Measurement of Some Thermodynamic and Acoustic Properties of Binary Solutions of N,N-Dimethylformamide with 1-Alkanols at 30°C and Comparison with Theories

Densities, and ultrasonic velocities, uof binary mixtures of N,N-dimethylformamide (DMF) + methanol, + ethanol, + 1-propanol, + 1-butanol, + 1-pentanol, and + 1-hexanol have been measured at 30°C. The ultrasonic velocities have been compared with values calculated from the free-length theory ( FLT) due to Jacobson and collision-factor theory ( CFT) due to Schaaffs. The measured data are used to compute adiabatic compressibility (k _s), deviation in adiabatic compressibility (k _s), intermolecular free length (L _f), molar volume (V _m), and available volume (V _a). The excess molar volume ( V _m ^E) and excess free length (L _f ^E) are also evaluated. For all systems, these results were satisfactorily correlated by the Redlich–Kister polynomial. These parameters are used to discuss dissociation of the self-associated 1-alkanol molecules and the formation of aggregates between unlike molecules through C=O...H–O hydrogen bonding.     

Effect of Ethylene Glycol on the Molecular Organization of H2O in Comparison with Methanol and Glycerol: A Calorimetric Study

Excess partial molar enthalpies of ethylene glycol, H ^E _EG, in binary ethylene glycol–H₂O, and those of 1-propanol, H ^E _IP, in ternary 1-propanol–ethylene glycol (or methanol)–H₂O were determined at 25°C. From these data, the solute–solute interaction functions, H ^E _EG–EG = N(H ^E _EG/n _EG) and H ^E _1P–1P = N(H ^E _1P/n _1P), were calculated by graphical differentiation without resorting to curve fitting. Using these, together with the partial molar volume data, the effect of ethylene glycol on the molecular organization of H₂O was investigated in comparison with methanol and glycerol. We found that there are three concentration regions, in each of which the mixing scheme is qualitatively different from the other regions. Mixing scheme III operative in the solute-rich region is such that the solute molecules are in a similar situation as in the pure state, most likely in clusters of its own kind. Mixing scheme II, in the intermediate region, consists of two kinds of clusters each rich in solute and in H₂O, respectively. Thus, the bond percolation nature of the hydrogen bond network of liquid H₂O is lost. Mixing scheme I is a progressive modification of liquid H₂O by the solute, but the basic characteristics of liquid H₂O are still retained. In particular, the bond percolation of the hydrogen bond network is still intact. Similar to glycerol, ethylene glycol participates in the hydrogen bond network of H₂O via-OH groups, and reduces the global average of the hydrogen bond probability and the fluctuations inherent in liquid H₂O. In contrast to glycerol, there is also a sign of a weak hydrophobic effect caused by ethylene glycol. However, how these hydrophobic and hydrophilic effects of ethylene glycol work together in modifying the molecular organization of H₂O in mixing scheme I is yet to be elucidated.     

Compressibility coefficients of water-2-propanol mixtures over the temperature and pressure ranges 278–323.15 K and 1–1000 bar

The compressibility coefficients k = (v ₀-v)/v ₀ of the water-2-propanol binary system were measured over the entire composition range, the temperature range 278–323.15 K, and the pressure range from atmospheric pressure to 1000 bar. The results are tabulated. Partial molar compressibility coefficients of the components were calculated. It was found that the partial molar compressibility coefficient of water decreased as the alcohol concentration in the mixture increased and became negative at x > 0.5–0.6 (x is the alcohol mole fraction).     

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.     

The effect of pressure on the ionization of water at various temperatures from molal-volume data1

The apparent molal volumes of dilute (0.002 to 1.0m) aqueous HCl and NaOH solutions have been determined at 0, 25, and 50°C and NaCl solutions at 50°C. The partial molal volumes ( ) of HCl, NaOH, and NaCl solutions have been determined from these apparent molal volumes and other reliable data from the literature. The partial-molal-volume changes ( ) for the ionization of water, H₂OH⁺+OH^–, have been determined from 0 to 50°C and 0 to 1m ionic strength from the partial molal volumes of HCl, NaOH, NaCl, and H₂O. The partial molal compressibilities ( for HCl, NaOH, NaCl, and H₂O have been estimated from data in the literature and used to determine the partial molal compressibility changes ( ) for the ionization of water from 0 to 50°C and 0 to 1m ionic strength. The effect of pressure on the ionization constant of water has been estimated from partial-molal-volume and compressibility changes using the relation from 0 to 50°C and 0 to 2000 bars. The results agree very well with the directly measured values.Contribution Number 1548 from the University of Miami.     

Heats of solution of 1∶1 electrolytes in 1-propanol,and derived enthalpies of transfer from water

Heats of solution of 13 11 electrolytes in 1-propanol have been determined calorimetrically at various electrolyte concentrations, and extrapolated to zero concentration to give H _s ^o values for these electrolytes. Together with literature data on three additional 11 electrolytes, these measurements yield a self-consistent set of single-ion enthalpies of transfer from water to 1-propanol. Values are tabulated for 10 univalent cations and five univalent anions. It is shown that the H _t ^o (Ph ₄ As⁺)=H _t ^o (Ph ₄ B^–) assumption yields chemically reasonable single-ion values. Using this assumption, it may be deduced that all the univalent ions studied have about the same enthalpy in 1-propanol as in methanol.     

The nanoheterogeneous structure of aqueous solutions of <Emphasis Type="Italic">n</Emphasis>-propanol

The results of positron spectroscopy and molecular light scattering studies, the data on radiationchemical yields and optical absorption spectra of solvated electrons formed under the action of ionizing radiation, and the data on the concentration dependences of viscosity, adiabatic compressibility, the velocity of sound, and partial molar volume were used to determine the structure of water-n-propanol mixtures. The conclusion was drawn that the insertion of alcohol molecules into water network voids over the range of alcohol mole fractions 0 < x ₂ < 0.05 strengthened the structure of water. A further increase in the concentration of the alcohol caused the destruction of the aqueous component and solution homogenization. At 0.01 < x ₂ < 0.3, mixtures resembled an emulsion of alcohol “nanodrops” suspended in water. At 0.3 < x ₂ < 0.9, the system again became homogeneous. Lastly, when water was added to pure n-propanol (1 > x ₂ > 0.9), its molecules combined into nanodrops.     

Transformation of benzonitrile into benzyl alcohol and benzoate esters in supercritical alcohols

The reactions of benzonitrile in supercritical methanol, ethanol, and 2-propanol were investigated under non-catalytic conditions. In supercritical methanol, benzonitrile was converted to methyl benzoate in high yield. The esterification reaction also occurred in supercritical ethanol to afford ethyl benzoate in moderate yield. The esterification could occur via a route analogous to the Pinner reaction. On the other hand, benzonitrile in supercritical 2-propanol yielded no ester. Benzyl alcohol was the major product in supercritical 2-propanol. We investigated the reaction of the CN bond in supercritical 2-propanol. In supercritical 2-propanol, N-benzylideneaniline was transferred to the reduction product (N-benzylaniline) and hydrolysis products (benzyl alcohol and aniline). The hydrolysis reaction was restricted when the reaction was carried out in supercritical 2-propanol with a low water content. This indicates that the water in the 2-propanol acts as a reagent for the hydrolysis of the CN bond. These results suggested the following reaction process: C₆H₅CN→C₆H₅CHNH→C₆H₅CHO→C₆H₅CH₂OH.     

Structure and mechanism of fragmentation of [C2H5O]+

The decomposition reactions of [C₂H₅O]⁺ ions produced by dissociative electron-impact ionization of 2-propanol have been studied, using ¹³C and deuterium labeling coupled with metastable intensity studies. In addition, the fragmentation reactions following protonation of appropriately labeled acetaldehydes and ethylene oxides with [H₃]⁺ or [D₃]⁺ have been investigated. In both studies particular attention has been paid to the reactions leading to [CHO]⁺, [C₂H₃]⁺ and [H₃O]⁺. In both the electron-impact-induced reactions and the chemical ionization systems the fragmentation of [C₂H₅O]⁺ to both [H₃O]⁺ and [C₂H₃]⁺ proceeds by a single mechanism. For each case the reaction involves a mechanism in which the hydrogen originally bonded to oxygen is retained in the oxygen containing fragment while the four hydrogens originally bonded to carbon become indistinguishable. The fragmentation of [C₂H₅O]⁺ to produce [CHO]⁺ proceeds by a number of mechanisms. The lowest energy route involves complete retention of the α carbon and hydrogen while a higher energy route proceeds by a mechanism in which the carbons and the attached hydrogens become indistinguishable. A third distinct mechanism, observed in the electron-impact spectra only, proceeds with retention of the hydroxylic hydrogen in the product ion. Detailed fragmentation mechanisms are proposed to explain the results. It is suggested that the [C₂H₅O]⁺ ions formed by protonation of acetaldehyde or ionization of 2-propanol are produced initially with the structure [CH₃CH?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}H] (a), but isomerize to [CH₂?CH? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}H₂] (e) prior to decomposition to [C₂H₃]⁺ or [H₃O]⁺. The results indicate that the isomerization a → e does not proceed directly, possibly because it is symmetry forbidden, but by two consecutive [1,2] hydrogen shifts. A more general study of the electron-impact mass spectrum of 2-propanol has been made and the fragmentation reactions proceeding from the molecular ion have been identified.     

Experimental Densities, Speeds of Sound, Isentropic Compressibilties and Shear Relaxation Times of CaSO4·2H2O + CaCl2 + H2O and CaSO4·2H2O + NaCl + H2O Systems at Temperatures 30 and 35 °C

Speeds of sound, u, have been measured as a function of concentration for the systems, CaSO₄·2H₂O +CaCl₂ + H₂O and CaSO₄·2H₂O + NaCl + H₂O, at temperatures of 30 and 35 °C. Derived parameters such as the isentropic compressibility, κ _S , and the shear relaxation time,τ,were calculated using the experimental speed of sound data in combination with viscosity values from our earlier work. Results have been compared with those of the CaCl₂+ H₂Oand NaCl + H₂O systems reported in literature,to examine the effect of adding CaSO₄·2H₂O(s).Values of κ _S for the system,CaSO₄·2H₂O + CaCl₂+H₂O,are smaller compared with those for the CaCl₂+ H₂O system.Values of τ are lower at lower concentrations and then cross over in a narrow concentration region.Values of κ _S for the system,CaSO₄·2H₂O+NaCl+H₂O, are also smaller when compared with those forthe NaCl +H₂O system.For this system the τ values are higher. These τ values reach a minimum at a certain concentration of NaCl in the solution and then increase with further increases in concentration.The influenceof solvent-separated and/or solvent-shared ion pairs plays a dominant role at higher concentrations for both systems.Results have been interpreted and discussed in terms of the expansion and contraction of the primary hydration shell of the ionic species present in the studied systems.     

Influence of Water on the Equilibria of Protonation of Mesoporphyrin IX Dimethyl Ether in Acetonitrile

The equilibria of protonation of mesoporphyrin IX dimethyl ether (H₂MP), namely, H₂MP + H⁺ H₃MP⁺ and H₃MP⁺ + H⁺ H₄MP²⁺, in the H₂MP(1.4 × 10^–5 mol/l)–HClO₄(0–0.01 mol/l)–H₂O(0.01–1.65 mol/l)–CH₃CN system at 298 K were studied using the spectropotentiometry method. It was established that the first-step equilibrium (logK ₁ = 11.95) is not affected by water. The dication forms two hydrates (H₂O)H₄MP²⁺ and (H₂O)₂H₄MP²⁺ with the step formation constants K _{h 1} = 8.50 and K _{h 2} = 1.39. The conventional constant of the second protonation step is related to the water concentration through the equation logK ₂ ^" = logK ₂ + log(1 + K _{h 1}[H₂O] + K _{h 1} K _{h 2}[H₂O]²). In anhydrous acetonitrile, logK ₂ = 7.51. The electronic absorption spectra of H₄MP²⁺ and of its hydrates are identical; therefore, K ₁ and K ₂ ^" cannot be distinguished in photometric determination of [H₄MP²⁺] in the presence of water.     

A Polarographic Study of Tl + , Pb 2 and Cd 2+ Complexes with Dicyclohexano-18-Crown-6 in Some Binary Mixed Solvents

The complexes of Tl⁺, Pb²⁺ and Cd²⁺ cations with the macrocyclic ligand, dicyclohexano-18-crown-6\linebreak(DC18C6) were studied in water/methanol (H₂₊O/MeOH), water/1-propanol (H₂₊O/1-PrOH), water/acetonitrile (H₂₊O/AN), water/dimethylformamide (H₂₊O/DMF), dimethylformamide/acetonitrile (DMF/AN), dimethylformamide/methanol (DMF/MeOH), dimethylformamide/1-propanol (DMF/1-PrOH) and dimethylformamide/nitromethane (DMF/NM) mixed solvents at 22 °C using differential pulse polarography (DPP), square wave polarography and conductometry. In general, the stability of the complexes was found to decrease with increasing concentration of water in aqueous/non-aqueous mixed solvents with an inverse relationship between the stability constants of the complexes and the concentration of DMF in non-aqueous mixed solvents. The results show that the change in stability of DC18C6.Tl⁺, vs the composition of solvent in DMF/AN and DMF/NM mixed solvents is apparently different from that in DMF/MeOH and DMF/1-PrOH mixed solvents. While the variation of stability constants of the DC18C6.Tl⁺ and DC18C6.Pb²⁺ complexes vs the composition of H₂₊O/AN mixed solvents is monotonic, an anomalous behavior was observed for variations of log K_f vs the composition of H₂₊O/1-PrOH and H₂₊O/MeOH mixed solvents. The selectivity order of the DC18C6 ligand for the cations was found to be Pb²⁺ > Tl⁺ > Cd²⁺.     

Studies of Thermodynamic Properties of Binary and Ternary Methanolic Solutions Containing KBr and 18-Crown-6 at 298.15 K

Experimental measurements of the speed of sound, density and osmotic vapour pressure are reported for binary 18-Crown-6 (18C6) + CH₃OH, KBr + CH₃OH and ternary KBr + 18C6 + CH₃OH solutions at 298.15 K. The density and compressibility data were processed to obtain the apparent molar volume (ø _V ) and apparent molar isentropic compressibility ( $\phi _{K_S } Experimental measurements of the speed of sound, density and osmotic vapour pressure are reported for binary 18-Crown-6 (18C6) + CH₃OH, KBr + CH₃OH and ternary KBr + 18C6 + CH₃OH solutions at 298.15 K. The density and compressibility data were processed to obtain the apparent molar volume (? _V ) and apparent molar isentropic compressibility () of the solutes in methanol. Expansivity data were obtained for the 18C6 + CH₃OH system from density data at different temperatures and were used for calculation of the isothermal compressibility values at 298.15 K. The isothermal compressibility and expansivity data are further used to obtain the apparent molar isothermal compressibility () and apparent molar expansivity (? _E ) of 18C6 in methanolic solutions and as well as the energy-volume coefficient parameter (∂ U/∂ V) _T in methanol solutions. The volume and compressibility changes due to complexation of KBr with 18C6 are obtained at infinite dilution for ? _V and ? _K . The results are compared with the similar data obtained by us previously for aqueous and CCl₄ solutions. The osmotic coefficient data were used to calculate activities and activity coefficients of each component at 298.15 K as a function of the concentration of binary and ternary methanolic solutions containing KBr and 18C6. The activity and activity coefficient data are used to evaluate the pair and triplet interaction parameters by making appropriate use of the McMillan-Meyer theory of solutions. The calculation of the thermodynamic equilibrium constant (K) is made using the pair interaction parameter, g _NE (non-electrolyte – electrolyte pair interaction), for the complexation equilibria. The nature of interactions present in the CH₃OH solutions is discussed.     

Enthalpies of 1,4-Dioxane, 1,2-Dimethoxyethane, and Ethylacetate Solvation in the Water–1-Propanol and Water–Glycerol Binary Mixtures

The enthalpies of 1,4-dioxane, 1,2-dimethoxyethane, and ethylacetate solution in binarymixtures of water with 1-propanol and glycerol were measured at 25°C using a precise isoperibol calorimeter. The enthalpies of the solute solvation were calculated and compared with the experimental data for other solutes. The results obtained were interpreted in terms of universal and specific solute solvation using parameters of a solvent polarity. It was found that the extreme shape of the curve _solv H° vs. X for ethylacetate in the mixtures of water with 1-propanol results from peculiarities of carbotylate-group solvation and appears to be not connected with the influence of alcohol microaggregates in the mixed solvent.     

Cation influence on the structure and electron density of water in some Men+·H2O complexes

The cation influence on the water molecule in the Li⁺·H₂O, Be²⁺·H₂O, Mg²⁺·H₂O and A1³⁺·H₂O complexes has been studied by means of quantum-mechanical ab initio calculations. A number of general trends are noted. (1) The calculated equilibrium water O-H distances increase with increasing binding energies, i.e. in the order Li⁺, Mg²⁺, Be²⁺, Al³⁺. The H-O-H angles differ by about ±1 ° from the calculated equilibrium angle for the free H₂O molecule; the variation has no systematic trend. (2) The electron density redistribution accompanying the change in the internal H₂O geometry in these complexes is considerably smaller than the redistribution brought about by the direct influence of the external field. (3) The harmonic O-H stretching force constant decreases with increased cation-water bonding. (4) The qualitative features of the density changes are very similar for the four complexes. The magnitudes of the interactions follow the relation Li⁺ < Mg²⁺ < Be²⁺ Al³⁺. An increased polarization of the H₂O molecule occurs with electron migration from the H atoms towards the O atom and an accumulation of electron charge approximately at the centre of the Meⁿ⁺—O bond, especially in Be²⁺·H₂O and A1³⁺·H₂O. An electron deficiency is found in the lone-pair region.     

Der unterschiedliche Charakter von Wasserstoffbindungen in Komplexen zwischen Wasser und organischen Basen

Zusammenfassung Die 11-Komplexe von H₂O mit Dioxan (als Beispiel einer schwachen Base) und Triäthylamin (Et ₃N) (als Beispiel einer starken Base) werden in verd. Lösung in nichtpolaren Lösungsmitteln (CCl₄, Benzol) untersucht. Wie erwartet, ist im Vergleich zu H₂O:Et ₃N die Komplexbildungskonstante von H₂O: Dioxan kleiner, die Frequenzverschiebung der OH-Fundamentalschwingung geringer und die Veränderung der chemischen Verschiebung des OH-Protons schwächer ausgeprägt. Auch ist die Volumenkontraktion im System H₂O+Dioxan weniger bedeutend als im System H₂O+Et ₃N. Andererseits vermag H₂O in verd. Lösungen in Dioxan beide H-Atome unter H-Brückenbildung zu einem 2 Dioxan: 1 H₂O-Komplex zu betätigen, während H₂O in verd. Lösungen inEt ₃N lediglich den 11-Komplex ergibt. Dieses Verhalten kann erklärt werden durch die unterschiedliche Polarität der 11-Komplexe. Während der H₂O: Dioxan-Komplex keine Erhöhung des Dipolmoments erkennen läßt, weist der H₂O:Et ₃N-Komplex infolge der Polarisierung der O–H...N-Bindung ein Inkrement des Momentes von ca. 0,4 D auf. Durch diese zusätzliche Polarisierung des H₂O-Moleküls wird die Ausbildung einer zweiten H-Bindung gehemmt.

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The different character of hydrogen bonds in complexes of water with organic bases

The 11 complexes of H₂O with 1.4-dioxane (as an example of a weak base) and triethylamine (Et ₃N) (as an example of a strong base) have been investigated in dilute solutions of non-polar solvents (CCl₄, benzene). Compared with the H₂O:Et ₃N complex, the complex H₂O: dioxane has a smaller complex formation constant, a smaller frequency shift of the OH fundamental, and the change of the chemical shift of the OH proton due to complex formation is less pronounced. The volume contraction of mixing in the system H₂O+dioxane is also smaller than in the system H₂O+Et ₃N. On the other hand, in dilute solutions of H₂O in dioxane a H₂O: (dioxane)₂ complex is formed in which both water protons are involved in H-bonds to a dioxane molecule, whereas in dilute solutions of H₂O inEt ₃N only the 11 complex exists. This behaviour can be explained by the difference in polarity of the 11 complexes. The H₂O: dioxane does not show an increment of the dipole moment, but the H₂O:Et ₃N complex shows an increment of ca. 0.4 D, due to the polarization of the O–H...N bond. This polarization of the H₂O-molecule hinders the formation of a second H-bond.

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Mit 8 Abbildungen

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Herrn Univ.-Prof. Dr.O. Kratky gewidmet.     

Interaction of Aluminium (III) with the f-Family Ions Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) in the Course of Simultaneous Hydrolysis

The interaction of Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) with Al(III) in solutions at pH 0–4 was studied by the spectrophotometric method. It was shown that, in the range of pH 3–4, the hydrolyzed forms of neptunyl and plutonyl react with the hydrolyzed forms of aluminium. In the case of Pu(VI), the mixed hydroxoaqua complexes (H₂O)₃PuO₂(-OH)₂Al(OH)(H₂O)₃ ²⁺ or (H₂O)₄PuO₂OAl(OH)(H₂O)₄ ²⁺ are formed at the first stage of hydrolysis. Np(VI) also forms similar hydroxoaqua complexes with Al(III). The formation of the mixed hydroxoaqua complexes was also observed when Np(IV) or Pu(IV) was simultaneously hydrolyzed with Al(III) at pH 1.5–2.5. The Np(IV) complex with Al(III) has, most likely, the formula (H₂O) _n (OH)Np(-OH)₂Al(OH)(H₂O)₃ ³⁺. At pH from 2 to 4.1 (when aluminium hydroxide precipitates), the Np(V) or Nd(III) ions exist in solutions with or without Al(III) in similar forms. When pH is increased to 5–5.5, these ions are almost not captured by the aluminium hydroxide precipitate.