Stability of ternary copper—nitrilotriacetic acid complexes

A copper-selective electrode was used to investigate ternary copper—nitrilotriacetic acid complexes by means of combined pH and pM measurements. The theory presented for the evaluation of the stability of mixed-ligand complexes is based on the conditional constants. The emphasis is on the formation of 1:1:1 complexes of the type copper(II)—NTA—(hydroxide, amino acid, ammonia, triphosphate).     

Kinetics and mechanism of the reaction of benzyl bromide with copper in dimethylacetamide in the presence of oxygen

The reaction of copper metal with benzyl bromide in dimethylacetamide in the presence of oxygen has been studied. Oxidative dissolution of copper follows the single-electron transfer mechanism with formation of benzaldehyde, benzyl alcohols, and copper(II) coordination compounds. The kinetic and thermodynamic parameters of the process have been determined by resistometry. Intermediately formed species have been identified and quantitated, and the reaction stereochemistry has been studied. The reaction mechanism is discussed.     

Complexing of cerium(IV) with nitrilotriacetic acid in the presence of sulfate and nitrate ions

Conclusions The authors have made a spectrophotometric investigation of the composition of the complexes formed in the system Ce(IV)-nitrilotriacetic acid in 1 M (NH₄)₂SO₄ and 1 M NH₄NO₃ solutions and have calculated the instability constants of CeX⁺ and CeX ₂ ^2– complexes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1448–1451, July, 1976.     

Kinetics and mechanism of the cleavage of phthalic anhydride in glacial acetic acid solvent containing aniline

Apparent second-order rate constants (k(n)(app)) for the nucleophilic reaction of aniline (Ani) with phthalic anhydride (PAn) vary from 6.30 to 7.56 M(-1) s(-1) with the increase of temperature from 30 to 50 degrees C in pure glacial acetic acid (AcOH). However, the values of pseudo-first-order rate constants (k(s)) for the acetolysis of PAn in pure AcOH increase from 16.5 x 10(-4) to 10.7 x 10(-3) s(-1) with the increase of temperature from 30 to 50 degrees C. The values of k(n)(app) and k(s) vary from 5.84 to 7.56 M(-1) s(-1) and from 35.1 x 10(-4) to 12.4 x 10(-4) s(-1), respectively, with the increase of CH(3)CN content from 1% to 80% v/v in mixed AcOH solvents at 35 degrees C. The plot of k(s) versus CH(3)CN content shows a minimum (with 10(4) k(s) = 4.40 s(-1)) at 50% v/v CH(3)CN. Similarly, the variations of k(n)(app) and k(s) with the increasing content of tetrahydrofuran (THF) in mixed AcOH solvent reveal respective a maximum (with k(n)(app) = 17.5-15.6 M(-1) s(-1)) at 40-60% v/v THF and a minimum (with k(s) = approximately 0-1.2 x 10(-4) s (-1)) at 60-70% v/v THF. The respective values of DeltaH* and DeltaS* are 15.3 +/- 1.2 kcal mol(-1) and -20.1 +/- 3.8 cal K(-1) mol(-1) for k(s) and 1.1 +/- 0.5 kcal mol(-1) and -51.2 +/- 1.7 cal K(-1) mol(-1) for k(n)(app), while the values of k(n) (= k(n)(app)/f(b) with f(b) representing the fraction of free aniline base) are almost independent of temperature within the range 30-50 degrees C. A spectrophotometric approach has been described to determine f(b) in AcOH as well as mixed AcOH-CH(3)CN and AcOH-THF solvents. Thus, the observed data, obtained under different reaction conditions, have been explained quantitatively. An optimum reaction condition, within the domain of present reaction conditions, has been suggested for the maximum yield of the desired product, N-phenylphthalamic acid.     

Kinetics of solvent extraction of 99mTC with 2-butanone in basic medium

本文以恒界面池法研究了碱性条件下丁酮对99mTc的萃取动力学性质.在一定条件下,考察了萃取时间对萃取率的影响,并测定了搅拌速度、各反应物初始浓度以及温度对萃取速率的影响.实验结果表明:萃取体系在约6h后达到平衡;搅拌速度(100-180 rpm)对萃取速率无显著影响,萃取反应的活化能为56.20(kJ/mol),萃取过程为化学反应控制模型.在碱性介质中,丁酮萃取99mTc的化学反应速率方程为:-dc (TcO4- )/dt=k c0.83(TcO4-)c1.90(CH3 COC2 H5),其中k=5218.85(L/L)-0.73·h-2.     

Protonation and solvent extraction of N-p-tolylbenzohydroxamic acid in hydrochloric acid medium

the protonation of N-p-tolylbenzohydroxamic acid (p-TBHA) in aqueous hydrochloric acid has been investigated by determination of its distribution between cyclohexane and hydrochloric acid. The pK(a) value found was - 2.30 +/- 0.02 at 30 degrees . The solubility of p-TBHA as a function of hydrochloric acid concentration has also been determined. At lower acid concentrations the solubility decreases owing to a salting-out effect, whereas at higher concentrations it increases because of formation of the more hydrophilic protonated species and a salting-in effect. Intramolecular hydrogen-bonding observed in p-TBHA provides evidence for protonation of the nitrogen atom.     

Studies on complexation and solvent extraction of lanthanides in the presence of diaza-18-crown-6-di-isopropionic acid

Stability constants of some lanthanides with K22DAP (diaza-18-crown-6-diisopropionic acid) were determined by potentiometric titration method. The logarithmic values of these constants for La(III), Nd(III), Sm(III), Gd(III), Tb(III), Dy(III), Er(III), and Lu(III) are 11.14, 11.43, 11.78, 11.74, 11.95, 12.09, 11.49, and 10.88, respectively. Solvent extraction studies were carried out on the K22DAP complexes of La(III), Nd(III) and Lu(III) using TTA (thenoyltrifluoroacetone) as an extractant in different diluents. It appears that nitrobenzene, a diluent with high dielectric constant, favors the extraction of the complexes. Extraction rates of the K22DAP complexes of lanthanides were investigated at pH 5.5 and 8.0 with TTA in chloroform. The rates of extraction are found to be dependent upon the nature of the extracted species. Competitive extractions were carried out to see if selective extractions could be achieved.     

Effect of phenyl substituent on the dimerization of copper(II)-carboxylate in solvent extraction of copper(II) with phenylacetic acid

The effects of the phenyl substituent on the dimerization of copper(II) carboxylate in the solvent extraction of copper(II) with phenylacetic acid using benzene and 1-octanol as a solvent were investigated, at 25 degrees and at the aqueous ionic strength of 0.1M (NaClO(4)). The dimerization of copper(II) phenylacetate has been found to be written as: 2CuA(2)Cu(2)A(4) in 1-octanol, and 2CuA(2)(HA)(2)Cu(2)A(4)(HA)(2) + (HA)(2) in benzene, with the dimerization constants, log K = 2.24 and log K = 4.19, respectively. It was proved that the phenyl group inhibits the formation of the dimeric copper(II) phenylacetate, and its effect is partially shielded by a methylene substituent.     

Thermodynamics of solvent extraction of thallium with diethylhexyl phosphoric acid

The equilibrium molalities Tl⁺ were measured in {Tl₂SO₄ + Na₂SO₄ + D₂EHPA + n-C₈H₁₈ + Water} system at ionic strength from 0.1 to 2.0 mol kg^?1 containing Na₂SO₄ as supporting electrolyte in aqueous phase and at constant molality extractant at temperatures from 278.15 K to 303.15 K in organic phase. The standard extraction constants K ⁰ at various temperatures were obtained by methods of extrapolation and polynomial approximation. Thermodynamic quantities for the extraction process were calculated.     

Kinetics and mechanism of Am(III) extraction with TODGA

In the present paper, N,N,N’,N’-tetraoctyl diglycolamide (TODGA) as the extractant and n-dodecane as the diluent, the extraction kinetics behavior of Am(III) in TODGA/n-dodecane–HNO₃ system were studied, including stirring speed, the interfacial area, extractant concentration in n-dodecane, extracted ions concentration, acidity of aqueous phase and temperature. The results show that: the extraction process is controlled by diffusion mode under 130 rpm of stirring speed and by chemical reaction mode above 150 rpm. The extraction rate equation and the apparent extraction rate constant of Am(III) by TODGA/n-dodecane in 170 rpm and at 25 °C are followed as: $$ \begin{aligned} r_{0} = \left. {\frac{{{\text{d}}[{\text{M}}]_{{{\text{org}} .}} }}{{{\text{d}}{{t}}}}} \right|_{t = 0} & = k\,\frac{S}{V}\left[ {\text{Am}} \right]_{{{\text{aq}} . ,0}}^{0.94} \left[ {{\text{HNO}}_{3} } \right]_{{{\text{aq}} . ,0}}^{1.05} \left[ {\text{TODGA}} \right]_{{{\text{org}} . ,0}}^{1.19} \\ & \quad k = \left( {24.17 \pm 3.43} \right) \times 10^{ - 3} \,{\text{mol}}^{ - 2.18} \,L^{2.18} \,{ \hbox{min} }^{ - 1} \,{\text{cm}},\;E_{\text{a}} \left( {{\text{Am}}\left( {\text{III}} \right)} \right) = 25.94 \pm 0.98\;{\text{kJ/mol}} .\\ \end{aligned} $$      

Kinetics and mechanism of the reaction of benzyl bromide with copper in hexamethylphosphoramide

The reaction of copper with benzyl bromides in hexamethylphosphoramide has been studied. The kinetic and thermodynamic parameters of the reaction have been obtained. Hammett plots of log (k/k^o) vs the substituent constant σ gave good correlations (ρ = 0.15, S_ρ = 0.02, r = 0.954). The structure of the organic group has little effect on the rate of reaction of benzyl bromide with copper. In the absence of atmospheric oxygen, the oxidative dissolution of copper occurred by the mechanism of single‐electron transfer with the formation of 1,2‐diphenylethane and copper(I) complexes. The stereochemistry and intermediates compound was also investigated. The reaction mechanism is discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 296–305, 2005     

Visible-light promoted photoprocesses on aqueous gallic acid in the presence of riboflavin. Kinetics and mechanism

Within the frame of possible precursory photoreactions in the generation of humic substances, the visible-light promoted interaction between riboflavin (Rf), a native photosensitizer in aqueous systems, and gallic acid (GA), a polyphenol naturally formed after lignin degradation, was investigated. A systematic kinetic and mechanistic study was conducted under aerobic conditions in aqueous media, through visible-light continuous photolysis, polarographic detection of oxygen uptake, stationary and time resolved fluorescence spectroscopy, time resolved near-IR phosphorescence detection and laser flash photolysis techniques. GA is degraded relatively fast in pH 7 aqueous solutions, where singlet molecular oxygen (O₂(¹Δ_g)), superoxide radical anion (O₂^?) and hydrogen peroxide (H₂O₂) – all three species photogenerated from triplet excited Rf – participate in the photoprocess. The general conclusion is that in natural waters GA can undergo spontaneous phototodegradation under environmental conditions. Radical species generated in the presence of Rf can participate in condensation or polymerization reactions promoting the natural synthesis of humic products.     

Kinetics and mechanism of chromic acid oxidation of oxalic acid in absence and presence of different acid media. A kinetic study

Kinetics and mechanism of the reaction of Cr(VI) with oxalic acid have been studied in presence and absence of H₂SO₄, HClO₄, and CH₃COOH by monitoring the formation of Cr(III)-oxalic acid complex at 560 nm. The effect of total [oxalic acid], [Cr(VI)], [H₂SO₄], [HClO₄], and [CH₃COOH] on the reaction rate was determined at 30°C. Formation of carbon dioxide was also confirmed. The oxidation rate increases with [oxalic acid] and [CH₃COOH] while it decreases with [H₂SO₄], [HClO₄], and pH. The rate law governing the oxidation of oxalic acid over a wide range of conditions is rate=k₁ K_es1 [oxalic acid]_T [Cr(VI)]_T 1+K_es1 [oxalic acid]_T, where only undissociated oxalic acid is kinetically active. Kinetic evidence for the formation of a Cr(VI)(SINGLEBOND)oxalic acid 1:1 complex has been obtained and the equilibrium constant for their formation has been determined. The 1:1 complex exists most likely in an open chain form. The rate-limiting step of the oxidation reaction involves the breaking of the C(SINGLEBOND)C bond in the 1:2 complex. Oxidizing ability of Cr(VI) species have been discussed. Mechanism with the associated reaction kinetics is assigned. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 335–340, 1998     

Kinetics and mechanism of nitrate and nitrite electroreduction on Pt(100) electrodes modified by copper adatoms

Kinetics and mechanism of nitrate and nitrite reduction on Pt(100) electrode modified by Cu adatoms have been studied in solutions of sulfuric and perchloric acids by means of cyclic voltammetry and in situ IR-spectroscopy. It has been shown that the surface redox process with participation of ammonia or hydroxylamine at 0.5–0.9 V occurs only on the Cu-free platinum. The causes of this effect could be low adsorption energy of nitrate reduction products on copper or changes in the composition of the products (ammonia for Pt(100) and N₂O for Pt(100)+Cu). Nitrate reduction on Pt(100)+Cu electrode is much faster in the perchloric acid solution (by several orders of magnitude) as compared with unmodified platinum as a result of induced adsorption of nitrate anions in the presence of partly charged Cu atoms. In the solutions of sulfuric acid the rate of nitrate reduction is considerably lower as copper adatoms facilitate adsorption of sulfate anions, which block the adsorption sites for the nitrate.     

Complexes of chromium(III) with nitrilotriacetic acid and their extraction by solutions of aliquat-336 in dichloro-ethane

It has been shown that chromium(III) and nitrilotriacetic acid (NTA; H₃Z) form only a series of 1:1 complexes in solution. The violet uncharged species [CrZ(H₂O)₂] cannot be extracted by a solution of the long-chain quaternary ammonium chloride, Aliquat-336, in dichloroethane. Its acid dissociation constant (pK₁ = 5.87) was determined spectrophotometrically. On increasing the pH of the solution the blue anion CrZ(H₂O)(OH)^- of pK₂=8.74 and its conjugate base the binegative anion CrZ(OH)^2-₂ of pK₃= 11.81 are successively formed. Both of these anionic species are extracted by Aliquat-336 with maximal extraction (ca. 60%) at about pH 9. At still higher pH values the olive-green anion, CrZ(OH)₃^3-of much lower or negligible extractability, is formed.     

Kinetics and mechanism of thermal decomposition of copper hypophosphite

On the basis of an elaborate investigation of the thermal decomposition reaction for crystalline copper hypophosphite by kinetic, radiospectroscopic and optical methods, and by a study of the peculiarities of the copper hypophosphite structure and defects, it has been found possible to suggest the mechanisms by which the decomposition kinetics are regulated.     

Kinetics and mechanism of styrene hydrocarboalkoxylation catalyzed by Pd0 complex in the presence of toluenesulfonic acid

The kinetics of the catalytic reaction of styrene with CO and n-butanol in the Pd(dba)₂—TsOH—Ph₃P system in dioxane (383 Ê) was studied. The initial rates of accumulation of regioisomeric products (butyl 2- and 3-phenylpropionates) were measured as functions of the CO pressure, reactant concentrations, and the catalytic system components. A kinetic model of the process and a hydride mechanism with the HPd(Ph₃P)₃ ⁺ cationic complex acting as a key intermediate were proposed.     

Kinetics and mechanism of decarboxylation of aspartic acid with ninhydrin

The kinetic study of the decarboxylation of aspartic acid has been carried out at various [ninhydrin], [H⁺] and at different temperature ranging from 60–95°C. The reaction follows an irreversible first-order reaction path under pseudo first-order kinetic conditions. The variation of pseudo first-order rate constant (k_obs) with ninhydrin concentration was found to be in agreement with equation 1/k_obs = B₁ + B₂/[Ninhydrin]. One mol of carbondioxide evolved from decarboxylation of α-COOH and second mol of carbondioxide comes from the decarboxylation of β-keto acid which is an intermediate and formed during the course of ninhydrin and aspartic acid reaction. On the basis of the observed data, a possible mechanism has been proposed.