Selective solvation of copper(I) thiocyanate in acetonitrile-water mixtures at 30°C

The selective solvation of copper(I) thiocyanate has been studied in water-acetonitrile (AN) mixtures at 30°C by solubility and EMF measurements. The solubility of the salt increases continuously and changes only slightly beyond X _AN =0.7 mole fraction. The Gibbs energy of transfer of copper(I) ion from water to mixtures with acetonitrile (determined on the basis of the ferrocene reference method) decreases continuously, while that of the thiocyanate ion increases with the addition of acetonitrile. The solvent transport number of acetonitrile passes through a maximum (=6.4) at X _AN =0.25. These results were interpreted as arising due to a heteroselective solvation of the salt, the copper(I) ion being preferentially solvated by acetonitrile and the thiocyanate ion by water in these mixtures.     

Kinetics of substitution of aqua ligands from cis-diaqua(ethylenediamine)platinum(II) perchlorate by DL-penicillamine in aqueous medium

The kinetics of the interaction of DL-penicillamine with [Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [DL-penicillamine] and temperature at pH 4.0. The reaction proceeds via rapid outer sphere association complex formation, followed by two slow consecutive steps. The first is the conversion of the aforementioned complex into the inner sphere complex and the second is the slower chelation step whereby another aqua ligand is replaced. The association equilibrium constant (K _E) for the outer sphere complex formation has been evaluated together with rate constants for the two subsequent steps. Activation parameters have been calculated for both steps using the Eyring equation (H ₁ = 46.5 ± 5.0 kJ mol^–1, S ₁ = – 143.0 ± 15.0 J K^–1 mol^–1, H ₂ = 44.3 ± 1.3 kJ mol^–1, S ₂ = –189.0 ± 4.2 J K^–1 mol^–1). The low enthalpy of activation and large negative entropy of activation values indicate an associative mode of activation for both aqua ligand substitution processes.     

A thermodynamic study of enantiomeric recognition of organic ammonium cations by pyridino-18-crown-6 type ligands in methanol and a 1: 1 methanol-1,2-dichloroethane mixture at 25.0°C

LogK, H, andTS values for interactions of (R) and (S) enantiomers of -(1-naphthyl)ethylammonium perchlorate (NapEt), -phenylethylammonium perchlorate (PhEt), and the hydrogen perchlorate salt of 2-amino-2-phenylethanol (PhEtOH) with a series of chiral and achiral pyridino-18-crown-6 type ligands and 18-crown-6 (18C6) were determined from calorimetric titration data valid in methanol and in a 1: 1 (v/v) methanol-1,2-dichloroethane (MeOH-1,2-DCE) mixture at 25.0°C. In the MeOH-1,2-DCE solvent mixture, the chiral macrocyclic ligands exhibit excellent recognition for enantiomers of the three organic ammonium cations as shown by large differences in logK values ( logK) which range from 0.4 to 0.6 (2.5- to 4.0-fold difference in binding constants). The logK values in the solvent mixture MeOH-1,2-DCE are increased by 0.1–0.5 logK units over those in absolute methanol, indicating a favorable effect of 1,2-dichloroethane on enantiomeric recognition. In 1,2-dichloroethane, however, the interactions are too strong (logK>6) to observe the degree of recognition by a direct calorimetric method. Complexation of organic ammonium cations by these macrocyclic ligands is driven by favorable enthalpy changes. The entropy changes ure unfavorable in all cases. The thermodynamic origin of enantiomeric recognition for NapEt in 1:1 (v/v) MeOH-1,2-DCE is enthalpic, but those for PhEt and PhEtOH are entropic. Effects of the ligand structure and flexibility and of the organic cation structure on recognition and complex stability are discussed on the basis of the thermodynamic quantities. Different thermodynamic behaviors of achiral 5 and 18C6 from those of chiral macrocyclic ligands indicate a difference between chiral and achiral macrocycle interactions with the chiral organic ammonium cations. The different thermodynamic behavior of NapEt enantiomers compared to those of PhEt and PhEtOH enantiomers supports the idea that the solution complex conformation of NapEt is different from those of PhEt and PhEtOH. - interaction is absent for the PhEt and PhEtOH complexes with diesterpyridino-18-crown-6 ligands in solution. Therefore, the higher degree of enantiomeric recognition for NapEt than for either PhEt or PhEtOH by these chiral macrocyclic ligands is a result of the presence of - interaction in the NapEt system.     

The relation between the nonlinear dielectric effect and solvent polarity

The relation between solvent polarity expressed through the Dimroth-Reichardt spectroscopic parameter E _T (30) and the nonlinear dielectric effect (NDE) expressed through the parameter /E² is demonstrated where is a change in the electric permittivity of a solvent in an external strong electric field E. Both E _T (20) and /E², determined in quite different ways, are extremely sensitive to the dielectric properties of a solvent which depend on molecular interactions. Linear correlations between /E² and E _T (30) have been found for n-alkanols representing hydrogenbond donor solvents, and for halogenobenzenes which are dipolar, aprotic, weakly-associated solvents.Part of this work was presented at The 22^nd International Conference on Solution Chemistry in Linz, Austria, July 1991.     

Thermodynamics of Solvation of 18-Crown-6 and Its Alkali-Metal Complexes in Various Solvents

Heats of solution of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) in acetonitrile, 1,2-dichloroethane, N,N-dimethylformamide, dimethyl sulfoxide, nitromethane, propylene carbonate, pyridine and water were measured at 25 °C and the enthalpies of the transfer of 18-crown-6 from waterto the aprotic solvents were derived. The thermodynamic quantities, G₁°, H₁° and T S₁°, for the formation of the[M(18-crown-6)]⁺ (M⁺ = Na⁺, K⁺, Rb⁺, Cs⁺, NH₄ ⁺) complexeswere determined by titration calorimetry in dimethyl sulfoxide containing0.1 mol dm^-3 (C₂H₅)₄NClO₄ as a constant ionic medium at 25 °C. These thermodynamic quantities suggest that the complexationof 18-crown-6 with the alkali-metal ions mainly reflects the different solvationof 18-crown-6 and also the different degree of solvent structure.     

Medium effects on the reactions of coordination complexes: Base hydrolysisof(αβS)(p-hydroxybenzoato)(tetraethylenepentamine) cobalt(III) in iso-propanol–water,tert-butanol–water and dimethyl sulfoxide–water media

The base hydrolysis of (S)(p-hydroxybenzoato)-(tetraethylenepentamine)cobalt(III) has been investigated in aqueous–organic solvent media using i-PrOH, t-BuOH and dimethyl sulfoxide (DMSO) as cosolvents at 20.0 T (°C) 40.0 (I=0.02 mol dm ^-3) with 80% (v/v) of cosolvents. Only the base-catalysed path (k_obs=k_OH[OH^-]) is observed. The relative second order rate constant k _OH ^os /k _OH ^ow at I=0 increases nonlinearly with increasing mol fraction (x_O.S.) of the cosolvents, the rate acceleration in alcoholic cosolvents being greater than in DMSO. The destabilization of ^-OH in mixed solvent media alone does not explain the observed rate acceleration. The solvent composition dependence, log k _OH ^os = log k _OH ^ow + a_ix _os ⁱ [i=1,2,k _OH ⁰ denotes k_OH at I=0 in mixed solvent(s) and water (w)] indicates specific solute–solvent interactions. The values of the relative transfer free-energy data [_TG(t.s.) - _TG^o (i.s.)](sw)(25 °C)(G), where t.s. and i.s. denote the transition state and initial state of the substrates respectively, are positive for all substrates at all compositions, indicating a greater destabilizing effect of the mixed solvent on the transition state than on the initial state. The G values also correlate with G^E(G = ax_O.S. + cG^E) for all solvents, supporting the fact that solvent structural effects mediate the rates and energetics of the reaction. However, the solvent effects on the solvation components of H and S are mutually compensating, thus indicating that there is no change in the mechanism.     

The use of thermal analysis in medical science with special reference to nephroliths

The applications of thermal methods in medical science have been summarized, with special regard to kidney stones. Complex thermal analysis can be used successfully for examination of human and animal urinary calculi, bones, odontoliths biological tissues (proteins, skin, callus, nail) etc.

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Zusammenfassung Es wurden die Anwendungen der Thermoanalyse auf medizinischem Gebiet unter besonderer Berücksichtigung von Nierensteinen zusammenfassend behandelt. Komplexe thermoanalytische Methoden eignen sich zur Prüfung von menschlichen und tierischen Harnsteinen, Knochen, Zahnstein, biologischem Gewebe (Proteine, Haut, Nägel, usw.)

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Résumé Revue des applications des méthodes thermoanalytiques dans le domaine médical avec mention particulière pour les calculs rénaux. L'emploi des méthodes d'analyse thermique mixtes donnent de bons résultats pour l'examen des calculs rénaux animaux et humains, du tartre dentaire et des tissus biologiques (protéines, peau, ongles), etc.

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, . , (, , , ) .

     

Thermodynamic study of solvent extraction of monovalent metal picrates with benzo-18-crown-6 into chloroform

Thermodynamic parameters (H _ex ⁰ and S _ex ⁰ ) for the overall extractions of monovalent metal (Na, K, Rb, and Tl) picrates with benzo-18-crown-6 (B18C6), and those (H _D,L ⁰ and S _D,L ⁰ ) for the distribution of B18C6 were determined between chloroform and water. All the extracted B18C6 complexes were l:1:1 complexes (B18C6:metal ion: picrate anion). The H _ex ⁰ and S _ex ⁰ values for all the metals are negative. Every extraction of the metal picrate with B18C6 is completely enthalpy driven. The H _D,L ⁰ and S _D,L ⁰ values of B18C6 are both positive, and the partition of B18C6 is entirely entropy driven. Enthalpy (H _ex,ip ⁰ ) and entropy changes (S _ex,ip ⁰ ) for ion-pair extractions of B18C6-metal ion complexes with picrate anions were calculated. All the H _ex,ip ⁰ and S _ex,ip ⁰ values are negative, and the ion-pair extractions are completely enthalpy driven.     

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.     

The conductance of lithium-7 fluoride in dioxane-water mixtures at 25°C

Conductance data for lithium-7 fluoride in dioxane-water mixtures covering the range 78.35>D>36 in dielectric constant are presented. These data and other previous data on lithium-7 chloride and lithium-7 iodide were analyzed by the Fuoss 1980 conductance equation in order to find the limiting conductance _o, the pairing distance R and the conductometric association constant K. Setting K_a=K/V_M (where V_M is the molar volume of the solvent), the thermodynamic pairing constant and the corresponding change of the free energy g were calculated. Correlation among the values found for R and g=h–Ts and the properties characteristic of the ions and solvents are discussed.R. M. Fuoss died on 1^st December 1987 before this work was completed. A D'Aprano and F. Accascina dedicate this paper to him with respect and affection.     

Square Wave Voltammetric-Thermodynamic Study of the Interaction Between Heavy Metal Ions and Some Macrocyclic Ligands in Water*

The interaction between Cd²⁺ and Pb²⁺ ions and 18-crown-6 (18C6), 1,10-diaza-18-crown-6 (C22) and 1,7-diaza-15-crown-5 (C21) were studied in water solvent at 25, 35, 45 and 55° using square wave voltammetric technique. The stoichiometry and stability of the complexes were determined by monitoring the shift in half-wave or peak potential of the polarographic waves of metal against the ligand concentration. Thermodynamic parameters such as G, H and S were obtained by using a polarographic double wall cell in which the temperature could be fixed to ±0.1°C. The results of all experiments show 1 : 1 complexes, but in addition to 1 : 1 ratio, a 2 : 1 ratio of ligand to cation is also obtained for C22–Pb²⁺ complex. The selectivity order for 18C6 and C22 is Pb²⁺ > Cd²⁺. The thermodynamic data G, H and S values show that the complexes are stabilized by both the enthalpy and entropy terms, but C22–Pb²⁺ complex is stabilized by only enthalpy term.     

Glass transition temperatures of polymer materials,measured by thermomechanical analysis

The linear expansions of two materials have been measured, a double-base propellant and a carboxyl-terminated polybutadiene. The glass transition temperature,T _g and expansion coefficients below and aboveT _g have been calculated. The influence of the heating and cooling rates and sample thickness has been investigated. The results show that the value ofT _g is dependent on the rates of heating and cooling but not on the sample thickness. Extrapolating to zero rate gives the sameT _g for both heating and cooling. The expansion coefficients are not influenced by the rates of heating and cooling or by the sample thickness.

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Zusammenfassung Die lineare Ausdehnung wurde an zwei Stoffen, einem doppelbasischen Triebstoff und einem Polybutadien mit Carboxyl-Endung gemessen. Die Glas-Übergangs-temperaturT _g und die Ausdehnungskoeffizienten unterhalb und oberhalb vonT _g wurden berechnet. Der Einfluss der Aufheiz- und Abkülhgeschwindigkeiten und die Stärke der Probe wurden geprüft. Die Ergebnisse zeigen, daß der Wert vonT _g der von Aufheiz- und Abkühlgeschwindigkeit, nicht aber von der Probenstärke abhängt. Die Extrapolierung auf die Geschwindigkeit 0 ergibt denselbenT _g -Wert bei Aufheizung und Kühlung. Die Ausdehnungskoeffizienten werden durch die Aufheiz- und Abkühlgeschwindigkeit oder durch die Probenstärke nicht beeinflusst.

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Résumé On a mesuré la dilatation linéaire de deux matériaux, un agent de propulsion à base double et un polybutadiène avec un carboxyle comme groupe terminal. On a calculé la températureT _g de la transition vitreuse ainsi que les coefficients de dilatation au-dessous et au-dessus deT _g . L'influence des vitesses de chauffage et de refroidissement ainsi que l'épaisseur de l'échantillon ont été étudiées. Les résultats montrent que la valeur deT _g dépend des vitesses de chauffage et de refroidissement, mais pas de l'épaisseur de l'échantillon. L'extrapolation à la vitesse zéro donne la même valeur de la températureT _g lors du chauffage et du refoidissement. Les coefficients de dilatation ne sont influencés ni par les vitesses de chauffage ou de refroidissement ni par l'épaisseur de l'échantillon.

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. T_{g g}. , . , _g , . _g , . , .

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This is the last paper belonging to the Fifth Scandinavian Symposium on Thermal Analysis.     

Factors influencing enantiomeric recognition of primary alkylammonium salts by pyridino-18-crown-6 type ligands

Equilibrium constant (K), enthalpy change (H), and entropy change (S) values were determined for the interactions of a series of chiral pyridino-18-crown-6 type ligands with enantiomers of several primary alkylammonium salts in various solvents. Good enantiomeric recognition in terms of logK was observed in many systems with logK values greater than 0.4. The extent of enantiomeric recognition and the stabilities of the chiral crown ether-ammonium salt complexes were found to depend on the rigidity of the macrocyclic frame of the ligand, the type and arrangement of the donor atoms on the ligand, the bulkiness of the substituents on the ligand's chiral centers, the location of the chiral centers on the ligand, and the solvent. The effects of these factors on the extent of enantiomeric recognition and on the stabilities of the complexes were examined for the systems studied.     

Infrared spectroscopy of hydrogen bond and substituent effects in electron donor molecules

The frequency shift, , of the O—H stretching mode in the IR spectra of the H-complexes of phenol with electron donor molecules BX_i (B is the n- or -donor center and X_i are substituents; a total of eight series), the change in the Gibbs free energy, G, due to H-complexation, and the parameter (a measure of the ability of BX_i molecules to donate an electron pair; two series) are determined by both the electrostatic interaction and charge transfer in the formation of H-complex. The , G, and values depend not only on the inductive and resonance effects, but also the polarizability of substituents characterized by the parameters.     

Elektrometrische Untersuchungen über die Komplexbildung von La(III) mit 3.5-Dinitrosalicylsäure

Zusammenfassung Die Komplexbildung zwischen La(III) und 3.5-Dinitrosalicylsäure in 0.1m-KNO₃ wurde potentiometrisch und konduktometrisch untersucht. Wir erforschten die Bildung von 11- und 12-Komplexen oberhalb pH 3.5. Der 11-Komplex bildet sich in Lösung, während der 12-Komplex ausfällt. Die Stabilitätskonstante des 11-Komplexes wurde durch Anwendung der vonCalvin undMelchior erweiterten Methode vonBjerrum bestimmt. Für logK fand man Werte von 4.92, 5.00 und 5.12 bei 25°, 30°, beziehungsweise 35° C. Die Werte für F, H und S wurden für 30° C berechnet und bestimmt zu–6.97 Kcal/Mol,–7.49 Kcal/Mol, beziehungsweise –1.70 cal/Mol/Grad.

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Electromeric studies on the complex formation between La(III) and 3.5-dinitrosalicylic acid

The complex formation between La(III) and 3.5-dinitrosalicylic acid in 0.1m-KNO₃ medium has been studied potentiometrically and conductometrically. The formation of 11 and 12 complexes beyond 3.5 pH was investigated. 11 complex is formed in solution while 12 complex is precipitated. The stability constant of the 11 complex was determined by applying the Calvin and Melchior's extension ofBjerrum's method. The logK values have been found to be 4.92, 5.00, and 5.12 at 25, 30 and 35°C, respectively. The values of F, H, and S have also been evaluated at 30°C and found to be–6.97 Kcal/mole,–7.49 Kcal/mole, and–1.70 Kcal/mole/degree, respectively.

     

Cyanoacetic ester pyrolysis in the gas phase

The gas-phase thermal decomposition of isopropyl cyanoacetate at 292–325°C and 44–178 Torr reveals a homogeneous unimolecular elimination with a first-order rate law. The rate constants are given by the Arrhenius equation: log k(sec^–1)=(13.01±0.54)–(43,100±1400 cal/mol)/2.303 RT. The data are compared with those for the corresponding -haloacetic esters.

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292–325°C 44–178 . : log k (^–1)=(13,01±0,54)–(43100±1400 /)/2,303 RT. , - .

     

Kinetics of the solvolysis oftrans-dichlorotetra-(4-t-butylpyridine)-cobalt(III) ions in water +t-butyl alcohol mixtures

Rates of solvolysis of the complex cation [Co(4tBupy)₄Cl₂]⁺ have been determined in mixtures of water with the hydrophobic solvent, t-butyl alcohol. The solvent composition at which the extremum is found in the variation of the enthalpy H^* and the entropy S^* of activation correlates well with the extremum in the variation of the relative partial molar volume of t-butyl alcohol in the mixture and the straight line found for the variation of H^* with S^* is coincident with the same plot for water + 2-propanol mixtures. A free energy cycle is applied to the process initial state (C ⁿ⁺) going to the transition state [M⁽ⁿ⁺¹⁾⁺...Cl^–] in water and in the mixture using free energies of transfer of the individual ionic species, G _t ^o (i), from water into the mixture. Values for G _t ^o (i) are derived from the solvent sorting method and from the TATB/TPTB method: using data from either method, changes in solvent structure on going from water into the mixture are found to stabilize the cation in the transition state, M⁽ⁿ⁺¹⁾⁺, more than in the initial state, C ⁿ⁺. This is compared with the application of the free energy cycle to the solvolysis of complexes [Co(Rpy)₄Cl₂]⁺ and [Coen₂LCl]⁺ in mixtures of water with methanol, 2-propanol or t-butyl alcohol: the above conclusion regarding the relative stabilization of the cations holds for all these complexes in their solvolyses in water+alcohol mixtures using values of G _t ^o (Cl^–) from either source.     

Pathways of formation of xenobiotics of the dioxin type: Quantum-chemical consideration. 2. 1,2-Ketocarbenes as intermediates in the conversions of polychlorophenols to dioxin

The AM1 method was used to calculate the enthalpies of formation of polychlorinated 1,2-ketocarbenes (PCKC) from polychlorophenols (PCP) according to a two-step scheme — deprotonation with the formation of polychlorophenolate anions (PCPA, H₁) and dechlorination to PCKC (H₂). It was shown that the biradical state of PCKC has a lower energy than the singlet state. The influence of the solvent on H₁ and H₂ was estimated within the framework of the solvation model. It was shown that H₁ decreases with increasing number of Cl atoms in PCP, which is evidence of an increase in the acidity, whereas H₂ increases, which is due to an increase in the relative stability of PCPA with increasing number of Cl atoms. A calculation of the dimerization of PCKC in the singlet state showed that this process occurs with virtually no activation energy. The electronic state of 1,2-ketocarbene and its analogs in the singlet state was studied by a nonempirical MO LCAO SCF method. A comparison with 1,2-thioketocarbene and its analogs was performed.For previous communication, see [1].A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1740–1745, August, 1992.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXIX. Solvent Effects on the Activation Parameters of Heterolysis of tert-Butyl Chloride

The kinetics of heterolysis of t-BuCl in sulfolane, PhCN, PhNO₂, acetophenone, cyclohexanone, chloroform, and 1,2-dichloroethane at 30-50°C were studied by the verdazyl method. Quantitative analysis of the effect of solvent parameters on the G , H , S , and log k _{2 5} values for heterolysis of t-BuCl in a set of 15 protic and 16 aprotic solvents and separately in either group of solvents was performed. In the above set of solvents, three H -S compensation effects are observed, associated with jump changes in the potential energy of the reaction.