The kinetics of the oxidation-reduction reaction between uranium(VI) and titanium(III) in HCl solution

The oxidation-reduction reaction between U(VI) and Ti(III) in HCl solution was studied spectrophotometrically. The reaction is second-order at all concentrations of reactants, HCl, ferrous chloride and mannitol used in this work. In 5M HCl the rate constantk increases with increasing Ti(III) concentration, whereas it decreases with increasing U(VI) concentration, with increasing HCl concentration from 1.00M to 7.17M and increases thereafter from 7.17M to 11.79M. The addition of mannitol causes a consistent decrease in the rate of reaction, whereas ferrous chloride has no effect. The activation energy for this oxidation-reduction reaction was 47.90±0.11 kJ·mol^–1. The values of H , G and S were 45.40±0.11 kJ·mol^–1, 72.50±0.17 kJ·mol^–1 and –91.10±0.22J·k^–1·mol^–1, respectively. The mode of reaction is discussed in the light of kinetic results.     

Saturated Vapor Pressure and Crystal Structure of Bis-(2-imino-4-pentanonato)copper(II)

A comprehensive study of copper(II) bis-ketoiminate including tensimetric analysis of sublimation and structure solution has been carried out. The temperature dependence of saturated vapor pressure over Cu(ki)₂ crystals derived by the flow method is expressed by the equation lnP_(atm)} = 25.31-13750/T, H _subl = -114.2 ± 1.3 kJ· mole^-1, S_subl =210.2 ± 3.0> J· mole^-1 · K^-1. Crystal data for CuO₂N₂C₁₀H₁₆: a=15.143(3), b=16.681(8), c=13.795(32) , space group Ccca, Z=12, d _calc = 1.47 g/cm³, R=0.029. The structure is molecular and consists of crystallographically independent Cu(ki)₂ complexes of two types, one with a cis structure and the other with a cis–trans disordering. The copper atom has a plane square environment of two oxygen and two nitrogen atoms. In the cis isomer, Cu–O 1.938 and Cu–N 1.895 ; in the disordered complex, all four Cu–O(N) distances are 1.901 .     

The determination of thermodynamics of oxygen complexes of anions of sulfur dioxide and fluoronitrobenzenes using atmospheric pressure ionization mass spectrometry

The thermodynamic properties of oxygen complexes of the negative ions of 1-fluoro-2,4-dinitrobenzene (FDNB), 1,5-difluoro-2,4-dinitrobenzene (DFDNB), and sulfur dioxide have been determined by measuring the temperature dependence of the pertinent ion ratios by using a mass spectrometer equipped with a⁶³Ni atmospheric pressure ionization source. The values of -H° and -S°are SO ₂ ^–(O₂), 101 ± 2.1 kJ mole¹ and 121 ± 3.8 J/K-mole; FDNB^–(O₂), 51.5 ±3.4 kJ mole^–1 ± 9.2 J/K-mole; and DFDNB^–(O₂), 65.7 ± 0.4 kJ mole^–2 and 110 ± 5.0 J/K-mole.     

Evaluation of sorption affinity of cadmium(II) on Haro river sand from aqueous solutions

The sorption of Cd(II) on Haro river sand from deionized water is reported. The sorption system obeyed according to the Freundlich and Dubinin–Radushkevich (D-R) isotherms. The Freundlich parameters 1/n = 0.67±0.05 and of A = 1.38±1.14 mmole·g^-1 have been ascertained. D-R isotherm yields the values of = -0.003741±0.000321 kJ²·mole^-2, X _m = 0.23±0.21 mole·g^-1 and of E = 11.6±0.5 kJ·mole^-1. The influence of common anions and cations on the sorption was examined. Trivalent Bi enhances the sorption whereas Fe, Cr, Al and chromate ions reduce the sorption significantly. Hf(IV) and Ag(I) indicate substantial sorption (61–98%) whereas Gd(III), Re(VII) and Sc(III) show low sorption (<5%). The elements having low sorption can be separated from elements indicating higher sorption using Haro river sand column.     

Thermochemistry of Amines: Experimental Standard Molar Enthalpies of Formation of N-Alkylated Piperidines

The standard molar enthalpies of formation _f H _m ^° (l) at the temperature T = 298.15 K were determined using combustion calorimetry for N-methylpiperidine (A), N-ethylpiperidine (B), N-propylpiperidine (C), N-butylpiperidine (D), N-cyclopentylpiperidine (E), N-cyclohexylpiperidine (F), and N-phenylpiperidine (G). The standard molar enthalpies of vaporization _l ^g H ^{m °} of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. From these data the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) were derived for: A –(61.39 ± 0.88); B –(88.1 ± 1.3); C –(105.81 ± 0.66); D –(126.2 ± 1.3); E ( –88.21 ± 0.75); F –(135.21 ± 0.94); G (70.3 ± 1.4) kJ · mol^–1. They are used to determine the strain enthalpies of the cyclic amines A–G. The N-alkylated piperidine rings have been found to be about strainless.     

Preparation and Thermochemistry of Complexes of Zinc Nitrate with Threonine

The solubility property of Zn(NO₃)₂–Thr–H₂O system (Thr—threonine) at 25°C in the entire concentration range has been investigated by the phase equilibrium semimicromethod. The corresponding phase diagram and refractive index diagram were constructed. From the phase equilibrium results, the incongruently soluble compounds of Zn(Thr)(NO₃)₂ · 2H₂O, Zn(Thr)₂(NO₃)₂ · H₂O, and Zn(Thr)₃(NO₃)₂ · H₂O were synthesized and characterized by IR, XRD, TG–DTG, chemical and elemental analyses. The constant-volume combustion energies of the compounds, _c E, determined by precision rotating bomb calorimeter at 298.15 K, were –6266.88 ± 3.72, –9263.28 ± 2.23, and –11 423.11 ± 6.81 J/g, respectively. The standard enthalpies of combustion for these compounds, _c H _m ^° (complex, s., 298.15 K), were calculated as –2147.40 ± 1.28, –4120.83 ± 0.99, and –6444.68 ± 3.85 kJ/mol and the standard enthalpies of formation, _f H _m ^° (complex, s., 298.15 K), are –1632.82 ± 1.43, –1885.55 ± 1.50, and –2770.25 ± 4.21 kJ/mol. The enthalpies of dissolution of the complexes in a medium of simulated human gastric juice (37°C, pH 1, in the solution of hydrochloric acid), _dis H _m ^° (complex, s., 310 K), which were also measured by a microcalorimeter to be 13.36 ± 0.06, 15.53 ± 0.06, and 17.04 ± 0.05 kJ/mol, respectively.     

Complexation,solubilities and thermodynamic functions for cerium(III) fluoride-water system

The solubility, solubility product and the thermodynamic functions for the CeF₃–H₂O system have been measured using the radiometric, conductometric and potentiometric techniques. The radiometric values for the solubility and solubility product, the lowest and more acceptable for reasons cited in previous papers, are 3.14·10^–5 M and 2.17·10^–17 respectively. The enthalpy change measured by the conductometric method is almost twice as that obtained by potentiometric method due to abnormal conductances registered at higher temperatures. The average values for H^o and G^o and S^o at 298 K are 53.0±17.4, 91.7±4.0 and –129.7±58.2 KJ·mol^–1 respectively. The positive values for H^o and G^o and the negative value for S^o are indicative of the low solubility of this salt in water. The stability constants for the mono- and difluoride complexes of Ce(III) have been determined potentiometrically using unsaturated solution mixtures of Ce(III) and F^–. These values for CeF⁺ and CeF ₂ ⁺ are 997±98 and (1.03±0.44)·10⁵, respectively. Studies on pH dependence of the solubility shows that the solubility reaches a minimum value at a pH of about 3.2.     

Etude des interactions a l'etat solide du nordazepam III-polyoxyethylene glycol 6000 et nordazepam III-acide succinique

We have determined the eutectic composition nordazépam (NDZ) polyoxyethylene glycol 6000 (PEG): 4% NDZ, 96% PEG (T _f =59,0±0,5°C H _f=155,9±2,4 J·g^–1; NDZ succinic acid: 0,32n (NDZ) and 0,68n (succinic acid) (T _f=163,8±0,4°C and H _f=119,34±2,1 J·g^–1). No solid solution has been found. The negative and high absolute value of mixing enthalpy indicates that the eutectic composition is formed by interactions between OH, CO, NH groups of carrier and drug with hydrogene bonds formation, confirmed by X-ray diffraction.

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Zusammensetzung Folgende eutektische Zusammensetzungen wurden bestimmt: Nordazepam (NDZ) Polyoxyethylenglykol 6000 (PEG): 4% NDZ, 96% PEG (T_f = 59,0±⁰.5°C H_f=155,9±2.4 J·g^–: NDZ Bernsteinsäure: 0,32n (NDZ) und 0,68 n (Bernsteinsäure) (T _f=163,8±0,4°C und H _f= 119,34±2,4 J·g^–1). Es wurden keine Mischkristalle gefunden. Der negative und absolut gesehen grosse Wert der Mischenthalpie zeigt, dass das Eutektikum durch Wechselwirkungen zwischen den OH CO NH Gruppen von Carrier und Droge in Form von Wasserstoffbrückenbindungen gebildet wird, was durch Röntgendiffraktion bestätigt wurde.

     

Nuclear magnetic resonance investigation of intramolecular scrambling processes in meso-(2,3-butylenediamine)tetraacetate. Diamagnetic complexes of transition metal ions

Summary The acetate scrambling processes (, conversion and N inversion) occurring in the complexes formed from meso-(2,3-butylenediamine)tetraacetic acid (BDTA) with zinc(II), cadmium(II), mercury(II), scandium(III), yttrium(III) and lanthanum(III) ions have been investigated by line shape analysis of their n.m.r. spectra. Between 308 and 373 K fast conversion between and isomers and slow nitrogen inversion occur except for mercury(II) and yttrium(III) in the latter case. H^* = 2.3±0.1 kJ mol^–1 and S^* = –6.9±0.2 mol^–1 J K^–1 for the mercury complex; H^* = 2.6 ±0.2 kJ mol^–1 and S^* = –5.5±0.5 mol^–1 JK^–1 for the yttrium complex. Exchange mechanisms proceeding through different reaction intermediates are discussed on the light of the results obtained in this work as well as previously on other polyaminepolycarboxylate complexes of the same ions.     

Spectrophotometric Determination of Thorium with Disodium Salt of Arsenazo-III in Perchloric Acid

A rapid and sensitive spectrophotometric method has been developed for the determination of thorium using 0.04% Arsenazo-III in a 2M perchloric acid solution. Absorbance was measured in 1 cm cell and the complex has a sensitive absorption peak at 654 nm. The complex is formed instantly in perchloric acid and remains stable for 45 minutes with constant absorbance. Beer's law is obeyed in the range 1–60 g·g^–1 of thorium concentration with a molar absorptivity at 654 nm = 3.07·10⁵ M^–1·cm^–1 at 24±2°C. The foreign ions interference in thorium determination have been checked. The cations were tested at >60-fold excess of thorium, Mn(II), Fe(III), Co(II) and Ni(II) interfere negatively, whereas only Ce(III) has increased the absorbance. Among the anions, cyanide, phosphate, thiocyanate and acetate at 150-fold excess of thorium cause significant interference. However, thorium can bedetermined in the presence of nitrate, chloride, oxalate, tartrate, ascorbate, thiosulphate and citrate. The method has been applied on certified reference material for thorium determination after extractive separation and the result was found in good agreement with the certified value. The method has been also applied successfully to determine thorium at g·g^–1 level in local ore samples with a precision of ±0.04%.     

Thermochemistry of Alcohols: Experimental Standard Molar Enthalpies of Formation and Strain of Some Alkyl and Phenyl Congested Alcohols

The standard molar enthalpies of formation _f H _m ^° (cr) at the temperature T = 298.15 K were determined using combustion calorimetry for di-tert-butyl-methanol (A), di-tert-butyl-iso-propyl-methanol (B), and di-phenyl-methyl-methanol (C). The standard molar enthalpies of sublimation _cr ⁸ H _m ^° of these compounds and of di-phenyl-methanol (D) were obtained from the temperature variation of the vapor pressure measured in a flow system. Molar enthalpies of fusion _cr ¹ H _m ^° of the compounds A–D and of tri-phenyl-methanol (E) were measured by differential scanning calorimeter (DSC). From these data and data available from the literature, the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) for A, (–397.0 ± 1.2); B, (–418.1 ± 2.3); C, (–34.2 ± 1.3); and D, (0.9 ± 2.1) kJ · mol^–1 were derived, which correspond to strain enthalpies (H _S) of 46.1, 114.7, 8.1, and 5.0 kJ · mol^–1, respectively.     

A study by pulse radiolysis of the radiation-chemical transformation of aqueous solutions of hydrazine in the presence of oxygen

It is shown by pulse radiolysis that in aqueous solutions of hydrazine containing oxygen the radical N₂H₃ reduces oxygen to O₂ ^– at pH > 7 (k 3·10⁹ dm³· mole^–1·sec^–1), while this reaction does not occur for the protonated form N₂H₄ ⁺ at pH < 7 (k, 5·10⁶ dm³·mole^–1·sec^–1). The rate constants for the disappearance of O₂ ^– have been determined in the pH range from 4 to 12. Rate constants have been calculated for the reaction of O^– with N₂H₄ [k=(1.6 ±0.2)·10⁹ dm³·mole^–1·sec^–1] and of O₃with N₂H₄ [k=(1.2 ±0.2)·10⁶ dm³· mole^–1·sec^–1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 341–345, February, 1991.     

The Influence of 4f Orbital Excitation in Eu(Fod)3 on Complexation with Sulfones in Benzene Solutions

Complexation of sulfones (S) with the -diketonate Eu(Fod)₃ (Fod–heptafluorodimethyloctanedione) in the ground and excited electronic states in benzene solutions was studied. The stability constants and thermodynamic parameters for the formation of complexes Eu(Fod)₃ · S in the ground state (K, H ₀, S ₀) and Eu(Fod)₃ ^* · S in the excited state (K*, H ₀ ^*, S ₀ ^*) were determined. The excitation of f–f transitions of Eu(III) was found to enhance the stability of Eu(Fod)₃ · S complexes, apparently due to an increase in the acceptor ability of the Eu(III) chelate. This fact confirms the involvement of the 4f orbital in the chemical bond formation. The compensation effect was observed for the thermodynamic parameters: S ₀ = (2.9 ± 0.3) × 10^–3H ₀ + (35.0 ± 4.0) in the ground and S ₀ ^* = (3.3 ± 0.3) × 10^–3H ₀ ^* + (49.0 ± 5.0) in the excited states of Eu(Fod)₃. It was shown that electronic excitation of the 4f orbital of Eu(Fod)₃ influences isotopic effects in complexation with sulfolanes.     

Extraction spectrophotometric investigation of mixed ligand complex of molybdenum(V) with thiocyanate and 4-acetyl-2-(acetylamino)-5-dimethyl-Δ2-1,3,4-thiadiazole

A sensitive spectrophotometric method is developed for the determination of small amounts of molybdenum based on the extraction of molybdenum-thiocyanate-4-acetyl-2-(acetylamino)-5-dimethyl- ²-1,3,4-thiadiazole complex into chloroform from hydrochloric acid medium which is orange red in colour. The complex has an absorption maximum at 470 nm with a molar absorptivity of 2.01×10⁴l·mole^–1·cm^–1. Beer's law is valid over the concentration range 0.06–2.5 ppm of molybdenum with an optimum concentration range of 0.15–2.2 ppm. The ternary complex is stable for over one week at room temperature. Equilibrium shift method indicates 142 composition for molybdenum-thio-cyanate-4-acetyl-2-(acetylamino)-5-dimethyl- ²-1,3,4-thiadiazole complex. The effects of acidity, reagent concentrations, time, temperature and diverse ions upon the absorbance of the complex are critically assessed. This method has been used successfully for the determination of molybdenum in molybdenum steels.     

Characterization of the molecular species formed by interaction of acetonitrile and copper(I) chloride in the liquid and solid phase

Summary The equilibrium vapour pressure of the solid complex, CuCl·MeCN, was measured at several temperatures. The enthalpy and entropy changes according to the following complex formation were determined: CuCl(s)+ MeCN(g)CuCl·MeCN(s); H=–56.9 kJ mol^–1 and S=–150 J mol^–1 K ^–1, respectively. Vapour pressure osmometry shows that a monomer-dimer equilibrium of CuCl exists in the acetonitrile solution. The equilibrium constant was found to be 0.93±0.08. A gas chromatographic technique was employed to determine the monomeric species as [Cu(MeCN)₄]Cl.     

Kinetics of stepwise oxidation of manganese(II) by peroxodisulphate in phosphoric acid medium

Summary The oxidation of Mn^II by S₂O₈ ^2– to Mn^VII in phosphoric acid medium proceeds via a stable Mn^III and Mn^IV species. The reaction is catalysed by Ag⁺ and exhibits first order dependence on [S₂O₈ ^2–], [Ag⁺] and, is independent of [Mn^II]. The [H⁺] has no significant effect on the reaction. It is observed that the PO₄ ^3– ion stabilises the transient manganese(III) and manganese(IV) species by forming a stable and soluble phosphato-complexes. The activation parameters for the two stages of oxidation, namely Mn^II Mn^IV and Mn^IVMn^VII at 25° C are E_a=52 ±4 kJ mole^–1, S^*=–57±2 JK^–1 mole^–1 and E_a =56±4 kJ mole^–1, S^*=–44±2 JK^–1 mole^–1, respectively. A mechanism consistent with the experimental observations is proposed.Presented at the National Symposium on Reaction Kinetics and Mechanism, Department of Chemistry, University of Jodhpur, Jodhpur, India, Nov. 15–18, 1986.     

Stabilities and thermodynamics of uranyl(II) and thorium(IV) complexes of 2-mercaptoethanol

The complexation of UO₂ ⁺² and Th⁺⁴ ions with 2-mercaptoethanol has been studied by potentiometric and conductometric titration techniques. Uranyl ion forms 11 and 12 complexes in the pH-range 3.3–6.5 and thorium ion forms 12, 13, and 14 complexes in the pH-range 3.2–4.8 with considerable overlapping. Their logk _stab. values are determined at 10, 20, and 30°C at ionic strength =0.1M (NaClO₄) by applyingCalvin-Melchior's extension of theBjerrum method. The overall changes in thermodynamic functions G, H, and S accompanying complexation determined at 20°C are –19.48 kcal/mole, –22.77 kcal/mole, –11.23 cal/deg·mole for uranyl complexes and –33.94 kcal/mole, –4.93 kcal/mole, 99.00 kcal/deg·mole for thorium complexes, resp.     

On the reliability of equilibrium data of the charge-transfer complex between 2,3-dichloro-1,4-naphthoquinone and hexamethylbenzene

In view ofHammond's warning⁶ about the Conspiracy of errors, found in the case of low values of equilibrium constants of charge-transfer complexes a case is made out for redetermining the values for the system hexamethylbenzene—2,3-dichloro-1,4-naphthoquinone. Uncertainties in the parameters were estimated using theLiptay ⁸ matrix procedure. The solvent used was dichloromethane. The following data were obtained at 25°C: vC T = 22,220 cm^–1;E _A=0.99 eV;K =2599±57 l²·cm^–1·mol^–2. _max= 1020 ± 148 cm^–1··1;K=2.55±0.37 l·mol^–1; –H=2.7±0.3 kcal·mol^–1.With 1 Figure     

On the interaction between gold and copper in mercury

On the base of cyclic voltammetry, chronoamperometry and potentiometry experiments with the use of the hanging mercury drop electrodes, there was found that a solid AuCu compound is formed in the complex Au-Cu amalgam. The stability of AuCu is controlled by its solubility product, which is equal (7.1±1.5)·10^–6 M ² at 298 K. The temperature dependence of the solubility product allowed to determine H _AuCu of formation in mercury. This value is compared with H _AuCu of the reaction in the binary system. On the basis of theBorn-Haber cycle one may conclude that the AuCu formed in mercury phase should have the same structure as in the binary alloy. Some thermodynamic aspects of reactions in the Au-Cu-Ga amalgam are discussed. The solubility of copper in mercury was experimentally confirmed and is equal (1.1±0.1) · 10^–2at.%.

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Über die Wechselwirkung zwischen Gold und Kupfer in Quecksilber

Zusammenfassung Mit Hilfe von voltammetrischen, chronoamperometrischen und potentiometrischen Experimenten mit der hängenden Quecksilbertropfelektrode wurde eine feste AuCu-Verbindung in Au-Cu-Amalgam gefunden. Die Beständigkeit der Verbindung AuCu wird durch das Löslichkeitsprodukt bestimmt, das gleich (7,1 ± 1,5) · 10^–6 M ² bei 298 K ist. Die Temperaturabhängigkeit des Löslichkeitsproduktes erlaubt die Bestimmung der Bildungswärme H _AuCu der Verbindung in Quecksilber. Dieser Wert wird mit der Bildungswärme H _AuCu im binären System verglichen. Auf der Basis desBorn-Haber-Kreisprozesses kann man schließen, daß das in Quecksilber gebildete AuCu dieselbe Struktur wie im binären System hat. Verschiedene thermodynamische Aspekte der Reaktionen in Au-Cu-Ga-Amalgam werden diskutiert. Die Löslichkeit von Kupfer in Quecksilber wurde experimentell bestätigt und beträgt (1,1 ± 0,1) · 10^–2 at.%.