Ethanol-water Medium Research Articles

Acid-base characteristics of naphthazarin and solution equilibria of yttrium(III) chelates

The spectral absorption and acid-base characteristics of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone,NAZA) in ethanol water medium containing 50% (v/v) ethanol have been studied, and thepKa values determined. Two equilibria are established in solution atpH 2.5–11.5, based on the acid dissociation of the nonionized form of the reagent. The existence of these equilibria is confirmed by potentiometricpH titrations and the precision of the equilibrium study is improved. The composition, molar absorptivities and stability constants of the chelates ofNAZA with yttrium(III) have been determined spectrophotometrically under the conditions encountered in this study. The complexation equilibria existing in solution are discussed. The Y(NAZA) monoligand chelate formed atpH 5.5 (ɛ=1.15×104lmol−1 cm−1 at 595 nm) allows the determination of 1.95–8.86 µg ml−1 yttrium. Interferences and their elimination have been studied.

Stability Constants of some Bivalent Metal Ions with N-(Phenyl and 2/3/4-Hydroxyphenyl)diacetylmonoxime In Water-Ethanol Medium

Stability Constants of some Bivalent Metal Ions with N-(Phenyl and 2/3/4-Hydroxyphenyl)diacetylmonoxime In Water-Ethanol Medium

Stability Constants of some Bivalent Metal Ions with N-(Phenyl and 2/3/4-Hydroxyphenyl)diacetylmonoxime In Water-Ethanol Medium

Stability Constants of some Bivalent Metal Ions with N-(Phenyl and 2/3/4-Hydroxyphenyl)diacetylmonoxime In Water-Ethanol Medium

Acid–base characteristics of naphthazarin and solution equilibria of yttrium(III) chelates

The spectral absorption and acid–base characteristics of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone; NAZA) in ethanol–water medium containing 50% v/v ethanol have been studied, and pKa values have been determined. Two equilibria are established in solution at pH 2.5–11.5, based on the acid dissociation of the non-ionized form of the reagent. The existence of these equilibria is confirmed by potentiometric pH titrations, and the precision of the equilibrium study is improved. The composition, molar absorptivities and stability constants of the chelates of NAZA with yttrium(III) have been determined by spectrophotometry under the conditions encountered in this study. The complexation equilibria existing in solution are demonstrated and characterized. The Y(NAZA) mono-ligand chelate formed at pH 5.5 (Iµ= 1.15 × 104 l mol–1 cm–1 at 595 nm) allows the determination of 1.95–8.86 µg ml–1 of yttrium. Interfering species and their elimination have been studied.

Spectrophotometric study of the complexation equilibria of iron(III) with 3-hydroxypicolinic acid and determination of iron in pharmaceutical preparations.

The complexation equilibria of iron(III) with 3-hydroxypicolinic acid (hypa) have been studied spectrophotometrically in 40% (v/v) ethanol-water medium at 25 degrees C and an ionic strength of 0.1 M NaClO4. The equilibria occurring in solution were established and the basic characteristics of the complexes formed were determined. The spectral study of the reaction solutions containing equimolar concentrations or an excess of one component in the pH range 1.5 to 10.5 gave the evidence for the formation of [FeLH]2+, [FeL]+ and [FeL2]- complex species, depending upon the pH of the medium (LH2 symbolising the molecular form of hypa). The possible complex transitions that occur in solution were demonstrated using graphical and logarithmic analysis of the absorbance-pH graphs. A simple, rapid, sensitive and selective method for spectrophotometric determination of trace levels of iron(III) was proposed based on the formation of Fe(hypa)2 complex at pH 5.5 (lambda = 440 nm, epsilon = 1.5 x 10(4) dm3 mol-1 cm-1). The interference of a large number of foreign ions was investigated. The method has been applied successfully to the analysis of multivitamin and mineral preparations containing iron.

Thermal Lens Spectrometric Detection of Catecholamines after Oxidation to Aminochromes

Abstract Experimental conditions for the spectrophotometric and thermal lens spectrometry (TLS) detection of catecholamines after oxidation to aminochromes with hexacyanoferrate (III) are optimized. At the low concentrations used in TLS, and in a 0.07 M citrate buffer, catecholamine oxidation can be performed at pH 7 and is immediate, whereas a lower pH value is required in spectrophotometry to avoid aminochrome polymerisation, the oxidation reactions being much slower. Similar TLS sensitivities are obtained for all catecholamines which facilitates HPLC evaluation. Sensitivity can be enhanced using a 50% ethanol-water medium. The linear dynamic range extends over two orders of magnitude, the limit of detection being about 1 ng ml−1 with a reproducibility of 2%, indicating that TLS is adequate to detect catecholamines as aminochromes in physiological samples after HPLC separation. A chromatogram of a urine sample extract is given.

Nitrosyl ethylenediaminetetraacetato ruthemium(III) — an efficient oxygen atom transfer agent for the oxidation of olefins by molecular O 2 and PhIO through ligand-mediated nitrosyl/nitro couple

The complexes [Ru III(EDTA—H)NO]BF 4 1 and [Ru III(EDTA)(NO)] 1a were synthesized and characterised by elemental analysis, IR and UV—Vis spectroscopy, conductivity, magnetic susceptibility, EPR and electrochemical studies. Complex 1a catalyses the oxidation by molecular oxygen of 1-hexene to 2-hexanone and cyclohexene to cyclohexene oxide through the ligand-mediated Ru III—EDTA—NO 1a/Ru v—EDTA—NO 2 2 oxygen atom transfer. The oxidation reactions were studied in 7:3 ethanol—water medium in the temperature range 30–45 °C (μ=0.1 M KCl). The oxidation of 1-hexene and cyclohexene proceeds with a turnover number of 50 and 44 moles product per mole catalyst per hour. The rate of oxidation is first order with respect to catalyst concentration and one-half order with respect to molecular oxygen concentration. At higher substrate concentrations, the reaction rate was found to be independent of substrate concentration. 18O 2 studies indicate that the source of O atom transferred to the substrate is from molecular O 2. The formation of an organometallic metallocyclic intermediate is proposed for the reaction. The rate of oxygenation of cyclohexene by iodosyl benzene catalyzed by 1a was found to be identical with that obtained with O 2 as oxidant. The rate of oxygenation of 1a to 2 was studied independently by an O atom transfer from iodosyl benzene.

Structure and Reactivity of Spruce Mechanical Pulp Lignins Part II. Organosolv Fractionation of Lignins in a Flow-Through Reactor

ABSTRACT Various spruce mechanical pulps were subjected to delignification with ethanol-water (1 : 1, v / v ) containing 0.1 M acetic acid at 175°C in a flow- through reactor. A thermomechanical pulp (TMP) and the corresponding samples derived from its bleaching (BTMP) and yellowing ( YBTMP ) treatments were delignified to a similar extent, about 70% of delignification degree, as compared with spruce wood. A series of five successive lignin fractions was recovered from each pulp sample and then characterized by various analytical methods. Large structural variations were observed within these fractions. The number of phenolic structures appeared to be an important factor influencing the dissolution of lignins in the ethanol-water medium. These lignin fractions were found to be different in the amount of β-aryl ether structures and in the relative importance of main carbon-carbon bonding patterns. The results are discussed in relation to the lignin fractionation in the flow-through reactor.

Polarographic and Voltammetric Determination of Chlorobenzene, Benzyl Chloride and Melphalan

Conditions were found for the determination of chlorobenzene and benzyl chloride in dimethylformamide and of Melphalan in ethanol-water medium (4 : 1) using tast polarography at a classical dropping mercury electrode in the concentration range 1 . 10-3 - 2 . 10-5 mol l-1. Differential pulse polarography permits the range for the determination of benzyl chloride to be extended to 1 . 10-5 - 2 . 10-6 mol l-1. The use of fast scan differential pulse voltammetry and linear scan voltammetry at a hanging mercury drop electrode did not lead to an increase in the sensitivity of the determination because of the very negative half-wave potential values and high irreversibility of the processes involved.

Preparation of micron-size monodisperse polymer microspheres having crosslinked structures and vinyl groups

Micron-size monodisperse polymer microspheres having crosslinked structures therein and vinyl groups thereon were prepared by seeded copolymerization of styrene and divinylbenzene with 2,2′-azobisisobutyronitrile as initiator in ethanolwater medium in the presence of 2.1-μm monodisperse polystyrene seed particles produced by dispersion polymerization. The optimum conditions of the seeded copolymerization for producing the microspheres with good monodispersity and colloidal stability were determined.

Preparation of micron-size monodisperse polymer particles by seeded polymerization utilizing the dynamic monomer swelling method

Utilizing a new type of monomer swelling method, 6.1 μm-size monodisperse polymer particles were prepared by seeded polymerization. 1.8 μm-size monodisperse polystyrene (PS) seed particles (1.8 μm in size) were prepared by dispersion polymerization in ethanol-water (80/20, v/v) medium in the presence of poly(acrylic acid) as stabilizer with 2,2′-azobisisobutyronitrile as initiator. The PS seed dispersion was mixed with ethanol-water (60/40, v/v) solution dissolving styrene (S) monomer, benzoyl peroxide as initiator, and poly(vinyl alcohol) as stabilizer. By slow, continuous, dropwise addition of water with a micro feeder into the mixture, the PS particles absorbed the many S monomers, which were separated from the medium and swelled from 1.8 μm to 8.4 μm while keeping the monodispersity high. We named this procedure the “dynamic swelling method”. Then, the seeded polymerization of the absorbed S monomer was carried out in the presence of NaNO2 as water-solube inhibitor.

Potentiometric studies on the complexation equilibria involving diacetylmono(lepidyl) hydrazone and bivalent metal ions in aqueous ethanolic medium

The ligand diacetylmono(lepidyl) hydrazone(DALH) has been synthesized in four steps and characterized by melting point, thin layer chromatography, elemental analysis, NMR and IR. Complex formation between transition metal ions Mn(II), Pb(II), Cd(II), Co(II), Ni(II), Cu(II), U02(II) and DALH has been investigated by potentiometric measurements of hydrogen ions liberated on complexation at 25, 30, 40 and 50±0·5°C in 0·02, 0·05, 0·1 and 0·2 M (NaCl) ionic strength and in 75% ethanol-water medium. From the potentiometric titration curves dissociation constants of the ligand and stability constants of its complexes have been determined. Using these stability constants, thermodynamic parameters such as free energy changes (ΔG), enthalpy changes (ΔH) and entropies (ΔS) of complex formation have calculated and reported. Thermodynamic stability constants (logK 1 0) have also been reported. The ligand field stabilization energy (δH) has been calculated for the first row transition metals which is in good agreement with the theory.

Synthesis and characterization of nickel(II) complexes of purine and pyrimidine bases. Crystal and molecular structure of trans-bis(cytosine-O2)bis(ethylenediamine)nickel(II) bis(tetraphenylborate). An unusual metal binding mode of cytosine

Three nucleobase complexes [Ni(en) 2 (Ade)]Cl 2 , [Ni(en) 2 (Hyp)] Cl.0.5CH 3 OH.H 2 O and [Ni(en) 2 (Cyt) 2 ] [B(C 6 H 5 ) 4 ] 2 (en=ethylenediamine; Ade=adenine; Hyp=hypoxanthine; Cyt=cytosine) have prepared by reaction of Ni(en) 2 Cl 2 and the corresponding purine or pyrimidine base in a methanol or an ethanol-water medium. The cytosine complex was obtained in the form of suitable crystals for X-ray crystallography. The complex crystallizes in the monoclinic space group P2 1 /a

The Influence of the Steric Effect of the Substituents on the Phosphorus Acids Dissociation

Abstract The dissociation processes of a series of phosphoric, phosphonic, and phosphinic acids have been studied by the modified method of potentiometry in water and water-ethanol media at 25°C. The influence of substituents on the acidic properties of these compounds has been investigated. As a measure of the substituents steric effects the Rs constants, calculated on the basis of frontal steric model (1), nave been used. A good linear relationship between pKa values in different media has been found. For all series of acids a linear relationship between pKa values and Rs constants of substituents at phosphorus has also been established. In the case of dialkylphosphates in water, for example, such a relationship is expressed by equation: pKa = (-0.717 ± 0.028)-(0.556 ± 0.009) Rs N = 7, R = 0.9932, So = 0.011 pKa value rises with the increase of the steric effect of the substituents at phosphorus which may be conditioned by the steric hindrance to the anion solvatation.

Determination of Ellagitannins in Extracts of Oak Wood and in Distilled Beverages Matured in Oak Barrels

A method is described for determination of ellagitannins in ethanol-water extracts of oak wood and in distilled alcoholic beverages matured in oak barrels. It is based on the combined ellagic acid content according to ellagitannin structure. Hydrolysis was carried out in the presence of hydrochloric acid under reflux in a 100 degrees C oil bath for 3 h. Total ellagic acid was thus determined by liquid chromatography (LC), and the free ellagic acid content present in the ethanol-water media was subtracted, the difference being the combined ellagic acid content corresponding to ellagitannins. A 5 micron C18 column was used with detection at 254 nm. The method is specific for ellagitannins, which is an advantage over other analytical techniques for overall evaluation of these substances extracted from wood. Results for spirits distilled from wine, grain, and sugarcane were highly variable.

Simultaneous determination of gallium and aluminium in biological samples by conventional luminescence and derivative synchronous fluorescence spectrometry

The simultaneous determination of gallium and aluminium by using conventional fluorimetry and derivative synchronous fluorescence spectrometry has been studied. These determinations are based on the formation of fluorescent complexes of gallium and aluminium with salicylaldehyde carbohydrazone (SACH). In the conventional method, two samples are analysed under different analytical conditions, and the results are evaluated by solving a system of two simultaneous equations. In the derivative synchronous method (at pH = 2.6, in an ethanol—water medium containing 72% of ethanol), the following conditions are used: a constant wavelength difference of 20 nm between the monochromator settings, a time-constant of 1.5 sec, a scan-speed of 120 nm/min, and a derivative wavelength difference of 10 nm; gallium can be determined in the range 7–38 ng/ml, and aluminium between 6 and 45 ng/ml. The synchronous method shows more advantages, and has been used in the determination of both metal ions in diverse biological samples (animal tissues and human serum) with good results.

Thermodynamic properties of the dissociation of several ?-oxooximes

The changes in free energy, enthalpy and entropy for the dissociation of several α-oxooximes (phenylglyoxal aldoxime, glyoxylanilide oxime,N-ethyl-glyoxylanilide oxime and 1-phenyl-1,2-propanedione-2-oxime) have been determined in water-ethanol medium (50% v/v) at 0.5M ionic strength (NaNO3) and 25 °C. The changes in dissociation free energy were calculated from the pKa values determined by glass-electrode potentiometry, and refined by using the programs MINIGLASS and SUPERQUAD. The dissociation enthalpies were determined by direct thermometric titration, and refined by using the programs MINITERM and MULTITERM.

New spectrophotometric method for the determination of trace amounts of palladium

A simple, rapid, selective, and sensitive method for the spectrophotometric determination of palladium is developed based on the reaction of Pd(II) with 1-amino-4-hydroxyanthraquinone (AMHA). The reaction is carried out atpH 3.8 in 50% (v/v) ethanol-water medium. The molar absorptivity of the complexed ligand is 1.1 · 104 l mol−1 cm−1 at 620 nm. Calibration plots are linear up to 17 µg Pd cm−3. The optimum concentration range (Ringbom plot) is between 3–14.5 µg cm−3. The spectral study of the reaction in solutions containing equimolar concentrations or an excess of one component, in thepH range ∼ 0.3–6.5, indicate the possible complex transitions that occur in solution. Complete graphical and logarithmic analysis of the absorbance-pH graphs was performed to demonstrate and characterize the complexation equilibria in solution. Under the optimum conditions, palladium can be determined as the noncharged complex Pd(AMHA)2 in the presence of a large number of foreign ions. Interferences caused by zirconium(IV) could be masked with fluoride ions.

Complexation equilibria between cadmium(II) and 4-(4′-methyl-2′-thiazolylazo)-2-methyl-resorcinol. A spectrophotometric study

The complexation equilibria between Cd II and 4-(4′-methyl-2′-thiazolylazo)-2-methyl-resorcinol have been spectrophotometrically studied in an ethanol-water medium (50 : 50, v/v) at I = 0.25 M (NaClO 4) and species CdHR 2 (logβ 112 = 20.38 ± 0.09) and CdH 2R 2 (logβ 122 = 27.00 ± 0.09) are established by a numerical calculation method.

Equilibrium constants of metal amino acid complexes

The complexation equilibria of the amino acids l-serine and l-leucine with the ions Mg 2+, Ca 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+, Cd 2+ and Pb 2+ have been studied at 298 K and ionic strength I = 0.1 M in various ethanol-water media. The complexes found and their equilibrium constants are discussed in terms of the acid-base characteristics of the amino acids and the properties of the cations.