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.     

Model calculations of changes of thermodynamic variables for the transfer of nonpolar solutes from water to water-d2

A recently introduced modified hydration shell hydrogen bond model for rationalizing the thermodynamic consequences of hydrophobic hydration is adapted for use with heavy water. The required adjustment of parameters employs the assumption that breaking hydrogen bonds in water-d₂ involves a greater enthalpy change and a larger entropy increase than bond breaking in ordinary water. It also makes some use of information derived from studies of gas solubilities in the two solvents, although a review of the data leads to serious questions about the reliability of results obtained in this way. The model permits calculations of hydrogen bonding contributions to the changes, G _t ^o , H _t ^o , S _t ^o , and C _p,t ^o , for transfer of nonpolar solutes from water to water-d₂ and implies that such data should show regular trends. Although some of the numerical results depend strongly on the values chosen for the parameters, the pattern defined by these trends is nearly independent of parameters. Predicted values of C _p,t ^o are large and positive for all nonpolar solutes, while S _t ^o is expected to be negative near 0°C, becoming progressively less negative on warming and eventually positive. Both of these quantities should be proportional to the molecular surface area of the solute. Analogous predictions regarding G _t ^o and H _t ^o can also be made, but only if it is permissible to neglect possible contributions to these quantities from van der Waals interactions.     

Free energy of transfer of cobalt(III) complexes from water into water—t-butyl alcohol mixtures

The solubility of trans-(Coen₂Cl₂)₂ReCl₆ has been determined in water and in water +t-butyl alcohol mixtures. By comparzng these values with the solubility of Cs₂ReCl₆ in similar mixtures, values for the difference in free energy of transfer, G _t ^o (i) between water and water + t-butyl alcohol can be calculated for i =[Coen₂Cl₂]⁺ and Cs⁺. The introduction of G _t ^o (Cs⁺) then produces values for G _t ^o (Coen₂Cl₂ ⁺). The difference in G _t ^o (i) for i=[Coon₂Cl]²⁺ in the transition state and i=[Coen₂Cl₂]⁺ in the initiad' tate for the solvolysis of the trans-[Coen₂Cl₂]⁺ ion in water + t-butyl alcohol can be derived from the application of a free energy cycle: using G _t ^o (Coen₂Cl₂ ⁺) determined from the solubility measurements allows the calculation of values for G _t ^o (Coen₂Cl²⁺). G _t ^o (i) in water + t-butyl alcohol for bis (1,2-diamino) cobalt (III) ions are compared with G _t ^o (i) for tetrapyridinecobalt (III) ions.     

Thermodynamics of the weak interaction between samarium cation and xylitol in water: A chemical model

The thermodynamic characterization of the weakly complexed model system Sm³⁺-xylitol has been carried out. The standard Gibbs energy enthalpy, entropy, volume and heat capacity of complexation of Sm³⁺ by xylitol have been determined in water at 25°. The stability constant and the enthalpy change have been simultaneously determined by using a calorimetric method. The thermodynamic properties characterizing solely the specific interaction between the cation and the complexing sequence of hydroxyl groups of the ligand have been isolated. The stability constant and the volume of complexation have also been estimated from a similar treatment of the apparent molar volumes. It was found that the reaction between Sm³⁺ and the complexing site of xylitol in water is characterized by: K = 8.1, _rG^o = –5.2 kJ-mol^–1, _rH^o = –13.7 kJ-mol^–1, T_rS^o = –8.5 kJ-mol^–1, _rV^o = 8.8 cm³-mol^–1 and _rC _p ^o = 51 J-K^–1-mol^–1.     

Effect of intramolecular rotational reorganization of reagents on the ratio between free energies of activation and reaction

Conclusions The relationship between the free energies of activation G and reaction G_o for proton transfer processes have been analyzed, taking into account the effect of hindered rotation of the reagents. We have shown that the considered effect can considerably affect the shape of the G=f(G_o) curve.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 77–81, January 1989.     

Acid properties of some phosphonocarboxylic acids

Thermodynamic acid dissociation constants were determined for phosphonoacetic acid (PAA) in aqueous solution at 25°C by coulometric titrations at different ionic strengths and extrapolation of the results to I=0. The respective values are pK₁2.0, pK₂=5.11±0.04, and pK₃=8.69±0.05. The enthalpy and entropy of dissociation for the second and the third dissociation steps, determined from the temperature dependence of pK's, are H ₂ ^o =0.2±0.3 kcal-mole^–1, S ₂ ^o =22.6±0.9 e.u., H ₃ ^o =1.3±0.4 kcal-mole^–1, and S ₃ ^o =11.7±0.4 e.u. Phosphorus-31 and carbon-13 NMR studies of PAA solutions as a function of pH gave the deprotonation sequence of the triacid. Acidity constants were also determined for phosphonoformic acid, 2-phosphonopropionic acid, and 3-phosphonopropionic acid at an ionic strenght of 0.05.To whom correspondence should be addressed.     

Thermodynamic quantities for the protonation of amino acid amino groups from 323.15 to 398.15 K

Flow claorimetry has been used to study the interaction of protons with glycine, DL--alanine, -alanine, DL-2-aminobutyric acid, 4-aminobutyric acid, and 6-aminocaproic acid in aqueous solutions at temperatures from 323.15 to 398.15 K. By combining the measured heats for amino acid solutions titrated with NaOH solutions with the heat of ionization for water, the log K, H^o, S^o, and C_p ^o values for the protonation of the amino groups of these amino acids have been obtained at each temperature studied. Equations are given expressing these values as functions of temperature. The H^o and S^o values increase while log K values decrease as temperacture increases. The trends for log K, H^o, S^o, and C_p ^o are discussed in terms of changes in long-range and short-range solvent effects. The trend in H^o, S^o, and C_p ^o values with temperature and with charge separation in the zwitterions is interpreted in terms of solvent-solute interactions and the electrostatic interaction between the two oppositely charged groups within the molecule.     

The autoxidation of δ10-dodecahydroacridine

The autoxidation of ¹⁰-dodecahydroacridine in heptane in an atmosphere of oxygen has given 12-hydroperoxy-¹⁰-dodecahydroacridine, which has been reduced to 12-hydroxy-¹⁰-dodecahydroacridine and has been converted into 5-azabicyclo[8,4, 0]tetradecane-6,11-dione. The two latter compounds were also isolated when ¹⁰-dodecahydro-acridine underwent autoxidation in air in the absence of a solvent.     

Enthalpy-entropy compensation in ionic micelle formation

The enthalpy-entropy compensation in ionic surfactant micellization process over a large temperature range is examined. The surfactants SDS and C₁₆TAB are investigated experimentally, and the enthalpy and entropy changes are evaluated based on phase separation or mass action models together with the other three surfactant systems. The relationship between compensation temperature and the reference temperatures is discussed.Notations C _p heat capacity change, J/mol-K - CMC critical micelle concentration,M - CMC₀ critical micelle concentration atT=T ₀,M - G Gibbs free energy change, kJ/mol - H enthalpy chang, kJ/mol - h _c enthalpy change for transfer of a methylene group to water, kJ/mol - R gas constant, 8.314 J/mol-K - S entropy change, J/mol-K - S _c entropy change for transfer of a methylene group to water, J/mol-K - S ^* entropy change atT=T ^*, J/mol-K - T temperature,K - T _c compensation temperature, K - T _H temperature at which H=0, K - T ₀ temperature at the minimum point, K - T ^* 112°C Greek Letters degree of dissociation     

Thermodynamics of adsorption of cerium on lead dioxide

Adsorption of cerium on lead dioxide from aqueous solutions has been studied as a function of shaking time, amount of adsorbent, pH, concentration of the adsorbate and temperature. The adsorption process is endothermic and the distribution coefficient (K_D) increases with increasing temperature. The data fit very well the Langmuir, Freundlich, and Dubinin-Raduskevich Isotherms and their corresponding constants were calculated. H^o and S^o were calculated from the slope and intercept of plots of lnK_D vs. 1/T. G^o values decreases with increasing temperature, showing that the adsorption of Ce(III) is more favorable at high temperature. The endothermacity of the adsorption process is discussed.     

Thermochemistry of aqueous solutions of alkylated nucleic acid bases. VIII. Enthalpies of hydration of 6-alkyluracils

Enthalpies of solution in water H _sol ^o and enthalpies of sublimation H _sub ^o were determined for a number of crystalline derivatives of uracil: 1,6-dimethyluracil (m ₂ ^1,6 Ura), 1,3,6-trimethyluracil (m ₃ ^1,3,6 Ura), 6-ethyl-1,3-dimethyluracil (e⁶m ₂ ^1,3 Ura), 6-propyl-1,3-dimethyluracil (pr⁶m ₂ ^1,3 Ura) and 6-butyl-1,3-dimethyluracil (but⁶m ₂ ^1,3 Ura). Standard enthalpies of hydration H _hydr ^o and standard enthalpies of interaction H _int ^o of the solutes with their hydration shells were calculated. The data obtained show that dependence of H _int ^o on the number of-CH₂- groups of n-alkyl chain added upon substitution of diketopyrimidine ring is nonlinear. This finding is discussed in connection with results of X-ray diffraction structure determinations for the crystalline compounds.     

Enthalpies of solution of thymine and uracil in water and dimethylsulfoxide

Enthalpies of solution of thymine and uracil in water and in dimethylsulfoxide (DMSO) were measured calorimetrically in the temperature range 25–40°C. H _s ^o at 25°C for thymine and uracil in water were found to be 23.1±0.5 and 29.5±0.3 kJ-mol^–1, respectively. In DMSO, H _s ^o were 7.9±0.1 and 10.2±0.1 kJ-mol^–1, respectively. In aqueous solution C _p ^o for the two nucleic acid bases were relatively large and positive with C _p ^o of thymine being larger. Both transfer quantities H _t ^o and C _p,t ^o for the proceses H₂ODMSO for the two nucleic acid bases were negative. It is proposed that, the differences in the values obtained for the two bases is due principally to increased order in the water adjacent to the methyl group in thymine.     

Absorption spectra of 2-styryl-4-phenyl-thiazole ethiodides in organic solvents of varying polarities and determination of the formation constant of the charge transfer complex formed

The electronic absorption spectra of some 2-styryl-4-phenyl-thiazole ethiodides are studied in organic solvents of different polarities. The shorter wavelength band appearing in the visible region is assigned to an intramolecular charge transfer (CT)-transition originating from the phenyl moiety to the positively charged hetero ring, while the longer wavelength one is due to an intermolecular CT-transition from the iodide ion to the 2-styryl-4-phenyl-thiazolinium cation. These assignments are based on the nature of the aldehydic residue and effects of solvent, concentration, and temperature on both the position and absorptivity of the CT complex-band. It is concluded that the CT complex formed will be highly solvated inDMF, DMSO, ethanol and methanol relative to in CHCl₃, dioxane and acetone. The formation constant of the CT complex in solutions of different polarities is determined at different temperatures. Furthermore, the thermodynamic parameters H ^o, G ^o and S ^o for complex formation are calculated and discussed.

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Absorptionsspektren von 2-Styryl-4-phenyl-thiazol-ethiodiden in verschiedenen Lösungsmitteln und Bestimmung der Bildungskonstanten der Charge-Transfer-Komplexe

Zusammenfassung Die Elektronenanregungsspektren einiger substituierter 2-Styryl-4-phenyl-thiazol-ethiodide wurden in einigen Lösungsmitteln unterschiedlicher Polarität untersucht. Die Absorption bei kürzerer Wellenlänge wird einem intramolekularen Charge-Transfer (CT)-Übergang zugeordnet, die langwellige Bande einem intermolekularen CT-Übergang (Jodid—organ. Kation). Die Diskussion erfolgt basierend auf Substitutions-, Lösungsmittel-, Konzentrations-, und Temperatur-Effekten. Die Komplexbildungskonstanten und die thermodynamischen Parameter H ^o, G ^o und S ^o werden angegeben.

     

Solubilities in aqueous mixtures oft-butanol andtrans-dichlorotetra(3-alkylpyridine) cobalt(III) hexachlororhenate(IV): Gibbs energies of transfer of the complex cations

The solubilities of the hexachlororhenate(IV) salts of the complex cations trans-[Co(3Mepy)₄Cl₂]⁺ and trans-[Co(3Etpy)₄Cl₂]⁺ have been determined in water+t-butyl alcohol mixtures. By reference to the solubilities of Cs₂ReCl₆ and the Gibbs energies of transfer of Cs⁺ from water into water+t-butyl alcohol mixtures, G _t ^o (Cs⁺), G _t ^o [Co(3Mepy)₄Cl ₂ ⁺ ] and G _t ^o [Co(3Etpy)₄Cl ₂ ⁺ ] are calculated. These latter values, when introduced into the equation for a free energy cycle applied to the process of the initial state going to the transition state for the solvolyses of these two cations, produces values for G _t ^o [Co(3Mepy)₄Cl^2+*] and G _t ^o [Co(3Etpy)₄Cl^2+*] for the Co³⁺ cations in the transition state. These values are compared with (G _t ^o (i) for i=[Co(Rpy)₄Cl₂]⁺, [Co(Rpy)₄Cl]^2+*, [Coen₂XCl]⁺ and [Coen₂X]^2+* to investigate the influence of the hydrophobicity of the surface of the complex on its stability in the mixtures. G _t ^o (i) (solvent sorting) are compared with G _t ^o (i) (TATB).     

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.     

Effect of pressure on the solubility of naphthalene in water at 25°C

Solubility of naphthalene in water was measured at 25°C and pressures up to 200 MPa. The solubility decreased with increasing pressure. From the pressure coefficient of the solubility, the volume change V accompanying the dissolution was estimated as 13.8±0.4 cm ³ -mol ^–1 . Further we estimated the volume change V _CH accompanying hydrophobic hydration as –0.1±0.6 cm ³ -mol ^–1 using the V value, the molar volume of crystalline naphthalene, and the partial molar volume of naphthalene in n-heptane. This V _CH is much larger (i.e., less negative) than that for hydrophobic hydration of alkyl-chain compounds and suggests that the hydration structure of naphthalene differs from that of alkyl-chain compounds.     

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.     

Influence of o-benzoquinone nature on initiation of radical polymerization by the o-benzoquinone—tert-amine system

o-Benzoquinones initiate radical polymerization of methacrylates under visible light irradiation in the presence of tertiary amines. Spectral sensitivity of the initiating system coincides with absorption bands of o-benzoquinone attributed to the S(*) (_max 400 nm) and S(n*) (_max 600 nm) transitions. The amine radicals (Am^·) initiating polymerization are generated by the photoreduction of Q in the presence of AmH from the triplet radical pair ³(QH^·, Am^·). The yield of Am^· depends on the difference between the volumes of substituents in the 3 and 6 positions of the quinoid ring and is maximal for symmetrically substituted o-benzoquinones. For a series of derivatives of symmetrical 3,6-di-tert-butyl-o-benzoquinone, the rate of photopolymerization of ,-bis(methacryloyloxyethyleneoxycarbonyloxy)ethyleneoxyethylene (OCM-2) in the presence of N,N-dimethylaniline is determined by the free energy (G _e) of electron transfer from the amine to photoexcited o-benzoquinone. The G _e value includes the energies of oxidation of the amines and reduction of the o-quinones and the energy of the 00 transition of the triplet excited state of o-benzoquinones, which are equal to their redox potentials. The photopolymerization rate is maximal for G _e 0.     

Thermodynamics of transfer of non-ionic solutes between immiscible liquid phases. I. Transfer of normal alcohols fromn-octane to water at 25°C

A recently developed calorimetric method has been employed to estimate the thermodynamic functions for transfer of 1-propanol, 1-butanol, 1-pentanol, 1-hexanol and 1-heptanol from n-octane to water at 25°C. A linear correlation for G _t ^o as a function of the number of carbon atoms of the alchohol molecule has been found but for H _t ^o and S _t ^o the dependence gave well defined minima.     

Mechanisms of 5'-O-Benzoyl-2,3'-anhydrothymidine Reactions with Nucleophiles: II. Kinetics of the Reaction with Triethylammonium Tetrazolide in DMF

The reaction of 5'-O-benzoyl-2,3'-anhydrothymidine with triethylammonium tetrazolide in DMF at 100-120°C is described by a second-order kinetic equation, following the first-order kinetics in each of the reactants. On the basis of the experimental activatin parameters, H298 = 80 kJ/mol, S = -116 J× mol^{- 1} K^{- 1}, a mechanism was proposed, according to which in the rate-determining stage of S_N2 reaction triethylammonium tetrazolide attacks the C^{3 '} atom of 5'-O-benzoyl-2,3'-anhydrothymidine with simultaneous loosening of the C^{3 '}ÄO² anhydro bond.