Enthalpies of dilution of tris-ethylenediaminocobalt(III) chloride in aqueous solution at 25°C

The enthalpies of dilution for aqueous solutions of [Co(en)₃]Cl₃, where en=1,2-diaminoethane, have been measured at 25°C, and up to m=1 mol-kg^–1, using a new large isoperibol calorimeter by the long-jump method. Relative apparent molar enthalpies L have been extracted as an empirical equation relating L and m. Comparison with other 31 and 13 aqueous systems confirms the previously suggested hydrophobic character of the [Co(en)₃]³⁺ cation.     

Study of the behavior of chromium(III) in potassium nitrate solutions at 25°C

Solubility in the KNO₃-Cr(NO₃)₃-H₂O system at 25°C was studied by an isothermal method. The existence of solid phases of potassium nitrate and chromium(III) nitrate nonahydrate was confirmed by constructing a phase diagram, chemical analysis, and IR spectroscopy. Crystallization of potassium nitrate from aqueous solutions was studied. Potassium nitrate does not interact with chromium(III) nitrate within the range of micro and macro concentrations. The capture of chromium(III) by KNO₃ crystals is due to adsorption and occlusion of a mother solution.     

Reductions of Carboxylic Acids and Esters with NaBH4 in Diglyme at 162°C

Abstract

Aromatic esters, including the extremely sterically hindered ester: t-amyl 2-chlorobenzoate, are readily reduced to the corresponding benzyl alcohols in high yield with NaBH₄ in refluxing diglyme (162°C). In sharp contrast, aliphatic esters usually gave only low yields of alcohols. Instead, diglyme fragmentation products are formed which undergo transesterification reactions, producing complex product mixtures including products such as RCOOCH₂CH₂OCH₃. The mechanism of this process involves sodium borohydride-induced S_N2 cleavage of diglyme (hydride attack) at high temperatures. However, when the extremely electron rich, 3,4,5-trimethoxybenzoic acid is treated with NaBH₄/diglyme at 162°C (with or without an equivalent of LiCl), no 3,4,5-trimethyoxybenzyl alcohol is formed. The electron rich and hindered ester, t-amyl-3,4,5-trimethoxybenzoate, also does not reduce under these conditions (with or without LiCl). However, both methyl and isopropyl 3,4,5-trimethoxybenzoate esters were converted into 3,4,5-trimethyoxybenzyl alcohol in good yields in NaBH₄/diglyme/LiCl at 162°C. These reductions did not occur unless LiCl was present, illustrating the electron releasing effect of the three methoxy functions which reduce the carbonyl group's reactivity.     

Activity and Osmotic Coefficients from the Emf of Liquid Membrane Cells. IX: Mn(ClO4)2 and MnSO4 in Water at 25°C

The relative activity coefficients of MnSO₄ and Mn(ClO₄)₂ were measured downto about 5×10^–5 mol-kg^–1 by means of cells with ion-exchange liquid membranes.The measurements at high dilution provide an answer to the age-old problem ofabsolute values of the activity coefficients for MnSO₄. They also lead to acorrection of the activity coefficients for Mn(ClO₄)₂, whose literature values arefound to be biased by ca. 6.5%. Like other bivalent metal sulfates, MnSO₄does not obey the Debye—Hückel law inasmuch as negative instead of positivedeviations from the limiting law are observed in the dilute regions. The possibilityfor this kind of behavior to denote ion association is discussed. The best-fitparameters of Pitzer's equation, able to provide accurate values of the activityand osmotic coefficients of the two salts for any concentration, are reported.     

Solubility and Solubility Product at 22°C of UO2(c) Precipitated from Aqueous U(IV) Solutions

Solubility studies on UO₂(c), precipitated at 90^°C from low-pH U(IV) solutions, were conducted under rigidly controlled redox conditions maintained by EuCl₂ as a function of pH and from the oversaturation direction. Samples were equilibrated for 24 days at 90^°C and then for 1 day at 22^°C. X-ray diffraction (XRD) analyses of the solid phases, along with the observed solubility behavior, identified UO₂(c) as the dominant phase at pH1.2 and UO₂(am) as the dominant phase at pH1.2. The UV-Vis-NIR spectra of the aqueous phases showed that aqueous uranium was present in the tetravalent state. Our ability to effectively maintain uranium in the tetravalent state during experiments and the recent availability of reliable values of Pitzer ion-interactionparameters for this system have helped to set reliable upper limits for the log K ^o value of –60.2 + 0.24 for the UO₂(c) solubility [UO₂(c) + 2H₂O U⁴⁺ + 4OH^–] and of >–11.6 for the formation of U(OH)₄(aq) [U⁴⁺+ 4H₂O U(OH)₄(aq) + 4H⁺]     

Volumetric Properties of Acetonitrile with 1,2-Alkanediols (C2–C6) at 20°C

Dilatometric measurements of excess molar volumes, V^E and excess partial molar volumes, [`(V)] <sub>\texti</sub><sup>\textE</sup>\overline V _{\text{i}}^{\text{E}} have been made for binary mixtures of acetonitrile with 1,2-ethanediol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, and 1,2-hexanediol at 20°C over the entire composition range. V<sup>E</sup> for acetonitrile + 1,2-ethanediol and 1,2-propanediol mixtures are negative over the entire range of mole fractions and positive values are obtained for all remaining mixtures. The results are explained in terms of dissociation of the self-associated 1,2-alkanediol molecules and the formation of aggregates between unlike molecules through O—H...N=C hydrogen bonding. From the experimental results, V<sup>E</sup> were calculated and correlated by Redlich–Kister type function in terms of mole fractions. The excess partial molar volumes were extrapolated to zero concentration to obtain the limiting values at infinite dilution, [`(V)] _\texti^\textE,o\overline V _{\text{i}}^{{\text{E,o}}} .     

Reaction of [Pt(NH3)4]Cl2 with NH4VO3 in an Alkaline Solution at 190°C in Autoclave

Russian Journal of General Chemistry - The reaction of [Pt(NH3)4]Cl2 with NH4VO3 in alkaline solution in an autoclave at 190°C was studied. The solid autoclave thermolysis product was...     

Thermodynamics of Cm(III) in Concentrated Salt Solutions: Carbonate Complexation in NaCl Solution at 25°C

The carbonate complexation reactions of Cm(III) were studied by time-resolved laser fluorescence spectroscopy in 0–6 m NaCl at 25°C. The ionic strength dependence of the stepwise formation constants for the carbonato complexes Cm(CO₃) _n ^3–2n with n = 1, 2, 3, and 4 is described by modeling the activity coefficients of the Cm(III) species with Pitzer's ion-interaction approach. Based on the present results and literature data for Cm(III) and Am (III), the mean carbonate complexation constants at I = 0 are calculated to be: log ₁₀₁ ^o =8.1 ±0.3, log ₁₀₂ ^o =13.0 ± 0.6, log ₁₀₃ ^o =15.2 ± 0.4, and log ₁₀₄ ^o =13.0 ± 0.5. Combining these equilibrium constants at infinite dilution and the evaluated set of Pitzer parameters, a model is obtained, that reliably predicts the thermodynamics of bivalent actinide An(III) carbonate complexation in dilute to concentrated NaCl solution.     

Isotopic concentration of uranium from alpha spectrum of electrodeposited source on 4H-SiC detector at 500 °C

4H-SiC alpha detectors were fabricated with a 21-μm thick depletion depth and were packaged into a stainless-steel casing with a mineral insulation cable and a standard BNC connector. The packaged detectors had a resolution of 0.624% FWHM at 5.486 MeV prior to salt immersion. The detectors were then immersed in a LiCl–KCl–UCl₃ molten salt at 500 °C, from which a thin layer of depleted uranium was electrodeposited onto the detectors. Alpha particle emission spectra were collected from the electrodeposited source. The energy resolution of the surviving detector was 2.29% FWHM at 4.198 MeV and was sufficient to separate the ²³⁴U from ²³⁸U alpha emissions (577 keV difference). The ²³⁴U/²³⁸U activity ratio and the isotopic concentrations of ²³⁴U and ²³⁸U were determined and are representative of the uranium source used in the electrodeposition.

     

Oxychlorination of methane to methyl chloride at 300°C in the system palladium(II) complexes-heteropolyacids-silica gel

The activity of systems, applied to silica gel from chloride solutions, in the oxychlorination of CH₄ to CH₃Cl at 300° Cincreases in the order H₃[PMo₁₂O₄₀]9[PMo₆V₆O_40]2(PdCl₂-H₉[PMo₆V₆O₄₀] (or H₃[PMo₁₂O₄₀]))<(PdCl₂-Na_nH_9–n[PMo₆V₆O₄₀]). Additions of NaCl (molar ratio of the components NaClSiO₂7100) lead to an increase in the yield of CH₃Cl. The mechanisms of CH₄ oxidation have been discussed which are electrophilic with the participation of Pd(II) complexes and involve chlorides with the participation of surface Cl atoms.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 1, pp. 29–33, January–February, 1995.     

Osmotic and Activity Coefficients of CH3SO4Na(aq) and CH3SO4K(aq) at 25°C

The osmotic and activity coefficients of aqueous sodium and potassium methyl sulfates have been determined at 25°C by the isopiestic method, in the molality range from ca.0.2 to 25 and 19 mol-kg^–1, respectively. The results have been discussed in terms of the ion–ion and ion–water interactions on the basis of the Pitzer and Mayorga model and a method developed in our laboratory.     

Complex formation between In(III) and 2-mercaptopropanoic acid in 3.0 M NaClO4 at 25°C

Complex formation reactions between In(III) and 2-mercaptopropanoic acid (H₂A) have been studied in 3.0 M NaClO₄ at 25°C, by measuring the EMF of the glass and In(Hg) electrodes as a function of the acidity of the solution. At −log|H⁺ > 5.5 the formation of a precipitate is observed. The EMF data obtained in the range 1 < −log|H⁺| < 5.5, treated by the general minimizing program LETAGROP, can be explained by assuming the formation of the species InA⁺, InA(OH) and InA(OH)₂⁻. A reaction equation is proposed and the formation constants for these species are given.     

Experimental determination of the liquidus of the binary system (Cu2O + CaO) in air at temperature from (1050 to 1500) °C

The liquidus of the binary system (Cu₂O + CaO) has been experimentally investigated over the temperature range from (1050 to 1500) °C in air. The liquidus has been quantified by the equilibration/quench/analysis technique. Equilibrated specimens were quenched in brine solution of 10 wt% NaCl. Specimens were then examined by Energy-Dispersive X-ray Spectroscopy (EDS) and Electron probe micro-analyzer (EPMA) to quantify liquid chemical compositions. This work reveals that the solubility of CaO in the liquid phase of the binary (Cu₂O + CaO) at higher temperatures is lower than previously reported, and the deviation systematically increases with a corresponding increase in temperature. This is predominant at temperatures between (1300 and 1500) °C where a deviation of up to 5 wt% in CaO solubility is observed. The solubility of Cu₂O in liquid phase for the cuprite saturated section of the binary however is consistent with all the previous authors.     

Stability,spectra and structure of the cobalt(II) chloride complexes in hexamethylphosphoramide solution at 25°C

Cobalt(II) chloride complexes were investigated spectrophotometrically in hexamethylphosphoramide (HMPA) solutions. It has been established that four consecutive tetrahedral chloro complexes of cobalt(II) are formed in the Co(ClO₄)₂-CoCl₂ and CoCl₂-LiCl-HMPA solutions. The formation constants of the complexes have been calculated: log K₁ = 9.0 (±0.5), log K₂ = 6.5 (±0.5), log K₃ = 3.05 (±0.05) and log K₄ = − 1.42 (±0.03). The high stability of the dichloro-complex results in the fact that this species is the only complex of cobalt(II) existing in HMPA solutions of CoCl₂.     

Copper(II)–Ammonia Complexation Equilibria in Aqueous Solutions at Temperatures from 30 to 250°C by Visible Spectroscopy

The spectra of copper(II)–ammonia solutions in 2 mol-kg^–1 NH₄NO₃(aq) were recorded as a function of pH with a new UV–visible flow cell, capable of operating at conditions up to 325°C and 300 bars. Equilibrium constants for the formation of copper(II)–ammonia complexes Cu(NH₃)_n ²⁺, 1 n 4, from 30 to 150°C were determined by evolving factor analysis and nonlinear least-squares regression. Measurements at higher temperatures were limited by thermal decomposition of NH₄NO₃(aq). The formation constants of Cu(NH₃)_n ²⁺ decrease with temperature, consistent with extrapolations of literature data from measurements below 100°C. Measurements above 150°C were carried out in 0.5 mol-kg^–1 CF₃SO₃H (aq), at the very high ammonia concentrations required to avoid the precipitation of CuO(s). The spectra are consistent with Cu(NH₃)₄ ²⁺ as the predominant species, based on extrapolations of peak maxima and molar absorptivities from lower temperatures. Shifts in the spectra of Cu²⁺ and the Cu(NH₃)_n ²⁺ species to higher wavelength and increases in molar absorbance with increasing temperature are discussed in terms of the structure of the complexes.     

Enthalpy of dissociation of water at 325°C and LogK, ΔH, ΔS,and ΔC p values for the formation of NaOH(aq) from 250 to 325°C

The aqueous reactions H⁺+OH^–=H₂O at 325°C and Na⁺+OH^–= NaOH(aq) at 250–325°C, were studied using a flow calorimeter. Heats of mixing of aqueous NaOH and HCl solutions were measured at 325°C. The enthalpy of water formation (H=95.9 kJ-mol^–1, valid at 12.4 MPa and infinite dilution) was obtained at this temperature from the heat of mixing data but differs significantly from that calculated from the Marshall-Franck equation. This calorimetric H at 325°C was used in combination with literaturelog K and H values at lower temperatures to derive equations representinglog K, H, S, and C_p for the formation of water from 250 to 325°C. Heats of dilution of aqueous NaOH solutions were measured at 250, 275, 300, and 325°C. Log K, H, and S for the formation of NaOH(aq) were determined at these temperatures from the fits of the calculated and measured heats while C_p values were calculated from the variation of H with temperature. No previous experimental results have been reported for the formation of NaOH(aq). The isocoulombic reaction principle is tested using thelog K values obtained in this study. The plot oflog K vs. 1/T for the isocoulombic reaction NaOH(aq) +H⁺=H₂O+Na⁺ is approximately linear.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.Taken in part from the Ph.D. Dissertation of Xuemin Chen, Brigham Young University, 1991.     

Reductions of Organic Functional Groups Using NaBH4 OR NaBH4/LiCl in Diglyme at 125 TO 162 °C

Reduction of nitro, amide, carboxylate, ester and nitrile functional groups to -NH₂, -CH₂NH₂, -CH₂OH, -CH₂OH and -CH₂NCHPh, respectively were achieved using NaBH₄ or NaBH₄/LiCl in diglyme at 125—162 °C. This greatly extends the range of functional group types which can be considered generally reducible by borohydride.     

La(CCl3COO)3-La(ClO4)3-H2O system at 25°C

The lanthanum trichloroacetate-lanthanum perchlorate-water ternary system was studied by the isothermal solubility method at 25°C. The compositions of solid phases were studied by the Schreinemakers method. The refraction indices, specific volumes, and viscosities of liquid phases were determined. The crystallization of the initial components and, the formation of a closed area of solid solutions were established in the system.     

Solubility in ternary aqueous systems including calcium chlorate and diethanolamine (triethanolamine) at 25°C

Solubility in ternary aqueous systems including calcium chlorate and diethanolamine (triethanolamine) has been studied at 25°C. Solubility diagrams have been constructed. Solubility curves consist of three branches corresponding to the crystallization of calcium chlorate, diethanolamine (triethanolamine), and compound Ca(ClO₃)₂ · NH(C₂H₄OH)₂ or Ca(ClO₃)₂ · N(C₂H₄OH)₃. The compounds have been isolated and identified by chemical analysis, X-ray powder diffraction, and thermal analysis.     

Solubility equilibria in the system Cd(II)-2-mercaptopropionic acid at 25°C

The solubility equilibria between Cd(II) and 2-mercaptoproprionic acid in 3.0 M NaClO₄ at 25°C have been studied by e.m.f. The e.m.f. measurement with both glass and Cd(Hg) electrodes in the range 2.5 < pH < 4.8 were made in solutions where a solid phase coexists with soluble complexes Cd_qA_p. Free ligand and metal ion concentrations were calculated in order to determine the solubility product of CdA (eqn 5). From the values of the formation constants for the soluble complexes and the solubility product, the solubility constants k_spq have been computed. A general equation for the redissolution of the precipitate is proposed and a set of equilibrium constants is given.