Structure and behavior of organic analytical reagents : Heats and entropies of formation of several divalent metal chelates of 2- and 4-methyl-8-hydroxyquinoline1

The Calvin-Bjerrum titration technique for the determination of chelate formation constants has been applied to the Cu(II), Ni(II), Co(II), Zn(II) and Mn(II) chelates of 2- and 4-methyl-8-hydroxyquinoline. Measurements were made at several temperatures in order to evaluate ΔH and ΔS values of chelation. The results obtained were interpreted in terms of steric hindrance of the 2-methyl group. In all cases the heats of formation of the chelates of 2-methyl-8-hydroxyquinoline were remarkably morepositive than those for the corresponding chelates of 4-methyl-8-hydroxyquinoline. This large difference in the strengths of the metal-chelate bonds is apparently due to the hindrance of the methyl groups which prevent the close grouping of the two reagent molecules around the metal in chelates of 2-methyl-8-hydroxyquinoline. The lower bond strength in chelates of 2-methyl-8-hydroxy-quinoline is partially compensated by a relatively larger entropy of formation. This is attributed to decreased solvent chelate interaction caused by the shielding of the polar O, N, and metal atoms by the 2-methyl groups. The determination of chelate fortmation constants of 2-phenyl-8-hydroxyqumoline has been carried out to further extend our study of steric effects in metal chelates.     

Preparative,infrared and thermogravimetric studies of three scandium 8-hydroxyquinolinates

The preparation of 3 scandium 8-hydroxyquinolinates is reported. Two were prepared by precipitation from homogeneous solution using 8-hydroxyquinoline generated by hydrolysis of 8-acetoxyquinoline, and the third by a solid-phase reaction. The first precipitate was obtained at pH 6.5 as a lemon-yellow compound with the composition ScQ₃.HQ (Q == C₉H₆NO). The second chelate was obtained at pH 8.8 as a bright-yellow compound of composition (ScQ₃)₂.HQ. The third scandium 8-hydroxyquinolinate was obtained by a solid-phase reaction between the lemon-yellow compound ScQ₃.HQ and 8-hydroxyquinoline. The orange compound has the composition (ScQ₃)₂.3HQ. Infrared spectra and pyrolysis curves indicated that the 3 chelates have very similar structures.     

A comparison of preconcentration reagents for flow injection analysis flame atomic spectrometry

A small range of new commercially available chelating resins are compared with a resin prepared in-house in terms of their applicability for on-line preconcentration and matrix separation. The flow injection manifold was designed for rapid matrix separation and the resins were tested for the determination of Cull, ZnII, CdII, MnII and NiII. The resin based on controlled pore glass was found to be better for this rapid procedure because it did not require conditioning, although the polymer based resins had better capacities. The commercially available controlled pore glass based iminodiacetate (IDA) resin had a comparable performance to the in-house controlled pore glass 8-hydroxyquinoline (CPG-8-HQ) resin. The IDA resin had a much higher capacity than the 8-HQ, however as with all IDA based resins, some retention of Call was observed. The sample throughput was 12 h⁻¹.     

Arene ruthenium oxinato complexes: Synthesis, molecular structure and catalytic activity for the hydrogenation of carbon dioxide in aqueous solution

Two families of arene ruthenium oxinato complexes of the types [(η⁶-arene)Ru(η²-N,O-L)Cl] and [(η⁶-arene)Ru(η²-N,O-L)(OH₂)]⁺ have been synthesized from the dinuclear precursors [(η⁶-arene)RuCl₂]₂ (arene = para-cymeme or hexamethylbenzene) and the corresponding oxine LH (LH = 8-hydroxyquinoline, 5-chloro-8-hydroxyquinoline, 5,7-dichloro-8-hydroxyquinoline, 5-nitro-8-hydroxyquinoline, 5,7-dimethyl-8-hydroxyquinoline, 5,7-dichloro-2-methyl-8-hydroxyquinoline). The molecular structures of the neutral chloro complexes [(η⁶-C₆Me₆)Ru(η²-N,O-L)Cl] (LH = 8-hydroxyquinoline, 5,7-dichloro-2-methyl-8-hydroxyquinoline) and [(η⁶-MeC₆H₄Prⁱ)Ru(η²-N,O-L)Cl] (LH = 5,7-dichloro-2-methyl-8-hydroxyquinoline) as well as those of the cationic aqua derivatives [(η⁶-MeC₆H₄Prⁱ)Ru(η²-N,O-L)(OH₂)]⁺ (LH = 8-hydroxyquinoline, 5,7-dimethyl-8-hydroxyquinoline), isolated as the tetrafluoroborate salts, show in all cases a piano-stool arrangement with the arene ligand, the chelating oxinato ligand and the chloro or the aqua ligand surrounding the ruthenium center in a pseudo-tetrahedral fashion. The analogous reaction of [(η⁶-MeC₆H₄Prⁱ)RuCl₂]₂ with other N,O-chelating ligands such as 2-pyridinemethanol or tetrahydrofurfurylamine did not give the expected analogs but resulted in the formation of the complexes [(η⁶-MeC₆H₄Prⁱ)Ru(η²-NC₅H₄CH₂OH)Cl]⁺ and [(η⁶-MeC₆H₄Prⁱ)Ru(η¹-NHCH₂C₄H₃O)Cl₂]. The neutral and cationic complexes of the types [(η⁶-arene)Ru(η²-N,O-L)Cl] and [(η⁶-arene)Ru(η²-N,O-L)(OH₂)]⁺ have been found to catalyze the hydrogenation of carbon dioxide to give formate in alkaline aqueous solution with catalytic turnovers up to 400.     

Solvent extraction of cobalt and nickel with 5,7-dichloro-2-methyl-8-hydroxyquinoline into chloroform

Summary The distribution equilibria of the cobalt and nickel complexes with 5,7-dichloro-2-methyl-8-hydroxyquinoline in the water-chloroform system have been studied. The influence of pH, reagent and metal concentrations, and the presence of NaClO₄ or Na₂SO₄ in the aqueous phase has been studied. From slope analysis of the distribution curves the compositions of the extracted species have been determined. The cobalt complexes extracted are [Co₂R₃(RH)]ClO₄, [Co₂R₃(RH)₃]ClO₄ and Co₂R₄; in all of them the metal is in oxidation state Co(II). For nickel the NiR₂ and NiR₂(RH) complexes are extracted.

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Die Extraktion von Kobalt und Nickel mit 5,7-Dichlor-2-methyl-8-hydroxychinolin in Chloroform

Zusammenfassung Die Verteilung der Kobaltund Nickel-Komplexe mit 5,7-Dichlor-2-methyl-8-hydroxychinolin in dem System Wasser-Chloroform wurde untersucht. Auch der Einfluß des pH, der Reagensund Metallkonzentration und der Anwesenheit von NaClO₄ oder Na₂SO₄ in der wäßrigen Phase auf das Verteilungsgleichgewicht wurde geprüft. Aus der Lage der Verteilungskurven wurde die Zusammensetzung der extrahierten Substanzen bestimmt. Die extrahierten Kobaltverbindungen waren [Co₂R₃(RH)]ClO₄, [Co_{2R 3}(RH)₃]ClO₄ und Co₂R₄; diese enthalten alle Co(II). Im Falle des Nickels wurden die Verbindungen NiR₂ und NiR₂(RH) beobachtet.

     

Comparison of chelating agents immobilized on glass with chelex 100 for removal and preconcentration of trace copper(II)

Three types of chelating agents immobilized on glass were compared with Chelex 100 for removing and preconcentrating trace Cu(2+) from laboratory-prepared solutions. Columns of immobilized N-propylethylenediamine (diamine), its bis(dithiocarbamate) (DTC) and immobilized 8-hydroxyquinoline (8-HQ) quantitatively remove Cu(2+) (10-200 mug l. ) from buffered solutions at pH 6.00. Addition of isolated natural organic matter at concentrations typical of organic-rich fresh waters (25-100 mug l. ) complexed Cu(2+) and hindered the performance of Chelex and the immobilized chelating agents. In the presence of organic matter the DTC performed very well, removing about 98% of the Cu(2+). However, the Cu(2+) removed could not be readily recovered from the column. Chelex gave the poorest results, removing only 62 and 75% of Cu(2+) at the two levels tested. The other immobilized reagents gave results that were strongly dependent on their contact time with the solution. Longer columns and slower flow-rates tended to improve results. Overall, the immobilized 8-HQ is probably the most suitable of the materials tested for preconcentration work. A batch titration of 8-HQ with Cu(2+) monitored by ion-selective electrode indicated a conditional stability constant of 6.2 x 10(7), which is larger than the corresponding value for the complex with non-immobilized 8-hydroxyquinoline, measured under the same conditions.     

Utility of 5-Diazo-1,2,4- Triazol-3-Carboxylic Acid for Colorimetric Determination of Certain 8-Hydroxyquinolines

Abstract

A colorimetric method for the determination of certain 8-hydroxyquinolines has been developed. The method is based on the coupling of 8-quinolinols with diazotriazole carboxylic acid in the presence of sodium carbonate (0.5% w/v) at ambient temperature (around 30°C). The resulting azo dyes are stable and give intense absorption in the range of 486–540 nm. Beer's law is valid in the concentration ranges of 1 – 8, 2.5 – 17.5, 5 – 35, 2 – 20, and 2 – 20 mcg/ml for 8-hydroxyquinoline (HQ), 5,7-diiodo-8-hydroxyquinoline (DIQ), 5,7-dibromo-8-hydroxyquinoline (DBQ), 5-chloro-7-iodo-8-hydroxyquinoline (CIQ) and 8-hydroxy-7-iodo-5-quinoline sulfonic acid (SIQ), respectively. The proposed method has been successfully applied for the determination of the studied compounds in pure form and in commercial formulations. The obtained results are in good agreement with those obtained from reported methods.     

Aluminum(III), gallium(III), and indium(III) 4-hydroxyacridinato complexes

4-Hydroxyacridine (HAcr) is an O,N-chelating ligand whose coordination chemistry toward group 13 M(III) ions has received little attention. The molecular structure of HAcr consists of a 2,3-disubstituted-8-hydroxyquinoline; thus, in order to compare 8-hydroxyquinoline (HQ), 2-methyl-8-hydroxyquinoline (HMeQ′), and 2,3-disubstituted-8-hydroxyquinoline (HAcr) for steric and/or electronic influence, HAcr chelating ability toward the Al(III), Ga(III), and In(III) triad has been investigated. Irrespective of the nature of M(III), only complexes containing two equivalents of deprotonated HAcr are obtained. This article describes the synthesis and characterization of different series of bis-chelated pentacoordinated (Acr)₂MY (M = Al, Ga, In; Y = Cl, Br, I, NCS, N₃) or (Acr)₂MZ (M = Ga or In; HZ = C₆H₅OH, C₆H₁₃OC₆H₄OH, C₆H₅COOH, or C₆H₁₃OC₆H₄COOH) six-coordinate neutral (Acr)₂In(acac) (H(acac) =acetylacetone), or ionic [(Acr)₂In(N,N)][CF₃SO₃] (N,N = 2,2′-bipyridine or 1,10-phenanthroline) complexes. These results significantly contribute to elucidating the complexation capability of HAcr.     

Preconcentration and Determination of Tin in Water Samples by Using Cloud Point Extraction and Graphite Furnace Atomic Absorption Spectrometry

A method based on cloud point extraction and graphite furnace atomic absorption spectrometry (GFAAS) was developed for the analysis of trace tin in water samples. After cloud point extraction, the tin in the water samples was preconcentrated and successfully separated from most interferents. During the procedure, 8-hydroxyquinoline (8-HQ) was used as chelating reagent, and Triton X-114 was added as surfactant. The parameters affecting the sensitivity and the extraction efficiency, such as solution pH, concentration of 8-HQ and Triton X-114, equilibration temperature and centrifuge time, were evaluated and optimized. Under the optimum conditions, a preconcentration factor of 96.2 was obtained for a 20 mL water sample. The detection limit (LOD) was as low as 0.012 ng mL⁻¹, and the analytical curve was linear in the range of 0.05–2.0 ng mL⁻¹ with satisfactory precision (RSD <4.1%). The proposed method was successfully applied to the determination of trace tin in water samples with recoveries in the range of 85.0–112.0%.     

Solvent extraction of zinc with 5,7-dichloro-2-methyl-8-hydroxyquinoline into chloroform

The distribution equilibria of the zinc complex with 5,7-dichloro-2-methyl-8-hydroxyquinoline in the water-chloroform system have been studied at 25 degrees . The influence of pH, reagent and metal concentrations, and the presence of sodium perchlorate in the aqueous phase has been determined. From quantitative evaluation of the extraction equilibrium data, it has been deduced that the complex extracted is the simple 1:2 chelate, ZnR(2), although at ligand concentrations higher than 0.3M, the self-adduct complex seems to begin to form. The extraction constant of the ZnR(2) species, refined by means of the program Letagrop-Distribution, has the value log K(ex) = - 6.15 +/- 0.07.     

Sequential Injection On-Line Sorption Preconcentration Using PEEK-Turnings Packed Micro-Column for Ultra-Trace Cobalt Determination by Electrothermal Atomic Absorption Spectrometry

A novel sequential injection on-line column preconcentration method for ultra-trace cobalt determination by electrothermal atomic absorption spectrometry (ETAAS) using poly(etheretherketone) (PEEK) turnings as sorbent material was developed. The method was based on the on-line chelate complex formation and retention of target analyte with ammonium pyrrolidine dithiocarbamate (APDC) on the surface of PEEK-turnings and elution with methyl isobutyl ketone (MIBK). A 40 µL fraction of MIBK containing the bulk of analyte complex introduced directly into the transversely heated graphite tube atomizer of ETAAS for quantification. Acidity of sample solution, chelating reagent concentration, and preconcentration time were investigated and optimized separately, while all other factors were optimized by full factorial design optimization methodology. The significance of the variables and their interactions was estimated by employing analysis of variance (ANOVA) and Pareto chart. Under the optimum conditions the enhancement factor for cobalt determination was 60. The detection limit was 6 ng L^?1 and the precision expressed as relative standard deviation (RSD) was 3.5% at 0.1 µg L^?1 Co(II) concentration level, respectively. The proposed method was evaluated by analyzing water certified reference materials and spiked environmental samples.     

Acid-base and distribution equilibria of 5,7-dichloro-2-methyl-8-hydroxyquinoline in Brij-35 micellar media solutions

The acid-base equilibria of 5,7-dichloro-2-methyl-8-hydroxyquinoline (HQ) have been examined spectrophotometrically in aqueous micellar solution of the non-ionic surfactant Brij-35. The differences between apparent pK(a) values at different surfactant concentrations can be quantitatively explained in terms of the extraction constants of the neutral species HQ and the ion-pair Na(+)Q(-). Calculations have been performed by means of SPDIS program, developed in this work to handle multiwavelength spectrophotometric data in micellar systems.     

Extraction of tungsten with 8-hydroxyquinoline and some of its derivatives

The extraction of tungsten by chloroform solutions of 8-hydroxyquinoline(I), 2-methyl-8-hydroxyquinoline(II), 5,7-dibromo-8-hydroxyquinoline(III) and 8-mercaptoquinoline(IV), as a function of the concentration of tungsten and reagent and the acidity of the aqueous phase, has been studied. Evidence was obtained for the quantitative extraction of tungsten over a wide range of acidity. The degree of extraction of tungsten at 10(-5)M concentration with I,III and IV gives two maxima when plotted against acidity. The extraction maximum for the more acidic solutions lies in the region where the reagents exist in the protonated form and its position depends on the reagent used. It is suggested that different tungsten complexes are extracted, depending on the acidity of the aqueous phase.     

Thermal behaviour of 8-hydroxyquinoline complexes with nickel(II)/copper(II)/zinc(II) hydroxides

Thermal behaviour of M(OH)₂(8-HQ)₂ (M=Ni, Cu and Zn; 8-HQ=8-hydroxyquinoline) has been studied by dynamic TG and DTA methods in nitrogen atmosphere. The percent weights lost in different temperature range was calculated from TG curves. The mode of decomposition has been supported by endotherms observed in DTA curves of the respective compounds.     

Theoretical studies on structures and reactivity of 8-hydroxyquinoline and its one-water complex in the ground and excited states

In this Letter, MP2, DFT and CASSCF calculations were carried out to investigate proton transfer reactions of 8-hydroxyquinoline (8-HQ) and its one-water complex (8-HQ-H₂O). Since the forward reactions from the normal form (N) to the tautomer form (T) in the ground state have a considerable barrier and the reverse processes nearly have no barrier, the tautomerization reactions from N to T proceed with little probability in the ground state of 8-HQ and 8-HQ-H₂O. After photoexcitation, the excited-state proton transfer reactions proceed very easily for both 8-HQ and 8-HQ-H₂O, which are mainly responsible for lack of fluorescence for 8-HQ in aqueous solution.     

Preconcentration of cadmium by MEUF in sodium dodecylsulphate solutions

The ultrafiltration preconcentration of Cd²⁺ using micellar extraction with 8-hydroxyquinoline (8-HQ), solubilized in anionic micelles of sodium dodecylsulphate (SDS)) were studied. The n-butanol was used as a co-surfactant. Ultrafiltration yields (R, %) on cellulose acetate membranes (wet, 20000 MW-CO) under 400 kPa pressure were determined. Distribution ratios (D) of cadmium between bulk liquid phase and micellar pseudophase were estimated. The constants (app.) for the cadmium-sodium exchange on SDS micelles surface at pH values of 4.8 and 5.3 (3.36 and 3.86, respectively) were determined. It was found, that the values of ultrafiltration yields of the cadmium (at constant concentration of 8-HQ) are influenced not only by the pH and by the concentration values, but also by the ratio of the concentrations of the metal and the anionic surfactant.     

基于电化学噪声研究缓蚀剂对AA6063铝合金点蚀的影响

采用电化学噪声(ECN)、电化学阻抗谱(EIS)和极化曲线研究了AA6063 铝合金在3% (w) NaCl 溶液中的亚稳态点蚀萌发和稳态点蚀生长特征, 着重探讨了CeCl₃、Na₂CrO₄、8-羟基喹啉(8-HQ)等三种不同类型缓蚀剂对亚稳态和稳态点蚀的抑制机理. 结果表明: 当铝合金表面阴极相(Al-Si-Fe)周边的Al 基体发生局部溶解后,会导致邻近区域pH值升高(>8.4), 引起Ce(OH)₃在蚀点中心区的阴极相表面优先沉积, 从而抑制局部腐蚀的阴极去极化过程. 随着缓蚀剂浓度的提高, 亚稳态噪声峰的平均积分电量(q)随之递减, 但噪声峰的平均寿命几乎没有变化, 表明Ce³⁺并不能直接加速亚稳态蚀点的修复, 但可降低蚀点内金属Al 的溶解速率. CrO₄^2-不但可加速蚀点修复, 还可降低亚稳态蚀点的形核速率. 8-HQ主要与Al³⁺、Mg²⁺等形成不溶性螯合物并沉积在铝合金表面,提高了铝基体的全面抗腐蚀能力, 但并不能显著提高其耐点蚀能力.     

Immobilization of 8-hydroxyquinoline onto silicone tubing for the determination of trace elements in seawater using flow injection ICP-MS

A rapid and simple on-line method is described for the preconcentration of Mn, Co, Ni, Cu, Zn, Cd and Pb from sea water using 8-hydroxyquinoline immobilized onto silicone tubing (Sil-8-HQ) via the Mannich reaction. Recoveries between 35 and 95% and limits of detection in the ppt range were obtained using a 2 m long Sil-8-HQ tube with a sample flow rate of 1.0 ml min(-1). A tube could be subjected to sample loading and elution cycles over 200 times. The capacity was 1.5 and 1.3 mug cm(-2) for Cu and Mn, respectively. Cu, Cd, Co, Pb, Mn, Zn and Ni were determined in coastal and open ocean seawater using flow injection inductively coupled plasma mass spectrometry (FI-ICP-MS). Good agreement with certified values for the certified reference materials NASS-4 and CASS-3 was demonstrated when quantitation was undertaken by the method of additions.     

The thermal decomposition of the 5,7-dihalo-8-quinolinol rare earth metal chelates

The thermal decomposition of the 5,7-dichloro-, 5,7-dibromo- and 5,7-duodo-8-quinohnol chelates of lanthanum, cerium, praseodymium, neodymium, samarium and yttrium was investigated on the thermobalance. The chelates decomposed in the temperature range from 65 to 125°C while the oxide levels were obtained from 395 to 805°C Although the chelate thermal stability temperatures varied little with the chelating agent, the minimum oxide level temperatures were largely dependent on the halogen substitution on the 8-quinolinol molecule. Results of this study were correlated with previous studies on the rare earth metal chclatcs with 8-quinolinol and 2-methyl-8-quinolinol.     

Cloud point extraction of iron(III) and vanadium(V) using 8-quinolinol derivatives and Triton X-100 and determination of 10(-7)moldm(-3) level iron(III) in riverine water reference by a graphite furnace atomic absorption spectroscopy

The cloud point extraction behavior of iron(III) and vanadium(V) using 8-quinolinol derivatives (HA) such as 8-quinolinol (HQ), 2-methyl-8-quinolinol (HMQ), 5-butyloxymethyl-8-quinolinol (HO₄Q), 5-hexyloxymethyl-8-quinolinol (HO₆Q), and 2-methyl-5-octyloxymethyl-8-quinolinol (HMO₈Q) and Triton X-100 solution was investigated. Iron(III) was extracted with HA and 4% (v/v) Triton X-100 in the pH range of 1.70-5.44. Above pH 4.0, more than 95% of iron(III) was extracted with HQ, HMQ, and HMO₈Q. Vanadium(V) was also extracted with HA and 4% (v/v) Triton X-100 in the pH range of 2.07-5.00, and the extractability increased in the following order of HMQ < HQ < HO₄Q < HO₆Q. The cloud point extraction was applied to the determination of iron(III) in the riverine water reference by a graphite furnace atomic absorption spectroscopy. When 1.25 × 10⁻³ M HMQ and 1% (v/v) Triton X-100 were used, the found values showed a good agreement with the certified ones within the 2% of the R.S.D. Moreover, the effect of an alkyl group on the solubility of 5-alkyloxymethyl-8-quinolinol and 2-methyl-5-alkyloxymethyl-8-quinolinol in 4% (v/v) Triton X-100 at 25 °C was also investigated.