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Thermodynamic Study of Dilute Aqueous-solutions of Organic-compounds .5. Open-chain Saturated Bifunctional Compounds
No full textValues have been determined at 25°C of the changes in the free energy, enthalpy and entropy corresponding to the process of transfer from the ideal gas state to dilute aqueous solution for ethylene-diamine, 2-methoxyethylamine, 3-methoxypropylamine, 1,2-dimethoxymethane and four 2-alkoxy-ethanols (methoxy to n-butoxy).
These data have been used to calculate the variations in the thermodynamic functions of hydration for the hypothetical process of introducing a Y group (Y = O, NH) into a monofunctional RX compound (X = O, NH, NH2, OH), either by breaking a C—C or a C—H bond. Evidence of strong interactions between hydrophilic centres in bifunctional compounds emerges. The strength and nature (entropic or enthalpic) of these interactions depend on both the type of functional groups and their relative distance
Thermodynamic and Kinetic Aspects of the Binding Reaction of Molecular Oxygen on Co(II) Complexes in Aqueous Solution
No full textA short survey is given of the main characteristics of the reaction of uptake of molecular oxygen by biological dioxygen carriers. Co(II) complexes able to bind dioxygen are then examined in order to determine whether the type and features of the peroxocomplexes formed are related to the nature of the ligand and the solvent. The thermodynamic and kinetic data relative to the formation in aqueous solution of peroxocompounds starting from Co(II) complexes with ligands belonging to three families (open-chain, macrocyclic and macropolytopic) of saturated polyamines are also examined in greater detail
Thermodynamic studies on the addition of molecular oxygen to cobalt(II)-1,4,8,12-tetraazacyclopentadecane in aqueous solution at 25°C
No full textAqueous solutions containing Co2+ and the macrocyclic ligand 1,4,8,12-tetraazacyclopentadecane (L) are able to bind reversibly molecular oxygen to form the species Co2L2O24+ between pH 5 and 7. This species at pH greater than 8 is replaced by the complex Co2L2O2 (OH)22+ whose concentration in the solution increases to about pH 10.5. At pH greater than 10.5, Co(II) exists totally in this μ-peroxobisydroxo complex. Both the above mentioned oxygenated forms suffer a relatively slow irreversible oxidation to Co(III). From oxygen binding curves, approximate values of the equilibrium constants were calculated for the addition of oxygen to CoL2+ to form the μ-peroxo and the μ-peroxo-bishydroxo complexes. The enthalpies of formation of this latter complex starting from both Co2+ or CoL2+ have been obtained by means of calorimetric measurements. The effects of the size of the macrocyclic ligand on the affinity and the enthalpy of oxygen binding have been considered. © 1986 Plenum Publishing Corporation
Compressibility changes in protonation of some organic aliphatic nitrogen compounds in aqueous solution
No full textDensity and sound velocity of aq. solns. contg. monofunctional primary, secondary and tertiary amines, as well as bifunctional primary and secondary amines (B), and their corresponding hydrochlorides, (BHCl), were measured; the apparent molar compressibilities were calculated. From the limiting apparent molar compressibilities of B, BHCl and HCl in aq. soln. the changes in compressibilities, Δφ°K,S, for protonation of B was obtained. The pattern shown by the Δφ°K,S values was similar to that presented by the changes, ΔX°r, of other thermodn. properties, such as Cp and V, for the formation of BHCl species from B and HCl. The different values of Δφ°K,S obsd. for amines having the same no. of hydrogens bonded to N but differing in the presence of a second hydrophilic group was attributed to the removal of the hydrophobic hydration of the alkyl groups brought about by this center
Calorimetric Study on Oxygen Addition to Cobalt(II) Complexes with Tris-(2-aminoethyl)amine and 3,7-Diazanonane-1,9-diamine
No full textThrough spectrophotometric and potentiometric measurements it has been verified that in aerated aqueous solutions of CoII containing tris(2-aminoethyl)amine (tren) as ligand, the doubly bridged μ-peroxo-μ-hydroxo dicobalt ion [Co2L2(O2)(OH)]3+ (L = tren) is totally formed at pH > 6.5. In aerated aqueous solutions of CoII and 3,7-diazanonane-1,9-diamine (dadn) at pH 6.5 only the singly bridged μ-peroxo dicobalt ion [Co2L2(O2)]4+ (L = dadn) is present. This complex at higher pH adds OH- ions in its axial positions; at pH > 10.5 the singly bridged μ-peroxo-dihydroxo dicobalt ion [Co2L2(O2)(OH)2]2+ is totally formed. The singly bridged complex [Co2L2(O2)]4+, after several hours, converts irreversibly into the doubly bridged μ-peroxo-μ-hydroxo ion [Co2L2(O2)(OH)]3+, while the single bridged [Co2L2(O2)(OH)2]2+ ion slowly autoxidizes to CoIII. By means of calorimetric measurements, usually carried out at constant pH, the enthalpies of formation of [Co2L2(O2)]4+ and [Co2L2(O2)(OH)2]2+ (L = dadn) and [Co2L2(O2)(OH)]3+ (L = tren) have been obtained. These results are compared with the enthalpies relative to the oxygen addition to [Co(trien)]2+ ion (trien = triethylenetetra-amine), and the enthalpy effects, connected with the change from a linear amine (trien) to its branched isomer (tren) and from the sequence 5,5,5 (trien) to the sequence 5,6,5 (dadn) of the chelate rings, are discussed
Volume Changes In Proton Ionization of Amines In Water .2. Amino-alcohols, Amino Ethers, and Diamines
No full textFrom density measurements (25 °C) of aqueous solutions at various concentrations of solute, apparent molar
volumes of some open-chain bifunctional amines, with the amine group being primary, secondary, and tertiary,
have been determined. The compounds studied were 2-aminoethanol, 3-amino-1-propanol, 2-methoxyethylamine,
3-methoxy-l-propylaminee,t hylenediamine, 1,3-diaminopropane,2 -(methylamino)ethanol, 2-(ethylamino)ethanol,
2-(dimethylamino)ethanol, 2-(diethylamino)ethanol, and their mono- and dihydrochlorides. The volume changes
for the first and second steps of proton ionization have been calculated from the limiting partial molar volumes.
The volume change values of the above bifunctional amines are compared with the corresponding values for monofunctional
amines. The difference in the volume changes caused by the introduction of the second hydrophilic center is discussed. The
volumes and entropies of ionization of the amines and carboxylic acids are compared and the deviations of
these functions from predictions based on simple electrostatic theories are considered
Free-energy and Enthalpy Changes For the Process of Transfer From Gas and From Dilute Aqueous-solutions of Some Alkanes and Monofunctional Saturated Organic-compounds
No full textStandard free energies, DELTA-solvG-degrees-(oct), and enthalpies, DELTA-solvH-degrees-(oct), of solvation in octan-1-ol of some alkanes (heptane, octane), ketones (propan-2-one, butan-2-one, hexan-2-one, heptan-4-one), ethers (dipropyl ether, dibutyl ether, tetrahydropyran), alkanols (butan-1-ol, butan-2-ol, 2-methylpropan-2-ol) and amines (pyrrolidine, N-methylpyrrolidine, and piperidine) with open-chain and cyclic structure have been determined at 298.15 K. The DELTA-solvG-degrees-(oct) values were obtained from measurements of partial vapor pressures of dilute solutions and the DELTA-solvH-degrees-(oct) values, by adding the heats of solution, determined by calorimetry, to known values of enthalpy of vaporization. These data are compared with the standard free energies and enthalpies of solvation in water, and the standard thermodynamic functions for the ideal transfer process of the solutes from pure water to pure octan-1-ol, DELTA-trX-degrees-(w-oct) (X = G, H) are calculated. For the examined solutes, hydrocarbons and monofunctional saturated organic compounds, the thermodynamic functions of solvation in octanol and in water are closely correlated to the position of the functional group in the molecular skeleton. The values of the enthalpy of transfer from water to octan-1-ol are also related more to the topologic characteristics of the solute molecules than to their size or to the nature of their functional group. In contrast, the size of the molecules, as well as the presence of a functional group, are important with regard to DELTA-trG-degrees-(w-oct). An increase of 1 cm3 mol-1 in the intrinsic volumes corresponds to an increase in the value of the partition coefficients of ca. 15%. The substitution of a part of the hydrocarbon surface with a polar surface produces a very large increase in the values of the partition coefficients. The values of the enthalpy of transfer from water to octan-1-ol are always positive, in contrast to the standard free energies of transfer. The entropic term operates by always favouring the transfer towards the alcoholic phase. The potential ability of anhydrous octanol to extract organic solutes of various molecular structure from water-saturated octanol and from hexadecane is also evaluated and discussed
Group Contributions To the Thermodynamic Properties of Non-ionic Organic Solutes In Dilute Aqueous-solution
No full textThe thermodynamic properties ΔG°h, ΔH°h, and ΔCp°h associated with the transfer of non-ionic organic compounds from gas to dilute aqueous solution and the limiting partial molar properties Cp°2 and V2° of these compounds in water are described through a simple scheme of group contributions. A distinction is made between groups made only of carbon and hydrogen, and functional groups i.e. groups containing at least one atom different from carbon and hydrogen. Each group is assigned a contribution, for each property, through a least squares procedure which utilizes only molecules containing at most one functional group. Finally, for compounds containing more than one functional group, correction parameters are evaluated as the differences between the experimental values and those calculated by means of the group contributions. The different behavior of hydrophilic compared with hydrophobic groups is discussed for the various properties. A rationale for the correction parameters, i.e. for the effects of the interactions among hydrophilic groups on the thermodynamic properties, is attempted
Thermodynamic and kinetic studies on the addition of dioxygen to Co(II) complexes with open-chain saturated polyamines
No full textThe systems Co(II)/N,N'-bis(3-aminopropyl)ethylenediamine, NH2(CH2)3NH(CH2)2NH (CH2)3NH2 (3,2,3-TET) and Co(II)/N,N'-bis(3-aminopropyl)propylenediamine, NH2(CH2)3NH(CH2)3NH (CH2)3NH2 (3,3,3-TET), have been investigated in aqueous solutions at 25-degrees-C, both under anaerobic and aerobic conditions, by means of potentiometric, spectrophotometric, calorimetric and dioxygen measurements carried out over a wide range of pH, in some cases at variable temperature. Under anaerobic conditions, at ligand-to-cobalt molar ratio C(L)o/C(Co)o of 1 and cobalt concentrations C(Co)o > 5 x 10(-3) M, the formation of cobalt(II) complexes with 3,2,3-TET and with 3,3,3-TET is complete at pH > 8.5 and at pH > 10, respectively. Under aerobic conditions, in the pH range from 6.5 to 8, the monobridged dicobalt mu-peroxo monohydroxo 3,2,3-TET complex is suggested to be formed which, in about thirty minutes, converts extensively to the dibridged mu-peroxo mu-hydroxo (olate) species. When Co(II) is added to aerated solutions of 3,2,3-TET at pH > 10.5, only the monobridged dicobalt-mu-peroxo dihydroxo complex is formed. This complex may also be slowly produced by increasing the pH of solutions containing the dibridged olate species to a value higher than 10.5. The three dioxygen adducts are also obtained in aerated solutions of Co(II) and 3,3,3-TET at different pH's. The thermodynamic standard functions DELTAX(o) (X = G, H, S) for the formation of the Co(II) complexes in anaerobic conditions are reported; kinetic and thermodynamic data concerning the dioxygen addition reactions, the isomerization of the monobridged mu-peroxo monohydroxo complexes to the debridged olate form, the conversion of the dibridged olate complex into the monobridged dicobalt mu-peroxo dihydroxo complex, and the irreversible oxidation of the Co(II) dioxygen adducts to Co(III) complexes have been evaluated. Finally, a comprehensive analysis has been carried out of the thermodynamic and kinetic features exhibited by the reaction of addition of dioxygen to Co(II) complexes with open-chain saturated tetraamines with ethylenic and/or propylenic chains
Volumetric properties of amphionic molecules in water. Part 2. Thermal expansibility and compressibility related to the formation of zwitterionic structures
No full textThe dependence of the partial molar volumes of a number of α-amino acids, ω-amino acids, dipeptides and diketopiperazines on temperature has been determined at various concentrations and for the temperature range 0-55°C using an automatic dilatometer; the limiting partial molar expansibilities, Φ°E, have been calculated. Measurements of the sound velocity at 15 MHz and at various concentrations allowed us to determine the compressibility of the solutions at 25°C and to calculate the limiting partial compressibilities, Φ°K,S, for some of the above mentioned compounds. Finally, by using the known values Φ°E and Φ°K,S together with the partial molar heat capacity of the solute and some physical properties of pure water, the limiting isothermal partial molar compressibilities, Φ°K,T, have been obtained. The values of Φ°E and Φ°K,S and the trends they show when the structure of the amphionic molecule is changed have been analysed by taking into account the features exhibited by Φ°E and Φ°K,S of related charged and non-charged compounds. The dependence on temperature and pressure of the internal and external proton-exchange reaction between a carboxyl and an amino group have been evaluated and compared
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