1 Departamento de Química Física y Termodinámica Aplicada, Facultad de Ciencias, Campus de Excele... more 1 Departamento de Química Física y Termodinámica Aplicada, Facultad de Ciencias, Campus de Excelencia Internacional Agroalimentario, CEIA3, Sede de Rabanales, edificio Marie Curie, Universidad de Córdoba, E-14014-Córdoba (Spain) 2 Departmento de Química of Agrícola y Edafología, Campus de Excelencia Internacional Agroalimentario, CEIA3, Sede de Rabanales, edificio Marie Curie, Universidad de Córdoba E-14014Córdoba (Spain) * E-mail: [email protected]
espanolLa presencia de herbicidas s-triazfnicos en los cursos fluviales suele ser problematico pa... more espanolLa presencia de herbicidas s-triazfnicos en los cursos fluviales suele ser problematico para las estaciones de tratamiento de aguas potables (ETAP) convencionales por su deficiente eliminacion. En este articulo se estudian cuatro s-triazinas (propazina, prometrina, prometon y simetrina) en aguas mediante la aplicacion de nueve tipos de carbon activo en polvo. La adsorcion responde a isotermas tipo Frumkin, cuya accion depende mas del adsorbato (herbicida) que del adsorbente (carbon). La secuencia de adsorcion es: propazina > prometrina > prometon > simetrina. La detoxificacion es del 70-85% tras 3-4 h de tratamiento, y ~ 80% tras 12 h de contacto carbon-agua, siendo su capacidad maxima de 23-27 mg/g. La efectividad adsorbente se relaciona con el area superficial, el indice de yodo del carbon y el tamano de sus particulas EnglishThis artiele is focused on the removing of the above compounds in natural waters added with s-triazines by using nine different active commer...
Financial supports from Junta de Andalucia (Research Group FQM-0198), CICyT (Research Project CTQ... more Financial supports from Junta de Andalucia (Research Group FQM-0198), CICyT (Research Project CTQ2010-15359) and Cordoba University are gratefully acknowledged.
This paper present ultraviolet-visible absorption spectra of imazamethabenz-methyl (IMBM) (mixtur... more This paper present ultraviolet-visible absorption spectra of imazamethabenz-methyl (IMBM) (mixture of the isomers methyl 6-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-m-toluate, m-imazamethabenz, and methyl 2-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-p-toluate, p-imazamethabenz) and the corresponding carboxylic acid, imazamethabenz-acid (IMBA). The spectral characteristics are determined as functions of the pH. The appreciable absorbance in the visible (or near-ultraviolet) region of the spectra indicates that the natural photolytic degradation is possible. From variations of the maximum absorbances of the bands, the pK values of 3.4 +/- 0.2 and 9.4 +/- 0.2 were obtained for protonation of the imidazol (=N-) nitrogen and dissociation of the NH imidazol nitrogen of IMBM, respectively. For IMBA, the dissociation pK of the carboxylic group is very close to that of the imidazol (=N-) nitrogen, both being close to 3.3. The dissociation pK of the NH imidazol nitrogen for IMBA is 9.6 +/- 0.2. The role of the acid-base reactions on the sorption on soils of these herbicides is discussed.
This paper presents polarographic and voltammetric studies of the reduction of the herbicide imaz... more This paper presents polarographic and voltammetric studies of the reduction of the herbicide imazamethabenz methyl (2/3-methyl-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-p-toluate), on mercury and carbon electrodes. The electrochemical studies were performed in strongly acidic media (0.1-2.7 M H 2 SO 4 ) as well as in the pH range of 1-12. The overall reduction process involves the uptake of two electrons. The results obtained in polarography show that there is the reduction of two species, related via an acid-base equilibrium, and having very close reduction potentials. The voltammetric results obtained with a glassy carbon electrode were very similar to those observed on mercury electrodes. The reducible group in the molecule is the imidazolinone ring. In strongly acidic media (pH < pK a ), the reaction mechanism proposed is the reduction of the protonated herbicide by an electrochemical-chemical-electrochemical (ECE) process, being the r.d.s. the second electron transfer. At pH > pK a the neutral form of the herbicide is reduced and the second electron transfer becomes reversible or quasi-reversible. In basic media, the species reduced is the deprotonated imazamethabenz methyl and the r.d.s. is the second electron transfer.
Measurements of differential capacity vs. potential have been made for a series of s-triazine her... more Measurements of differential capacity vs. potential have been made for a series of s-triazine herbicides at different concentrations. In all cases the decrease in capacity was independent of the applied potential, so the adsorption is also independent of the potential. From the measurements it can be established that the adsorption follows Langmuir type isotherms. Adsorption constants were obtained for the different herbicides at 25 8C (simetryn, simazine, terburyn and prometon) as well as those to simetryn at different temperatures, from which the adsorption enthalpy of this herbicide was calculated being its value of 17.5 kJ mol À1 .
Carbon electrodes with in situ electrodeposited copper are used to the determination of aminometh... more Carbon electrodes with in situ electrodeposited copper are used to the determination of aminomethylphosphonic acid (AMPA), the major metabolite of the herbicide Glyphosate (N-(phosphonomethyl) glycine) in drinking waters. The oxidation signal to form Cu (II) ions ...
Adsorption of Simazine on a Glassy Carbon Electrode Sara Pintado and José Miguel Rodríguez Mellad... more Adsorption of Simazine on a Glassy Carbon Electrode Sara Pintado and José Miguel Rodríguez Mellado* Departamento de Química Física y Termodinámica Aplicada, Universidad de Córdoba, Campus de Rabanales, Edificio Marie Curie 2 Planta, E-14014 Córdoba, Spain ...
Resumen: La presencia de herbicidas s-triazfnicos en los cursos fluviales suele ser problemático ... more Resumen: La presencia de herbicidas s-triazfnicos en los cursos fluviales suele ser problemático para las estaciones de tratamiento de aguas potables (ETAP) convencionales por su deficiente eliminación. En este artículo se estudian cuatro s-triazinas (propazina, ...
Polarographic (dc and DP) studies have been made on the reduction of the imidazolinone herbicides... more Polarographic (dc and DP) studies have been made on the reduction of the imidazolinone herbicides imazapyr[2-(4- isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) nicotinic acid], imazethapyr[5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin- 2-yl) nicotinic acid] and imazaquin[2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) quinoline-3-carboxylic acid] in the acidity range 2.7 M H2SO4 to pH 13. At pH<7 the DP polarograms showed two sets of peaks that depended strongly on the pH and can be assigned to the reduction of the two reducible parts of the molecule, i.e., the pyridinic (or quinolinic) and the imidazolinic rings. The results suggest that the set of peaks appearing at more negative potentials could be related to the pyridinic/quinolinic ring reduction, being the assignation of the peaks appearing at less negative potentials more difficult.
This paper presents polarographic and voltammetric studies of the reduction of the herbicide imaz... more This paper presents polarographic and voltammetric studies of the reduction of the herbicide imazamethabenz acid on mercury electrodes. The electrochemical studies were performed from strongly acidic media (0.1 to 2.7 M H 2 SO 4) to pH range 12. The overall reduction process involves the uptake of two electrons. The results obtained show that three species are reduced related via acid-base equilibria, being the reducible group the imidazolinone ring. In strongly acidic media (pH<pK a), the reaction mechanism proposed is the reduction of the protonated herbicide by an irreversible process, being the r.d.s. the second electron transfer. At pH>pK a two H + ions are uptaken prior the reduction. In the reduction of the carboxylate unprotonated form of the herbicide, the second electron transfer becomes reversible or quasi-reversible. The possibility of the reductive degradation in natural waters is discussed.
Se ha estudiado el comportamiento electroquímico de los herbicidas imidazolinónicos imazametabenz... more Se ha estudiado el comportamiento electroquímico de los herbicidas imidazolinónicos imazametabenz metilo, imazametabenz ácido, imazapir, imazetapir, imazaquin y otros. Se han establecido los valores de las consatntes de disociación ácida, o de protonación en su caso, para los equilibrios ácido base de estos herbicidas. Sobre la base de los resultados voltamétricos y polarográficos, así como de otras técnicas complementarias, se han propuesto mecanismos de reducción. Se estudia también la adsorción sobre electrodos de carbón vitrificado de herbicidas s-triazínicos modelo simazina, simetrina, terbutrina y prometón. Esta adsorción es independiente del potencial y sigue una isoterma de Langmuir, pudiéndose determinar los valores de las constantes de adsorción y de las entalpías de adsorción. Se han investigado los herbicidas quinolínicos quinmerac, quinclorac y un compuesto modelo, ácido 8-quinolino carboxílico. En los procesos de reducción, el electrodo se recubre mediante nucleaciones...
Collection of Czechoslovak Chemical Communications, 2011
Using chronoamperometric measurements at pH 12 it is shown that the oxidation mechanism of niazid... more Using chronoamperometric measurements at pH 12 it is shown that the oxidation mechanism of niazid adsorbed on the mercury electrode changes with respect to the mechanism reported in the literature for the electrooxidation of the molecules reaching the electrode by diffusion. A compact monolayer of niazid molecules is formed on the electrode surface, being the hydrazide oxidized through a two-electron process. The oxidation product is not able to dissociate a H+ ion, and the oxidation process does not proceeds beyond. For isoniazid the monolayer never becomes compact.
The electroreductions of 8-quinolinecarboxylic acid and his derivative quinmerac (a quinolinic he... more The electroreductions of 8-quinolinecarboxylic acid and his derivative quinmerac (a quinolinic herbicide) are studied by cyclic and differential pulse voltammetry on mercury electrodes. The use of surfactants was found essential to avoid the adsorption of reactants on the mercury surface. In both cases the electroreduction processes corresponded to electrodimerization reactions in competition with ECE processes, depending on the experimental conditions. The oxidation of the radicals formed after the first electron transfers differ from 8-quinolinecarboxylic acid to quinmerac, being more complicated in this last case.
This paper presents polarographic (direct current, dc, and differential pulse, DP) and voltammetr... more This paper presents polarographic (direct current, dc, and differential pulse, DP) and voltammetric (linear-sweep cyclic voltammetry) studies on the electroreduction of 6-chloronicotinic acid (6CNA) on mercury electrodes. In order to obtain the dissociation constants of 6CNA, UV–vis spectra were recorded as a function of pH. pK values of −0.80±0.05 (–COOH group) and 3.2±0.1 (pyridinic nitrogen) were obtained. The electrochemical studies
1 Departamento de Química Física y Termodinámica Aplicada, Facultad de Ciencias, Campus de Excele... more 1 Departamento de Química Física y Termodinámica Aplicada, Facultad de Ciencias, Campus de Excelencia Internacional Agroalimentario, CEIA3, Sede de Rabanales, edificio Marie Curie, Universidad de Córdoba, E-14014-Córdoba (Spain) 2 Departmento de Química of Agrícola y Edafología, Campus de Excelencia Internacional Agroalimentario, CEIA3, Sede de Rabanales, edificio Marie Curie, Universidad de Córdoba E-14014Córdoba (Spain) * E-mail: [email protected]
espanolLa presencia de herbicidas s-triazfnicos en los cursos fluviales suele ser problematico pa... more espanolLa presencia de herbicidas s-triazfnicos en los cursos fluviales suele ser problematico para las estaciones de tratamiento de aguas potables (ETAP) convencionales por su deficiente eliminacion. En este articulo se estudian cuatro s-triazinas (propazina, prometrina, prometon y simetrina) en aguas mediante la aplicacion de nueve tipos de carbon activo en polvo. La adsorcion responde a isotermas tipo Frumkin, cuya accion depende mas del adsorbato (herbicida) que del adsorbente (carbon). La secuencia de adsorcion es: propazina > prometrina > prometon > simetrina. La detoxificacion es del 70-85% tras 3-4 h de tratamiento, y ~ 80% tras 12 h de contacto carbon-agua, siendo su capacidad maxima de 23-27 mg/g. La efectividad adsorbente se relaciona con el area superficial, el indice de yodo del carbon y el tamano de sus particulas EnglishThis artiele is focused on the removing of the above compounds in natural waters added with s-triazines by using nine different active commer...
Financial supports from Junta de Andalucia (Research Group FQM-0198), CICyT (Research Project CTQ... more Financial supports from Junta de Andalucia (Research Group FQM-0198), CICyT (Research Project CTQ2010-15359) and Cordoba University are gratefully acknowledged.
This paper present ultraviolet-visible absorption spectra of imazamethabenz-methyl (IMBM) (mixtur... more This paper present ultraviolet-visible absorption spectra of imazamethabenz-methyl (IMBM) (mixture of the isomers methyl 6-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-m-toluate, m-imazamethabenz, and methyl 2-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-p-toluate, p-imazamethabenz) and the corresponding carboxylic acid, imazamethabenz-acid (IMBA). The spectral characteristics are determined as functions of the pH. The appreciable absorbance in the visible (or near-ultraviolet) region of the spectra indicates that the natural photolytic degradation is possible. From variations of the maximum absorbances of the bands, the pK values of 3.4 +/- 0.2 and 9.4 +/- 0.2 were obtained for protonation of the imidazol (=N-) nitrogen and dissociation of the NH imidazol nitrogen of IMBM, respectively. For IMBA, the dissociation pK of the carboxylic group is very close to that of the imidazol (=N-) nitrogen, both being close to 3.3. The dissociation pK of the NH imidazol nitrogen for IMBA is 9.6 +/- 0.2. The role of the acid-base reactions on the sorption on soils of these herbicides is discussed.
This paper presents polarographic and voltammetric studies of the reduction of the herbicide imaz... more This paper presents polarographic and voltammetric studies of the reduction of the herbicide imazamethabenz methyl (2/3-methyl-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-p-toluate), on mercury and carbon electrodes. The electrochemical studies were performed in strongly acidic media (0.1-2.7 M H 2 SO 4 ) as well as in the pH range of 1-12. The overall reduction process involves the uptake of two electrons. The results obtained in polarography show that there is the reduction of two species, related via an acid-base equilibrium, and having very close reduction potentials. The voltammetric results obtained with a glassy carbon electrode were very similar to those observed on mercury electrodes. The reducible group in the molecule is the imidazolinone ring. In strongly acidic media (pH < pK a ), the reaction mechanism proposed is the reduction of the protonated herbicide by an electrochemical-chemical-electrochemical (ECE) process, being the r.d.s. the second electron transfer. At pH > pK a the neutral form of the herbicide is reduced and the second electron transfer becomes reversible or quasi-reversible. In basic media, the species reduced is the deprotonated imazamethabenz methyl and the r.d.s. is the second electron transfer.
Measurements of differential capacity vs. potential have been made for a series of s-triazine her... more Measurements of differential capacity vs. potential have been made for a series of s-triazine herbicides at different concentrations. In all cases the decrease in capacity was independent of the applied potential, so the adsorption is also independent of the potential. From the measurements it can be established that the adsorption follows Langmuir type isotherms. Adsorption constants were obtained for the different herbicides at 25 8C (simetryn, simazine, terburyn and prometon) as well as those to simetryn at different temperatures, from which the adsorption enthalpy of this herbicide was calculated being its value of 17.5 kJ mol À1 .
Carbon electrodes with in situ electrodeposited copper are used to the determination of aminometh... more Carbon electrodes with in situ electrodeposited copper are used to the determination of aminomethylphosphonic acid (AMPA), the major metabolite of the herbicide Glyphosate (N-(phosphonomethyl) glycine) in drinking waters. The oxidation signal to form Cu (II) ions ...
Adsorption of Simazine on a Glassy Carbon Electrode Sara Pintado and José Miguel Rodríguez Mellad... more Adsorption of Simazine on a Glassy Carbon Electrode Sara Pintado and José Miguel Rodríguez Mellado* Departamento de Química Física y Termodinámica Aplicada, Universidad de Córdoba, Campus de Rabanales, Edificio Marie Curie 2 Planta, E-14014 Córdoba, Spain ...
Resumen: La presencia de herbicidas s-triazfnicos en los cursos fluviales suele ser problemático ... more Resumen: La presencia de herbicidas s-triazfnicos en los cursos fluviales suele ser problemático para las estaciones de tratamiento de aguas potables (ETAP) convencionales por su deficiente eliminación. En este artículo se estudian cuatro s-triazinas (propazina, ...
Polarographic (dc and DP) studies have been made on the reduction of the imidazolinone herbicides... more Polarographic (dc and DP) studies have been made on the reduction of the imidazolinone herbicides imazapyr[2-(4- isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) nicotinic acid], imazethapyr[5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin- 2-yl) nicotinic acid] and imazaquin[2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) quinoline-3-carboxylic acid] in the acidity range 2.7 M H2SO4 to pH 13. At pH<7 the DP polarograms showed two sets of peaks that depended strongly on the pH and can be assigned to the reduction of the two reducible parts of the molecule, i.e., the pyridinic (or quinolinic) and the imidazolinic rings. The results suggest that the set of peaks appearing at more negative potentials could be related to the pyridinic/quinolinic ring reduction, being the assignation of the peaks appearing at less negative potentials more difficult.
This paper presents polarographic and voltammetric studies of the reduction of the herbicide imaz... more This paper presents polarographic and voltammetric studies of the reduction of the herbicide imazamethabenz acid on mercury electrodes. The electrochemical studies were performed from strongly acidic media (0.1 to 2.7 M H 2 SO 4) to pH range 12. The overall reduction process involves the uptake of two electrons. The results obtained show that three species are reduced related via acid-base equilibria, being the reducible group the imidazolinone ring. In strongly acidic media (pH<pK a), the reaction mechanism proposed is the reduction of the protonated herbicide by an irreversible process, being the r.d.s. the second electron transfer. At pH>pK a two H + ions are uptaken prior the reduction. In the reduction of the carboxylate unprotonated form of the herbicide, the second electron transfer becomes reversible or quasi-reversible. The possibility of the reductive degradation in natural waters is discussed.
Se ha estudiado el comportamiento electroquímico de los herbicidas imidazolinónicos imazametabenz... more Se ha estudiado el comportamiento electroquímico de los herbicidas imidazolinónicos imazametabenz metilo, imazametabenz ácido, imazapir, imazetapir, imazaquin y otros. Se han establecido los valores de las consatntes de disociación ácida, o de protonación en su caso, para los equilibrios ácido base de estos herbicidas. Sobre la base de los resultados voltamétricos y polarográficos, así como de otras técnicas complementarias, se han propuesto mecanismos de reducción. Se estudia también la adsorción sobre electrodos de carbón vitrificado de herbicidas s-triazínicos modelo simazina, simetrina, terbutrina y prometón. Esta adsorción es independiente del potencial y sigue una isoterma de Langmuir, pudiéndose determinar los valores de las constantes de adsorción y de las entalpías de adsorción. Se han investigado los herbicidas quinolínicos quinmerac, quinclorac y un compuesto modelo, ácido 8-quinolino carboxílico. En los procesos de reducción, el electrodo se recubre mediante nucleaciones...
Collection of Czechoslovak Chemical Communications, 2011
Using chronoamperometric measurements at pH 12 it is shown that the oxidation mechanism of niazid... more Using chronoamperometric measurements at pH 12 it is shown that the oxidation mechanism of niazid adsorbed on the mercury electrode changes with respect to the mechanism reported in the literature for the electrooxidation of the molecules reaching the electrode by diffusion. A compact monolayer of niazid molecules is formed on the electrode surface, being the hydrazide oxidized through a two-electron process. The oxidation product is not able to dissociate a H+ ion, and the oxidation process does not proceeds beyond. For isoniazid the monolayer never becomes compact.
The electroreductions of 8-quinolinecarboxylic acid and his derivative quinmerac (a quinolinic he... more The electroreductions of 8-quinolinecarboxylic acid and his derivative quinmerac (a quinolinic herbicide) are studied by cyclic and differential pulse voltammetry on mercury electrodes. The use of surfactants was found essential to avoid the adsorption of reactants on the mercury surface. In both cases the electroreduction processes corresponded to electrodimerization reactions in competition with ECE processes, depending on the experimental conditions. The oxidation of the radicals formed after the first electron transfers differ from 8-quinolinecarboxylic acid to quinmerac, being more complicated in this last case.
This paper presents polarographic (direct current, dc, and differential pulse, DP) and voltammetr... more This paper presents polarographic (direct current, dc, and differential pulse, DP) and voltammetric (linear-sweep cyclic voltammetry) studies on the electroreduction of 6-chloronicotinic acid (6CNA) on mercury electrodes. In order to obtain the dissociation constants of 6CNA, UV–vis spectra were recorded as a function of pH. pK values of −0.80±0.05 (–COOH group) and 3.2±0.1 (pyridinic nitrogen) were obtained. The electrochemical studies
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