Comparative evaluation of Dy(III) selective poly(vinyl) chloride based membrane electrodes of macrocyclic tetraimine Schiff's bases

Three different derivatives of macrocyclic tetraimine Schiff's base have been synthesized and explored as a neutral ionophores for preparing poly(vinyl chloride) based membrane sensors selective to Dy³⁺. The addition of sodium tetraphenyl borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor no. 1 having membrane of Schiff's base (SL-1) with composition (w/w) SL-1 (4.5%): PVC (30.5%): o-NPOE (59.5%): NaTPB (5.5%). This sensor exhibits Nernstian response with slope 19.4 mV/decade of activity in the concentration range of  10⁻⁸ to 1.0 × 10⁻² M Dy³⁺, performs satisfactorily over wide pH range of (2.8-7.2) with a fast response time (10 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of acetonitrile, methanol or ethanol. The proposed sensor can be used over a period of 1.5 months without significant drift in potentials. The sensor has been also utilized for the determination of Dy³⁺ level in different soil samples.     

Chromium(III) ion selective electrode based on glyoxal bis(2-hydroxyanil)

A poly(vinyl chloride) membrane based on glyoxal bis(2-hydroxyanil) as membrane carrier was prepared and investigated as a Cr(III)-selective electrode. The electrode has a linear dynamic range of 3.0×10⁻⁶-1.0×10⁻² mol l⁻¹, with a Nernstian slope of 19.8±0.5 mV per decade and a detection limit of 6.3×10⁻⁷ mol l⁻¹. It has a fast response time of <20 s and can be used for at least 3 months without any considerable divergence in potential. The proposed electrode revealed good sensitivities for Cr(III) over a wide variety of metal ions and could be used in a pH range of 2.7-6.5. Above all, the membrane sensor has been used very successfully for the analysis of some food materials and alloys for the determination of Cr(III) ion.     

Solvent effects on the oxidative free radical reactions of 2-amino-1,4-naphthoquinones

Solvent effects on the manganese (III) initiated oxidative free radical reactions of 2-amino-1,4-naphthoquinones are described. This free radical reaction provides a novel method for the synthesis of benzo[f]indole-4,9-diones, benzo[f]indole-2,4,9-triones, benzo[b]carbazole-6,11-diones and benzo[b]acridine-6,11-diones. High chemoselectivity was observed in different solvents.     

Terbium(III) Ion-Selective Electrochemical Sensor Based on Hematoporphyrin

Abstract

A polyvinyl chloride (PVC) based membrane sensor for terbium ions was prepared by employing Hematoporphyrin (HP) as an ionophore. The sensor revealed a very good selectivity (expect for the Fe³⁺ion) with respect to common alkali, alkaline earth and heavy metal ions. The plasticized membrane electrode exhibits a Nernstian response for Tb³⁺ ions over a wide concentration range (1.0 × 10^?6 ? 1.0 × 10^?2 M) with a slope of 19.8±0.3 mV per decade and low detection limit of 7.4 × 10^?7 M. The developed sensor was used in determination of F^? in mouth wash preparation sample.     

PVC-based dicyclohexano-18-crown-6 sensor for La(III) ions

A new ion-selective electrode (ISE) based on dicyclohexano-18-crown-6 (DC18C6) as a neutral carrier is developed for lanthanum(III) ions. The electrode comprises of dicyclohexano-18-crown-6 (6%), PVC (33%), and ortho-nitrophenyl octyl ether (o-NPOE) (61%). The electrode shows a linear dynamic response in the concentration range of 10⁻⁶ to 10⁻¹ M with a Nernstian slope of 19 mV per decade and a detection limit as 5×10⁻⁷ M. It has a response time of <30 s and can be used for at least 5 months without any significant divergence in potentials. The selectivity coefficients for mono-, di-, and trivalent cations indicate good selectivity for La(III) ions over a large number of interfering cations. The sensor has been used as an indicator electrode in the potentiometric titrations of La(III) with EDTA. The membrane is successfully applied in partially non-aqueous medium. It can be used in the pH range 4-9.     

Unexpected reaction of 2-amino-1,4-naphthoquinone with aldehydes: new synthesis of naphtho[2,1-d]oxazole compounds

Treatment of 3-substituted 2-amino-1,4-naphthoquinones 3 with an aldehyde in a solution of hydrobromic acid in acetic acid led to 2,4-disubstituted naphtho[2,1-d]oxazol-5-ols. The outcome of this simple conversion is even more remarkable in view of the very similar reactions reported in literature, which all give rise to completely different products. Furthermore, the acquired naphthoxazoles 5-11 could be oxidatively ring opened by means of PIFA or CAN into a series of N-acylated 2-amino-1,4-naphthoquinones. A synthetic pathway towards 2-substituted naphtho[2,3-d]oxazole-4,9-diones was also disclosed as the outcome of CAN mediated oxidation of a 4-chloronaphtho[2,1-d]oxazol-5-ol.     

Synthesis of 2-(3-amino-2-oxoindolin-3-yl)-3-hydroxynaphthalene-1,4-dione derivatives via a one-pot,three-component reaction under catalyst-free conditions

A concise, facile and straightforward synthetic method has been described for the synthesis of 2-(3-amino-2-oxoindolin-3-yl)-3-hydroxynaphthalene-1,4-dione derivatives by a one-pot, three-component reaction of isatins, 2-hydroxy-1,4-naphthoquinone and ammonium acetate under catalyst-free conditions in ethanol. This protocol becomes highly efficient due to its mild reaction conditions, operational simplicity, and overall good to excellent yields (80–99%).     

A novel oxidative free radical reaction between 2-amino-1,4-benzoquinones and benzoylacetonitriles

The manganese(III) initiated oxidative free radical reaction between 2-amino-1,4-benzoquinones and benzoylacetonitriles is described. This free radical reaction provides a novel method for the synthesis of spirodione 3 and spirolactone 4. With 5,6-dimethyl-2-methylamino-1,4-benzoquinone, spirodione 3 was obtained exclusively. On the contrary, with 5-methyl-2-methylamino-1,4-benzoquinone, spirolactone 4 was produced in high chemo- and regioselectivity. By heating with sodium acetate, spirodione 3 can be converted to 4 effectively.     

A novel tetrachlorothallate (III)-PVC membrane sensor for the potentiometric determination of thallium (III)

A novel tetrachlorothallate (III) (TCT)-selective membrane sensor consisting of tetrachlorothallate (III)-2,3,5-triphenyl-2-H-tetrazolium ion pair dispersed in a PVC matrix plasticized with dioctylphthalate is described. The electrode shows a stable, near-Nernstian response for 1×10⁻³-4×10⁻⁶ M thallium (III) at 25 °C with an anionic slope of 56.5±0.5 over the pH range 3-6. The lower detection limit and the response time are 2×10⁻⁶ M and 30-60 s, respectively. Selectivity coefficients for Tl(III) relative to a number of interfering substances were investigated. There is negligible interference from many cations and anions; however, iodide and bromide are significantly interfere. The determination of 0.5-200 μg ml⁻¹ of Tl(III) in aqueous solutions shows an average recovery of 99.0% and a mean relative standard deviation of 1.4% at 50.0 μg ml⁻¹. The direct determination of Tl(III) in spiked wastewater gave results that compare favorably with those obtained by the atomic absorption spectrometric method. The electrode was successfully applied for the determination of thallium in zinc concentrate. Also the tetrachlorothallate electrode has been utilized as an end point indicator electrode for the determination of thallium using potentiometric titration.     

Oxidative free radical reactions between 2-amino-1,4-benzoquinones and carbonyl compounds

The manganese(III) initiated oxidative free radical reactions of 2-amino-1,4-benzoquinone are described. The free radical reaction of 5,6-dimethyl-2-methylamino-1,4-benzoquinone (1) provides a novel method for the synthesis of indole-4,7-dione and indole-2,4,7-trione. High chemoselectivity was observed in different solvents. The regioselectivity of this reaction was also studied with 5-methyl-2-methylamino-1,4-benzoquinone (19). In most cases, indole-4,7-diones 20 and 21 were produced in high regioselectivity.     

Manganese(III) Acetate Initiated Oxidative Free Radical Reaction between 2-Anilino-1,4-naphthoquinones and Diethyl Malonate

A free radical reaction between 2-anilino-1,4-naphthoquinones and diethyl malonate initiated by manganese (III) acetate is described. This reaction provides a novel method for the synthesis of 5,6,11,12-tetra-hydro-6,11-dioxo-benzo[b]acridines. With a meta substituent on the anilino group, this reaction shows poor to high regioselectivity depending on the steric effect of the substituents on the anilino group and malonate.     

Potentiometric studies on the chelation behaviour of lanthanons with 3-hydroxy-2-methyl-1,4-naphthoquinone (HMNQ)

The chelation behaviour of complexes of La(III), Pr(III), Nd(III), Y(III), Sm(III) and Tb(III) with 3-hydroxy-2-methyl-1,4-naphthoquinone has been studied potentiometrically in 75% (v/v) aqueous dioxan medium at various ionic strengths. The method ofBjerrum andCalvin, as modified byIrving andRossotti, has been used to find values of andpL. The stability constants and the values ofS _min have been calculated. The order of stability constants was found to be: La<Pr<Nd<Sm<Tb.

---

Potentiometrische Untersuchungen des Komplexierungsverhaltens von Lanthanid-Ionen mit 3-Hydroxy-2-methyl-1,4-naphthochinon (HMNQ)

Zusammenfassung Das Komplexierungsverhalten der Komplexe von La(III), Pr(III), Nd(III), Y(III), Sm(III) und Tb(III) mit 3-Hydroxy-2-methyl-1,4-naphthochinon wurde potentiometrisch in 75% (v/v) wäßrigem Dioxan bei verschiedenen Ionenstärken untersucht. Die Methode vonBjerrum undCalvin in der Modifikation nachIrving undRossotti wurde zur Bestimmung der Werte für undpL benutzt. Es wurden die Stabilitätskonstanten und dieS _min -Werte berechnet; die Stabilitätskonstanten ergaben folgende Reihung: La<Pr<Nd<Sm<Tb.

     

Novel platinum(II) selective membrane electrode based on 1,3-bis(2-cyanobenzene)triazene

A plasticized poly (vinyl chloride) membrane electrode based on 1,3-bis(2-cyanobenzene)triazene (CBT) for highly selective determination of platinum(II) (in PtCl₄²⁻ form) is developed. The electrode showed a good Nernstian response (29.8 ± 0.3 mV decade⁻¹) over a wide concentration range (1.0 × 10⁻⁶ to 1.0 × 10⁻² mol L⁻¹). The limit of detection was 5.0 × 10⁻⁷ mol L⁻¹. The electrode has a response time of about 40 s, and it can be used for at least 1 month without observing any considerable deviation from Nernstian response. The proposed electrode revealed an excellent selectivity toward platinum(II) ion over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, and it could be used in the pH range of 3.2-5.1. The practical utility of the electrode has been demonstrated by its use in determination of platinum ion in, alloy, tap, mineral and river water samples.     

PVC-based bis(2-nitrophenyl)disulfide sensor for zinc ions

A PVC membrane electrode based on bis(2-nitrophenyl)disulfide carrier exhibits a very good response for Zn²⁺ in a wide concentration range (from 2.9×10⁻⁷ to 3.2×10⁻² mol l⁻¹) with a slope of 29.9±0.4 mV per decade of Zn²⁺ concentration. The response time of the sensor is about 10 s and the membrane can be used for more than 3 months without any observed divergence in potentials. The proposed sensor exhibits very good selectivity for Zn²⁺ over many cations and can be used in a wide pH range (2-9). This assembly served also as an indicator electrode in potentiometric titrations involving zinc ions and direct potentiometric determination of zinc ions in real and synthetic samples.     

Comparative studies of neodymium (III)-selective PVC membrane sensors

Sensors based on two neutral ionophores, N,N′-bis((1H-pyrrol-2-yl)methylene)cyclohexane-1,2-diamine (L₁) and 3,3′-(cyclohexane-1,2-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(5-hydroxymethyl)pyridine-2-ol) (L₂) are described for quantification of neodymium (III). Effect of various plasticizers; 2-nitrophenyloctylether (o-NPOE), dibutyl butylphosphonate (DBBP), tri-n-butyl phosphates (TBP), dioctylpthalate (DOP) and chloronapthalen (CN) and anion excluder, sodiumtetraphenylborate (NaTPB) has been studied. The membrane composition of PVC:o-NPOE:ionophore (L₁):NaTPB (w/w; mg) of 150:300:5:5 exhibited best performance. The sensor with ionophore (L₁) exhibits significantly enhanced selectivity towards neodymium (III) in the concentration range 5.0 × 10⁻⁷ to 1.0 × 10⁻² M with a detection limit of 1.0 × 10⁻⁷ M and a Nernstian compliance (19.8 ± 0.3 mV decade⁻¹ of activity) within pH range 4.0-8.0. The response time of sensor was found as 10 s. The influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. The fast and stable response, good reproducibility and long-term stability of the sensor are observed. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for neodymium. The proposed electrode shows fairly good discrimination of neodymium (III) from other cations. The application of prepared sensor has been demonstrated in the determination of neodymium (III) in spiked water samples.     

Erbium(III) PVC Membrane Ion-Selective Sensor based on 4-(2-Thiazolylazo)resorcinal

Abstract

4-(2-Thiazolylazo)resorcinol (TR) was used as a new compound to play the role of an excellent ion carrier in the fabrication of an Er(III) membrane electrode. The electrode shows a very good selectivity toward Er(III) ions over a wide variety of cations, including alkali, alkaline earth, transition, and heavy-metal ions. The proposed sensor exhibits a Nernstian behavior (with slope of 19.6 ± 0.6 mV per decade) over a wide concentration range (1.0 × 10^?6 to 1.0 × 10^?2 M). The detection limit of the sensor is 6.6 × 10^?7 M. It has a very short response time, in the whole concentration range (～10 s), and can be used for at least 12 weeks in the pH range of 2.8–9.3. The proposed sensor was successfully applied as an indicator electrode for the potentiometric titration of a Er(III) solution, with EDTA. It was also successfully applied to the F^? ion determination in some mouthwashing solutions.     

The radical reactions of imine radicals produced from the metal salts oxidation of 2-amino-1,4-benzoquinones

The metal salts mediated oxidative free radical reaction of 2-amino-1,4-benzoquinones is described. Imine radicals can be generated by the oxidation of 2-amino-1,4-benzoquinones with Mn(III) and Ag(II). The dimeric products 4 and 14 were formed via the intermolecular radical coupling reaction of the corresponding radical intermediates 5 and 15. In the presence of styrene, twistane 17 was afforded from 2-phenylamino-1,4-benzoquinone 1 via a radical annulation reaction of imine radical 5.     

Gliclazide as novel carrier in construction of PVC-based La(III)-selective membrane sensor

A PVC-based sensor for La³⁺ ions based on N-[hexahydrocyclopentapyrol-2((1H)yl)amino]carbonyl]-4-methyl benzene sulfonamide (gliclazide) as a novel carrier was prepared. The electrode exhibits a Nernstian response for La³⁺ over a wide concentration range (1.0×10⁻¹-1.0×10⁻⁶ M) with a slope of 20.1 mV per decade. The limit of detection is 8.0×10⁻⁷ M. The sensor has a very short response time (<15 s) and a useful working pH range of 4.0-8.0. The proposed membrane sensor shows excellent discriminating ability towards La³⁺ ions with regard to several alkali, alkaline earth, transition and heavy metal ions. The electrode was successfully applied for determination of La³⁺ in binary mixtures.     

Comparative studies of ONNO-based ligands as ionophores for palladium ion-selective membrane sensors

Palladium sensors based on two neutral ionophores, N,N′-bis(acetylacetone) cyclohexanediamine (L₁) and N,N′-bis(o-hydroxyacetophenone)-1,2-cyclohexanediamine (L₂) for quantification of palladium ions are described. Effect of various plasticizers (o-NPOE, DBP, DEP, DOP, TBP, and CN) and anion excluder, sodium tetra phenyl borate (NaTPB) has been studied. The best performance is obtained with a membrane composition of PVC:o-NPOE:ionophore (L₁):NaTPB of 150:300:5:5 (%, w/w). The sensor exhibits significantly enhanced selectivity towards palladium ion over the concentration range 1.0 × 10⁻⁸ to 1.0 × 10⁻¹ M with a lower detection limit of 4.0 × 10⁻⁹ M and a Nernstian compliance (29.1 ± 0.3 mV decade⁻¹ of activity) within pH range 2.0-6.0 and fast response time of 10 s. Influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. Fast and stable response, good reproducibility and long-term stability of the sensor are demonstrated. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 4 months. Selectivity coefficients determined with fixed interference method (FIM) indicate high selectivity for palladium. The proposed electrode shows fairly good discrimination of palladium from other cations. The application of prepared sensor has been demonstrated in determination of palladium ions in spiked water sample.     

Comparative study of Ag(I) selective poly(vinyl chloride) membrane sensors based on newly developed Schiff-base lariat ethers derived from 4,13-diaza-18-crown-6

The six Schiff-base lariat ether chelates based on 4,13-diaza-18-crown ether, have been synthesized and explored as a neutral ionophores for preparing poly(vinyl chloride) based membrane sensors selective to silver(I). The addition of potassium tetrakis(4-chlorophenyl) borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor no. 5 having membrane of chelate (A₆) with composition (w/w) chelate (2.8%):PVC (45.7%):o-NPOE (48.6%):KTpClPB (2.8%). This sensor exhibits Nernstian response with slope 59.3 mV/decade of activity in the concentration range 5.6 × 10⁻⁸-1.0 × 10⁻¹ M Ag(I), performs satisfactorily over wide pH range of (3.0-8.0) with a fast response time (12 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 25% (v/v) content of acetonitrile, methanol or ethanol and can tolerate the concentration 1.0 × 10⁻² M of ionic (SDS, TBC) and nonionic (Triton X-100) surfactants. The proposed sensor can be used over a period of 4 months without significant drift in potentials. The response of the sensor was highly selective to Ag⁺ over a large number of cations and it could therefore be used for Ag⁺ estimation in blood of occupationally exposed persons.