate herbicide used in rice paddies worldwide. Microbial degradation plays a crucial role in the dissipation of thiobencarb in the environment. However, the physiological and genetic mechanisms underlying thiobencarb degradation remain unknown. In this study, a novel thiobencarb degradation pathway was proposed in Acidovorax sp. strain T1. Thiobencarb was oxidized and cleaved at the C-S bond, generating diethylcarbamothioic S-acid and 4-chlorobenzaldehyde (4CDA). 4CDA was then oxidized to 4-chlorobenzoic acid (4CBA) and hydrolytically dechlorinated to 4-hydroxybenzoic acid (4HBA). The identification of catabolic genes suggested further hydroxylation to protocatechuic acid (PCA) and finally degradation through the protocatechuate 4,5-dioxygenase pathway. A novel two-component monooxygenase system identified in the strain, TmoAB, was responsible for the initial catabolic reaction. TmoA shared 28 to 32% identity with the oxygenase components of pyrimidine monooxygenase from Agrobacterium fabrum, alkanesulfonate monooxygenase from Pseudomonas savastanoi, and dibenzothiophene monooxygenase from Rhodococcus sp. TmoB shared 25 to 37% identity with reported flavin reductases and oxidized NADH but not NADPH. TmoAB is a flavin mononucleotide (FMN)-dependent monooxygenase and catalyzed the C-S bond cleavage of thiobencarb. Introduction of tmoAB into cells of the thiobencarb degradation-deficient mutant T1m restored its ability to degrade and utilize thiobencarb. A dehydrogenase gene, tmoC, was located 7,129 bp downstream of tmoAB, and its transcription was clearly induced by thiobencarb. The purified TmoC catalyzed the dehydrogenation of 4CDA to 4CBA using NAD+ as a cofactor. A gene cluster responsible for the complete 4CBA metabolic pathway was also cloned, and its involvement in thiobencarb degradation was preliminarily verified by transcriptional analysis.IMPORTANCE Microbial degradation is the main factor in thiobencarb dissipation in soil. In previous studies, thiobencarb was degraded initially via N-deethylation, sulfoxidation, hydroxylation, and dechlorination. However, enzymes and genes involved in the microbial degradation of thiobencarb have not been studied. This study revealed a new thiobencarb degradation pathway in Acidovorax sp. strain T1 and identified a novel two-component FMN-dependent monooxygenase system, TmoAB. Under TmoAB-mediated catalysis, thiobencarb was cleaved at the C-S bond, producing diethylcarbamothioic S-acid and 4CDA. Furthermore, the downstream degradation pathway of thiobencarb was proposed. Our study provides the physiological, biochemical, and genetic foundation of thiobencarb degradation in this microorganism.

PH-dependent KOW provides new insights in understanding the adsorption mechanism of ionizable organic chemicals on carbonaceous materials

The dominant adsorption mechanism of ionizable organic chemicals (IOCs) on carbonaceous materials is still unclear. This study used benzoic acid (BA), o-chlorobenzoic acid (2-CBA) and p-chlorobenzoic acid (4-CBA) as representatives of IOCs to investigate the dominant adsorption mechanism on graphene oxide (GO) and graphite (GP), with a specific emphasis on the impact of pH-dependent KOW. The order of apparent adsorption of the investigated chemicals changed with pH, which could not be explained by their constant KOW. According to our measurement, KOW varied greatly with pH. The pH-dependent adsorption of BA, 2-CBA and 4-CBA were significantly correlated with pH-dependent KOW for both GO and GP. Our observations indicated that the hydrophobic effects may dominate the apparent adsorption of BA, 2-CBA and 4-CBA on GO and GP. Electrostatic repulsion played a minor role in their reduced adsorption at high pH. Negative charge-assisted H-bond and π-π interactions may explain the adsorption of negatively charged BA, 2-CBA and 4-CBA on negatively charged GO. This study implied that pH-dependent KOW rather than constant KOW should be incorporated to understand IOC adsorption as affected by pH.

Compact light-emitting diode optical fiber immobilized TiO2 reactor for photocatalytic water treatment

A key barrier to implementing photocatalysis is delivering light to photocatalysts that are in contact with aqueous pollutants. Slurry photocatalyst systems suffer from poor light penetration and require post-treatment to separate the catalyst. The alternative is to deposit photocatalysts on fixed films and deliver light onto the surface or the backside of the attached catalysts. In this study, TiO2-coated quartz optical fibers were coupled to light emitting diodes (OF/LED) to improve in situ light delivery. Design factors and mechanisms studied for OF/LEDs in a flow-through reactor included: (i) the influence of number of LED sources coupled to fibers and (ii) the use of multiple optical fibers bundled to a single LED. The light delivery mechanism from the optical fibers into the TiO2 coatings is thoroughly discussed. To demonstrate influence of design variables, experiments were conducted in the reactor using the chlorinated pollutant para-chlorobenzoic acid (pCBA). From the degradation kinetics of pCBA, the quantum efficiencies (Φ) of oxidation and electrical energies per order (EEO) were determined. The use of TiO2 coated optical fiber bundles reduced the energy requirements to deliver photons and increased available surface area, which improved Φ and enhanced oxidative pollutant removal performance (EEO).

Electrical energy per order and current efficiency for electrochemical oxidation of p-chlorobenzoic acid with boron-doped diamond anode

Electrochemical oxidation (EO) is an advanced oxidation process for water treatment to mineralize organic contaminants. While proven to degrade a range of emerging pollutants in water, less attention has been given to quantify the effect of operational variables such applied current density and pollutant concentration on efficiency and energy requirements. Particular figures of merit were mineralization current efficiency (MCE) and electrical energy per order (EEO). Linear increases of applied current exponentially decreased the MCE due to the enhancement of undesired parasitic reactions that consumed generated hydroxyl radical. EEO values ranged from 39.3 to 331.8 kW h m−3 order−1. Increasing the applied current also enhanced the EEO due to the transition from kinetics limited by current to kinetics limited by mass transfer. Further increases in current did not influence the removal rate, but it raised the EEO requirement. The EEO requirement diminished when decreasing initial pollutant loading with the increase of the apparent kinetic rate because of the relative availability of oxidant per pollutant molecule in solution at a defined current. Oxidation by-products released were identified, and a plausible degradative pathway has been suggested.

Effect of graphene oxidation degree on the catalytic activity of graphene for ozone catalysis

The potential of graphene-based materials, including graphene oxide (GO), over-oxidized graphene oxide (oGO), and non-oxidized graphene (nOG), for catalytic ozonation was investigated, along with the mechanism of ozone catalysis. Increasing the extent of oxidation of graphene led to the formation of hydroxyl and carboxyl groups on the graphene surface, which then partially converted into epoxy groups. The catalytic efficiency of oGO was much higher than that of both GO and nOG. Graphene’s extent of oxidation might be a significant factor in catalytic ozonation. The hydroxyl radical exposure to ozone exposure ratio (Rct) of 25mgL−1 ozone/oGO was 75-fold higher than that of an ozone alone process. The ozone decomposition rate and para-chlorobenzoic acid removal efficiency were higher at pH 9 than at any other pH. The Rct of ozone/oGO at pH 9 was 2.35×10−5. Temperature affected ozone adsorption on the nOG surface. Ozone/graphene experiment with an excess of tert-butyl alcohol was proposed that hydroxyl radicals generated by GO and oGO existed mainly in the solution phase, while those generated by nOG existed in both solution and surface phases.

Copper nanoparticles catalyzed economical synthesis of 3-substituted isocoumarins from 2-chlorobenzoic acids/amides and 1,3-diketones

Copper nanoparticles were utilized as a highly efficient catalyst for a facile and economical synthesis of 3-substituted isocoumarins with 2-chlorobenzoic acids and 1,3-diketones as starting materials. The copper nanoparticles catalyst showed highly catalytic activity for the 2-chloro-substituted substrates to afford 3-substituted isocoumarins in good to excellent yields. Furthermore, good catalytic activity was also observed when 2-chlorobenzoic amides were utilized as substrates instead of the benzoic acids.

Homogeneous and heterogeneous electrocatalytic reduction of halo-organic compounds by (NiIILi)2+ (Li = tetraaza-macrocyclic ligand) in aqueous solutions

The electrocatalytic reduction of bromoacetic, chloroacetic, bromobenzoic and chlorobenzoic acids by four Ni macrocyclic complexes (NiIILi)2+, was studied in both homogeneous and heterogeneous systems using glassy-carbon, nafion and carbon-paste modified electrodes. The results indicate that the electrocatalytic reduction of the bromo-compounds is more efficient than that of the chloro-compounds. The electrocatalytic activity increases with the redox potential of the electrocatalyst. The nafion-modified electrodes show poor electrocatalytic ability, whereas the carbon-paste electrodes are good electrocatalysts for the reduction of bromo-alkyls only. For this purpose, the latter electrode is better than the bare glassy-carbon electrode. The results show that the rates of reduction of the halo-organic compounds by the (NiILi)+ are slowed down when the complexes are incorporated into the modified electrodes.

35Cl NQR study of deuteration effect on proton dynamics in chlorobenzoic acid

35Cl NQR frequencies and spin-lattice relaxation times T1 were measured of some deuterated chlorobenzoic acid, 3,5-dichlorobenzoic acid-d1 (35ClBA-d1), 2,6-dichlorobenzoic acid-d1 (26ClBA-d1), and 4-amino-3,5- dichlorobenzoic acid-dn (4A35ClBA-dn). The slightly higher frequencies were observed for the deuterated analogues. The temperature dependence of the T1 showed a minimum which can be explained by the fluctuation of electric field gradient (EFG) due to the proton transfer motion in the dimeric chlorobenzoic acid molecules. By the deuteration, the 35Cl T1 minimum shifted to the high-temperature side and showed approximately one order of magnitude shorter value. From comparison with the T1 data of the normal compounds, the tunneling contribution to the proton transfer motion in the dimeric molecular unit of chlorobenzoic acid in the crystal is discussed.